November 7-9, 2019

DAE-BRNS Theme Meeting on Ultrafast SciencesRoom No-21, VMCC

We gratefully acknowledge the assistance and support of our sponsors and partners

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Gold Sponsors:

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Schedule

November 7

0830-0900 Registration

0900-0930 Inauguration. Chief Guest: Prof. Milind Atrey, Dean (R&D), IIT Bombay

0930-1010 Session 1: Plenary lecture 1: Chair: P. A. Naik

H. N. Ghosh “Exciton, Bi-Exciton, Trion and Polaron Dissociation Dynamics in

Nano-Structured Hetero Interface: Implication in Solar Devices”

1010-1040 High tea

1040-1230 Session 2: Invited Lectures (IL): Chair: S. K. Sarkar

IL 1: Vandana Sharma, “Transient Negative Polarizability Frustrates Alignment

in Ultrashort Laser Induced Fragmentation of Molecules”

IL 2: Jyotishman Dasgupta, “Elucidating the Transient Raman Signature of a

Twisted Intramolecular Charge Transfer State”

Session 3: Invited Lectures (IL): Chair: Rajib Mitra

IL 3: Jean C. Tremblay, “Probing Molecular Chirality via Laser-Induced

Electronic Fluxes”

IL 4: Sayan Bagchi, “Hydrocarbon Chain-Length Dependence of Solvation

Dynamics in Alcohol-Based Deep Eutectic Solvents: A 2D IR Spectroscopic

Investigation”

1230-1310 Session 4: Plenary Lecture 2 Chair: D. Goswami

K. Tominaga, “Hydrogen-Bond Dynamics of 9-Fluorenone Derivatives in Water

Probed by 2D-IR Spectroscopy”

1310-1400 Lunch

1400-1550 Session 5: Invited Lectures (IL): Chair: K. G. Suresh

IL 5: Mahesh Hariharan, “Ultrafast Excited State Dynamics of Twisted

Aromatics”

IL 6: Prasun Mandal, “Effect of Alloy-Shelling on Ultrafast Dynamics in

Semiconductor Quantum Dots”

Session 6: Invited Lectures (IL): Chair: S. Prabhu

IL 7: Anand Moorti, “Electron Acceleration using Laser Fields at Extreme

Intensities in Plasmas: An Advanced Accelerator Concept”

IL 8: K.P. Singh, “Ultrathin attosecond delay-lines with absolute zero delay

reference”

1550-1620 Tea

1620-1700 Session 7: Plenary Lecture 3: Chair: P. K. Datta

D. D. Sarma, “Experiments in the Sub-ps Regime to Understand Properties of

Opto-Electronic Materials”

1705-1815 Session 8: Technical talk 1: Anatech, Invited Lectures (IL): Chair: J. Jayabalan

IL9: Pankaj Mandal, “Probing the origin of self-trapped excitons in hybrid lead

halide perovskites using time-resolved spectroscopy”

IL 10: Sivarama Krishnan, “Opportunities in ultrafast science with laser

generated XUV pulses”

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November 8

0930-1010 Session 9: Plenary Lecture 4: Chair: G. Dixit

S. Mukamel, “Nonlinear spectroscopy and imaging of molecules with x-ray,

quantum, and noisy light”

1015-1105 Session 10: Invited Lectures (IL): Chair: Suman K. Pal

IL11: Anshu Pandey, “Temporal Evolution of Radiative Rate Reveals the

Localization of Holes in CuInS2-based quantum dots”

IL12: Rajesh Kushwaha, “Photoionization of Polyatomic Molecules: Molecular

Structure, Ultrafast Dynamics and Molecular Movie”

1105-1135 Tea

1135-1215 Session 11: Plenary Lecture 5: Chair: T. K. Mukherjee

G. Ravindra Kumar, “Ultrafast Evolution of Dense, Hot Plasmas

Physics and Measurements in Extreme Conditions”

1220-1310 Session 12: Invited Lectures (IL): Chair: P. Sen

IL 13: Parinda Vasa, “Ultrafast Dyjnamics inMetal/Semiconductor

Nanostructures”

IL 14: Adam Kirrander, “Ultrafast X-ray Scattering of Molecular Dynamics”

1310-1400 Lunch

1400-1640 Poster + Tea

1640-1830 Session 13: Technical talk 2: Partha Pal, Wiley,

Invited Lectures (IL): Chair: P. Purkayastha

IL 15: Dipanshu Bansal, “Probing Lattice Instabilities in Thermoelectric SnSe

using Spectroscopic Studies”

IL 16: G. Naresh Patwari, “Intermolecular Tuning of Non-Adiabatic Dynamics

via Hydrogen Bonding”

November 9

0930-1120 Session 13 Invited Lectures (IL): Chair: T. Kundu

IL 17: Sobhan Sen, “Origin of Slow Solvation Dynamics in DNA: What is the

Biological Significance?”

IL 18: Bhargava Ram Nirghantam, “Ultrafast Photoelectron-Photoion

Coincidence Imaging Spectrometer to Explore Molecular Chirality”

IL 19: Mukesh Jewariya, “Real-Time Four-Dimensional Spatio-Temporal

Terahertz Imaging using Intense Terahertz Pulse”

1120-1150 Tea

1150-1240 Session 14: Plenary Lecture 6: Chair: D. K. Palit

S. Umapathy “Ultrafast Raman spectroscopy: Applications to chemical

dynamics”

1245-1315 Closing session

1315 Lunch

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Table of Contents:

PLENARY

ABSTRACTS

November 7

PLENARY

TALK 1

Hirendra N.

Ghosh

Exciton, Bi-Exciton, Trion and Polaron Dissociation

Dynamics in Nano-Structured Hetero Interface:

Implication in Solar Devices

10

PLENARY

TALK 2 Keisuke Tominaga

Hydrogen-bond dynamics of 9-fluorenone derivatives

in water probed by 2D-IR spectroscopy 11

PLENARY

TALK 3 D. D. Sarma

Experiments in the sub-ps regime to understand

properties of opto-electronic materials 12

November 8

PLENARY

TALK 4 Shaul Mukamel

Nonlinear spectroscopy and imaging of molecules

with x-ray, quantum, and noisy light 13

PLENARY

TALK 5

G. Ravindra

Kumar

Ultrafast evolution of dense, hot plasmas Physics and

measurements in extreme conditions 14

PLENARY

TALK 6 S. Umapathy

Ultrafast Raman spectroscopy: Applications to

chemical dynamics 15

INVITED

LECTURES

ABSTRACTS

November 7

INVITED

LECTURE 1 Vandana Sharma

Transient negative polarizability frustrates

alignment in ultrashort laser induced fragmentation

of molecules

16

INVITED

LECTURE 2

Jyotishman

Dasgupta

Elucidating the Transient Raman Signature of a

Twisted Intramolecular Charge Transfer State 17

INVITED

LECTURE 3

Jean Christophe

Tremblay

How to use electronic flux density maps as a tool to

unravel ultrafast correlated electron dynamics 18

INVITED

LECTURE 4 Sayan Bagchi The curious case of warfarin photophysics 19

INVITED

LECTURE 5

Mahesh

Hariharan

Ultrafast Excited State Dynamics of Twisted

Aromatics 20

INVITED

LECTURE 6 Prasun K. Mandal

Effect of Alloy-Shelling on Ultrafast Dynamics in

Semiconductor Quantum Dots 21

6

INVITED

LECTURE 7 Anand Moorti

Electron Acceleration using Laser Fields at Extreme

Intensities in Plasmas: An Advanced Accelerator

Concept

22

INVITED

LECTURE 8 Kamal P. Singh 23

INVITED

LECTURE 9 Pankaj Mandal

Probing The Origin of Self Trapped Excitons in

Hybrid Lead Halide Perovskites Using Time-

Resolved Spectroscopy

24

INVITED

LECTURE 10

Sivarama

Krishnan

Opportunities in ultrafast science with laser

generated XUV pulses 25

November 8

INVITED

LECTURE 11 Anshu Pandey 26

INVITED

LECTURE 12

Rajesh K

Kushawaha

Photoionization of polyatomic molecules: Molecular

structure, ultrafast dynamics and molecular movie 27

INVITED

LECTURE 13 Parinda Vasa

Ultrafast dynamics in metal/semiconductor

nanostructures 28

INVITED

LECTURE 14 Adam Kirrander Ultrafast X-ray Scattering of Molecular Dynamics 29

INVITED

LECTURE 15 Dipanshu Bansal

Probing lattice instabilities in thermoelectric SnSe

using spectroscopic studies 30

INVITED

LECTURE 16 G. Naresh Patwari

Intermolecular Tuning of Non-Adiabatic dynamics

via Hydrogen Bonding 31

November 9

INVITED

LECTURE 17 Sobhan Sen

Origin of Slow Solvation Dynamics in DNA: What is

the Biological Significance? 32

INVITED

LECTURE 18 N Bhargava Ram

Ultrafast photoelectron-photoion coincidence

imaging spectrometer to explore molecular chirality 33

INVITED

LECTURE 19 Mukesh Jewariya

Real-Time Four-Dimensional Spatio-Temporal

Terahertz Imaging using Intense Terahertz Pulse 34

POSTER

ABSTRACTS

POSTER 1 Annyesha Biswas Stabilization and sensing of G-quadruplex DNA

structures with indolylquinolinium based probes 36

POSTER 2 Nibedita Pal Enzyme product releasing mechanism under

piconewton force manipulation: A single molecule 37

7

investigation using photon time-stamping

spectroscopy

POSTER 3 Partha Pyne Polyethylene glycols affect electron transfer rate in

phenosafranin-DNA 38

POSTER 4 Sk Imadul Islam Investigation on the ESPT Dynamics of D‑Luciferin

in Aqueous trifluoroethanol and ethanol Mixtures 39

POSTER 5 Arup Kundu Formation of Long Lived Triplets through Singlet

Fission in Lycopene Aggregates 40

POSTER 6 Sneha Paul Conformational Dynamics of c-MYC Promoter

based i-Motif DNA in Crowded Environments 41

POSTER 7 Tanuja Kistwal Solvation dynamics in solvent free protein – polymer

surfactant biomolecular assemblies 42

POSTER 8 Narayan Chandra

Matiy

Solute and Solvent Dynamics in Neat, and Wet-

Octanol: Steady State and Time Resolved

Fluorescence Measurements

43

POSTER 9 Rohit Goswami Ultrafast Control for Perfumery Industries 44

POSTER 10 Meghna Ghosh

Unveiling the Effect of Sugars on Dynamics of

Different Fluorophores in the Interior of Aerosol OT

Lamellar Structures: From Picosecond-to-

Femtosecond Study

45

POSTER 11 Harsh Bhatia

Use of Dimeric Excited States of the Donors in D4-A

Systems for Accessing White light Emission,

Afterglow and Invisible Security Ink

46

POSTER 12 Deepika Sardana Origin of Slow Solvation Dynamics in DNA: DAPI in

Dickerson-DNA 47

POSTER 13 Arnab Sil

Impact of Urea on Structure and Dynamics of an

Ionic Deep Eutectic Solvent: Exploration through

Reactive and Non-Reactive Solute Centered

Dynamics

49

POSTER 14 Pranav Adhyapak Solvation Dynamics in Mycobacterial Membranes

Probed by Time-Resolved Laurdan Fluorescence 50

POSTER 15 Sangita Kundu

Modulating Interaction Mechanism of Duplex DNA

with Graphene Oxide Employing Two Diverse

Binders

51

POSTER 16 Tanmay Goswami

Room Temperature Exciton and Trion Formation in

Monolayer MoS2 Followed by Dissociation in

Presence of Au NPs

52

POSTER 17 Fariyad Ali Ultrafast carrier dynamics of Cu doped CdSe

nanotetrapods 53

POSTER 18 Surya Narayan

Panda

Ultrafast all-optical detection of interfacial spin

transparency for pure spin current transport in

CoFeB/β-Ta thin films

54

POSTER 19 Apurba De

Synthesis and Carrier Dynamics of Highly

Luminescent Violet- and Blue-Emitting Perovskite

Nanocrystals

55

POSTER 20 Debashis Panda Facets of Carbon Nanodot: Fundamentals and

Applications 56

POSTER 21 Soumyadip

Bhunia

Ultrafast photoinduced electron transfer dynamics

between cyclometalated rhodium and iridium

complexes and cyan emitting copper nanoclusters

57

8

POSTER 22 T. Singha Determination of dispersion of the third order

optical nonlinearity of Carbon Dots 58

POSTER 23 Sayan Prodhan

Investigation of Improved Charge Carrier Dynamics

of Core-Shell Nanocrystal Modified Perovskite using

Transient Absorption Spectroscopy

59

POSTER 24 Sushanta Lenka

Study of Non-colinear Femtosecond Second

Harmonic and Sum Frequency Generation using

BBO crystals

61

POSTER 25 Hemen Gogoi Solvent Mediated Relaxation Dynamics of Core-Shell

Au-SiO2 Nanoparticles 62

POSTER 26 Bala Gopal M Ultrafast dynamics of gold dimers and trimers 63

POSTER 27 Gurpreet Kaur

Slow Charge Carrier cooling in Type-1 3D/0D Core-

Shell CsPbBr3@Cs4PbBr6 Perovskite system: Role

of Polaron Formation

64

POSTER 28 Jamuna K.

Vaishnav

Long-Range Resonance Coupling-Induced Surface

Energy Transfer from CdTe Quantum Dot to

Plasmonic Nanoparticle

65

POSTER 29 Binit Mallick

Time Dependent Optical Second Harmonic

Generation from Si/SiO2 Interface and Its Variation

with Doping Concentration

66

POSTER 30 Arundhati

Adhikari

Direct Observation of -Phonon Driven Ultrafast

Magnetization Dynamics in Ferromagnetic Nanodot

Arrays

67

POSTER 31 Kamlesh Kumar

Chauhan

Comprehensive study of femtosecond transient

carrier dynamics in mixed halide perovskite 68

POSTER 32 D. P. Khatua

Carrier Dynamics Measurement on MoS2

Monolayers Using Ultrafast Pump-Probe

Spectroscopy

69

POSTER 33 Manobina

Karmakar

Exploring the Dynamics of Excited Excitonic

Rydberg Series in Layered MoS2 70

POSTER 34 R. Rathore

Comparative study of ultra-fast thermal strain

evolution in Ge (111) sample induced by

fundamental and second harmonic pump pulse

71

POSTER 35 Sourav Sahoo Ultrafast Magnetization Dynamics in Ferromagnetic

Nanodot Arrays Connected by Nanochannels 72

POSTER 36 Nihit Saigal

CuFeS2 Quantum Dots based broadband (visible to

MIR) photodetector for detecting radiation from

ultrafast sources

73

POSTER 37 Koustuv Dutta Ultrafast Spin-Wave Dynamics in Ferromagnetic

Diamond Antidot Lattice 74

POSTER 38 Chayan Kumar De

Understanding Optical Behaviour of InP Based Core

Alloy Shell QDs through Ultrafast dynamics and

Single Particle Spectroscopy

75

POSTER 39 Asha Singh

Ultrafast Response of Nanoplatelets Around its

Particle Plasmon Resonance: Effect of Size

Distribution

76

POSTER 40 Amitabha Nandi

Singlet Fission within Ultrafast Time Scale and near

Unity Yield in 5,12–bis (phenylethynyl)tetracene thin

film

77

POSTER 41 Subhadip Roy

Cosolvents at Aqueous Interface: As Observed by

“Classical” and “Heterodyne-Detected” Vibrational

Sum Frequency Generation Spectroscopy: Subhadip

Roy

78

POSTER 42 Swetapuspa

Soumyashree

Cold Target Recoil Ion Momentum Spectroscopy:

Design and Simulation 79

9

POSTER 43 Madhusudhan P Study of molecular alignment using femtosecond

laser pulses 80

POSTER 44 Remya

Ramakrishnan

Anomalous Halogen–Halogen Interaction Assists

Radial Chromophoric Assembly 81

POSTER 45 Reshma Mathew

Excited state structural dynamics of 4-cyano-4’-

hydroxystilbene: deciphering the signatures of

proton-coupled electron transfer using ultrafast

Raman loss spectroscopy

82

POSTER 46 Srijan Chatterjee

Hydrocarbon Chain-Length Dependence of Solvation

Dynamics in Alcohol-based Deep Eutectic Solvents:

A 2D IR Spectroscopic Investigation

83

POSTER 47 Animesh Patra

Extremely Weakly Interacting O-H in the Hydration

Shell of High Charge Density Metal Ions as Observed

Raman Difference with Simultaneous Curve Fitting

(RD-SCF) Spectroscopy

84

POSTER 48 Atanu

Bhattacharya Attosecond (10-18 second) Charge Migration 86

POSTER 49 Kanika Jain

Energy Transfer followed by Sequential Electron

Transfer in a Supramolecular Tetrad Composed of

Phenothiazine, Zinc Porphyrin,

Borondipyyromethene, and Fullerene: Charge

Stabilization in “Antenna-Reaction Center” Mimic

87

POSTER 50 Lasitha P

Squaramide Based, “Turn-on” Schiff Base Multi-

analyte Sensors for Zn2+ and Cd2+: Influence of

Acetate ion and Co-operativity

88

POSTER 51 Sharmistha Das Dynamics of Preferential Solvation of 5-

Aminoquinoline in Hexane-Alcohol Solvent Mixtures 89

POSTER 52 Souradip

Dasgupta Excited State Dynamics of Fluorogenic Molecules 90

POSTER 53 C. Aparajit Efficient Generation of Ultrahigh-Contrast High-

Intensity Laser Pulses 91

POSTER 54 Habib Ali Enhanced Two-Photon Activity with Extended

Molecular Conjugation 92

POSTER 55 Kamalesh Jana

Femtosecond time resolved, micrometer space

resolved two dimensional velocity mapping of an

ultraintense laser driven solid plasma

93

POSTER 56 Pranav Bhardwaj Design and Development of a new High Harmonic

Generation (HHG) setup and XUV beamline 94

POSTER 57 Sunandita Paul Towards Light Induced Carbocation Generation in a

Supramolecular Cavity 95

POSTER 58 H. Singhal High order harmonic generation from noble gases

using annular laser beam 96

POSTER 59 Chinmoy Biswas

Femtosecond Transient Absorption Dynamics of π-

Extended Thioalkyl Substituted Tetrathiafulvalene

Sensitizers on TiO2 Thin Films

97

POSTER 60 Sukriti Santra Effect of charge state on the ultrafast dynamics of

molecular rotor 100

POSTER 61 Mrudul M S High-Harmonic generation from spin-polarised

defects in solids 101

POSTER 62 Sucharita Giri Probing molecular chirality via laser-induced

electronic fluxes 102

POSTER 63 Irafana N. Ansari

Characterizing Laguerre-Gaussian pulses using

Angle-resolved Attosecond

Streaking

103

POSTER 64 Sushil S. Sakpal The curious case of warfarin photophysics 104

POSTER 65 Ankur Mandal IR-IR control of High Harmonic Generation 105

10

POSTER 66 Arpita Mukherjee Temporal evolution of radiative rate reveals the

localization of holes in CuInS2-based quantum dots

PLENARY TALK 1:

Exciton, Bi-Exciton, Trion and Polaron Dissociation Dynamics in Nano-

Structured Hetero Interface: Implication in Solar Devices

Hirendra N. Ghosha, b

a Professor, Institute of Nano Science and Technology, Mohali, Punjab 160064 b Scientic Officer,, Bhabha Atomic Research Centre, Mumbai-400085, India

E-mail: hnghosh@inst.ac,in, hnghosh2004@gmail.com

Exciton and multi-exciton harvesting from semiconductor quantum dot is an

important phenomena to improve the photo-conversion efficiency in solar cell devices in

particular quantum dot sensitized solar cells (QDSC) and also photodetectors. Till date, not

many reports are available where relation between exciton/multi-exciton/trion dissociation

in semiconductor hetero-structure and boosting the power conversion efficiency (PCE) of

QDSC are discussed. Herein we report detailed ultrafast spectroscopic investigation on the

dissociation dynamics of exciton, bi-exciton and trion on metal-semiconductor hetero-

interface with the help of Femto-second broad-band pump-probe spectrometer. Ultrafast

transient absorption studies suggest that in metal-semiconductor hetero-interface exciton,

bi-exciton and trion dissociates very efficiently and as a proof-of-concept efficiency in

QDSC was found to increase by more than double. In addition to that ultrafast hot carrier

cooling is the key loss channel which limits achievable solar conversion efficiency.

Delaying the carrier cooling high efficient hot-carrier solar cell can be realized. Herein we

have demonstrated dramatic dip in the cooling rate in Type‑ 1 3D/0D CsPbBr3@Cs4PbBr6

core−shell NCs as compared to CsPbBr3 NCs in similar condition. Clear evidence of

polaron formation was observed in the core−shell system which was suppressed in the case

of CsPbBr3 NCs. The above findings can be efficient approaches towards the design and

development of efficient solar cell and optoelectronic devices using the principles of

multiexciton/trion generation and extracting them in metal-semiconductor nano-hybrid

system and slowing down the charge carriers through polaron formation in Type-1 core-

shell system.

REFERENCES:

1. T. Goswami, R. Rani, K. S. Hazra, and H. N. Ghosh*

J. Phys. Chem. Lett, 2019, 10, 3057.

11

2. G. Kaur, K. J. Babu, N. Ghorai, T. Goswami, S. Maiti, and H. N. Ghosh*

J. Phys. Chem. Lett, 2019, 10, 5302.

3. T. Debnath and H. N. Ghosh*J. Phys. Chem. Lett, (Perspective) 2019, 10,

(Accepted)

PLENARY TALK 2:

Hydrogen-bond dynamics of 9-fluorenone derivatives in water probed

by 2D-IR spectroscopy Masaki Okuda, Kaoru Ohta, Keisuke Tominaga

Molecular Photoscience Research Center, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe, Hyogo 657-

8501, Japan .

In aqueous solution, hydrogen bond (HB) between solute and solvent molecules

strongly perturbs dynamic and static properties of the solute molecules, which affects the

reactivity of chemical reaction in solution. Vibrational frequency is well-known to be

sensitive to the environmental change around solute molecules in solution. Two-

dimensional infrared (2DIR) spectroscopy is a powerful tool to quantify the vibrational

frequency fluctuation of solute molecules, which results from the temporal fluctuation in

solute-solvent interaction on an ultrafast time scale (sub-ps ~ ps time scale).

In this study, by using 2DIR spectroscopy, we have investigated the vibrational

frequency fluctuations of two different 9-fluorenone derivatives (FL-2COO− and FL-

4COO−) in D2O. From the center line slope analyses for their 2D-IR spectra, we found that

the frequency-frequency time correlation function (FFTCF) of the CO stretching mode of

FL-4COO− has a decay time constant of 2.7 ps, which is much longer than those of ionic

vibrational probe molecules (~1 ps) observed in many studies so far. The decay time of

FFTCFs of the related compounds shows a strong correlation with the size of the

hydrocarbon part, which is hydrophobic in nature; acetaldehyde, the smallest size molecule

has a time constant of 1.4 ps. Consequently, our 2D-IR results clearly demonstrate that the

size of the hydrocarbon part plays an important role in the vibrational frequency

fluctuations in water. To understand the effect of the hydrocarbon part on local

environment at a molecular level, we conducted the theoretical analyses with classical

molecular dynamics (MD) simulations for the FL-4COO−/water system. We found that the

hydrogen bond dynamics between solute and water and the reorientational relaxation of a

single water molecule in the vicinity of solute are similar to those in the bulk, which

suggests that the slow decay of the FFTCF is not solely due to single-molecule dynamics

around the solute. By calculating the radial dependence of the Coulomb electrostatic

potential on the vibrational probe from water molecules, we found that the solute interacts

electrostatically with water molecules in a sphere of a radius 8 Å from the solute. From this

result, we conclude that collective water dynamics, which is intrinsically slower than the

single-molecule dynamics, makes a strong impact on the vibrational frequency fluctuations

of FL-4COO− in water.

On the other hand, the IR spectrum of FL-2COO− in D2O exhibits the asymmetric

lineshape, which likely results from two different types of solute-water HB complexes. We

found that the relative amplitude of the cross peak (SAB) to the diagonal peak signals (SAA)

becomes larger with population time T, which reflects the making and breaking of a HB

12

between FL-2COO− and a water molecule. Based on these 2DIR results, we conclude that

the position of the COO− group plays an important role for the solute-water HB dynamics.

PLENARY TALK 3:

Experiments in the sub-ps regime to understand properties of opto-

electronic materials

D. D. Sarma Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru 560012,

sarma@iisc.ac.in

Self-absorption has been a major impediment to utilizing brilliant and tunable

photoluminescence from semiconductor nanocrystals, as it reduces drastically the quantum

efficiency at any reasonable optical density. In this context, defect emissions are interesting

because of their Stokes shifts that make them impervious to self-absorption, but this comes

often at the cost of the quantum efficiency and the tunability. We have been addressing

these issues for many years and have overcome these challenges in carefully designed

systems.1-4 Ultrafast spectroscopic studies allow us to probe the origin of the high quantum

efficiencies in such systems and I shall discuss two such systems in this talk.

If time permits, I shall also discuss a fundamental issue related to the spectacular

photovoltaic properties observed in hybrid perovskite halides and address the intriguing

possibility of an excited state polarization of the material due to the presence of dynamical

dipoles in the ground state.5

These three examples illustrate different time-resolved techniques that we employ

to understand properties of materials within our group.

REFERENCES:

1. Abhijit Hazarika et al., Phys. Rev. Lett. 2013, 110, 267401.

2. Abhijit Hazarika, Anshu Pandey, and D. D. Sarma, J. Phys. Chem. Lett. 2014, 5, 2208.

3. Abhijit Hazarika et al., unpublished results

4. Shyamashis Das et al., unpublished results.

5. Sharada Govinda et al., J. Phys. Chem. Lett. 2017, 8, 4113.

13

PLENARY TALK 4:

Nonlinear spectroscopy and imaging of molecules with x-ray, quantum,

and noisy light Shaul Mukamel

Department of Chemistry and Department of Physics and Astronomy, University of California, Irvine,

Irvine, California 92697-2025, USA

s.mukamel@uci.edu

Ultrafast nonlinear x-ray spectroscopy is made possible by newly developed free

electron laser and high harmonic generation sources. The attosecond duration of X-ray pulses

and the atomic selectivity of core X-ray excitations offer a unique combination that can monitor

elementary molecular events with high spatial and temporal resolution. Applications of these

techniques to spectroscopy and imaging of molecules will be presented. X ray sum frequency

generation, circular dichroism and time- and frequency-resolved ultrafast diffraction of noisy

X-ray pulses will be discussed.

Quantum light opens up new avenues for spectroscopy by utilizing parameters of the

quantum state of light as control knobs and through the variation of photon statistics by

coupling to matter. When a molecule interacts with an external field, the phase information is

imprinted in the state of the field in a detectable way. Nonlinear optical signals induced by

quantized light fields and entangled photon pairs will be discussed. Combined time and

frequency resolution not possible by classical light can be achieved. A novel quantum

diffraction-based imaging technique whereby one photon of an entangled pair is diffracted of

a sample and detected in coincidence with its twin is presented. Imaging with weak quantum

fields is possible, avoiding damage to delicate biological samples.

REFERENCES: [1] Jérémy R. Rouxel, Markus Kowalewski, Kochise Bennett, Shaul Mukamel. Phys. Rev. Lett. 2018,120,

243902

[2] Frank Schlawin, Konstantin E. Dorfman and Shaul Mukamel. Acc. Chem. Res., 2018,51, 2207-2214

[3] Shahaf Asban, Konstantin E. Dorfman, and, Shaul Mukamel. PNAS. 2019, 116, 11673-11678

[4] Shahaf Asban, Daeheum Cho, and Shaul Mukamel. J.Phys.Chem.Lett, 2019, 10, 5805-5814

14

PLENARY TALK 5:

Ultrafast evolution of dense, hot plasmas

Physics and measurements in extreme conditions

G. Ravindra Kumar Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005.

(grk@tifr.res.in; www.tifr.res.in/~uphill)

High intensity, ultrashort light pulses (>1018 W cm-2, femtosecond duration) create

unusually hot and dense plasmas, enabling laboratory simulation of astrophysical

phenomena, relativistic optics, particle acceleration on a table top, real time x-ray

diffraction of the condensed phase, biological imaging or medical therapies for cancer1.

Visible/infrared laser light (~eV photon energy) can create relativistic (> MeV) electrons

in a target via collective plasma processes. Much of the subsequent physics and resulting

applications demand a good understanding of the generation and transport of these

electrons. A big challenge is to capture the experimental signature of a particular

phenomenon, given the highly noisy, turbulent and rapidly changing environment in the

plasma.

This talk will illustrate several aspects of the ultrafast evolution of relativistic

electron beam transport in a solid2, its energy dissipation3, megagauss magnetic fields4

that these electrons generate, extremely strong shocks5-7 caused by the laser pulse etc,- all

using pump-probe methods. Similarities between our results and astrophysical

observations indicate exciting possibilities that table top terawatt lasers offer for

laboratory astrophysics8.

REFERENCES:

1. S.V. Bulanov et al., Plasma Physics Reports, 2015, 41, 1

2. G. Chatterjee et al., Phys. Rev. Lett. 2012, 108, 235005

3. M. Shaikh et al., Phys. Rev. Lett. 2018,120, 065001

4. S. Mondal et al., Proc. Natl. Acad. Sci. (USA) 2012, 109, 8011

5. S. Mondal et al., Phys. Rev. Lett. 2010, 105, 105002

6. A. Adak et al., Phys. Rev.Lett. 2015, 114, 115001

7. K. Jana et al., 2019 (in preparation)

8. G. Chatterjee et al., Nat. Commun. 2017, 8, 15970

15

PLENARY TALK 6:

Ultrafast Raman spectroscopy: Applications to chemical dynamics S Umapathy 1,2

1 Dept. of Inorganic and Physical Chemistry 2Department of Applied Physics and Instrumentation, Indian Institute of Science, India.

Nonlinear spectroscopy [1] (NL) uses multiple (n) laser fields to extract the molecular

properties. Several nonlinear spectroscopic techniques have been introduced to provide

better understanding of the molecular properties. Nonlinear Raman spectroscopy

(NLR) is one such nonlinear process where the Raman pump and the Raman probe

beams drive the Raman transition in the system. Nonlinear Raman spectroscopy is very

promising and is very useful in understanding the structural and dynamical information

of a complex polyatomic molecular system. Femtosecond stimulated Raman

spectroscopy (FSRS) [2-3] is a NLR process wherein Raman pump (picosecond pulse)

and Raman probe, a white light continuum (femtosecond pulse) drive the Raman

transition and is a promising technique to understand the structural and dynamical

information of molecular systems. It provides good spectral (~15cm-1) and temporal

resolution (~50fs).

Ultrafast Raman loss spectroscopy (URLS), [4-10] also a NLR process of third order

developed by our group is more sensitive than FSRS. URLS provides twice the

intensity of FSRS signals and doesn’t interfere with fluorescence background on

resonance excitation which is usually a big hurdle in spontaneous Raman

measurements and sometimes in FSRS. URLS has been applied to get the Raman

spectra of several systems ranging from non-fluorescent to fluorescent systems. The

interaction of the solute with the surrounding molecules, usually solvent molecules

influences the Raman frequency and its linewidths. The dephasing times of vibrational

modes range from subpicosecond to picoseconds which depend on the kind of

interaction and molecular system. URLS has been applied to understand and measure

the dephasing process in vibrational modes both in the electronic ground and excited

molecular states. The response of the Raman line shapes on resonance excitations [8-

9] has been studied using URLS. The femtosecond time resolved Raman spectra of t-

stilbene and other systems will be discussed.

References

[1]. F. Ariese, K. Roy, V. Ravi Kumar, H. C. Sudeeksha, S. Kayal, and S. Umapathy, John Wiley and Sons,

DOI: 10.1002/97804- 70027318.a9555, (2017).

[2]. K. Roy, S. Kayal, N. K. Rai, and V. Ravikumar, Chapter: Editors: J. A. K. Howard, H. A. Sparkes, P. R.

Raithby, A.V. Churakov, Springer pp. 25-42, (2014).

[3]. B. Mallick, A. Lakshmanna, V. Radhalakshmi, S. Umapathy Curr. Sci. 95, 1551 (2008).

[4]. S. Umapathy, A. Lakshmanna, B. Mallick J. Raman Spectrosc. 40, 235 (2009).

[5]. A. Lakshmanna, B. Mallick, S. Umapathy Curr. Sci. 97, 210 (2009).

[6]. B. Mallick, A. Lakshmanna, S. Umapathy J. Raman Spectrosc. 42, 1883 (2011).

[7]. N. K. Rai, A. Lakshmanna, V. Namboodary, S. Umapathy J. Chem. Sci. (2011).

[8]. S. Umapathy, B. Mallick, A. Lakshmanna J. Chem. Phys. 133, 024505 (2010).

[9] K. Roy, S. Kayal, V. Ravi Kumar, F. Ariese, A. Beeby, S. Umapathy. J. Phys. Chem. A 35, 6538 (2017).

[10] K. Roy, S. Kayal, F. Ariese, A. Beeby and S. Umapathy. J. Chem. Phys. 146, 064303 (2017).

16

INVITED LECTURES: IL 1

Transient negative polarizability frustrates alignment in ultrashort

laser induced fragmentation of molecules

Arnab Sen1, T. Sairam2, B. Bapat1, R. Gopal2*,V. Sharma3*

1 Indian Institute of Science Education and Research, Pune, Maharashtra, 411008, India 2 Tata Institute of Fundamental Research, Hyderabad, 500107, India

3 Indian Institute of Technology, Hyderabad, 502285, India

*email address: ramgopal@tifrh.res.in, vsharma@iith.ac.in

Polarizability is a fundamental molecular property governing inter-molecular and

light-molecule interactions. Molecules, seeking to minimize their energy in the presence

of a short lived but intense laser field, undergo rotation and alignment mediated through

the static polarizability. Here, we demonstrate an anomalous suspension of this alignment,

as observed through the velocity imaging of the fragmentation following the strong field

ionization of O2 molecule by ultrashort (35 fs, 400 nm) laser pulses. Alternately, in

concomitant experiments with 800 nm laser pulses (25 fs), the expected alignment is indeed

observable. We analyze these results in conjunction with a semi-classical model of the

induced rotation in the molecular ion involving polarizabilities of the participating excited

states. It emerges that a transient negative polarizability on the time scales of several

femtoseconds frustrates the alignment of the molecular ion. This singular molecular

behaviour, visualized here for the first time in fragmentation, is not only of fundamental

interest, but can potentially be applied for terahertz photonics.

17

INVITED LECTURES: IL 2

Elucidating the Transient Raman Signature of a Twisted

Intramolecular Charge Transfer State Jyotishman Dasguptaa

a Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai.

Charge transfer (CT) states provide a facile access to separate strongly bound

excitons (electron-hole pairs) in organic materials thereby enabling robust initiation of

photochemistry. From photocatalytic fuel synthesis to functional materials for photovoltaic

devices, the efficiencies of all the light-triggered processes critically depend on tuning the

energy, spatial extent and lifetime of the CT states. In this talk, I will describe our efforts

to visualize the ‘twisted intramolecular charge transfer’ (TICT) state in biomolecular

fluorescent probes that show large structural relaxation in the excited state. We find an

unequivocal transient Raman signature of the TICT state in mitochondrial staining donor-

π-acceptor class of stillbazolium dyes. Resonance-enhanced femtosecond stimulated

Raman spectroscopy (FSRS)1 of 4 N,N-diethylamino-4˝-Nˊ-methyl-stilbazolium tosylate

(DEST) revealed the appearance of a distinct blue-shifted vibrational peak at 1650 cm-1.2

Using electronic structure calculations with explicit solvent models, the peak was assigned

to a new mode: an isolated pyridinium ring symmetric C=C stretch belonging to the TICT

excited state of DEST. The rise and decay of the TICT 1650 cm-1 Raman marker mode

captured by FSRS correlates with the excited state dynamics obtained via femtosecond

broadband transient absorption (TA) spectroscopy. Our study demonstrates that time-

resolved vibrational Raman spectra, interpreted with support from appropriate electronic

structure calculations can be an effective structural probe for identifying the spatial location

of the “twist” in TICT-based molecular dyes.

REFERENCES:

1. Palas Roy,

2. Shreetama Karmakar, to be submitted.

18

INVITED LECTURES: IL 3

How to use electronic flux density maps as a tool to unravel ultrafast

correlated electron dynamics Jean Christophe Tremblaya

a Laboratoire de Physique et Chimie Théoriques CNRS/Université de Lorraine - UMR 7019, 1 Bd Arago,

57070 Metz (France) jean-christophe.tremblay@univ-lorraine.fr

Understanding how electrons flow during reactions remains a question of central

importance in chemistry, as it helps unravelling the mechanism of electron rearrangements

leading to chemical transformations and to the emergence of specific properties. In this

contribution, I illustrate how time-dependent electronic current density maps can be used

to visualize and interpret such processes from first principles many-electron dynamics

simulations. These quantities are related by the quantum continuity equation, which is a

reformulation of the many-body Schro ̈dinger equation into a one-body hydrodynamic-like

transport equation.

I will first introduce a many-body wave-function simulation method, the Time-

Dependent Determinantal Configuration Interaction (TD-detCI), to study light-induced

ultrafast charge migration dynamics in rigid molecules and nanostructures. A posteriori

reduction of the many-body electronic wave packets dynamics then leads to the electronic

continuity equation, which allows to follow the time-evolution of electrons as the flow of

an electronic fluid. I will further show how time-resolved X-ray diffraction measurements

are related the transient electronic flux density.

To investigate chemical reactions, I will explain how an electronic continuity

equation can be derived within the Born-Oppenheimer approximation, and how the

associated current density can be used to extract mechanistic information about electron

reorganization during simple reactions. This new visualization technique provides an

unbiased first principles approach for drawing curly arrows – a concept dear to the chemists

when rationalizing reaction mechanisms.

REFERENCES:

1. G. Hermann, V. Pohl, and J.C. Tremblay “An Open-Source Framework for Analyzing N-Electron

Dynamics: II. Hybrid Density Functional Theory/Configuration Interaction Methodology”, J.

Comput. Chem. 38, 2378 (2017).

2. G. Hermann, V. Pohl, G. Dixit, and J.C. Tremblay “Probing Electronic Fluxes via Time-Resolved

X-ray Scattering”, arXiv:1907.00891 (2019).

3. V. Pohl and J.C.Tremblay “Adiabatic Electronic Flux Density: A Born-Oppenheimer Broken

Symmetry Ansatz”, Phys. Rev. A 93, 012504 (2016).

19

INVITED LECTURES: IL 4

Hydrocarbon Chain-Length Dependence of Solvation Dynamics in Alcohol-Based

Deep Eutectic Solvents: A 2D IR Spectroscopic Investigation

Sayan Bagchi, Srijan Chatterjee, Deborin Ghosh, Tapas Haldar, Pranab Deb, Sushil S.

Sakpal, Samadhan H. Deshmukh, Somnath M. Kashid

Physical and Materials Chemistry Division, CSIR-National Chemical Laboratory, Pune 411008, India

Deep eutectic solvent (DES) has gained popularity in recent years as an

environmentally benign, inexpensive alternative to organic solvents for diverse

applications in chemistry and biology. Among them, alcohol-based DESs serve as useful

media in various applications due to their significantly low viscosity as compared to other

DESs. Despite their importance as media, little is known how their solvation dynamics

change as a function of the hydrocarbon chain-length of the alcohol constituent. In order

to obtain insights into the chain-length dependence of the solvation dynamics, we have

performed two-dimensional infrared spectroscopy on three alcohol-based DESs by

systematically varying the hydrocarbon chain-length. The results reveal that the solvent

dynamics slow down monotonically with increase in the chain-length. This increase in the

dynamic timescales also show a strong correlation with the concomitant increase in the

viscosity of DESs. In addition, we have performed MD simulations to compare with the

experimental results, thereby testing the capacity of simulations to determine the

amplitudes and timescales of the structural fluctuations on fast timescales under thermal

equilibrium conditions

REFERENCES

1. J. Phys. Chem B, DOI: 10.1021/acs.jpcb.9b08954

20

INVITED LECTURES: IL 5

Ultrafast Excited State Dynamics of Twisted Aromatics

Mahesh Hariharana

a School of Chemistry, IISER Thiruvananthapuram, mahesh@iisertvm.ac.in

Self-assembling of organic chromophoric systems into elegant supramolecular

architectures with emergent properties has received prodigious attention in recent years.1

The notion of ‘emergence upon assembly’ is evidenced in the unusual photoexcited state

dynamics exhibited by chromophoric assemblies. In the first example, a naphthalene-

naphthalimide donor-acceptor (D-A) dyad assembled into segregated D-A stacks in the

crystalline state (Figure 1). The photo-induced charge separated state in the aggregate state

lasts 10,000 times longer than the monomeric dyad. The femtosecond transient absorption

spectra depicted the spectroscopic signature for naphthalene dimer radical cation indicating

the migration of charges through the stacks.2 In the second example, we report the

crystalline evidence for Greek cross‐dipole (α=90°) stacking of 1,7‐dibromoperylene‐3,4,9,10‐tetracarboxylic tetrabutylester (PTE‐Br2) displaying null excitonic coupling and

thereby monomeric optical behavior. Additionally, the semi‐classical Marcus theory of

charge‐transfer rates predicted a selective hole transport phenomenon in the orthogonally

stacked PTE‐Br2.3 In the third example, we showcase a radial assembly of 1,8-

dibromonaphthalene(2,6-diisopropylphenyl)imide (NIBr2) in crystalline phase driven by

hexabromine synthon.4 NIBr2 exhibits ultrafast intersystem crossing5 and solid-state room

temperature phosphorescence. We believe the fundamental understanding of noncovalent

interactions dictating the unorthodox assembly of chromophores6 and probing of emergent

properties are paramount for the rational design and construction of robust functional

materials.

Figure 1. Representative strategies adopted in our group to spatially organize organic

chromophores for emergent properties.

REFERENCES

1. R. T. Cheriya, A. R. Mallia, M. Hariharan, Energy Environ. Sci. 2014, 7, 1661.

2. A. R. Mallia, P. S. Salini, M. Hariharan, J. Am. Chem. Soc. 2015, 137, 50, 15604.

3. E. Sebastian, A. M. Philip, A. Benny, M. Hariharan, Angew. Chem., Int. Ed. 2018, 57, 15696.

4. M. A. Niyas, R. Ramakrishnan, V. Vijay, E. Sebastian, M. Hariharan, J. Am. Chem. Soc. 2019, 141, 4536.

5. K. Nagarajan, A. R. Mallia, K. Muraleedharan, M. Hariharan, Chem. Sci. 2017, 8, 1776.

6. R. Ramakrishnan, M. A. Niyas, M. P. Lijina, M. Hariharan, Acc. Chem. Res. 2019, 52, ASAP

21

INVITED LECTURES: IL 6

Effect of Alloy-Shelling on Ultrafast Dynamics in Semiconductor Quantum Dots

Prasun K. Mandala,b aDepartment of Chemical Sciences, bCentre for Advanced Functional Materials, Indian Institute of Science

Education and Research (IISER) Kolkata, Mohanpur, West Bengal, 741246, India.

e-mail:prasunchem@iiserkol.ac.in

Ultra-bright and ultra-stable semiconductor quantum dots (QDs) are becoming

popular towards different applications such as LEDs, photovoltaics, optoelectronics, bio-

imaging etc.1-3 Different kinds of chemical modification towards obtaining optically

superior QDs will be discussed.4-10 QDs tend to follow Kasha's rule (i.e. excitation

wavelength independent PL emission maximum) but not the Vavilov's rule (i.e. excitation

wavelength independent PL quantum yield). Ultrafast dynamical investigations have been

employed to reveal details of exciton (both electron and hole) dynamics and also the effect

of interaction of the excitons with trap states towards modifications of the exciton

dynamics.7 Results obtained from these detailed analyses could explain why QDs follow

Kasha's rule but not Vavilov's rule.

Results from different types of core/alloy-shell QDs will be elaborated.

REFERENCES

1. J. S. Yao, J. Ge, B. N. Han, K. H. Wang, H. B. Yao, H. L. Yu, J. H. Li, B. S. Zhu, J. Z. Song, C.

Chen, Q. Zhang, H. B. Zeng, Y. Luo, S. H. Yu, J. Am. Chem. Soc. 2018, 140, 3626.

2. Q. A. Akkerman, M. Gandini, F. Di Stasio, P. Rastogi, F. Palazon, G. Bertoni, J. M. Ball, M. Prato,

A. Petrozza, L. Manna, Nat. Energy 2016, 2, 16194.

3. H. Zhang, X. Wang, Q. Liao, Z. Xu, H. Li, L. Zheng, H. Fu, Adv. Funct. Mater. 2017, 27, 1604382.

4. D. Hahm, J. H. Chang, B. G. Jeong, P. Park, J. Kim, S. Lee, J. Choi, W. D Kim, S. Rhee, J. Lim, et

al. Chem. Mater. 2019, 31, 3476-3484.

5. X. Shen, Y. Zhang, S. V. Kershaw, T. Li, C. Wang, X. Zhang, W. Wang, D. Li, Y. Wang, M. Lu,

L. Zhang, C. Sun, D. Zhao, G. Qin, X. Bai, W. W. Yu, A. L. Rogach, Nano Lett. 2019, 19, 1552-

1559.

6. D. Roy, T. Routh, A. V. Asaithambi, S. Mandal, P. K. Mandal, J. Phys. Chem. C 2016, 120, 3483-

3491.

7. D. Roy, A. Das, C. K. De, S. Mandal, P. R. Bangal, P. K. Mandal, J. Phys. Chem. C, 2019, 123,

6922-6933.

8. D. Roy, S. Mandal, C. K. De, K. Kumar, P. K. Mandal, Phys. Chem. Chem. Phys. 2018, 20, 10332-

10344.

9. C. K. De, T. Routh, D. Roy, S. Mandal, P. K. Mandal, J. Phys. Chem. C 2018, 122, 964-973.

10. C. K. De, D. Roy, S. Mandal and P. K. Mandal, J. Phys. Chem. Lett. 2019, 10, 4330-4338.

22

INVITED LECTURES: IL 7

Electron Acceleration using Laser Fields at Extreme Intensities in

Plasmas: An Advanced Accelerator Concept

Anand Moortia,b

a Advanced Plasma Acceleration Section, Laser Plasma Division, RRCAT, Indore 452013 b Faculty of Physics, Homi Bhabha National Institute, Anushakti Nagar, Mumbai 400094

E-mail: moorti@rrcat.gov.in

LASER is one of the greatest inventions in the modern time, and along with variety

of direct applications in almost every aspect of life, has also been recognized as a

ubiquitous tool for the progress of advanced science and technology. It could be possible

due to development of variety of lasers covering a wide range of parameters during last

several decades. In case of pulsed lasers, with successive advancements in the mode-

locking techniques, pulse duration has eventually been brought down in the femtosecond

(ultra-short) regime. Subsequently, using Chirped Pulse Amplification (CPA) technique,

ultra-short pulse duration laser systems providing peak powers of several Terawatt (TW)

to few Petawatt (PW) level became a reality. In CPA technique, an ultra-short duration

laser pulse is first temporally stretched, and after desired level of amplification in the

various amplifier stages, is compressed back to the ultra-short duration providing high peak

power. Impact of this technique on utilization of ultra-short pulse duration lasers in variety

of fields was widely appreciated when inventors of this scheme, G. Mourou and D.

Strickland, were jointly awarded Nobel Prize in Physics, 2018.

Availability of high-power ultra-short duration laser systems, providing extreme

intensities (~1018 Wcm-2 to greater than 1020 Wcm-2) when focused to a tiny spot of several

microns diameter, has dramatically changed the physics and applications of high-intensity

laser matter interaction1. One of the areas where it could have a profound impact is the

development of particle accelerators. Various advanced accelerator concepts on utilization

of huge electric fields associated with intense, ultra-short laser pulses have been proposed

and being investigated. Potential techniques based on laser plasma interaction at ultra-high

intensities, and utilization of laser as well as fields generated in plasma has been

developed2. For example, intense, ultra-short laser pulse could drive giant electron plasma

wave which could be used for accelerating electrons to few GeV in a small interaction

length of few cm. Such compact accelerators could also facilitate development of laser

driven synchrotron (x-rays and -rays) sources. In this talk, a brief overview of laser plasma

based advanced acceleration techniques, and recent experimental investigations performed

in this area at RRCAT, Indore, would be presented.

REFERENCES:

1. A. Moorti, Kiran: A Bulletin of the Indian Laser Association, 2015, 26(2), 19.

2. A. Moorti, Physics News, Bulletin of the Indian Physics Association, 2018, 48(3), 19.

23

Invited Lectures: IL 8

Kamal P. Singh

24

INVITED LECTURES: IL 9

PROBING THE ORIGIN OF SELF TRAPPED EXCITONS IN HYBRID LEAD

HALIDE PEROVSKITES USING TIME-RESOLVED SPECTROSCOPY

Shabnum M. Bhat, Sneha Banerjee and Pankaj Mandal Department of Chemistry, Indian Institute of Science Education and Research, Pune 411008, Maharashtra

India

Lead halide perovskites have emerged as an interesting class of materials

because of their marvelous photo-physical properties like high PL quantum yield, narrow

emission bandwidth, low threshold lasing, high PCE, etc.1 These unique properties are due

to their intrinsic defect tolerant band structure as compared to conventional

semiconductors. Lead halide perovskites crystalize in a variety of structures ranging from

3D to 0D. Lower dimensional lead halide perovskites (2D, 1D, 0D) show some interesting

optoelectronic properties. Interestingly, the optical properties in lower-dimensional lead

halide perovskites strongly depend upon A-site cation, which is not the case in 3D analogs.

In addition to quantum confinement, the lower dimensional perovskites also show

dielectric confinement.

We synthesized strongly confined one dimensional (1D) Pyridinium lead

bromide (PyPbBr3) perovskite single crystals. Due to strong confinement in two

dimensions and the presence of an aromatic cation, these perovskite crystals show

interesting optical properties. A strong and highly stokes shifted PL emission is observed,

at room temperature. The origin of this emission is attributed to exciton self-trapping.2 We

used Optically Heterodyned-Optical Kerr Effect Spectroscopy (OH-OKE) to understand

the mechanistic origin of this self-trapped excitonic emission and the role of aromatic π-

electron cloud in exciton self-trapping. Indeed there is a strong influence of presence of

this cation, which manifests in its optical properties and structural dimensionality.

REFERENCES:

[1] Akkerman Q., et.al, Nat. Mater., (2018), 394, 17.

[2] Smith D., et.al, Acc. Chem. Res., (2018), 619, 51.

25

INVITED LECTURES: IL 10

Opportunities in ultrafast science with laser generated XUV pulses Sivarama Krishnan

1 Department of Physics, Indian Institute of Technology – Madras, Chennai 600036, India.

Email:srkrishnan@iitm.ac.in

In this talk we will present some perspectives of intense laser matter interaction

leading to the generation of XUV pulses from commonly available NIR femtosecond

pulses and possible opportunities in using these to explore nanoscale matter based on

currently ongoing studies using synchrotron light. An analysis of the Strengths,

Weaknesses, Opportunities and Threats (SWOT) in this approach in comparison with

synchrotron and fast evolving free-electron laser pulses will be attempted. Bringing up

issues of coherence, mono- vs. poly-chromaticity, tenability, brilliance and related issues,

this talk intends to initiate and provoke discussion at this meeting, which will possibly be

both stimulating and spontaneous.

REFERENCES:

1. Krishnan, SR; Gopal, R; Rajeev, R; Jha, J; Sharma, V; Mudrich, M; Moshammer, R; Krishnamurthy,

M; Photoionization of clusters in intense few-cycle near infrared femtosecond pulses Physical Chemistry

Chemical Physics 16, 19, 8721-8730 (2014).

2.Buchta, Dominic; Krishnan, S. R et al., Charge transfer and penning ionization of dopants in or on

helium nanodroplets exposed to EUV radiation, The Journal of Physical Chemistry A 117, 21, 4394-

4403 (2013).

26

INVITED LECTURES: IL 11

Ansu Pandey

27

INVITED LECTURES: IL 12

Photoionization of polyatomic molecules: Molecular structure, ultrafast

dynamics and molecular movie

Rajesh K Kushawaha

AMOPH division, Physical Research Laboratory, Ahmedabad, 380009

Molecular rotations and vibrations are in picosecond to femtosecond time scale and

electron dynamics within atoms or molecules is in atto second time scale. Chasing and

controlling these dynamics will open an opportunity to do molecular engineering. The

femtosecond time resolved electron and ion imaging has been converted to movies for

understanding the structure and dynamics of molecular systems. In this talk, I will discuss

about photo induced processes in polyatomic molecules1. The molecular alignment using

pump-probe scheme and Velocity Map Imaging spectrometer will also be discussed. Recent

studies on the temporal evolution of electronic and nuclear wave packets created in strong-

field excitation of the carbon dioxide molecule using momentum-resolved ion spectroscopy

and channel-selective Fourier analysis will be presented. We found signatures of both,

electronic and vibrational excitations, which involve the ground and the first excited

electronic states, depending on the particular final state of the fragmentation2. Finally,

molecular movies on molecular rotation will be shown and related fundamental science will

be discussed.

REFERENCES: 1. Rajesh Kumar Kushawaha et al., Phys. Chem. Chem. Phys., 2019, 21, 13600-13610

2. Artem Rudenko et al, Faraday Discuss., 2016 194, 463-478

.

28

INVITED LECTURES: IL 13

Ultrafast dynamics in metal/semiconductor nanostructures Parinda Vasa

Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India

In this talk we shall discuss ultrafast pump-probe experiments performed in the

visible range on metal and metal/semiconductor nanostructures [1,2]. The experiments

performed on gold thin films show transient reflectivity changes in the visible, which

are related to the electron distribution around Fermi energy. In case of metal-

semiconductor hybrid nanostructures, the transient absorption exhibit the manifestation

of Purcell effect or the polariton formation depending on the strength of light-matter

interaction energy. A significant reduction in the relaxation time of the emitters is

observed in the strong coupling regime [1, 2].

REFERENCES:

1. P. Vasa and C. Lienau, ACS Photonics 2018, 5, 2.

2. A. Singh, G. Sharma, B. P. Singh, and P. Vasa, J. Phys. Chem. C 2019, 123, 16965.

29

INVITED LECTURES: IL 14

Ultrafast X-ray Scattering of Molecular Dynamics Adam Kirrandera

a University of Edinburgh, School of Chemistry, Edinburgh, EH9 3FJ, UK, Adam.Kirrander@ed.ac.uk

Rapid developments of new x-ray and electron scattering experiments provide

exciting opportunities for the study of ultrafast photochemical and photophysical

processes1–4. The focus of this talk is on the intersection of theory, simulations, and

experiments5–7. In particular, we will discuss new types of experiments that might

transgress the distinction between structural dynamics and spectroscopy7. Using

comprehensive simulations of nonresonant ultrafast x-ray scattering from a molecular

wavepacket, we examine the components that contribute to the total scattering signal. The

simulations demonstrate how the elastic component, which can be used to determine the

spatio-temporal structural dynamics of the molecule, also carries an imprint of the

electronic structure, and how the inelastic component depends on the geometry of the

molecule. Most interestingly, mixed coherent contributions to the scattering directly probe

transient electronic coherences in the molecule.

Figure 1. An XUV pump pulse excites a wave packet from the ground state of H2 onto an excited state. After

excitation, an x-ray pulse probes the system by nonresonant ultrafast scattering7.

REFERENCES:

1. M. P. Minitti et al., Phys. Rev. Lett. 2015, 114 255501.

2. H.-W. Yong et al., J. Phys. Chem. Lett. 2018, 9, 6556.

3. B. Stankus et al., Nature Chem. 2019, 11, 716.

4. J. M. Ruddock et al., Science Adv. 2019, 5, eaax6625.

5. A. Kirrander et al., J. Chem. Theory Comput. 2016, 12, 957.

6. A. Kirrander, P. M. Weber, Applied Science 2017, 7, 534.

7. M. Simmermacher et al., Phys. Rev. Lett. 2019, 122 073003.

30

INVITED LECTURES: IL 15

Probing lattice instabilities in thermoelectric SnSe using spectroscopic

studies Dipanshu Bansala

a Department of Mechanical Engineering, IIT Bombay, Mumbai, MH 400076 Understanding of lattice instabilities is critical to rationalize the underlying

physics of wide-range of materials, including thermoelectrics. Thermoelectrics hold

immense potential for technological breakthroughs in power requirement for deep space

missions and waste-energy recovery and are being rapidly commercialized. In this talk, I

will present our combined experimental (inelastic neutron scattering, nuclear resonance

inelastic x-ray scattering, time-resolved x-ray scattering measurements from X-ray free

electron lasers) and theoretical studies (anharmonic phonon simulations) of

thermoelectric SnSe as a function of temperature, pressure, and photoexcitation1-4.

In the thermoelectric conversion of thermal gradients into useful electrical energy,

the figure of merit, zT=S2σT/κ correlates inversely with thermal conductivity, κ (S is the

Seebeck coefficient and σ the electrical conductivity). As κ in a semiconductor is

dominated by the lattice component, κlat, sustained efforts seek to design materials that

suppress phonon propagation.

In thermoelectric SnSe, zT is found to be exceptionally high close to the phase

transition at 805 K, which is driven by condensation of the lattice instability5,6. This

lattice instability can also be triggered by pressure and photoexcitation. We probe the

lattice instability as a function of temperature, pressure, and photoexcitation using

neutron, x-ray, and free-electron laser sources. Combining measurements with

anharmonic phonon simulations, we rationalize the thermal transport and consequently

high thermoelectric conversion efficiency in SnSe. Experimental and theoretical tools

used here have broad applicability and can be applied to, for example, ferroelectrics and

superionic conductors to decipher the origin of the spontaneous polarization and liquid-

like thermal transport7,8.

REFERENCES:

1. D. Bansal, J. Hong, C.W. Li, A.F. May, W. Porter, M.Y. Hu, D.L. Abernathy, and O. Delaire.

“Phonon anharmonicity and negative thermal expansion in SnSe.” Physical Review B, Vol. 94,

054307, 2016.

2. C.W. Li, J. Hong, A. May, D. Bansal, S. Chi, T. Hong, G. Ehlers, and O. Delaire. “Orbitally-

driven giant phonon anharmonicity in SnSe.” Nature Physics, Vol. 11, No. 12, pg. 1063-1069,

2015.

3. S. Yang, D. Bansal et al., Unpublished.

4. T. Lanigan-Atkins, D. Bansal et al., Unpublished.

5. L.-D. Zhao, G. Tan, S. Hao, J. He, Y. Pei, H. Chi, H. Wang, S. Gong, H. Xu, V. P. Dravid, C.

Uher, G. J. Snyder, C. Wolverton, and M. G. Kanatzidis, Science 351, 141, 2016.

6. L.-D. Zhao, S.-H. Lo, Y. Zhang, H. Sun, G. Tan, C. Uher, C. Wolverton, V. Dravid, and M.

Kanatzidis, Nature (London) 508, 373, 2014.

7. D. Bansal, J.L. Niedziela, R. Sinclair, V. Ovidiu Garlea, D.L. Abernathy, S. Chi, Y. Ren, H. Zhou,

and O. Delaire. “Momentum-resolved observations of the phonon instability driving geometric

improper ferroelectricity in yttrium manganite.” Nature Communications, Vol. 9, Article No. 15,

2018.

31

8. J.L. Niedziela,* D. Bansal,* A. May, J. Ding, T. Lanigan-Atkins, G. Ehlers, D.L. Abernathy, A.

Said, and O. Delaire. “Selective breakdown of phonon quasiparticles across superionic transition

in CuCrSe2.” Nature Physics, Vol. 15, pg. 73-78, 2019. (*co-first authors)

INVITED LECTURES: IL 16

Intermolecular Tuning of Non-Adiabatic dynamics via Hydrogen

Bonding G. Naresh Patwari,a

a Department of Chemistry, Indian Institute of Technology Bombay, naresh@chem.iitb.ac.in

The excited state dynamics in several hydrogen-bonded complexes of

phenylacetylene and its fluorinated analogues were investigated using electronic

spectroscopic methods. The fluorescence properties of these complexes could be

modulated by changing one of the hydrogen bonding partners, either by appropriate

fluorine substitution on the phenyl ring or by modifying its hydrogen bonding partner. For

example, in the case of phenylacetylene complex with methylamine two distinct hydrogen-

bonded isomers were observed. The first one is characterized by the presence of C–H∙∙∙N

hydrogen bond while the other one consists of N–H∙∙∙π hydrogen bonding. Interestingly,

the N–H∙∙∙π complex was fluorescent in nature, while the C–H∙∙∙N hydrogen-bonded was

non-fluorescent. The most interesting aspect of the phenylacetylene-methylamine complex

is the structure dependent fluorescence quenching behavior. Evidently, the formation of

the C–H∙∙∙N hydrogen-bonded complex leads to fluorescence quenching while the

fluorescence is observed for the N–H∙∙∙π hydrogen-bonded complex. Amines are known to

be effective quencher via the electron transfer mechanism. In the case of N–H∙∙∙π complex

lone pair electrons on the nitrogen atom are free and relatively at a closer distance from the

π electron cloud of the benzene ring, which carries the excitation, for effective quenching.

Contrary to such expectation, the N–H∙∙∙π complex was found to be fluorescent, while

fluorescence quenching is effective in the C–H∙∙∙N hydrogen-bonded complex, wherein the

lone-pair electrons are engaged in hydrogen-bond formation. In an effort to determine the

excited state dynamics of phenylacetylene and two of its methylamine complexes and to

rationalize the fluorescence quenching behavior, time-resolved picosecond pump-probe

experiments were carried out The single exponential fits to excited state decay profiles of

N–H∙∙∙π and C–H∙∙∙N complexes yield lifetime of 0.56 ns and 2.95 ns, respectively.

However, it is very surprising to note that the excited state lifetime of the fluorescent N–

H∙∙∙π complex (0.56 ns) is lower than the non-fluorescent C–H∙∙∙N complex (2.95 ns),

which is completely counterintuitive to normal quenching mechanism, including the

electron transfer quenching mechanism. Given the fact that the excited state lifetime of the

non-fluorescent C–H∙∙∙N complex is higher than the fluorescent N–H∙∙∙π complex, the

fundamental question that arises is the, “what is the nature of the excited state?” The

experimental observations can be rationalized on the basis of non-adiabatic dynamics

introduced due to hydrogen bonding.

32

INVITED LECTURES: IL 17

Origin of Slow Solvation Dynamics in DNA: What is the Biological

Significance? Sobhan Sen

Spectroscopy Laboratory, School of Physical Sciences, Jawaharlal Nehru University, New Delhi 110067,

sens@mail.jnu.ac.in

Water around biomolecules is special for behaving strangely both in terms of

structure and dynamics, while ions are found to control various interactions in

biomolecules such as DNA, proteins and lipids. The questions that how water and ions

around these biomolecules behave in terms of their structure and dynamics, and how they

affect the biomolecular functions have triggered tremendous research activities worldwide.

Such activities not only unfolded important static and dynamic properties of water and ions

around these biomolecules, but also the debate regarding their explanation and role in

biological functions. DNA being negatively charged, it interacts strongly with surrounding

dipolar water and positively charged counterions – leading to complex electrostatic

coupling of water and ions with the DNA. Recent time-resolved fluorescence stokes shift

experiments and related computer simulation studies from our group and other laboratories

have unfolded many unique features of slow water and ion dynamics near DNA. In this

talk, it will be discussed how combining results from time-resolved fluorescence Stokes

shifts experiments from femtoseconds to nanoseconds and large-scale atomistic molecular

dynamics (MD) simulation on DNA one can unfold unique dynamic features of perturbed

water and ions near DNA. In particular, it will be shown that unlike in proteins and lipids,

the coupled (solvation) dynamics of water, ions and DNA can lead to dispersed slow

relaxation over broad time over several decades, whose origin lies mainly with the

dynamically coupled DNA-water motions.1 It is also found that such slow solvation

dynamics can possibly link to the DNA base-mismatch specific dynamics, which may act

as qunique cues in ultrafast time-scale for mismatch specific DNA regognition by

mismatch-repair enzymes.2

REFERENCES:

1. D. Sardana, K. Yadav, H. Shweta, N. S. Clovis, P. Alam, S. Sen, J. Phys. Chem. B 2019 (DOI:

10.1021/acs.jpcb.9b09275).

2. H. Shweta, M. K. Singh, K. Yadav, S. D. Verma, N. Pal, S. Sen, J. Phys. Chem. B 2017, 121, 10735.

33

INVITED LECTURES: IL 18

Ultrafast photoelectron-photoion coincidence imaging spectrometer to

explore molecular chirality. Saurabh Shuklaa, Sagnik Dasa, Rishabh Tripathia, Vinod Kumara and N Bhargava

Rama* a Department of Physics, IISER Bhopal

*nbhargavram@iiserb.ac.in

We have recently commissioned a dual velocity map imaging spectrometer capable

of measuring photoelectrons and photoions in coincidence at IISER Bhopal to study

photoionization dynamics in polyatomic molecules and specifically chiral molecules in the

UV and VUV regime. It is now established that chiral molecular potential leads to

asymmetric scattering of photoelectrons upon ionization by left and right circular polarized

light [1, 2, 3]. The use of short femtosecond pulses in the UV and the VUV regime in

combination with an electron-ion spectrometer will provide us complete kinematic and

differential information. I will describe the capabilities of the newly-built spectrometer and

our recent measurements. I will also review some latest developments on photoelectron

circular dichroism research from across the world.

REFERENCES:

1. B. Ritchie, Phys Rev A 13, 1411 (1976)

2. I Powis, Adv, in Chemical Physics 138, 267 (2008)

2. C S Lehmann, N Bhargava Ram, I Powis and MHM Janssen, J Chem Phys 139, 234307 (2013)

34

INVITED LECTURES: IL 19

Real-Time Four-Dimensional Spatio-Temporal Terahertz Imaging

using Intense Terahertz Pulse

Mukesh Jewariya,

CSIR-National Physical Laboratory-New Delhi-110012

E.mail: jewariya.mukesh@nplindia.org

We demonstrated four-dimensional spatio-temporal (4D-ST) terahertz (THz) imaging and

its applications for THz tomography, THz spectral imaging, and THz spectral computed

tomography (CT). The 4D-ST THz imaging enables to achieve incompatible high-speed

data acquisition. 3D THz reflection tomography is effectively used to visualize internal

structure of an object whereas 4-D image is its chemical composition.

In the recent years THz imaging with pulsed THz radiation has emerged an innovative tool.

The first demonstration of THz imaging was reported in 1995 by Hu et.al [1-3], later

several other THz imaging techniques have been reported by many other authors like

reflection tomography [4], spectral imaging [5], and computed tomography (CT) [6]. In

THz tomography the internal structure of the sample can be easily visualized by the

distribution of the group refractive index. This technique adopts a time-of-flight

measurement of THz echo pulses. In this method THz pulse is incident upon the sample in

transmission or reflection geometry. The commercially available method such as

ultrasound and X-ray need a “contact” for investigation and these are “invasive”. There is

a potential of damage and only external imaging information is obtained whereas THz

wave acts as a non-contact and non-invasive probe and obtain its internal structure and

chemical composition.

The 3D THz CT system is based on an amplified Ti:Sapphire laser with 1 kHz repetition

rate, 0.8 mJ/pulse, 800 nm central wavelength and 150 fs pulse duration. To perform fast

3D THz CT, the sample is set vertically (Y-axis) and first horizontally scanned with a

constant speed of 2 mm/s along the X-axis so that a whole 2D-ST image set can be acquired

for a given projection angle. Finally, for each projection angle and at every horizontal and

vertical sample positions, the pixel value is extracted by measuring the peak-to-peak value

of the THz temporal waveform pulse. After FFT of temporal data, the spectral amplitude

at a given frequency could also be extracted for spectral imaging [8]. Then, the application

of the well-known filtered backprojection (FBP) algorithm implemented in the ImageJ

software will numerically provide the multiplanar slices of the sample in order to finally

reconstruct the 3D volume [9]. The temporal data extracted from it added extra dimension

and tells about its chemical composition. This added temporal profile is the 4th dimension.

It is well-known that FBP suffers from several drawbacks such as beam hardening, which

can induce cupping, streaks and blurring because rays from some projection angles are

hardened to a differing extent than rays from other angles, confusing the reconstruction

algorithm. To reduce this phenomenon, it is important to record at least 36 projections. Of

35

course, depending on maximum data storage and acquisition time fixed by the operator, it

is also possible to record 72 projections with a 2.5° angle step. However, we considered

that the best compromise between reconstruction quality (contrast, intensity and geometric

preservation) and acquisition time consists in recording only 36 projections [10].

The main advantage of the proposed method relies on real-time THz line projection

providing 10 ms acquisition time of 2D-ST THz image. Therefore, 3D THz CT has been

performed in only a few minutes, representing a significant improvement compared with

common systems, which can be powerful for sensing, non-destructive inspection and

material characterization in real world applications.

REFERENCES:

[1] D. M. Mittleman, Sensing with THz radiation. Berlin: Springer, 2003.

[2] M. Tonouchi, “Cutting-edge terahertz technology,” Nature Photon., vol. 1, no. 2, pp. 97 – 105, Feb.

2007.

[3] B. B. Hu and M. C. Nuss, “Imaging with terahertz waves,” Opt. Lett., vol. 20, iss. 16, pp. 1716-1718,

Aug. 1995.

[4] D. M. Mittleman, S. Hunsche, L. Boivin, and M. C. Nuss, “T-ray tomography,” Opt. Lett., vol. 22, iss.

12, pp. 904-906, Jun. 1997.

[5] T. Löffler, T. Bauer, K. Siebert, H. Roskos, A. Fitzgerald, and S. Czasch, Opt. Express, vol. 9, iss. 12,

pp. 616-621, Dec. 2001.

[6] B. Ferguson, S. Wang, D. Gray, D. Abbott, and X.-C. Zhang, Opt. Lett., vol. 27, iss. 15, pp. 1312-

1314, Aug. 2002.

[7] A. J. Fitzgerald, B. E. Cole, and P. F. Taday, J. Pharm. Sci., vol. 94, no. 1, pp. 177-183, Jan. 2005.

[8] W.L. Chan, J. Deibel, and D. M. Mittleman, Rep. Prog. Phys. 70, 1325–1379 (2007).

[9] G. T. Herman, Image Reconstruction From Projections: The Fundamentals of Computerized

Tomography (Academic Press Inc., 1980).

[10] E. Abraham, A. Younus, C. Aguerre, P. Desbarats, and P. Mounaix, Opt. Comm. 283(10), 2050-2055

(2010).

36

Stabilization and sensing of G-quadruplex DNA structures with

indolylquinolinium based probes

Annyesha Biswas,a and Pradeepkumar P.I.* b a Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, India,

annyeshabiswas123@gmail.com

b Professor, Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, India,

pradeepkumarpi@gmail.com

G-quadruplexes (G4s), four stranded motifs formed by G-rich DNA/RNA

sequences of the genome or transcriptome and harbour significant biological importance.1

Owing to their dynamic existence and polymorphic nature, specific recognition of G4

structures by small molecule ligands is challenging.2 The ligands, which could turn-on

fluorescence upon interaction with G4 structures provide a powerful and direct tool for

their direct detection inside the cells.3,4 Towards this end, we report the synthesis of

fluorescent probes based on indolylquinolinium moiety, which are expected to have the

potential to stabilize and sense cellular G4 structures with high target selectivity and

specificity. CD melting experiments have shown, the best molecule InQEtPy acts as a G4

stabilizer with preferential stabilization of parallel topology of promoter c- MYC and c-

KIT1 G4s, over telomeric G4 and duplex DNAs. Fluorimetric titration data revealed ~10

fold fluorescence enhancement on interaction with c-MYC G4 structures. TCSPC

experiments of the dye in unbound state showed relatively faster lifetime than the bound

state with different DNAs with two excited state lifetime possibly indicating two binding

modes.The findings of this research work are expected to provide new fluorescent turn-on

probes for G4 nucleic acids, which could be utilized for diagnostic applications.

REFERENCES 1. Bochman, M.L.; Paeschke, K.; Zakian, V.A., DNA secondary structures: stability and function of G- quadruplex structures, Nature Reviews Genetics, 13, 770–780 (2012) 2. Hertsch, R.H.; Antonio, M.D.; Balasubramanian, S., DNA G-quadruplexes in the human genome: detection, functions and therapeutic potential, Nature Reviews Molecular Cell Biology ,18, 279–284 (2017) 3. Mohanty, J.; Barooah, N.; Dhamodharan, V.; Harikrishna, S.; P. I. Pradeepkumar.; Bhasikuttan, A.C.,Thioflavin T as an Efficient Inducer and Selective Fluorescent Sensor for the Human Telomeric G-Quadruplex DNA, J. Am. Chem. Soc., 135, 367−376 (2013) 4. Zhang, S.; Sun, H.; Wang, L.; Liu, Y.; Chen, H.; Li, Q.; Guan, A.; Liu, M.; Tang, L. Real-time Monitoring of DNA G-quadruplexes in Living Cells with a Small-molecule Fluorescent Probe, Nucleic Acids Res. 46, 7522-7532 (2018)

Figure 1.G- quadruplex

sensing by small

molecule ligand

37

Enzyme product releasing mechanism under piconewton force manipulation: A

single molecule investigation using photon time-stamping spectroscopy

Nibedita Pal, a Meiling Wu,b and H. Peter Lu*b

a Present address: Indian Institute of Science Education and Research (IISER) Tirupati, Andhra Pradesh

517507, India

b Department of Chemistry, Center for Photochemical Sciences, Bowling Green State University, Ohio

43403, USA

*hplu@bgsu.edu

The exploration of the conformational fluctuation of an enzyme during catalytic event has

significance implication in the field of enzymology. However, monitoring the

conformational fluctuation of an enzyme during essential steps of a catalytic reaction is

challenging due to transient nature of the intermediates. Using single molecule total

internal reflection fluorescence microscopy (TIRFM) guided confocal photon time-

stamping spectroscopy we have interrogated the conformational dynamics of Horseradish

Peroxidase enzyme. A nascent formed fluorogenic product is used as a probe reporting the

active site conformational behavior. We have unraveled the presence of complex

conformations during product release and the effect of mechanical perturbation on it.

38

Polyethylene glycols affect electron transfer rate in phenosafranin-DNA

Partha Pyne,a Nirnay Samanta,a Animesh Patra,a Aritra Das,b Pratik Sen,b Rajib Kumar

Mitraa aDepartment of Chemical, Biological and Macromolecular Sciences, S N Bose National Centre for Basic

Sciences, Block-JD, Sector-III, Salt Lake, Kolkata-700106, India; parthapyne@bose.res.in bDepart of Chemistry, Indian Institute of Technology Kanpur, Kanpur – 208 016, India

Real cellular environments are crowded to almost 40% of the total volume. It stands

interesting to study electron transfer (ET) rate during drug-DNA interaction in crowded

milieu. We have studied the emission characteristics of phenosafranine (PSF) intercalated

to calf thymus DNA in the presence of polyethylene glycols (PEGs) of different chain

lengths. The emission of PSF quenches severely when intercalated to DNA; the quenching

is released upon the addition of PEGs. The structural conformation of the CT DNA has

been established using circular dichroism spectroscopy. ps-resolved fluorescence

measurements reveal significant decrease in the contribution of the DNA induced quenched

time-constant of PSF upon the addition of PEGs, however, fs-resolved measurements show

nominal changes in the time constants. Our study shows that the electron hopping rate

through the guanine base in DNA core remains unaffected whereas the ‘through space’ ET

process is affected in the presence of crowders.

Fig a) Representative CD signal of DNA under PEG200. b) Plot of Tm with PEG

concentration. c) Representative fluorescence intensity of PSF under different PEG20

concentration. Relative fluorescence intensity under complete intercalating condition

(inset). d) Relative contribution of faster component with PEG concentration.

[PEG] (% W / V)0 5 10 15 20 25 30

Tm

(0C

)

55

60

65

70

75

80 EG

PEG200

PEG400

PEG1000

(b)

Wavelength (nm)

220 240 260 280

Elli

pticity (

mdeg

)

-12

-8

-4

0

4

8

DNA

10%

20%

30%

(a)

[PEG] (%W/V)

0 10 20 30

Rel. c

ontr

. of

fa

ste

r

0.0

0.2

0.4

0.6

0.8

1.0

EG

PEG200

PEG400

PEG1000

(d)

Wavelength (nm)

540 570 600 630 660

Flu

ore

scence I

nte

nsity (

a.u

)

0

2

4

6

8

10

Water

0%

10%

20%

30%

(c)

[PEG] (%W/V)

0 5 10 15 20 25 30

1

10

Rel. int.

EGPEG200 PEG400 PEG1000

39

Investigation on the ESPT Dynamics of D-Luciferin in Aqueous trifluoroethanol

and ethanol Mixtures Sk Imadul Islam1, Sumana Pyne1, Debasish Das Mahanta1, Souradip Dasgupta3, Anindya

Dutta3, Dipak Kumar Palit2 and Rajib Kumar Mitra1

1 Department of Chemical, Biological & Macromolecular Sciences, S. N. Bose National Centre for Basic

Sciences, Block JD, sector-III, Salt Lake, Kolkata-700106, INDIA, e-mail: imadulislam@bose.res.in 2 UM-DAE Centre for Excellence in Basic Sciences, Mumbai University, Kalina Campus, Santacruz (E),

Mumbai 400098, INDIA 3 Department of Chemistry, Indian Institute of Technology, Bombay, Powai, Mumbai 400076, INDIA

Proton transfer in binary mixture solvent has received much attention in the field of

chemistry and biology as biological proton transfer reactions ususlly take place in the

interfaces and liquid mixture can often reproduce such platform.1,2 We have investigated

intermolecular excited-state proton transfer (ESPT) of firefly’s chromophore D-luciferin

in two different aqueous-alcohol binary mixtures (ethanol, EtOH-water and

trifluoroethanol, TFE-water) using steady-state and ps as well as fs-resolved fluorescence

spectroscopic techniques. We aim to understand the differences of H-bonding affinity of

EtOH and TFE with water and its subsequent effect on the ESPT mechanism in these two

mixtures. We observe contrasting behaviour in emission intensity, fluorescence quantum

yield, fluorescence lifetime, radiative/non-radiative decay constant and ESPT kinetics of

both the forms (protonated and deprotonated) of D-luciferin in these two alcohol-water

binary mixtures. We have found that ESPT kinetics of D-luciferin in EtOH-water is faster

than that in TFE-water mixture. It increases near-linearly with Xw (mole fraction of water

in the mixture) in EtOH while in TFE the change is not linear. From the time-resolved

emission measurements at different wave lenghts, we construct the time resolved area

normalized emission spectra (TRANES) and find an iso-emissive point for TFE-water

system (upto Xw=0.6) while it is not evident in EtOH-water mixture. We infer that the

solvation dynamics and ESPT kinetics are comparable in EtOH while it is not so in TFE-

water mixture.

REFERENCES

1. Cohen, B.; Martin Álvarez, C.; Alarcos Carmona, N.; Organero, J. A.; Douhal, J Phys. Chem. B

2011, 115, 7637-7647.

2. Simkovitch, R.; Shomer, S.; Gepshtein, R.; Shabat, D.; Huppert, J Phys. Chem. A, 2014, 118,

1832-1840

40

Formation of Long Lived Triplets through Singlet Fission in Lycopene Aggregates

Arup Kundu, Jyotishman Dasgupta* Department of Chemical Sciences, 1 Homi Bhabha Road, Tata Institute of Fundamental Research, Mumbai

400005, India. Carotenoids are natural conjugated chromophores that efficiently harvest light

through singlet states as well as form photo-protective machinery in photosynthesis

through the formation of nascent triplet states.1 In recent years these chromophores have

been used in organic photovoltaic devices as materials for high-quantum yield triplet

generation through a process called singlet fission (SF). Singlet fission is a process by

which two triplets can be generated at the cost of one photon through an intermediate

singlet state which has a multi-excitonic triplet-triplet character localized over two distinct

molecules.2 It is however a challenge to stabilize these triplet states formed through SF for

utilization as charge carriers since they tend to recombine to re-form the parent singlets.

Here we use lycopene, a major plant carotene to demonstrate that tuning the aggregate

structures enables efficient singlet fission with long-lived triplet states. We prepared

lycopene H-aggregates from organic solution and probed the photoexcited dynamics using

femtosecond transient pump-probe spectroscopy in conjunction with steady-state

resonance Raman spectroscopy. Through a detailed kinetic analysis we confirmed the

emergence of a correlated triplet pair in 20 ps timescale which subsequently lead to the

formation of long lived triplet sate with lifetime of 155 μs.3 We envision that our results

provide a facile access to long-lived triplets and may have a potential application in organic

photovoltaics.

REFERENCES

1. a) Horton, P.; Ruban, A. V.; Walters, R. G. Regulation of Light Harvesting in Green Plants. Annu. Rev.

Plant Physiol. Plant Mol. Biol., 1996, 47, 655−684; b) Frank, H. A.; Cogdell, R. J. Carotenoids in

Photosynthesis. Photochem. Photobiol. 1996, 63, 257−264; c) Pascal, A. A.; Liu, Z.; Broess, K.; van Oort,

B.; van Amerongen, H.; Wang, C.; Horton, P.; Robert, B.; Chang, W.; Ruban, A. Molecular Basis of

Photoprotection and Control of Photosynthetic Light harvesting. Nature, 2005, 436, 134−137.

2. a) Wang C. and Tauber M. J., High-Yield Singlet Fission in a Zeaxanthin Aggregate Observed by

Picosecond Resonance Raman Spectroscopy, J. Am. Chem. Soc, 2010, 132, 13988–13991; b) Musser A. J.,

Maiuri M., Brida D., Cerullo G., Friend R. H.,and Clark J., The Nature of Singlet Exciton Fission in

Carotenoid Aggregates, J. Am. Chem. Soc. 2015, 137, 5130−5139; c) Smith M. B., and Michl J. Singlet

Fission, Chem. Rev. 2010, 110, 6891–6936.

3. A. Kundu and J. Dasgupta; to be submitted

41

Conformational Dynamics of c-MYC Promoter based i-Motif DNA in Crowded

Environments

Sneha Paul, Sk Saddam Hossain, Anunay Samanta a School of Chemistry, University of Hyderabad, Gachi Bowli, Hyderabad-500046,

sneha.paul0027@gmail.com

Cytosine-rich DNA sequences fold into secondary structures called i-Motifs, which are

usually stable at acidic pH.1 However, molecular crowding agents like polyethylene glycol

(PEG) are known to facilitate the formation of these structures even at neutral pH.2 As

crowding mimics the intracellular environment and not much is known about the folding

pathway of i-Motifs in such constrained condition, we have probed in detail the

conformational dynamics of a 22-mer c-MYC promoter based C-rich sequence (Py22) in

presence of PEG, employing single-molecule Förster resonance energy transfer (smFRET)

and fluorescence lifetime measurements. We find that the conformational change is not a

simple two-state transition (as observed in ensemble measurements) between a random coil

and folded i-Motif structure. Rather, it involves a partially folded conformation as

intermediate where the bases are not as efficiently stacked as in completely folded i-Motif.

The relative population of each species is found to be governed by the size and

concentration of PEG and 30% (w/w) PEG6000 is the optimum condition for the folding

of Py22. Under this condition, ~ 80% of Py22 exists in the fully folded i-Motif form and ~

15% of it is in the partially folded state.

REFERENCES

1. H. A. Assi, M. Garav, C. Gonzalez, M. J. Damha, Nucleic Acids Res. 2018, 46, 8038.

2. J. Cui, P. Waltman, V. H. Le, E. A. Lewis, Molecules 2013, 18, 12751.

42

Solvation dynamics in solvent free protein – polymer surfactant biomolecular assemblies

Tanuja Kistwala, Anasua Mukhopadhyaya, Kamendra Sharmaa, and Anindya Dattaa

a Department of Chemistry, Indian Institute Of Technology Bombay, Powai, Mumbai 400076,India

Solvent-free proteins have attracted tremendous attention in recent times, due to its

potential use as a green, nonaqueous solvent with low-volatility, for the synthesis of an

organic and inorganic compounds, as electrolytes, catalysis, etc.1,2 While dynamics of dye

labelled HSA has been reported3,4,5, We focus on solvation dynamics of solvent-free

protein, labelled with CPM dye (7-dimethylamino-3-(4-maleimidophenyl)-4-methyl-

coumarin to understand bound water dynamics. This study has been done using

Fluorescence correlation spectroscopy (FCS) with a conformational dynamics model of

data analysis and also a comparitive examination of hydrodynamic radii of different CPM

labelled HSA modified system. Solvent free causes blue shift in the emission maxima from

CPM covalently bound to HSA. The average solvation time is increased from 700 ps (CPM

bound to HSA) to 2 ns in presence of solvent free CPM labelled HSA. FCS suggest that in

solvent free system, diffusion coefficient decreases and hydrodynamic radius increases

which implies larger protien size.

REFERENCES

1. A. Mukhopadhyay, T. Das, A. Datta and K. P. Sharma, Biomacromolecules, 2018, 943–950, 19.

2. F. X. Gallat, A. P. S. Brogan, Y. Fichou, N. McGrath, M. Moulin, M. Härtlein, J. Combet, J.

Wuttke, S. Mann, G. Zaccai, C. J. Jackson, A. W. Perriman and M. Weik, J. Am. Chem. Soc., 2012,

13168–13171, 134.

3. U. Mandal, S. Ghosh, G. Mitra, A. Adhikari, S. Dey and K. Bhattacharyya, Chem. - An Asian J.,

2008, 1430–1434, 3.

4. D. K. Sasmal, T. Mondal, S. Sen Mojumdar, A. Choudhury, R. Banerjee and K. Bhattacharyya, J.

Phys. Chem. B, 2011, 13075–13083, 115.

5. S. K. Pal, J. Peon and A. H. Zewail, Proc. Natl. Acad. Sci., 2002, 1763–1768, 99.

43

Solute and Solvent Dynamics in Neat, and Wet-Octanol: Steady State and Time

Resolved Fluorescence Measurements

Narayan Chandra Matiy, Kajal Kumbhakar, Ranjit Biswas Chemical Biological and Macromolecular Sciences (CBMS)

S. N. Bose National Centre for Basic Sciences, JD Block, Sector III, Salt Lake, Kolkata 700106 India E-

mail: ranjit@bose.res.in

Neat 1-octanol and wet-octanol has been the subject of numerous studies due to

their property of membrane mimics.1-3Interaction and dynamics of different external

fluorescent solutes in neat and wet-octanol and as well as solvent dynamics have been

investigated via steady state and time-resolved fluorescence (TRF) measurements in the

temperature range of 283≤T/K≤323 with various mole fraction of water (XH2O = 0 to 0.20)

in the octanol rich region. Coumarin 153 (C153), Coumarin 343 (C343), trans-2-[4'-

(dimethylamino)styryl]benzothiazole DMASBT have been employed to investigate solute-

centre reactive and non-reactive relaxation dynamics in this aqueous mixture. Excitation

wavelength dependence of fluorescence emissions4,5 suggest that both the neat and aqueous

binary mixtures, within the lifetime of C343 (<life > 3-4 ns)6 and DMASBT (<life > 0.5

ns),7 are spatially heterogeneous. Fluorescence anisotropy studies with C153 and C343 in

neat and wet-octanol have been used to explore the solute-medium frictional coupling.

Inspite of nearly same size, rotation dynamic of C153 shows fractional viscosity

dependence while C343 nearly follows the Stoke-Einstein-Debye model. Dynamic

fluorescence stoke shift measurements detected fast (sub-nanosecond) and slow

(nanosecond) solvent relaxation time scale in these media.

REFERENCES

1. 1. S. E. Debolt, P. A. Kollman, J. Am. Chem. Soc. 1995, , 5316-5340, 117.

2. S. A. Best, K. M. Merz, C. H. Reynolds, J. Phys. Chem. B 1999, 714-726, 103.

3. J. L. MacCallum, D. P. Tieleman, J. Am. Chem. Soc. 2002, 15085-15093, 124.

4. Z. Hu, C. J. Margulis, PNAS 2006, 831-836, 103(4).

5. P. K. Mandal, M. sarkar, A. Samanta, J. Phys. Chem. B 2004, 9048-9053, 108.

6. S. Koley , H. Kaur and S. Ghosh, Phys. Chem. Chem. Phys. 2014, 22352, 16.

7. M. Kondo, X. Li, M. Maroncelli, J. Phys.Chem. B 2013, 12224–12233, 117.

44

Ultrafast Control for Perfumery Industries

Rohit Goswami,a Ashwini Kumar Rawat, b Debojit Chakrabarty,c Debabrata Goswamid a Department of Chemistry, IIT Kanpur, rgoswami@iitk.ac.in, a Department of Chemistry, IIT Kanpur, rashwini@iitk.ac.in b Head R&D and Quality, Jyothy Laboratories Ltd., debojit.chakrabarty@jyothy.com

c Faculty of Chemistry, IIT Kanpur, dgoswami@iitk.ac.in

The thermal lens (TL) effect is governed by the refractive index changes in a semi-

transparent medium and the subsequent competition between the convective and

conductive modes of heat dissipation1. Recent studies2 have shown the utility of this effect

as a probe for complex systems. The signal in alcohols3 is notable as it establishes a strong

correlation between the TL signal and physical properties, like mobility, steric effects, and

hydrogen bonding. The perfumery industries, unlike the rest of the chemical process

industries, remain largely untouched by the scientific community. The ‘accords’ or

perfumery primitives are still generated by manual labor, though a qualitative analysis of

perfumes is defined4 by the pyramid shown in Fig. 1. Quantitative estimators are few and

far apart, as empirical correlations like the odor value4 (OV) have to typically account for

variations in sociological conditions such and geography, gender and require a large

number of trained human specialists. The intractable complexity of multi-component

mixture analysis5 precludes the ability of the equation of state (EOS) methods to aid the

industry. Leveraging thermal lens effects as a control parameter obtained from our ultrafast

laser experiments, we have found a clear correlation between our TL data and are able to

use this as a quantitative measure to determine the optimal accord concentration. This shall

be of immense use to the perfumery industries, and also provides key insights into the

interplay of light-matter interactions.

Figure 1: The qualitative approach to traditional perfumery analysis4 where the

notes are analysed by odor-value correlations.

REFERENCES

1. I. Bhattacharyya, P. Kumar, D. Goswami, J. Phys. Chem. B, 2011, 115, 2

2. S. Singhal, S. Goswami, A. Banerjee, D. Goswami 2019 URSI AP-RASC 2019.

3. P. Kumar, S. Dinda, A. Chakraborty, D. Goswami, Phys. Chem. Chem. Phys. 2014, 16, 24.

4. M. A. Teixeira, O. Rodriguez, P. Gomes, V. Mata, A. Rodrigues, Oxford, England: Butterworth-

Heinemann 2012.

R. Taylor, R. Krishna, Taylor, John Wiley & Sons 1993.

45

Unveiling the Effect of Sugars on Dynamics of Different Fluorophores in the

Interior of Aerosol OT Lamellar Structures: From Picosecond-to-Femtosecond

Study

Meghna Ghosh, Rupam Dutta, Arghajit Pyne, Nilmoni Sarkar*

Department of Chemistry, Indian Institute of Technology, Kharagpur 721302, WB, India.

E-mail: nilmoni@chem.iitkgp.ac.in and nilmonisarkar1208@gmail.com

The anionic surfactant aerosol OT (AOT) can self-aggregate to produce

microheterogeneous confined assemblies such as reverse micelles (RMs) and lamellae

which can potentially mimic biological interfaces like cell membranes etc. On the other

hand, sugar molecules can stabilize biomembranes against extreme temperature changes.

In this study, we have performed a combination of steady-state and time-resolved

fluorescence measurements using three Coumarin dyes having significantly different

hydrophobicity to unveil the location of the sugars (sucrose and sucralose) and their

interactions with the lamellar structures. Our study reveals that sucrose molecules are

mostly present in the interfacial region whereas the most probable location of sucralose is

the interior of the AOT bilayer. This study provides an interesting aspect about the location

of two structurally similar sugar molecules inside the lamellae and their effect on the

dynamics of different Coumarin dyes.

REFERENCES

1. R. Dutta, M. Ghosh, A. Pyne, N. Sarkar J. Phys. Chem. B 2019,123, 117. 2. N. Nandi, K. Bhattacharyya, B. Bagchi Chem. Rev. 2000, 100, 2013.

3. D. De, A. Datta Langmuir 2013, 29, 7709.

46

Use of Dimeric Excited States of the Donors in D4-A Systems for Accessing White

light Emission, Afterglow and Invisible Security Ink

Harsh Bhatia,a Debdas Rayb

aDepartment of Chemistry, Shiv Nadar University, NH-91, Tehsil Dadri, Gautam Buddha Nagar, Greater

Noida, Uttar Pradesh, 201314, India

b Faculty of Chemistry, Shiv Nadar University, NH-91, Tehsil Dadri, Gautam Buddha Nagar, Greater

Noida, Uttar Pradesh, 201314, India, debdas.ray@snu.edu.in

Pure organic white light emitters with persistent room temperature

phosphorescence (RTP) feature have unique advantages and various potential applications.

However, the studies of single-component organic white light emitters with AG and visible

light excitation (VLE)-dependent efficient RTP features remain a challenging area of

research in photophysics. Herein, we synthesized three terephthalonitriles in which 2,3,5,6-

positions are covalently attached to 2-fluoro-phenoxy (TOF), 2-chloro-phenoxy (TOC),

and 2-methoxy-phenoxy groups (TOM)1 to give twisted geometries. We observed that

powder samples of both TOC and TOM show white light emission with CIE coordinates

of (0.32, 0.38) and (0.26, 0.33), respectively, while TOM gives VLE-dependent efficient

RTP under ambient conditions. In addition, both TOC and TOF exhibit a dim AG feature.

Spectroscopic studies reveal that emission of these chromophores originates via radiative

decay of monomeric excited states (singlet, triplet), dimer-like excited states (DLES)

(singlet, triplet), and aggregated triplet states. Detailed spectroscopic and X-ray analyses

reveal the signature of DLES that is formed via conformational reorganization of the

phenoxy donors in the excited states. Single-crystal X-ray diffraction analysis shows that

the multiple lp(O)···π(C≡N)/C≡C, Cl/F···π, and hydrogen-bonding interactions in the X-

ray structures play a significant role in facilitating intersystem crossing2, stabilizing

multiple triplet states, and suppressing nonradiative decay, thereby triggering dim

afterglow under ambient conditions. We found that TOC and TOF exhibit persistent RTP

with lifetimes of 139 and 736 ms, respectively, when embedded in polyvinyl alcohol

matrix. Given the persistent RTP feature, invisible security ink application is developed.

These results provide a strategy to design white light-emitting materials with afterglow and

visible light-activated efficient RTP features.

REFERENCES

1. H. Bhatia, D. Ray, DOI: 10.1021/acs.jpcc.9b07762.

M. A. El-Syed, J. Chem. Phys. 1963, 38, 2834.

47

Origin of Slow Solvation Dynamics in DNA: DAPI in Dickerson-DNA

Deepika Sardana, Kavita Yadav, Him Shweta, Ndege Simisi Clovis, Parvez Alam,

Sobhan Sen*

School of Physical Sciences, Jawaharlal Nehru University,

New Delhi, India

Email: sens@mail.jnu.ac.in

Time-resolved fluorescence Stokes shift (TRFSS) experiments measure dynamics of

complex biomolecules and their surrounding environment from femtoseconds to

nanoseconds. These

experiments unravel

anomalously slow solvation

dynamics in DNA beyond

~100 ps, whose origin remains

incomprehensible. We

compare results of TRFSS

experiments to MD

simulations of minor groove-

bound DAPI in Dickerson-

DNA over five decades of

time from 100 fs to 10 ns.1 We

show the solvation time-

correlation function (TCF)

calculated from (200 ns)

simulation trajectory captures

most features of slow

dynamics, as measured in

experiment. Decomposition

of TCF into components

resolves that slow dynamics originate from dynamically coupled DNA-water motion. This

dynamically coupled DNA-water motion dominate in the slow solvation relaxation when

probed by minor groove-bound DAPI in Dickerson-DNA, although the effect of water-Na+

coupled motion on slow dynamics cannot be overlooked. We find that freezing DNA

fluctuations in simulation eliminates slower dynamics beyond ~100 ps, where water and

Na+ dynamics become faster, although signature of strong anti-correlation is captured.

Results show that primary origin of slow dynamics lies within slow fluctuations of DNA-

parts which perturb nearby water and ions to govern the slow concerted solvation dynamics

in Dickerson-DNA.

REFERENCES:

[1] Verma, S. D.; Pal, N.; Singh, M. K.; Sen, S. Sequence- Dependent Solvation Dynamics of Minor-Groove

Bound Ligand inside Duplex-DNA. J. Phys. Chem. B 2015, 119, 11019-11029.

Figure 1. Left - Snapshot from MD simulation showing 22 water

molecules and 3 Na+ which reside within 4 Å from the DAPI in

minor-groove of Dickerson-DNA scales at a probe-site inside

biomolecule (blue probe-molecule inside groove of DNA). Purple

and green balls represent ions. Right- Comparison of absolute Stokes

shifts of DAPI in Dickerson-DNA calculated from TRFSS

experiments and simulation. And inset shows Linear response

decomposition (LRD) of total simulated TCF(white) into partial-

TCFs of water (blue), DNA (green), Na+ (red) and Cl (purple)

48

[2] Sardana, D.; Yadav, K.; Shweta, H.; Clovis, N. S.; Alam, P, Sen, S. Origin of Slow Solvation Dynamics

in DNA: DAPI in Minor Groove of Dickerson-DNA. (Manuscript Submitted)

49

Impact of Urea on Structure and Dynamics of an Ionic Deep Eutectic Solvent:

Exploration through Reactive and Non-Reactive Solute Centered Dynamics

Arnab Sil,Sirshendu Dinda,Ranjit Biswas

Department of Chemical Biological & Macromolecular Sciences Technical Research Centre

S.N.Bose National Centre For Basic Sciences, JD Block, Sector III, Salt Lake, Kolkata-700106

E-mail: ranjit@bose.res.in

We have prepared electrolyte and amide based deep eutectic solvents (DES)

where both acetamide and urea have been used as amide source. The effect of urea on the

structural and dynamical heterogeneities in these DESs have been studied in detail by

both steady state and time-resolved fluorescent measurements of fluorescent solute

coumarine153 (C153)1. The result shows strong decoupling of viscosity from diffusion

for all the DESs studied and addition of urea does not modify this decoupling. The

decoupling in these DESs is attributed to the presence of structural and dynamical

heterogeneities2. After characterizing these DESs, we have applied these DESs medium

to study the medium impact on photo induced trans to cis isomerisation of trans- 2-[4’-

(Dimethylamino) styryl] benzothiazole (DMASBT). It has been observed that presence of

urea does not alter the rate of reaction but addition of electrolyte (keeping the amide

percentile constant in the DESs) enhances the photochemical reaction.

REFERENCES

1. Manuscript under preparation: Sirshendu Dinda, Arnab Sil, Ranjit Biswas

2. M. D. Ediger, C. A. Angell and S. R. Nagel, The Journal of Physical Chemistry 1996,

13200-13212 ,100 (31).

3. M. Kondo, X. Li, M. Maroncelli, J. Phys.Chem. B 2013, 12224–12233, 117.

50

Solvation Dynamics in Mycobacterial Membranes Probed by Time-Resolved

Laurdan Fluorescence

Pranav Adhyapaka, Shobhna Kapoora a Department of Chemistry, Indian Institute of Technology Bombay, shobhnakapoor@chem.iitb.ac.in

Mycobacterium Tuberculosis serves as an epitome of how lipids—next to

proteins—can be utilized as central effectors in pathogenesis and arduously construct an

excellent barrier against most drugs.1-2 Aptly, mycobacteria use substantial amount of its

genome to synthesis atypical long (C60–90) chained and branched lipid molecules and

employs an array of specialized protein machinery to localize these lipids to distinct spatial

locations, inner (IM) and outer membrane (OM). The hydration properties of the lipid

membrane are highly essential for cell membrane activity ranging from regulating protein

function to lipid diffusion and drug transport3 and the significance of same especially in

structurally unique mycobacterial membranes remain hitherto unknown. By combining

steady state and time-resolved fluorescence using solvatochromic lipid probe Laurdan, we

have obtained unprecedented insights into the solvation dynamics of these unusual lipid

assemblies. Further we compare the behavior of mycobacterial lipids with eukaryotic

phospholipids thus elucidating the role of long acyl chains and branches in the lipid

structure on solvation properties. Finally, with fluorescence recovery after photobleaching

(FRAP), we correlate the water hydration dynamics to diffusion of lipids within

mycobacterial membranes. Investigating the solvation properties of the inner and outer

membrane lipids in a systematic manner presents a golden opportunity to deepen our

understanding of these spatially and compositionally distinct membrane platforms and their

plausible functional roles in bacterial survival, drug resistance, and pathogenesis.

REFERENCES

1. M. Mishra, S. Kapoor. Scientific Reports. 2019. https://doi.org/10.1038/s41598-019-49343-2

2. M. Siegrist, CR. Bertozzi. Cell Host Microbe. 2014, 15, 1-2.

3. P. Adhyapak and S. Kapoor. J Membrane Biol. 2019. https://doi.org/10.1007/s00232-019-00087-0

51

MODULATING INTERACTION MECHANISM OF DUPLEX DNA WITH

GRAPHENE OXIDE EMPLOYING TWO DIVERSE BINDERS

Sangita Kundu, Nilmoni Sarkar* Department of Chemistry, Indian Institute of Technology Kharagpur, Kharagpur 721302, WB, India

E-mail: sangitakundu13@gmail.com

Aside from the conventional genetic roles, double stranded DNA molecules (dsDNA) are

employed in versatile applications in the field of the chemistry, biology and medical. The

amalgamation of these molecules with the graphene based nanomaterials making them

more potent in the biomedical, sensing and bioimaging applications. Here, we have

successfully explored the strong interaction of duplex DNA with graphene oxide (GO) and

the detailed analysis of the photophysical behaviour has been carried out using two

different DNA binding probes. The rotational and translational diffusion properties of these

fluorophores in presence of this DNA-GO bioconjugate are different depending on the

preferential location inside the DNA helix. Ultrafast spectroscopy has been employed to

elucidate the quenching mechanism of the two dye labeled DNA in presence of GO.

Furthermore, conformational alteration of dsDNA in presence of intercalator, EB

(Ethidium Bromide) and groove binder, DAPI (4'-6-diamidino-2-phenylindole) facilitate

the unusual restricted interaction of duplex DNA with GO. Our present finding can provide

a deep understanding of the unusual interaction between duplex DNA and GO. This

nanostructured biointerface material can be used as the potential candidate in cell imaging,

drug delivery and biosensing in near future.

Figure 1. Structural deformation of DNA in presence of GO and the effect on the dynamics

and diffusion properties of dye bound DNA in presence of GO.

REFERENCES

1. X.Zhao. J. Phys. Chem. C, 2011,115, 6181-61897.

2. L. Tang, H.Chang, Y. Liu, J. Li. Adv. Funct. Mater, 2012, 22, 3083-3088.

3. S.Kundu, R. Dutta, A. Pyne and N. Sarkar. J. Phys. Chem. C, 2018,122, 6876-6888.

0.0

0.7

-1 0 1 40 500.0

0.7

0.0

0.7

0.0

0.7

No

rm

alize

d C

ou

nts

Delay Time (ps)

0 2 4 6 8 10 12

0.1

0.2

0.3

0.4

Time (ns)

48 g/ml

0 g/ml GO

r (t

)

10 100 1000 10000 1000000.0

0.4

0.8

1.2 0 g/ml GO

10 g/ml GO

20 g/ml GO

40 g/ml GO

50 g/ml GO

60 g/ml GO

70 g/ml GO

G(

)

Time (s)10 1000 100000

0.0

0.4

0.8

0 g/ml GO

10 g/ml GO

20 g/ml GO

40 g/ml GO

70 g/ml GO

G(

)

Time (s)

Static Quenching

Electron Transfer

52

Room Temperature Exciton and Trion Formation in Monolayer MoS2

Followed by Dissociation in Presence of Au NPs

Tanmay Goswami,a Renu Rani,a Kiran Shankar Hazra,b Hirendra N. Ghosh*,c

a PhD student, Institute of Nano Science & Technology, Habitat Centre, Sector 64, Mohali, Punjab

b Faculty, Institute of Nano Science & Technology, Habitat Centre, Sector 64, Mohali, Punjab

c Professor, INST, Mohali, Punjab; On deputation from Bhabha Atomic Research

Centre(BARC), Mumbai

Email ID: tanmay.ph17208@inst.ac.in

2D transition metal dichalcogenides have gained incredible interest and importance in

recent times, owing to their unique tunable optical, electronic and mechanical behaviours.

Reduced dielectric constant in 2D system, results in strong interactions between

quasiparticles, allowing formation of several stable many body states like excitons1, bi-

excitons2, and trions3 even at room temperature. Photophysical properties of 2D materials

are dominated by the behaviour of these quasiparticles and they are instrumental for various

applications of those materials. Here, we have studied carrier dynamics of monolayer MoS2

deposited on SiO2/Si substrate, before and after Au NP deposition, using broad band

femtosecond transient absorption spectroscopy4. Presence of both exciton and trion was

confirmed from steady state Photo-Luminescence (PL) measurements. MoS2 PL was

drastically quenched after deposition of Au NPs, indicating photo-excited electron transfer

from MoS2 to Au. From ultrafast spectroscopy we have calculated that, free carriers

generated from high energy pump excitations, turn into excitons within a time scale of

~500 fs and eventually form trions within ~1.2 ps. Excitons and trions are quickly

dissociated in presence of Au, with time scale of ~ 600 fs and ~3.7 ps respectively.

Fig: (a) TA spectra of monolayer MoS2; (b) TA kinetics of exciton A, exciton B and trion

A-; and (c) Comparative TA kinetics of pristine MoS2 and Au/MoS2 heterojunctions.

REFERENCES

(1) Scheuschner, N.; Ochedowski, O.; Kaulitz, A.-M.; Gillen, R.; Schleberger, M.;

Maultzsch, J. Phys. Rev. B 2014, 89, 125406. (2) Sie, E. J.; Frenzel, A. J.; Lee, Y.; Kong,

J.; Gedik, N. Phys. Rev. B 2015, 92, 125417. (3) Heinz, T. F.; Mak, K. F.; He, K.; Lee,

C.; Shan, J.; Hone, J.; Lee, G. H. Nat. Mater. 2012, 12, 207–211. (4) Goswami, T.; Rani,

R.; Hazra, K. S.; Ghosh, H. N. J. Phys. Chem. Lett. 2019, 10, 11, 3057.

53

Ultrafast carrier dynamics of Cu doped CdSe nanotetrapods

Fariyad Ali,a Sucheta Banerjee,a Anindya Datta.ab

a Department of chemistry, IIT Bombay, Powai, Mumbai, 400076 b Faculty, Department of Chemistry, IIT Bombay, adutta@iitb.ac.in

It is important to know the carrier relaxation in excited state of Cu doped CdSe

nanotetrapods (NTPs) as it has many applications in in different fields like LEDs,

photovoltaic devices, solar cells and transisters etc.1,2 We have studied the optical

properties and exciton dynamics after Cu doping in CdSe TPs in excited state. The PLQYs

of CdSe TPs increased from 1.42% to 9,8% after Cu doping and the PL decay time also

increased because conduction band electron recombine to the Cu2+ (d-level) hole instead

of direct electron-hole recombination.3,4 We have performed Transient Absorption (TA)

Spectroscopy to know the hot electron cooling time and recovery kinetics of exciton at

different pump power in excited state. It is observed that the hot electron relaxation time

increased from 580fs to 720fs and recovery kinetics also slowed after Cu doping in CdSe

TPs. So slow electron and recovery kinetics is depends on dopant concentration.5

REFERENCES

1. Zou, H.; Liu, M.; Zhou, D.; Zhang, X.; Liu, Y.; Yang, B.; Zhang, H. J. Phys. Chem.

C 2017, 121, 5313−5323.

2. Archer, P. I.; Santangelo, S. A.; Gamelin, D. R, Nano Lett. 2007, 7, 1037−1043.

3. Viswanatha, R.; Brovelli, S.; Pandey, A.; Crooker, S. A.; Klimov,V. I, Nano Lett.

2011, 11, 4753−4758.

4. Brovelli, S.; Galland, C.; Viswanatha, R.; Klimov, V. I, Nano Lett. 2012, 12,

4372−4379.

5. Dutta, A.; Bera, R.; Ghosh, A.; Patra, A, J. Phys. Chem. C 2018, 122 (29), 16992–

17000.

54

Ultrafast all-optical detection of interfacial spin transparency for pure spin current

transport in CoFeB/β-Ta thin films

Surya Narayan Panda1, Sucheta Mondal1, Samiran Choudhury1, Jaivardhan Sinha1, 2 and

Anjan Barman1,* 1Department of Condensed Matter Physics and Material Sciences, S. N. Bose National

Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata -700 106, India 2Department of Physics and Nanotechnology, SRM Institute of Science and Technology,

Kattankulathur-603203, Tamil Nadu, India

*Email address: abarman@bose.res.in

Spin pumping effect is an efficient mechanism for generating pure spin current, which is

the backbone of energy efficient new generation spintronic devices. Here we have

investigated the spin pumping effect [1] in sputter deposited β-Ta/CoFeB bilayer thin films

by measuring its imprint on Gilbert damping using all-optical femtosecond time-resolved

magneto-optical Kerr effect (TR-MOKE) technique. Thickness of Ta (t) and CoFeB (d)

have been varied from 1.0 to 20.0 nm and 1.0 to 13.0 nm, respectively, during the

experiment. The alternative interfacial effects on transport of pure spin current is also

investigated by introducing a Cu dusting layer of varying thickness, c (0.4 ≤ c ≤ 1.0 nm)

in-between the Ta and CoFeB layers. The precessional magnetization dynamics is

measured by using optical pump-probe technique with 10 mJ/cm2 pump pulse (λ = 400 nm,

pulse width = 50 fs) and 2 mJ/cm2 probe pulse (λ = 800 nm, pulse width = 40 fs) under a

constant in-plane bias magnetic field [2]. By analyzing the time-resolved Kerr rotation,

effective damping (αeff) parameter is extracted [fig. 1(a)]. The non-monotonic variation of

αeff with Ta thickness is modeled using spin pumping formalism to extract the spin

diffusion length of β-Ta as 2.44 ± 0.1 nm (fig. 1(b)) and its intrinsic spin-mixing

conductance as 7.22±0.05×1014 cm-2. The effective spin-mixing conductance is found to

be: 6.92±0.04×1014 cm-2 from the variation of αeff with the thickness of CoFeB layer (fig.

1 (c)). From these, we have obtained the interfacial spin transparency (T) of β-Ta/CoFeB

as 0.50 ± 0.03 by using the spin-Hall magnetoresistance effect model [3], which has direct

correlation with the effective spin-mixing conductance [4]. We have further inserted a Cu

dusting layer of varying thickness c between the β-Ta and CoFeB layer to eliminate the

other possible interface effects in the variation of damping such as interfacial hybridization,

two-magnon scattering, spin memory loss and Rashba effect. Invariance of αeff with Cu

layer thickness rationalizes our interface spin transparency argument in support of

electronic band matching and confirms the role of spin transparency in generation of pure

spin current by spin pumping effect.

We acknowledge financial support from S. N. Bose National Centre for Basic Sciences

(grant no.: SNB/AB/18-19/211). SNP and SC acknowledge S. N. Bose National Centre for

Basic Sciences, while SM acknowledge DST-INSPIRE scheme for respective research

fellowships.

REFERENCES [1] Y. Tserkovnyak, A. Brataas, G. E. W. Bauer, Phys. Rev. Lett. 88,117601 (2002).

[2] A. Barman and J. Sinha, Spin Dynamics and Damping in Ferromagnetic Thin Films and

Nanostructures, Springer, 2018, DOI: 10.1007/978-3-319-66296-1.

[3] W. F. Zhang, W. Han, X. Jiang, S. H. Yang, S. S. P. Parkin, Role of transparency of in determining

the intrinsic magnitude of the spin Hall effect. Nat. Phys. 11, 496 (2015).

[4] S. N. Panda, S. Mondal, J. Sinha, S. Choudhury, A. Barman, All-optical detection of interfacial spin

transparency from spin pumping in β-Ta/CoFeB thin films. Sci. Adv. 5, eaav7200 (2019).

55

Synthesis and Carrier Dynamics of Highly Luminescent Violet- and Blue-Emitting

Perovskite Nanocrystals

Apurba De, Somnath Das, Navendu Mondal and Anunay Samantaa aSchool of Chemistry, University of Hyderabad, Hyderabad- 500046, India,

Email: anunay@uohyd.ac.in.

Among the lead halide perovskites, photoluminescence quantum yield (PLQY) of violet-

emitting CsPbCl3 nanocrystals (NCs) is the lowest (<5%), which is an impediment to the

development of perovskite-based materials for optoelectronic applications covering the

entire visible region.1 While PLQY of the green- and red-emitting perovskites of this class

has been raised to near-unity, achieving a similar level for violet- and blue-emitting NCs is

still quite challenging.2,3 We report a novel method of simultaneously passivating the

surface defects and crystal disorder of violet-emitting CsPbCl3 NCs to dramatically

enhance (by a factor of∼120) the PLQY and stability without affecting the peak wavelength

(403 nm) and full-width at half-maximum (FWHM) of the photoluminescence (PL) band.4

We show that the addition of the correct quantity of CuCl2 during the hot-injection

synthesis of CsPbCl3 NCs leads to doping of Cu+ into the NCs, which rectifies octahedral

distortion of the crystal and the Cl- passivates the surface; the combined influence of the

two results in huge PL enhancement.4 NCs emitting throughout the blue region (430-460

nm) with near-unity PLQY (92%-98%) can then be obtained by partial halide-exchange of

the doped sample. Femtosecond transient absorption studies have been carried to

investigate the intrinsic photophysics and it suggest major suppression of the ultrafast

carrier trapping process in the doped NCs. The results might help in extending the utility

of these materials in optical applications by covering the entire violet−blue region.

REFERENCES

1. L. Protesescu,S. Yakunin,M. I. Bodnarchuk, F. Krieg, R. Caputo, C. H. Hendon, R. X. Yang, A.

Walsh and M. V. Kovalenko, Nano Lett. 2015, 15, 3692.

2. S. Seth, T. Ahmed, A. De and A. Samanta, ACS Energy Lett. 2019, 4, 1610.

3. N. Mondal, A. De and A. Samanta, ACS Energy Lett. 2019, 4, 32.

4. A.De, S. Das, N. Mondal and A. Samanta, ACS Materials Lett. 2019, 1, 116.

56

Facets of Carbon Nanodot: Fundamentals and Applications

Debashis Panda,a Surja Kanta Pal, Farogh Abbas, Shibam Saha a Rajiv Gandhi Institute of Petroleum Technology, An Institute of National Importance, Uttar Pradesh

dpanda@rgipt.ac.in

The synthetic origin of nanodimension and its role on the luminescence properties

of carbon nanodots, in particular, citric acid derived ones, remain an enigma to date.1 We

have identified that the citrazinic acid alone builds a nanocarbon structure upon incubation

in dimethyl formamide at room temperature. The emission properties of incubated

fluorophore resemble that of a nanodot. The dispersion of the H-bonded cluster’s size

originated from citrazinic acid only is the cause of excitation-dependent emission. We have

shown that the steric hindrance caused by the presence of alkyl chain of butyl amine

restricts such dispersions, resulting in excitation-independent emission, a molecular

behavior.1

We have made attempt to undersatnd the photoluminescence dynamics of so-called

doped nanodot in solid polymer matrix and that even in the presence of silver nanoparticle.

Surprisingly, it has been observed that the nanodot exhibits anomalous behavior metallic

nanoparticle. We also identify the existence of blue-, green-, and red-emissive fluorophores

in a product obtained from solvothermal reaction. The red luminescence has been used for

logic-gate operation for achiving molecule-on-a-Chip. Nanodot-embedded PVA/PVP film

has been used for down energy convesrsion to White Light using GaN UV-LED Chip.2

The mechanism of white light emission is attributed to effective energy transfer among

fluorophores.4

REFERENCES

1. Kaleem, W.; Kumar, A.; Panda, D. J. Phys. Chem. C 2018, 122, 26722.

2. Nandy, A.; Kumar, A.; Dwivedi, S.; Pal, S.K.; Panda, D. J. Phys. Chem. C 2019, 123, 20502.

Abbas, F.; Kumar, S.; Panda, D. (Communicated, 2019)

57

Ultrafast photoinduced electron transfer dynamics between cyclometalated rhodium

and iridium complexes and cyan emitting copper nanoclusters

Soumyadip Bhunia, Pradipta Purkayastha

Department of Chemical Sciences, Indian Institute of Science Education and Research (IISER) Kolkata,

Mohanpur 741246, WB, India, ppurkayastha@iiserkol.ac.in

In recent times, copper nanoclusters (Cu NCs) have become promising as

interesting nanomaterials for their potential applications in optoelectronics, sensing,

catalysis and bioimaging.1 Herein, we have synthesized L–Cysteine protected Cu NC in

1:1 water:acetonitrile (ACN) solvent possessing bright cyan emission (λem=495 nm) with

10.4% fluorescence quantum yield.2 Furthermore, the cyclometalated complexes of Ir(III)

and Rh(III) are light harvesters and applied in photoinduced electron and energy transfer

and photocatalysis. Three such cyclometalated complexes of Rh and Ir have been used over

here,3 which on electrostatic interaction with Cu NCs in 1:1 water:ACN medium,

dramatically quench the fluorescence of the Cu NCs. This quenching could be suitably

attributed to photoinduced electron transfer (PET) where the Cu NCs act as electron

acceptor. PET was confirmed by steady state and time resolved fluorescence spectroscopy

as well as by ultrafast femtosecond upconversion and transient absorption spectroscopy.

We have studied the dynamics of PET using the ultrafast spectroscopic techniques to

provide an elaborate description of the phenomenon. The present studies, thus, provide a

new pathway in light harvesting research and expected to be applicable in creating energy

devices.

Figure 1. Photoinduced electron transfer from Cyclometalated complexes to Cu NC.

REFERENCES

1. S. Kundu, A. Patra, Chem. Rev. 2017, 117, 712.

2. S. Bhunia, S. K. Seth, P. Gupta, M. Karmakar, P. K. Datta, P. Purkayastha, Chemistry Select 2019, 4,

8568.

3. S. K. Seth, P. Gupta, P. Purkayastha, New J. Chem. 2017, 41, 6540.

58

Determination of dispersion of the third order optical nonlinearity of Carbon

Dots

T. Singha1, M Bera2, S. Bhattacharya1,3, N.D. Pradip Singh2, P.K. Datta1

1Department of Physics, Indian Institute of Technology Kharagapur, Kharagpur, India 721302 2Department of Chemistry, Indian Institute of Technology Kharagapur, Kharagpur, India 721302 3currently at Department of Chemistry, University of Sheffield, Sheffield S3 7HF, United Kigdom

Excellent tunable fluorescence properties of carbon dots (C-dots) facilitate diverse

biological applications owing to their stability, good biocompatibility and low toxicity.1 C-

dots are zero dimensional, spherical shaped nanoparticles with diameter less than 10nm,

composed of non-toxic C, O and N elements. C-dots consist of two parts, carbon core and

surface functional groups (-OH, -COOH, -NH2, etc). In the carbon core, carbon atoms form

sp2 hybridized C=C bonds and the surface functional groups form sp3 hybridized bonds.2

The band gaps vary with their sizes which is promising for tunable nonlinear optical

phenomena. Panagiostis et al. had studied the sizable nonlinear absorption and the negative

nonlinear refraction of C-dots in ns regime.3

The microwave synthesized carbon dots are spherical in shape with particle sizes ~3nm.

The UV-Visible absorption spectrum shows that carbon dots exhibiting the first band-gap

(Eg1) at ~5.17 eV and second band-gap (Eg2) at ~3.65 eV. We have studied the dispersion

of third order nonlinearity (n2) 4,5 of C-dots using single beam Z-Scan technique6 with

different photon energies. Since carbon dots behave as semiconductors7, they show

dispersion property of n2. The measurements were taken by laser pulses (pulse width

~100fs) at wavelength range varying from 480nm (2.58eV) to 600nm (2.06eV) (in 20nm

wavelength spacing). It has been found that the n2 values are negative above the first and

second half band gap (Eg1/2=2.58eV, Eg2/2=1.82eV) and are positive below first half band

gap (Eg1/2=2.58eV) of carbon dots. This study highlights the tunable nonlinear optical

properties of C-dots which have potential for many optical devices like optical limiters,

optical switches, etc.

REFERENCES:

1. Ju Wang, J. Mater. Chem. A, 2017, 5, 3717

2. Namasivayam Dhenadhayalan, J. Phys. Chem. C 2016, 120, 1252−1261

3. Panagiostis Aloukos, Optics Express 12013, 22, 10, 2014

4. M. Sheik-Bahae. PRL, vol. 65, no. 1, July 1990

5. Ningning Dong, Optics Letters, 3936, 41, 14, 2016

6. M. Sheik-Bahae. IEEE Journal of Quantum Electronics. vol. 26. no. 4, April 1990

Monoj Kumar Barman, J. Phys. Chem. C 2014, 118, 20034−20041

59

INVESTIGATION OF IMPROVED CHARGE CARRIER DYNAMICS OF

CORE-SHELL NANOCRYSTAL MODIFIED PEROVSKITE USING

TRANSIENT ABSORPTION SPECTROSCOPY

Sayan Prodhan1#, Kamlesh Kumar Chauhan2, Anima Ghosh3, Sayan Bhattacharaya3,

Prasanta Kumar Datta1*

1Department of Physics, Indian Institute of Technology (IIT) Kharagpur, Kharagpur – 721302, India 2Department of Electrical Engineering, Indian Institute of Technology (IIT) Kharagpur, Kharagpur –

721302, India 3Department of Chemical Sciences, and Centre for Advanced Functional Materials, Indian Institute of

Science Education and Research (IISER) Kolkata, Mohanpur 741246, India

*E-mail address: sayan.prodhan@gmail.com

Recent discoveries of highly efficient solar cells based on organic-inorganic lead

halide perovskites attract a surge in research activity. Its improvement in solar cell

efficiency from 10% to 25.2% in just one decade has shown its very promising future as

solar cell. The reason behind its amazing performance is its high absorption coefficient;

high PLQY, high charge carrier mobility, long diffusion length, and low trap state density

that affects the performance of perovskite based solar cell. We have modified MAPbI3-

XClX perovskite using Au/CZTS core/shell nanocrystal (NC) and it improves the solar cell

efficiency from 12.83% to 19.97%. Understanding the photo-carrier dynamics and

interactions are crucial for elucidating the working mechanisms and improvement

pathways of mixed halide perovskite based solar cells. Transient absorption spectroscopy

has been performed on both unmodified and modified mixed halide perovskite to

investigate its photo-carrier dynamics. We have used 480 nm (2.58 ev) as pump at a fluence

of ≈ 12.5 μJ/cm2 which is way above its band-gap and white light (350nm-850nm) as

probe. The transient absorption spectra shows increased bleaching magnitude and

increased bleaching bandwidth after the nano-crystal modification. Increase in bleaching

magnitude is the result of the increased absorption coefficient due to the plasmonic effect

of the Au/CZTS core/shell NC. Decay kinetic study of the photo-bleaching signal for both

unmodified and modified MAPbI3-XClX perovskite is performed with the help of tri-

exponential function and various phenomenon like hot carrier cooling, trap state

recombination and auger recombination has been correlated with the decay time constants.

After modification, the hot carrier cooling time is increased from 0.3ps to 6.45 ps indicating

hot phonon bottleneck effect1,2 due to the increase in number of excited carriers. High

number of excited carrier suppress the decay of LO phonon to LA phonon and results in

60

reheating of the excited carriers. Passivation effect3,4 of Au/CZTS core/shell NC decreases

the trap state density as it smoothen the surface. It increases trap state recombination time

from 48.3ps to 850 ps. Also the core-shell configuration5,6 induces spatial separation

between those participating electron and hole that hinders the auger recombination. This

increases the auger recombination time from 452ps to 8212ps. The combined effect of

increase in the absorption coefficient and the elongation in the charge carrier lifetime due

to the modification improves the overall efficiency of the perovskite solar cell.

REFERENCES 1. Ye Yang, David P. Ostrowski, Ryan M. France, Kai Zhu, Jao van de Lagemaat, Joseph M. Luther

and Matthew C. Beard. Observation of a hot-phonon bottleneck in lead-iodide perovskites. Nature

Photonics 2016, 10, 53–59

2. M. B. Price, J. Butkus, T. C. Jellicoe, A. Sadhanala, A. Briane, J. E. Halpert, K. Broch, J. M.

Hodgkiss, R. H. Friend, and F. Deschler, "Hot-carrier cooling and photoinduced refractive index

changes in organic–inorganic lead halide perovskites," Nat. Commun. 6, 8420 (2015).

3. Qi Jiang , Zema Chu, Pengyang Wang, Xiaolei Yang, Heng Liu, Ye Wang Zhigang, Yin Jinliang

Wu, Xingwang Zhang and Jingbi You. Planar-Structure Perovskite Solar Cells with Efficiency

beyond 21%. Adv. Mater. 2017, 29, 46

4. Dae-Yong Son, Jin-Wook Lee, Yung Ji Choi, In-Hyuk Jang, Seonhee Lee, Pil J. Yoo, Hyunjung

Shin, Namyoung Ahn, Mansoo Choi, Dongho Kim and Nam-Gyu Park. Self-formed grain boundary

healing layer for highly efficient CH3 NH3 PbI3 perovskite solar cells. Nature Energy 2016, 1,

16081

5. Young-Shin Park, Wan Ki Bae, Lazaro A. Padilha, Jeffrey M. Pietryga and Victor I. Klimov. Effect

of the Core/Shell Interface on Auger Recombination Evaluated by Single-Quantum-Dot

Spectroscopy. Nano Lett.2014,14 , 396-402

6. Florencio García-SantamaríaYongfen, ChenJavier, VelaRichard D. SchallerJennifer A.

Hollingsworth and Victor I. Klimov. Suppressed Auger Recombination in “Giant” Nanocrystals

Boosts Optical Gain Performance. Nano Lett.2009,9, 10, 3482-3488

61

Study of Non-colinear Femtosecond Second Harmonic and Sum Frequency

Generation using BBO crystals. aSushanta Lenka, aSailab Singh Bodra,b Kamlesh Kumar Chauhan, Prasanta Kumar Datta

a,b aDepartment of Physics, IIT Kharagpur, West Bengal, , India – 721302.

bDepartment of Electrical, Engineering IIT Kharagpur, West Bengal, India – 721302.

For generating second harmonic generation (SHG) and sum frequency

generation (SFG) in femtosecond regime, mostly we have to keep in mind

about the following three parameters. (1) Special overlap, (2) Zero delay, (3)

Phase matching. We have used fiber based femtosecond laser pulses of

repetation rate 80MHz (Average Output power > 100mW). First,we have

generated non collinear SHG of two input femtosecond pulses (780nm) using

BBO crystal of thickness 3mm and cut axis 26 degree. Secondly, we have

generated non collinear SFG of two different input femtosecond pulses

(780nm and 1560nm) using BBO crystal of thickness 6mm and 0.5mm. For

type- 1 interaction , we have fixed two input pulses are ordinary polarized (o

& o-polarized). The input power pulses are maintained as 32mW and the

spectral band width is around 17nm as observed using Avantage spectrometer

.The powers of generated SHG pulses are measured around 0.62mW with the

spectral bandwidth of 4 nm.The high quality image of generated SHG signal

is captured by high resolution camera. The generated SHG power is 0.42mW

with spectral bandwidth of 6nm. Both theritical and experimental

investigation we have performed.

The narrow spectral width of SFG pulse is obtained from the result. It

is due to the relation that the spectral bandwidth is inversely proportional to

crystal thickness. The spectral band width can be enhance by compromising

the thickness of the BBO crystal. The power conversion efficiency of

generated SHG is around 1.5 %. The conversion efficiency we have improved

by controling the phase matching angle by changing external angle between

two input femtosecond pulses and thickeness of BBO crystal.

REFERENCES

1. Andrew J. W Brown, Mark S. Bowers, Ken W Kangas, and Charles H. Fishers

OPTICS LETTERS.

2. O. Gobert,1 G. Mennerat,1 R. Maksimenka,1,2 N. Fedorov,1 M. Perdrix,1D.

Guillaumet,1 C. Ramond,3,4 J. Habib,3,4,5,6 C. Prigent,3,4 D. Vernhet,3,4 T.

Oksenhendler,2 and M. Comte1, APPLIED OPTICS.

62

Solvent Mediated Relaxation Dynamics of Core-Shell Au-SiO2 Nanoparticles

Hemen Gogoi,a Bala Gopal Maddala,b Anindya Dattaa a Department of Chemistry, Indian Institute of Technology Bombay

bIITB-Monash Research Academy

Mumbai, Maharashtra-400076

The inherent plasmonic property of nanosized gold particles makes it useful for various

applications ranging from photovoltaics to photothermal therapy.1 The crucial heat

dissipation dynamics of these nanostructures can be effectively probed with the help of

transient absorption spectroscopy. This technique helps us to understand the different

pathways involved in the relaxation dynamics of excited Au-SiO2 core-shell

nanoparticles.2 Initially gold nanoparticles are synthesized by reducing the gold precursor

and then coated with silica by using tetraethyl orthosilicate (TEOS) to enhance its stability.3

Synthesized nanoparticles were dispersed in solvents with different thermal conductivities.

By exciting the solutions with a strong laser pulse, the evolution of the excited state

dynamics in different surrounding environment has been monitored. The electron-phonon

relaxation time of Au-SiO2 nanoparticles has been found to be increased with decrease in

thermal conductivity of the solvent while the phonon-phonon relaxation time remains

unaffected.

REFERENCES

1. Carattino, A.; Caldarola, M.; Orrit, M. Nano Lett. 2018, 18, 874.

2. Mohamed, M. B.; Ahmadi, T. S.; Link, S.; Braun, M.; El-Sayed, M. A. Chem. Phys.

Lett. 2001, 343, 55.

3. Fernández-López, C.; Mateo-Mateo, C.; Álvarez-Puebla, R. A.; Pérez-Juste, J.;

Pastoriza-Santos, I.; Liz-Marzán, L. M. Langmuir 2009, 25, 13894.

63

Ultrafast dynamics of gold dimers and trimers

Bala Gopal M,abc Alison Funston,ab Anindya Dattaac (a) IITB-Monash Research Academy, Mumbai, India (b) School of chemistry, Monash University, Melbourne, Australia

(c) Department of chemistry, IIT Bombay, Mumbai, India

Ultrafast dynamics of nanoparticles have garnered much attention in the past decade due to their optical

nonlinear properties.1-3 In the present study, the excited state electron relaxation dynamics of gold dimers and

trimers were studied employing femtosecond laser pump probe spectroscopy. Controlled assemblies of gold

nanospheres such as gold dimers and trimers were prepared using a dithiol linker molecule.4 Different optical

response was observed in dimer and trimers as compared to monomers in solution phase. Global fit analysis

was employed to understand the relaxation dynamics and we compared the results with conventional kinetic

fit analysis underlying its disadvantages in assembled systems where there is huge spectral overlap of positive

and negative signals in the red shifted plasmon coupling region. Our results suggest that enhanced electron-

phonon and phonon-phonon coupling time in higher assemblies as compared to monomers. This is attributed

to higher spectral overlap of electron oscillation and phonon spectrum in the region of enhanced electric field

intensity.2,5

Figure 1. Gold nanoparticle assemblies

Figure 2. Pseudo color heat map of Transient absorption spectra of a) gold NP monomers b) Dimers c)

Trimers

References

1. Xia, Y.; Xiong, Y.; Lim, B.; Skrabalak, S. E. Angew. Chemie Int. Ed. 2009, 48 (1), 60.

2. Link, S.; El-Sayed, M. A. Annu. Rev. Phys. Chem. 2003, 54 (1), 331.

3. Kelly, K. L.; Coronado, E.; Zhao, L. L.; Schatz, G. C. J. Phys. Chem. B 2003, 107 (3),668.

4. Bidault, S.; Polman, A. Int. J. Opt. 2012, 2012.

5. Fernández-López, C.; Mateo-Mateo, C.; Álvarez-Puebla, R. A.; Pérez-Juste, J.;Pastoriza-

Santos, I.; Liz-Marzán, L. M. Langmuir 2009, 25 (24), 13894.16

64

Slow Charge Carrier cooling in Type-1 3D/0D Core-Shell CsPbBr3@Cs4PbBr6

Perovskite system: Role of Polaron Formation

Gurpreet Kaur a, K. Justice Babu b and Hirendra N. Ghosh c

a PhD student, Institute of Nanoscience and Technology (INST), Habitat Center, Sector 64, Mohali

b Post Doctoral Fellow, Institute of Nanoscience and Technology (INST), Habitat Center, Sector 64, Mohali

c Professor, INST, Mohali, Punjab; On deputation from Bhabha Atomic Research

Centre(BARC),Mumbai

a Email id: gurpreet.ph17205@inst.ac.in

Fast hot carrier cooling is the key parameter surpassing all the other possible energy loss

pathways, which are broadly encountered in every other single junction solar cell, hence

setting a thermo-dynamical bar on the achievable solar energy conversion

efficiency(Shockley Quiesser limit~33%).1 Thus, retardation of hot carrier cooling rate in

the cell absorber layer can make hot carrier extraction a less cumbersome task ,making

the realization of hot carrier solar cell practical(boosting the solar cell performance

beyond 67%).2 Recently, there have been plentitude of reports concerning the slow carrier

cooling in lead halide perovskite materials, which eventually triggered growing interest in

the radical understanding of the native photophysics playing an important role in the

device design3. Here in this finding, a further dramatic dip in the cooling rate has been

discerned upon growing a Cs4PbBr6 shell over CsPbBr3 core NCs in crude contrast to the

bare CsPbBr3core NCs. Using the broadband ultrafast Transient Absorption (TA)

spectroscopy, we have investigated the disparity in the thermalisation pathways taken up

by the hot carriers in the CsPbBr3 and CsPbBr3@Cs4PbBr6 core-shell NC systems under

same incident laser fluence, which can be validated as a corollary of large polaron

formation taking place in the later NC systems. There are clear evidences of polaron

formation in the femtosecond TA data of the core-shell system which is much suppressed

in case of CsPbBr3.This knowledge can be steered to drive towards the achievement of

higher Voc,which is a commanding factor detrimental for the efficiency of the solar cell.

References

1. Protesescu, L.; Yakunin, S.; Bodnarchuk, M. I.; Krieg, F.; Caputo, R.; Hendon, C. H.; Yang, R. X.;

Walsh, A.; Kovalenko, M. V. Nano Lett. 2015, 15 (6), 3692–3696.

2. Manser, J. S.; Kamat, P. V. Nat. Photonics 2014, 8, 737.

3. Kaur, G.; Babu, K. J.; Ghorai, N.; Goswami, T.; Maiti, S.; Ghosh, H.N.; J. Phys. Chem. Lett., 2019,

10, 5302.

65

Long-Range Resonance Coupling-Induced Surface Energy Transfer

from CdTe Quantum Dot to Plasmonic Nanoparticle

Jamuna K. Vaishnav and Tushar Kanti Mukherjeea aDiscipline of Chemistry, Indian Institute of Technology Indore, Simrol, Indore

E-mail: tusharm@iiti.ac.in

Fundamental understanding and precise control of complex nonradiative processes in

nanoscale system finds significant interest in recent times due to their importance in various

nanophotonics applications. Here we have systematically investigated the mechanism

behind photoluminescence (PL) quenching of mercaptosuccinic acid (MSA) capped CdTe

QDs in the near field of gold and silver nanoparticles (Au and Ag NPs) by using steady-

state and time-resolved photoluminescence (PL)spectroscopy. Resonance coupling

between excitonic emission and localized surface plasmon resonance (LSPR) of Au NPs

has been tuned by varying the size of QDs.

Herein, three differently sized MSA-capped CdTe QDs have been synthesized

namely,2.1 ± 0.7, 3.1 ± 0.4, and 3.9 ± 0.3 nm with emission in green, yellow and red region

of the electromagnetic spectrum, respectively. It has been observed that both the

luminescence intensity and lifetime of green QDs quench significantly in the near field of

20 nm sized Au NPs. In contrast, the luminescent intensity and lifetime of yellow and red

QDs remain unaltered in the presence of Au NPs. Moreover, it has been observed that

ligand exchange at the surface of Au NPs with Poly(ethylene glycol) methyl ether thiol

(PEG-SH) decreases the quenching efficiency of the green QD-Au NP pair significantly.

In addition, the extent of quenching strongly depends on excitation wavelength. The

observed quenching is more efficient at the excitation wavelength close to the LSPR of Au

NP. These results have been explained on the basis of a size-dependent nanometal surface

energy transfer (NSET) model by incorporating the changes in the complex dielectric

function and the absorptivity of the Au NP. On the contrary, irrespective of the sizes of

QDs,significant PL quenching has been observed in the presence of 10 nm sized citrate-

capped Ag NPs as a consequence of photoinduced electron transfer (PET). The present

findings of size and wavelength-dependent long-range nonradiative electromagnetic

coupling in hybrid QD-metal NP system can be useful to understand and optimize the

performance of various nanophotonic devices.

REFERENCES

1. J. K. Vaishnav, T. K. Mukherjee, J. Phys. Chem. C 2018, 122, 28324-28336.

66

Time Dependent Optical Second Harmonic Generation from Si/SiO2 Interface and

Its Variation with Doping Concentration

Binit Mallicka, Anindya Duttab, Swaroop Gangulyc a Department of Electrical Engineering, IITB

b Department of Chemistry, IITB, anindya@chem.iitb.ac.in

c Department of Electrical Engineering, IITB, sganguly@ee.iitb.ac.in

We have investigated a nondestructive and contactless characterisation technique

using time dependent optical second harmonic generation (TDSHG). The TDSHG method

is used to probe electron trapping phenomena on silicon dioxide surface from silicon

(Si)/silicon dioxide (SiO2) interface. A phenomenological explanation is provided for the

time dependent second harmonic (TDSH) intensity. We have studied the relationship

between SH intensity and its time dependent behaviour with varying doping concentration

and oxide thickness. We have also studied the rotational asymmetrical nature of SH

intensity from Si/SiO2 interface. An explanation is provided for the observed trend.

REFERENCES

1. J. G. Mihaychuk, J. Bloch, Y. Lui, and H. M. van Driel, Opt. Lett. 20, 2063 (1995).

2. J. Bloch, J. Mihaychuk, H. M. van Driel, Phys. Rev. Lett. 77, 920 (1996).

3. J. I. Dadap, X. F. Hu, M. H. Anderson, M. C. Downer, J. K. Lowell, and O. A. Aktsipetrov, Phys.

Rev. B 53, R7607(R),(1996).

4. J. G. Mihaychuk, N. Shamir, and H. M. van Driel, Phys. Rev. B 59, 2164, (1999)

Julie L. Fiore, Vasiliy V. Femenko, Dora Bodlaki and Eric Borguet , Appl. Phys. Lett. 98, 041905 (2011).

67

Direct Observation of -Phonon Driven Ultrafast Magnetization Dynamics in

Ferromagnetic Nanodot Arrays

Arundhati Adhikari, Koustuv Dutta, Anulekha De and Anjan Barman*

Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic

Sciences, Block JD, Sector III, Salt Lake, Kolkata 700 106, India

*abarman@bose.res.in

Ultrafast dynamic response in ordered nanomagnet arrays1 has remained a field of immense

interest for researchers because of its huge potential application in the next generation

spintronic and magnonic devices. In recent years, researchers have explored various new

routes to enhance the functionality of magnonic crystals by manipulating the spin-wave

dynamics, by various external stimuli and coupling with various quasiparticles and a new

field of cavity magnonics has emerged2. In such ordered system, the coupling of magnons

with phonon, photon or another magnon is very interesting from the perspective of

fundamental understanding as well as novel devices. Here, we have investigated phonon

driven magnon dynamics in Permalloy (Ni80Fe20) nanodots of square shape arranged in

closely packed hexagonal symmetry in femto to nanosecond time scale. We have used a

custom-built time-resolved magneto-optical Kerr effect (TRMOKE) microscope where an

ultrashort laser pulse (80 fs) of wavelength 800 nm is used to probe the dynamics of both

the magnetic and non-magnetic origin after being excited by the second harmonic of this

laser of 400 nm wavelength. We observe prominent oscillation in the time-dependent

reflectivity signal that ensures the generation of elastic vibration (phonon) in the system,

which is strongly correlated with the array geometry3. The frequency spectra of the elastic

mode show multiple peaks in GHz frequency regime, which also overlaps with the magnon

modes in certain bias field regime. The bias field variation reveals the coupling between

the magnon and phonon modes from the observed crossing/anti-crossing between the two

modes. The magnon-phonon coupling is interpreted on the basis of existing analytical

theory. The observation of tunability of this strong magnon-phonon coupling with lattice

parameters would be important for the emerging field of cavity magnonics and

magphonics.

We gratefully acknowledge the financial support from S. N. Bose National Centre for Basic

Sciences (SNB/AB/18-19/211). AA acknowledges S. N. Bose Centre and KD and AD

acknowledge DST (INSPIRE Scheme) for research fellowship.

REFERENCES

1. B. Rana et al., ACS Nano, 2011, 9559, 5

2. Y. P Wang et al., Phys. Rev. Lett. 2018, 057202, 120

3. A. Comin et al., Phys. Rev. Lett. 2006, 217201, 97.

68

Comprehensive study of femtosecond transient carrier dynamics in mixed halide

perovskite

Kamlesh Kumar Chauhan, a Sayan Prodhan, b Sayan Bhattacharyya, c Pranab Kumar

Dutta, a Prasanta Kumar Datta b a Department of Electrical, Engineering IIT Kharagpur, West Bengal, India – 721302.

b Department of Physics, IIT Kharagpur, West Bengal, , India – 721302.

c Department of Chemical Science, IISER Kolkata, Mohanpur, West Bengal, India – 741246.

Organic-inorganic perovskite "a third generation photovoltaic" has completely

attracted the interest among photovoltaic research community. Its novel optical properties

like high absorption coefficient1, high carrier mobility2, large carrier diffusion length3,

slow hot carrier cooling4 etc. are responsible for attaining maximum power conversion

efficiency of 25.2%5. The detailed study of photo-excited carrier dynamics is capable in

describing the improved device properties. The present work experimentally demonstrates

the carrier density dependent bleaching dynamics in organic-inorganic mixed halide

(CH3NH3PbI3-XClX) perovskite using transient absorption spectroscopy. The mixed halide

perovskite is excited well above the band-gap (1.6 eV) using the femtosecond pump pulse

of 480 nm (2.58 eV) and a white light probe (350-850 nm) pulse is utilized to observe the

transient carrier dynamics by measuring the change in absorption (ΔA) of probe due to

pump excitation. The transient absorption (TA) spectra shows a broad negative ΔA band

over 600-780 nm peaks at 730 nm which corresponds to joint effect of ground state

bleaching and state filling due to free carriers. The decay of band-limited bleaching signal

is analyzed well and shows the linear variation within the excited carrier density of 1018-

1019 cm-3. The bleaching decay is sequential fitted with the rate equation given by

2 3

1 2 3( ) ( ) ( ) ( )d

n t k n t k n t k n tdt

, where k1- monomolecular, k2- bimolecular and k3- tri-

molecular decay rate constants. The fitted results give the radiative recombination rate (k2)

of 10-11 cm-3s-1 resulting in the maximum attainable diffusion length of ~10 µm in mixed

halide perovskite. Our finding shows the potential of mixed halide perovskite in thin film

solar cell application.

REFERENCES

1. M Green, A Baillie, H Smith, Nature Photonics, 2014, 8, 506–514.

2. Y. Chen, H. T. Yi, X. Wu, R. Haroldson, Y. N. Gartstein, Y. I. Rodionov, K. S. Tikhonov,A.

Zakhidov,X. -Y. Zhu , V. Podzorov, Nature Comm., 2016, 7, 12253.

3. Ponseca et al J. Am. Chem. Soc. 2014, 136, 145, 189-5192.

4. Yang et al, Nature Photonics, 2016, 10, 1, 53-59.

National renewable energy laboratory, “Efficiency chart,” 2019,

https://www.nrel.gov/pv/assets/pdfs/best-research-cell-efficiencies.20190703.pdf

69

Carrier Dynamics Measurement on MoS2 Monolayers Using Ultrafast Pump-Probe

Spectroscopy

D. P. Khatua1,2,a), Asha Singh1, Sabina Gurung1,2 and J. Jayabalan1,2

1Nano Science Laboratory, Materials Science Section, Raja Ramanna Centre for Advanced Technology,

Indore, India-452013. 2Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai, India - 400085.

a)Corresponding author: khatuadurgaprasad03@gmail.com

Extensive research on two-dimensional materials (2DM) is being carried out in recent time due to their

application in optoelectronic and valleytronic devices. Among 2DM, monolayers of Molybdenum Disulfide

(MoS2) has attracted lot of interest due to its stability, existence of direct band gap and its larger exciton

binding energy [1, 2]. For understanding the optical response of MoS2, it is necessary to examine carrier

dynamics at various excitation densities. We have measured the ultrafast optical response of two-dimensional

MoS2 monolayer flakes using femtosecond oscillator-amplifier-OPA system in standard pump-probe

transmission geometry (Fig.1) and pulse width at the sample place is about 140 fs. The pump and probe

wavelengths were 400 nm and 420 nm respectively. Figure 2 shows the time evolution of transient

transmission (T/T) measured at different pump fluences near 1.0 mJcm-2. With increasing pump fluence the

peak change in T/T reduces. Transient measurement with increasing pump fluence in the range of 0.1 to 0.5

mJcm-2 showed a saturation behavior [3]. In the present case the reduction in peak change in T/T is

attributed to increased carier-carrier scattering process which starts the relaxation of carriers at earlier times

at higher excitation densities. It will also be shown that the decay time of T/T reduces with increase in pump

fluence. Reduction in decay times at higher fluence can be attributed to auger recombination process and

capture of carriers by defect states [4].

Fig.1: Schematic of pump-probe setup used for transient absorption measurements. The pump beam was generated by frequency doubling in BBO and probe beam was 420 nm.

Fig.2: Transient transmission of MoS2 sample at different pump fluences (dots). The green line shows the best fit to the data with increasing absorption density and single-exponential decay.

REFERENCES

1. Singh, A., Tran, K., Kolarczik, M., Seifert, J., Wang, Y., Hao, K., Pleskot, D., Gabor, N.M.,

Helmrich, S., Owschimikow, N. and Woggon, U., Phys. Rev. Lett., 117, 257402 (2016).

2. Miró, P., Audiffred, M., and Heine, T., Chem. Soc. Rev., 43, 6537-6554 (2014).

3. Seo, M., Yamaguchi, H., Mohite, A. D., Boubanga-Tombet, S., Blancon, J. C., Najmaei, S., and

Prasankumar, R. P., Sci. Rep., 6, 21601 (2016).

4. Wang, H., Zhang, C., Rana, F., Nano lett., 15, 339-345 (2014).

70

Exploring the Dynamics of Excited Excitonic Rydberg Series in Layered MoS2

Manobina Karmakar1, Sayantan Bhattacharya1,2, Subhrajit Mukherjee3,4, Barun

Ghosh5, Rup Kumar Chowdhury1, Amit Agarwal5, Samit Kumar Ray1,6 and Prasanta

Kumar Datta1

1Department of Physics, Indian Institute of Technology Kharagpur, Kharagpur, India 721302. 2currently at Department of Chemistry, University of Sheffield, Sheffield S3 7HF, United Kingdom. 3Advanced Technology and Development Centre, Indian Institute of Technology Kharagpur, Kharagpur,

India 721302. 4currently at Technion - The Israel Institute of Technology, Haifa, Israel. 5Department of Physics, Indian Institute of Technology Kanpur, Kanpur, India 208916. 6S. N. Bose National Centre for Basic Sciences, Kolkata, India 700106.

While optoelectronic technology is inching towards excitonic devices, external control and

manipulation of these neutral quasiparticles is an essential step towards realizing potential

applications. In this regard, transition metal dichalcogenides (TMDC) are the leading

candidates owing to their strongly bound excitons and associated unique optical

properties1-5. In this work, we explore the ultrafast response of ground (1s) and first excited

(2s) state of excitons in a few-layered TMDC (MoS2) upon above-bandgap photo-

excitation. Apart from Pauli blocking effect in 1s excitons, we observe a dynamically-

enhanced absorption of the 2s state. This is caused by the reduction in dielectric

permittivity, which is triggered by reduced 1s-2s energy separation upon photo-excitation,

at the particular resonance. Further, we estimate the contributions of various Coulomb

screening effects that determine the dynamical resonance energy separation of the 1s and

2s states and therefore lead to the interesting phenomenon of enhanced absorption. While

many of the existing studies in excitonic systems fail to distinguish electronic and optical

bandgap renormalization and observe the resultant effect in optical (i.e. excitonic)

bandgap6, we could de-couple the dynamic contribution from free electronic and bound

electronic effects. Our study provides key understanding for bandgap engineering and

insight into how Coulomb interactions respond to external perturbations in a few-layered

TMDC.

REFERENCES:

1. Cunningham, P. D.; Hanbicki, A. T.; McCreary, K. M.; Jonker, B. T. Photoinduced Bandgap

Renormalization and Exciton Binding Energy Reduction in WS2. ACS Nano 2017, 11, 12601–12608.

2. Chernikov, A.; Berkelbach, T. C.; Hill, H. M.; Rigosi, A.; Li, Y.; Aslan, O. B.; Reichman, D. R.;

Hybertsen, M. S.; Heinz, T. F. Exciton Binding Energy and Nonhydrogenic Rydberg Series in Monolayer

WS2. Phys. Rev. Lett. 2014, 113, 076802.

3. Ugeda, M. M.; Bradley, A. J.; Shi, S.-F.; da Jornada, F. H.; Zhang, Y.; Qiu, D. Y.; Ruan, W.; Mo, S.-K.;

Hussain, Z.; Shen, Z.-X. et al. Giant bandgap renormalization and excitonic effects in a monolayer

transition metal dichalcogenide semiconductor. Nature Materials 2014, 13, 1091.

4. Shi, H.; Yan, R.; Bertolazzi, S.; Brivio, J.; Gao, B.; Kis, A.; Jena, D.; Xing, H. G.; Huang, L. Exciton

Dynamics in Suspended Monolayer and Few-Layer MoS2 2D Crystals. ACS Nano 2013, 7, 1072–1080.

5. Raja, A.; Chaves, A.; Yu, J.; Arefe, G.; Hill, H. M.; Rigosi, A. F.; Berkelbach, T. C.; Nagler, P.;

Schüller, C.; Korn, T. et al. Coulomb engineering of the bandgap and excitons in two-dimensional

materials. Nature Communications 2017, 8, 15251.

6. Pogna, E. A. A.; Marsili, M.; De Fazio, D.; Dal Conte, S.; Manzoni, C.; Sangalli, D.;

Yoon, D.; Lombardo, A.; Ferrari, A. C.; Marini, A. et al. Photo-Induced Bandgap Renormalization

Governs the Ultrafast Response of Single-Layer MoS2. ACS Nano 2016, 10,

1182–1188.

71

Comparative study of ultra-fast thermal strain evolution in Ge (111) sample induced

by fundamental and second harmonic pump pulse

R. Rathorea,b*, H. Singhala,b and J. A. Chakeraa,b aHomi Bhabha National Institute, Training school Complex, Anushaktinagar, Mumbai - 400094

bLaser Plasma Division, Raja Ramanna Centre for Advanced Technology, Indore 452 013

*Email: ranjana@rrcat.gov.in

The study of photo-induced thermal strain propagation in semiconductor material is

especially important as the change in thermal properties may influence the performance of the ultra-

fast semiconductor devices. Excitation of semiconductor sample with an ultra-short laser pulse of

photon energy more than the band gap of the semiconductor sample results in single photon

absorption of the laser in the sample. This leads to heating of the sample and eventually dilation of

the lattice. The effect of laser excitation with different wavelengths (photon energy) but similar

fluence on the sample may be different as they will have different absorption depths. In view of

this, we have studied the evolution of thermal strain in the sample by the excitation of fundamental

(800 nm) and second harmonic (SH, 400nm) laser pulse. The temporal evolution of photo-induced thermal strain in a material can be studied by

time resolved x-ray diffraction (TXRD) technique1,2. TXRD is a pump probe technique in which

the sample is first excited by the ultra-short laser pulse, then the generated strain in the sample is

probed by ultra-short x-ray pulse (by recording the x-ray diffraction pattern). The temporal

evolution of strain is then studied by changing the delay between pump and probe pulses. In this

study, the ultra-short x-ray source (Cu Kα) was generated by the kHz Ti:sapphire (800 nm) laser

produced Cu plasma. The x-ray photon flux was ~ 2.5x109 photons/sr./s at a laser intensity of ~

3.3x1016 W/cm2. The sample was pumped by fundamental and SH laser pulse at a fluence of ~ 6.5

mJ/cm2.

We report a comparison of thermal strain evolution in Ge (111) sample (band gap 0.66

eV) induced by fundamental (1.5 eV) and SH (3 eV) pump beams. The maximum observed strains

with fundamental and SH pump were ~ 6.210-4 and ~ 2.910-3 occurring at ~ 50 ps and ~ 15 ps

probe delay respectively. The difference in the maximum strains and their timings is due to the

lower absorption depth of SH pump pulse. The lower absorption depth results in laser energy

deposition in less number of lattice planes initially and hence these planes experience larger strain.

The strain propagation in the sample was studied upto ~ 2 ns probe delay. At this time, the residual

strains for fundamental and SH pump were ~ 310-4 and ~ 510-4 respectively which will reduce

further with delay.

REFERENCES 1. R. Rathore, H. Singhal, and J. A. Chakera J. Appl. Phys. 2019, 105706, 126.

2. A. Rousse, C. Rischel, and J.-C. Gauthier, Rev. Mod. Phys. 2001, 17, 73.

72

Ultrafast Magnetization Dynamics in Ferromagnetic Nanodot Arrays Connected by

Nanochannels

Sourav Sahoo a, Surya Narayan Panda a, Saswati Barman b, Anjan Barman a,*, a Department of Condensed Matter Physics and Material Sciences, S. N. Bose National

Centre for Basic Sciences, Block JD, Sector III, Salt lake, Kolkata 700 106, India b Institute of Engineering and Management, Kolkata 700091, India

*Corresponding author: abarman@bose.res.in

Magnonic crystals (MCs) are periodically patterned magnetic media, the magnetic

counterparts of the photonic and phononic crystals, where spin waves act as information

carrier. Two-dimensional (2D) artificially patterned nanodot arrays have long been

interesting systems due to their interesting spin configuration, magnetization reversal

properties, spin dynamics as well as their potential applications in high density magnetic

storage, memory, logic, transistor and communication devices. Several studies have

reported the magnetization dynamics in 2D arrays of magnetostatically coupled nanodot

arrays1.

Here, we investigate the spin-wave (SW) dynamics of 2D array of square Ni80Fe20

nanodots joined by rectangular nanochannels (NCs) of the same material which directly

couple the dots via exchange interaction. The Ni80Fe20 nanodot arrays of thickness 20 nm

are fabricated by using the combination of e-beam lithography, e-beam evaporation and

ion milling on Si (100) substrate. The size (s) of the square nanodot varies as 865(S1), 660

(S2) and 465 (S3) nm and the connector length (l) as 330, 210 and 105 nm, respectively,

while the width (w) of the connector is kept fixed around 260 nm. Custom build time-

resolved magneto optical Kerr effect (TRMOKE) microscope2 is exploited to probe the

precessional dynamics. The damped nonuniform oscillation consists of multiple-frequency

modes which shows high stability with bias magnetic field. Corresponding fast Fourier

transform (FFT) spectra show the presence of seven, five and three distinct SW modes for

the array S1, S2 and S3 respectively. The SW mode numbers decrease with the decrease in

dot size and the NC length. This is probably due to the modification of magnetostatic field

distribution around the edges of NCs and dots. Further, the spatial power profile of the SW

modes reveals that the presence of edge, extended, quantized and mixed quantized mode

in these systems. All the SW modes are coupled between the dots via the vertical NC

(VNC), perpendicular to applied magnetic field (H) except the highest frequency mode,

which shows a mixed behavior and the power of the mode is mainly concentrated inside

the horizontal NC (HNC), parallel to H. Inside the HNC, the highest frequency mode shows

uniform nature. This behavior is prominent for S1. Further, using numerical simulations

we show a modulation of higher frequency modes due to exchange coupling between the

dots by varying the length of the NC. The observed modulation of SW dynamics opens the

possibility of development of rich class of magnonic devices by controlling the propagation

of spin wave.

REFERENCES 1. B. Rana, D. Kumar, S. Barman, S. Pal, Y. Fukuma, Y. Otani and A. Barman, ACS

Nano, 2011, 9559, 5.

2. A. Barman, and J. Sinha, 2018, Spin Dynamics and Damping in Ferromagnetic Thin

Films and Nanostructures, (Springer Publishing AG, Switzerland).

73

CuFeS2 Quantum Dots based broadband (visible to MIR) photodetector for

detecting radiation from ultrafast sources

Nihit Saigal, Anumol Sugathan, Guru Pratheep Rajasekar and Anshu Pandey

Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore-560012

We report the characterization of a p-n junction photodetector based on a heterostructure

comprised of heavily doped n-type Silicon and p-type CuFeS2 quantum dots films. We

measure the photoresponse of the device using femtosecond visible and near infrared

(NIR) light obtained by feeding the fundamental output of a 100 femtosecond laser into

an optical parametric amplifier. The device is shown to have a very broadband

photoresponse, extending from visible (500nm) to near infrared (2200nm) wavelengths.

The device shows fast time response (~35µs) in NIR. It shows a non-linear dependence

of the photocurrent on the pulsed excitation power in the NIR region. This behavior has

been understood by invoking the mechanism of defect filling due to photogenerated

charge carriers. We further characterize the mid infrared (MIR) response of the device

using radiation from a source heated to 200-300 oC. The device response at MIR

wavelengths is slower and is understood to be bolometric in nature.

74

Ultrafast Spin-Wave Dynamics in Ferromagnetic Diamond Antidot Lattice

Koustuv Dutta, Anulekha De, Arundhati Adhikari and Anjan Barman*

Department of Condensed Matter Physics and Material Sciences, S N Bose National Centre for Basic

Sciences, Block-JD, Sector-III, Salt Lake, Kolkata-700106, India. *Email address: abarman@bose.res.in

Over last few decades, both fundamental and application-oriented research have

gained immense interest in studying the ultrafast spin dynamics of magnetic nanostructures

to meet with the ever-increasing demand in the information storage, memory and

processing industry. Manipulation of spin in one-, two- or three-dimensional peridically

patterned nanostructures (magnonic crystals) have great application potential in the on-

chip data processing and communication devices. In a typical two-dimensional antidot

lattice (ADL), a distinct class of Magnonic Crystals, nanohole arrays are arranged in a

particular lattice symmetry giving rise to a specific type of configurational anisotropy and

it can significantly modulate the spin-wave propagation and localization in that system1.

Here, we present an all-optical femtosecond time-resolved study of two-dimensional

diamond shaped Ni80Fe20 (permalloy) antidot lattice arranged in square and hexagonal

lattice symmetry (Fig. 1(a)). A custom-built Time-resolved Magneto-Optical Kerr Effect

(TRMOKE) microscope2 set-up based on two-colour colinear pump-probe geometry has

been employed for the present study. The samples have been fabricated using the e-beam

lithography followed by e-beam evaporation process. Experimental studies unfold a rich

variation of spin-wave dynamics with the change of the strength and orientation of the

applied bias magnetic field. The configurational anisotropy of hexagonal lattice displays a

complex pattern due to superposition of anisotropic contribution on behalf of nanohole

shape and lattice symmetry which significantly differs from the four-fold anisotropy of the

square lattice (Fig. 1(b)-(c)). These experimental observations are reproduced by

micromagnetic simulation. The calculated spin-wave mode profiles and internal field

distributions underpins the observed anisotropic behaviour of spin waves in such

structures.

We acknowledge financial support from S. N. Bose National Centre for Basic

Sciences (grant no.: SNB/AB/18-19/211). KD and AD acknowledge DST-INSPIRE

scheme while AA acknowledges SNBNCBS for respective research fellowships. REFERENCES:

1. R. Mandal et al., ACS Nano 2012, 6, 3397.

2. A. Barman et al., Nano Lett. 2006, 6, 2939.

Fig. 1. a) Scanning electron micrograph of the sample. Bias-field angle dependence of spin-wave frequency for d) square lattice and e) hexagonal lattice.

a)

H

x

y

ϕ

0 45 90 135 180

6

8

10

12

M1

M2

M3

M4

M5

Fre

qu

en

cy (

GH

z)

Bias Field Angle (degree)

b)

0 45 90 135 1806

8

10

12

M1

M2

M3

M4

M5

Fre

qu

en

cy (

GH

z)

Bias Field Angle (degree)

c)

75

Understanding Optical Behaviour of InP Based Core Alloy Shell QDs through

Ultrafast dynamics and Single Particle Spectroscopy

Chayan Kumar Dea, Prasun K. Mandal*a,b aDepartment of Chemical Sciences, bCentre for Advanced Functional Materials, Indian Institute of Science

Education and Research (IISER) Kolkata, Mohanpur, West Bengal, 741246, India.

E-mail: ckd12ip019@iiserkol.ac.in, prasunchem@iiserkol.ac.in*

InP based core alloy shell (CAS) QDs with high photoluminescence quantum yield

(PLQY~65%) have been synthesized using ‘one pot hot injection’ method. These newly

developed CAS QDs possess a compositionally smoothened and softened interface which

provides enhanced confinement for the photogenerated charge-carriers, excellent

photochemical stability and lesser number of trap state at core shell interface.1 It has been

observed that smoothing out the confinement potential can decrease the Auger

recombination rate by more than three orders of magnitude in comparison to an abrupt

confinement potential boundary.2 As a result blinking of QDs which is mainly originate

from non-radiative Auger recombination has been found to be suppressed in CAS QDs

than CS QDs.2,3

Spectral (steady state optical behaviour (PLQY)) and temporal (excited-state decay

dynamics) optical behaviour of different colour emitting InP based CAS QDs could be

successfully correlated at the ensemble level. The role of each time component of

multiexponential decay could be understood reasonably well.1 Rate of charge carrier

detrapping/ rate of charge carrier trapping (a single particle property) has been correlated

with PLQY (an ensemble property) for differently emitting CAS QDs. Suppression of

blinking has been achieved with small sized InP based QDs in reduced air atomphere which

is very rare for InP based QDs.3 Moreover, it has been shown that for InP based CAS QD

and core/shell (CS) QD with similar ensemble properties like similar emission maxima

(555 nm), similar PLQY (~ 65%), and similar PL lifetime, CAS QD is optically far superior

to CS QD at the single particle level.

Excitation wavelength dependent PLQY of InP based CAS QDs, which is an

apparent violation of Vavilov rule has been investigated in detail using femtosecond

ultrafast pump-probe dynamics at ensemble level for different excitation wavelengths.

Lower normalized transient population (ΔA/A) and slower exciton (predominantly

electron) relaxation at lower wavelength excitation indicates that hot exciton trapping is

more prominent at lower wavelength excitation. From excitation wavelength dependent

single particle blinking measurement it has been observed that trapping gets suppressed

and detrapping gets enhanced with increasing excitation wavelength. Similar observation

has been noted for CdSe based QDs.4 All these observations are in line with the

enhancement of the PLQY with increasing excitation wavelength.

REFERENCES

1. C. K. De, T. Routh, D. Roy, S. Mandal, P. K. Mandal, J. Phys. Chem. C, 2018, 122, 964-973.

2. Y.S. Park, W. K. Bae, T. Baker, J. Lim, V. I. Klimov, Nano Lett. 2015, 15, 7319-28.

3. C. K. De, D. Roy, S. Mandal, P. K. Mandal, J. Phys. Chem. Lett, 2019, 10, 4030-4038.

4. D. Roy, A. Das, C. K. De, S. Mandal, P. R. Bangal, P. K. Mandal, J. Phys. Chem. C 2019, 123, 6922-

6933.

76

Ultrafast Response of Nanoplatelets Around its Particle Plasmon Resonance: Effect of Size

Distribution

Asha Singh,1, a) Salahuddin Khan1 and J. Jayabalan1,2

1Nano Science Laboratory, Materials Science Section, Raja Ramanna Centre for Advanced Technology,

Indore, India-452013. 2Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai, India - 400085.

a)Corresponding author: asha@rrcat.gov.in

The optical response of metal nanostructures plays a key role in deciding the operation of plasmonic devices.

For operating at different wavelengths it is essential to tune the localized surface plasmon resonance (LSPR)

and this can be done by controlling the aspect ratio of the nanoparticles [1]. LSPR of small silver nanospheres

is less sensitive to its diameter distribution whereas other shapes do show stronger dependence on size

distribution since LSPR depends on aspect ratio. Fig-1 shows the extinction coefficient of colloidal solution

of silver nanoplatelets in water. The in-plane dipole peak occurs at 784 nm. The TEM images show an average

diameter and thickness of the nanoplatelets were 43 nm and 7 nm respectively. Degenerate transient

transmission measurements were carried out using ~190 fs, 82 MHz repetition laser operated in the range

760 nm to 830 nm (Fig-2). The peak intensity at all the wavelengths were kept constant (~0.5 MWmm-2).

The magnitude of transient transmission (|T/T|) at all wavelength shows an increase with the arrival of the

pump and decays subsequently with increasing delay (Fig-2) [2]. The sign of T/T was found to be negative

for wavelengths longer than LSPR. The maximum change in the |T/T| (|T/T|pk) shows a dip near to the

LSPR peak (Fig-3). Using a theoretical model and experimental results, we show that the observed variation

in the peak response is caused by the size distribution as well as the dispersion of nonlinear response of

nanoplatelets [3, 4]. This leads to a minima of |T/T|pk near the LSPR wavelength.

Fig-1: The extinction spectrum of the silver colloid. Inset shows TEM image of the sample.

Fig-2: Transient transmission through the sample at different wavelengths.

Fig-3: The dependence of peak change in transmission with pump-probe wavelength.

REFERENCES

1. Z. Starowicz, R. Wojnarowska-Nowak, P. Ozga, and E. M. Sheregii, Colloid and polymer

science, 296, 1029 (2018).

2. J. Jayabalan, Asha Singh, Rama Chari, Salahuddin Khan, Himanshu Srivastava, and S. M. Oak,

Appl. Phy. Lett., 94, 181902 (2009).

3. X. Zhang, C. Huang, M. Wang, P. Huang, X. He and Z. Wei, scientific reports., 8, 10499 (2018).

J. Jayabalan, Opt. Soc. Am. B., 28, 2448 (2011).

77

Singlet Fission within Ultrafast Time Scale and near Unity Yield in 5,12–bis

(phenylethynyl)tetracene thin film

Amitabha Nandia,b, Biswajit Mannaa, and Rajib Ghosha

anandi@barc.gov.in aRadiation and Photochemistry Division, Bhabha Atomic Research Center, Mumbai 400085, India bHomi Bhabha Nation Institute, Training School Complex, Anushakti Nagar, Mumbai, 400094, India

5,12–bis (phenylethynyl)tetracene (BPET) thinfilm, having thickness of 100 nm,

was prepared following thremal evaporation method. Steady state absorption measurement

shows ~80 nm red shift of absorption band (as compared to that of the monomer) and well

coverage of solar spectrum. Interestingly, the BPEA thinfilm observed to show three order

less emission yield as compared to its monomeric form. The time resolved emission

studyies also indicates singlet lifetime reduction from 7.3 ns to ~1 ps, as the sample changes

from monomer to thinfilm. To unravel the asoociated fast exciton deactivation mechanism,

ultrafast pump-probe experiments were carried out. As evident from the figure 1A and 1B,

immediately after photoexcitation the singlet excitons goes for prompt decay with lifetime

of 0.8 ps (the excited state absorption 670-740 nm). It causes formation of a meta stable

state which is assigned as triplet correlated pair state having excited state absorption (ESA)

in the 520-600 nm wavelength region. The triplet correlated pair state further undergoes

for some structural relaxation in the initial 10 ps time sacle. This is ensured from the

observed red shift of maximum of the associated ESA band. With further time delay, we

observe enhancement in ground state bleach (GSB) signal at 610-650 nm and a

concomitent growth of ESA band in the 580-620 nm region. This is associated with the

seperated triplet excition production with the time constant of ~18 ps. Simulteneous growth

of triplet ESA band (580-620 nm) and GSB signal (610-650 nm) is the signature of

presence of singlet fission process in the BPET thinfilm sample. The singlet fission yield

was estimated to be about 94%. The high singlet fission yield and well coverage of solar

spectrum by the thinfilm sample of this commercially available dye may appear very useful

for photovoltaic application.

-0.02

0.00

0.02

0.04

0.1 ps

0.5 ps

2 ps

5 ps

10 ps

A

bso

rpti

on

(O

D)

Wavelength (nm)

1A

500 600 700

-0.01

0.00

0.01

0.02

10 ps

20 ps

50ps

100ps

0

15

30560nm:- 2.3(-0.0145), 240(-0.0158)

0

5

10

600nm, :- 2.3(-0.0061), 19.2(0.012), 250(-0.0091)

0

2

4

6

A

bs

orp

tio

n (

OD

)

730nm, :- 0.78(-0.0067), 15(-0.00085)

0 10 20 30 40 60 120 180

-10.0

-7.5

-5.0

-2.5660nm, :- 3.5(0.0057), 17.7(-0.0068), 240(0.0076)

Time (ps)

1B

Figure 1: (1A) Transient absorption spectra recorded at different delay times for BPET

thin film after excitation with 390 nm light (1B) temporal profiles along with fitted data.

78

Cosolvents at Aqueous Interface: As Observed by “Classical” and “Heterodyne-

Detected” Vibrational Sum Frequency Generation Spectroscopy

Subhadip Roy, and Jahur A. Mondal* Radiation and Photochemistry Division, BARC, HBNI, Mumbai-400085,

Email-mondal@barc.gov.in

Aqueous interface plays critical roles in diverse fields, including atmospheric, chemical,

biology and applied aspects. Preferential adsorption of cosolvents, ions, and amphiphiles

as well as their mutual interactions create a unique environment at the interface, leading to

interface-specific chemical reactions. Advanced laser spectroscopy, such as sum frequency

generation, provided a molecular level understanding of the interaction of charged

amphiphiles and ions at the aqueous interface. However, the corresponding knowledge for

the cosolvent is limited. Here, we show that cosolvents, such as alcohol and ether, affect

the average hydrogen-bonding and preferred orientation of interfacial water negligibly but

the interface becomes increasingly dry (decreased water content) with increasing cosolvent

concentration.

We investigated the effect of small alcohols and ethers, which are used as cosolvents, at

the air-water interface using “narrowband classical” as well as “broadband heterodyne-

detected” vibrational sum frequency generation (C-VSFG and HD-VSFG) and surface

tensiometry techniques.1-3 Details of the VSFG setup will be discussed during the

presentation. The C-VSFG provides information about the packing and conformational

change of the cosolvents by measuring the high resolution |χ(2)|2 spectrum (χ(2) is the second

order electric susceptibility at the interface) of their sharp CH-stretch bands (2800-3000

cm-1), while the HD-VSFG measurements elucidate the ordering of interfacial water by

monitoring the imaginary-χ(2) signal of its broad OH stretch band (3000-3600 cm-1). Figure

1 shows the HD-VSFG results of the air-water-propanol interface (Imχ(2) spectra of other

amphiphiles and the corresponding C-VSFG (|χ(2)|2) results are not shown) for different

proportions of alcohol and water. The negative CH-stretch signal (2800-3000 cm-1; Figure

1) shows the methyl-up orientation of propanol at the air-water interface.2 With increasing

propanol concentration, the signal in the CH stretch region does not increase, but that in

the OH stretch region (3000-3600 cm-1) decreases without significant change in band

shape. At the neat air-alcohol interface, the signal in the CH stretch region is similar to that

of the diluted air-water-alcohol system; but that in the OH

stretch region is almost zero. This shows that the alcohol-OH

has negligible contribution in the measured interfacial

spectra. Accordingly, the decreased OH stretch signal (3000-

3600 cm-1) suggests reduced water content of the interface

for the alcohol-water mixture. In other words, the interface

dehydrates in presence of alcohol (or ether; results not

shown) as a cosolvent in water.

REFERENCES

1. Du, Q.; Superfine, R.; Freysz, E.; Shen, Y. R. Phys Rev. Lett. 1993,

70, 2313

2. Nihonyanagi, S.; Yamaguchi, S.; Tahara, T. J.Chem. Phys. 2009, 130, 204704

3. Ahmed, M.; Namboodiri, V.; Mathi, P.; Singh, A. K.; Mondal, Jahur. A.. J. Phys. Chem. C 2016, 120

(19), 10252-10260

Figure 1. Imspectra of the air-water-

propanol interface at different bulk

concentrations of propanol.

79

Cold Target Recoil Ion Momentum Spectroscopy: Design and Simulation

Swetapuspa Soumyashree, Rituparna Das, R.K. Kushawaha

Physical Research Laboratory, Ahmedabad, swetapuspa@prl.res.in, kushawaha@prl.res.in

For understanding the fragmentation dynamics of molecular ions induced by the

femtosecond laser (800 nm, 1 kHz, 25 fs), a novel electron-ion coincidence momentum

imaging technique “Cold Target Recoil Ion Momentum Spectrometer (COLTRIMS)”

setup is under development at PRL Ahmedabad. The ion and electron momentum imaging

technique is based on two Wiley-McLaren type spectrometers which consist of 16

extraction plates, two drift tubes and two position sensitive detectors (Figure 1). From the

measurement of the time of flight and position of impact for each charged particle, the

momentum vectors are determined.

Designing of the spectrometer and the simulation of the ion trajectories are carried out

using SIMION 8.0 package. For the energy and mass resolution of the spectrometer, a

MATLAB code was written to find the FWHM of time of flight profile of given ion. Figure

1 shows the ion trajectories of 10000 particles of energy 2eV in this spectrometer. The

electron and ion trajectories simulation, energy range and mass resolution will be

presented. This Setup will be combined with femtosecond pump-probe setup. Preliminary

calibration TOF results will be presented in this conference.

Figure 1. Ion trajectory simulation in COLTRIMS setup

REFERENCES

1. R. Dörner et al., Physics Reports 2000, 330, 95-192

W. C. Wiley and I. H. McLaren, Rev. Sci. Instrum. 1955, 26, 1150–1156

80

Study of molecular alignment using femtosecond laser pulses

Madhusudhan P, Rituparna Das, Pranav Bharadwaj, Swetapuspa Soumyashree, Pooja

Chandravanshi, and Rajesh K Kushawaha Atomic, Molecular, and Optical Physics, Physical Research Laboratory, Ahmedabad

madhusudhanp@prl.res.in

kushawaha@prl.res.in

In the process of observing and controlling molecular dynamics in gas phase,

angular momentum of molecules takes precedence1. Controlling the evolution of angular

momentum would be reflected as the control of molecular rotation. Dynamic alignment of

molecules using an ultrashort laser source would facilitate in the measurements. Alignment

of N2 and CO2 molecules using femtosecond laser (25fs, 1Khz, 10mJ) in pump-probe

scheme and Velocity Map Imaging spectrometer2 has been performed. Theoretical

analysis3 of the alignment has been performed considering various experimental

parameters4, and simulated using a program developed in-house. The results on molecular

alignment are presented in this conference.

REFERENCES

1. Richard N. Zare. Wiley-Interscience. 1988, Angular Momentum: Understanding Spatial Aspects in

Chemistry and Physics.

2. Kling, N. G., Paul, D., Gura, A., Laurent, G., De, S., Li, H., ... & Litvinyuk, I. V. Journal of

Instrumentation. (2014), 9(05), P05005.

3. Zhang, S., Lu, C., Jia, T., Wang, Z., & Sun, Z, Phys. Rev. A. 2011, 043410, 83.

4. Xioming Ren, Kansas State University. 2013, Laser-driven rotational dynamics of gas-phase

molecules: control and applications.

81

Anomalous Halogen–Halogen Interaction Assists Radial Chromophoric Assembly

Remya Ramakrishnan,†a Niyas M. A.,†a Vishnu Vijay,a Ebin Sebastian,a Mahesh

Hariharanb a School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram, Vithura,

Thiruvananthapuram, Kerala, India 695551

b Faculty of Chemistry, School of Chemistry, Indian Institute of Science Education and Research

Thiruvananthapuram, Vithura, Thiruvananthapuram, Kerala, India 695551, mahesh@iisertvm.ac.in † These authors contributed equally

ABSTRACT: The engineering of highly efficient supramolecular architectures that

mimic competent natural systems n a comprehensive knowledge of noncovalent

interactions. Halogen bonding is an excellent noncovalent interaction that forms

halogen−halogen (X2) as well as trihalogen interacting synthons.1 Herein, we report the

first observation of a symmetric radial assembly of 1,8-dibromonaphthalene(2,6-

diisopropylphenyl)imide (NIBr2) (R3̅c space group) composed of a stable hexabromine

interacting synthon (Br6) that further push the limits of our understanding on the nature,

role, and potential of noncovalent halogen bonding.2 Contrary to the destabilization

proposed for Type-I X2 interactions,3 Br6-synthon-possessing Type-I X2 interactions

exhibit a stabilizing nature owing to the exchange-correlation component. The radial

assembly of chromophores is further strengthened by intermolecular through-space charge

transfer interaction. The radial assembly of chromophores is additionally strengthened by

an intermolecular charge transfer interaction between the 2,6-diisopropylphenyl moiety

and naphthalimide core. Crystalline NIBr2 exhibits room temperature phosphorescence

with a lifetime of 23 μs. The femtosecond transient absorption spectra of NIBr2 in

chloroform captured the ultrafast intersystem crossing from the singlet to triplet state (kisc

= 7.33 × 1010 s−1) and nanosecond transient absorption spectra exhibited spectroscopic

signatures of the triplet state of the chromophore ( t = 3.1 μs) at 400 and 500 nm. Br6-

synthon-driven 3-fold symmetric radial assembly render a lattice structure that reminisces

the chromophoric arrangement in the light harvesting system 2 of purple bacteria.

REFERENCES

1. G. Cavallo, P. Metrangolo, R. Milani, T. Pilati, A. Priimagi, G. Resnati, G. Terraneo, Chem. Rev.

2016, 116, 2478.

2. M. A.Niyas, R. Ramakrishnan, V. Vijay, E. Sebastian, M. Hariharan, J. Am. Chem. Soc. 2019,

141, 4536−4540.

S.Tothadi, S. Joseph, G. R. Desiraju, Cryst. Growth Des. 2013, 13, 3242.

82

Excited state structural dynamics of 4-cyano-4’-hydroxystilbene: deciphering the

signatures of proton-coupled electron transfer using ultrafast Raman loss

spectroscopy

Reshma Mathew,a Surajit Kayal,b Adithya Lakshmanna Yapamanuc* a School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram, Vithura,

Thiruvananthapuram 695551, India b School of Chemistry, University of Nottingham, Nottingham.NG7, 2RD, UK. c Research Institute for Electronic Science, Hokkaido University, Sapporo 001-0021, Japan.

*adithya@es.hokudai.ac.jp

The Photo-initiated proton-coupled electron transfer (PCET) process plays a crucial

role in the context of light harvesting in various biological and chemical systems.

Molecular model systems are typically employed to understand the mechanisms underlying

the functioning of complex biological systems. Some molecular dyads based on the PCET

property are particularly designed to achieve efficient sunlight-to-fuel production.1 Organic

photoacids are potential sources for such applications since they exhibit enhancement in

their acidity upon photoexcitation, facilitating the mimicking of some of the biological

processes. p-hydroxybenzylideneimidazolinone (p-HBI), an organic photoacid is a key

chromophore in green fluorescence protein which exhibits green emission due to excited

state proton transfer.2

Herein, we investigate the structural changes and dynamics of 4-cyano-4’-

hydroxystilbene (CHSB) in presence of an external base, t-butylamine (TBA) using the

techniques of ultrafast transient absorption, emission and ultrafast Raman loss

spectroscopy.3 Femtosecond fluorescence up-conversion measurements of the CHSB-TBA

adduct reveal a precursor-successor relationship between the ~420 and ~530 nm emission

bands, which implies that the adduct evolves predominantly through the electron-proton

transferred state. Further, Raman measurements show a clear distinction in the dynamics

of the C=C stretch of CHSB in presence and absence of TBA in terms of the amplitude

growth (0.45 ps vs. instantaneous) and the central frequency (1584 vs. 1523 cm-1).

REFERENCES

1. J. C. Lennox, D. A. Kurtz, T. Huang, J. L. Dempsey, ACS Energy Lett., 2017, 2, 1246-1256

2. J. Dong, K. M. Solntsev, O. Poizat, L. M. Tolbert, J. Am. Chem. Soc., 2007, 129, 10084-10085.

R. Mathew, S. Kayal, A. L.Yapamanu, Phys. Chem. Chem. Phys. 2019, DOI: 10.1039/c9cp02923k.

83

Hydrocarbon Chain-Length Dependence of Solvation Dynamics in Alcohol-based

Deep Eutectic Solvents: A 2D IR Spectroscopic Investigation

Srijan Chatterjee,a Deborin Ghosh,b Tapas Haldar,c Pranab Deb,c Sushil S. Sakpal,c

Samadhan H. Deshmukh,a Somnath M. Kashid*,c and Sayan Bagchi* d

a JRF, Physical and Materials Chemistry Division, CSIR-National Chemical Laboratory, Pune b SERB-NPDF, Physical and Materials Chemistry Division, CSIR-National Chemical Laboratory, Pune c SRF, Physical and Materials Chemistry Division, CSIR-National Chemical Laboratory, Pune

d Principal Scientist, Physical and Materials Chemistry Division, CSIR-National Chemical Laboratory,

Pune, s.bagchi@ncl.res.in

Deep eutectic solvent (DES) has gained popularity in recent years as an

environmentally benign, inexpensive alternative to organic solvents for diverse

applications in chemistry and biology.1,2 Among them, alcohol-based DESs serve as useful

media in various applications due to their significantly low viscosity as compared to other

DESs. Despite their importance as media, little is known how their solvation dynamics

change as a function of the hydrocarbon chain-length of the alcohol constituent. In order

to obtain insights into the chain-length dependence of the solvation dynamics, we have

performed two-dimensional infrared spectroscopy on three alcohol-based DESs by

systematically varying the hydrocarbon chain-length. The results reveal that the solvent

dynamics slow down monotonically with increase in the chain-length. This increase in the

dynamic timescales also show a strong correlation with the concomitant increase in the

viscosity of DESs. In addition, we have performed MD simulations to compare with the

experimental results, thereby testing the capacity of simulations to determine the

amplitudes and timescales of the structural fluctuations on fast timescales under thermal

equilibrium conditions.

REFERENCES

1. Q. Zhang, K. De Oliveira Vigier, S. Royer, F. Jérôme, Chem. Soc. Rev. 2012, 41, 7108.

E. L. Smith, A. P. Abbott, K. S. Ryder, Chem. Rev. 2014, 114, 11060.

84

Extremely Weakly Interacting O-H in the Hydration Shell of High Charge Density

Metal Ions as Observed Raman Difference with Simultaneous Curve Fitting (RD-

SCF) Spectroscopy

Animesh Patra†, Subhadip Royǂ, Subhamoy Sahaǂ, Dipak K. Palit†, Jahur A. Mondalǂ ǂRadiation & Photochemistry Division, BARC, Homi Bhabha National Institute, Mumbai †School of Chemistry, UM-DAE Centre for Excellence in Basic Sciences, Mumbai

The mutual interaction between ion and water plays a pivotal role in living and

nonliving systems. Understanding the structure of water in the metal-ion hydration shell is

essential in elucidating their reactivity. For selective extraction of the native spectral

response of water associated to a metal ion, one needs to circumvent the response of

counterion-affected water (here anion) and bulk water (ion-unaffected water). To extract

metal ion (Mz+; z = 1, 2, 3) hydration shell spectrum, we introduced Raman difference with

simultaneous curve fitting (RD-SCF) analysis. For example, to extract the Mg2+ hydration

shell spetrum (𝑆()𝑀𝑧+ ), we used MgCl2 (0.3M) solution as sample (𝑆()𝑒𝑥𝑝

), NaCl

(0.6M) solution as reference (𝑅()𝑒𝑥𝑝

) and fitted the sample spectrum using equation (1).

Then, the metal ion-affected water spectrum, (𝑆()𝑀𝑧+ ), is obtained by equation (2),

which remove the response of bulk water and that of Cl--associated water from the sample

spectrum. It is noteworthy that the effect of Na+ cation on water is negligible hence, Na+-

affected water is similar to the bulk water.

𝑆()𝑓𝑖𝑡

= ∑ (𝑎𝑛 exp (−( − 𝑛)2/2 𝑛2

)𝑛

𝑛=1+ 𝑓𝑅()

𝑒𝑥𝑝 + 𝑎0 (1)

𝑆()𝑀𝑧+

∑ (𝑎𝑛 exp (−( − 𝑛)2/2 𝑛2

)𝑛

𝑛=1= 𝑆()

𝑒𝑥𝑝 − 𝑓𝑅()𝑒𝑥𝑝 − 𝑎0 (2)

Where, 𝑓 is the fraction of 𝑅()𝑒𝑥𝑝

carried by the 𝑆()𝑒𝑥𝑝

; 𝑎𝑛,𝑛, 𝑛 are the amplitude,

peak center and fwhm of the nth component band of the multi-component fitted curve, 𝑎0

is the constant background difference between the (𝑆()𝑒𝑥𝑝

) and 𝑅()𝑒𝑥𝑝

. The RD-SCF-

extracted Lu3+ hydration shell spectrum and bulk water is shown in Fig.1 for comparison.

The higher relative intensity of 3200 cm-1 band compared to bulk water, suggesting

increased H-bonding of water in the hydration shell. Interestingly, apart from 3200 cm-1

band, there is a distinct band in the extreme high frequency region (~3600 cm-1) of the OH

stretch, which clearly manifests the existence of extremely weakly H-bonded O-H in the

hydration shell. Based on controlled experiments, such as variation of charge density,

concentration, counterions, pH, we further propose that such weakly interacting O-H is

largely confined within the surface of the first hydration shell, where a second hydration

shell water donates H-bond to the first hydration shell

water (Scheme in Fig. 1). The oxygen atom the of first

hydration shell water donates significant amount of

charge to the high charge density metal ion, consequently

become a weak H-bond acceptor, resulting the weakly H-

bond O-H in the hydration shell. Such weakly interacting

OH is observed in the hydration shell of trivalent

lanthanides, bivalent alkaline earths and even monovalent

Li+ ions. Fig. 1. Typical Raman spectra (OH stretch) of bulk water and water

in the hydration shell of high charge density metal ion (Lu3+; blue

85

curve). The scheme illustrates the strongly and weakly H-bonded water in the hydration shell.

REFERENCES

[1]. Collins, K. D., Biophysical Journal 1997, 72 , 65.

[2]. Ahmed, M.; Namboodiri, V.; Singh, A. K.; Mondal, J. A.; Sarkar, S. K., J. Phys. Chem. B 2013, 117,

16479.

86

Attosecond (10-18 second) Charge Migration

Atanu Bhattacharya

Assistant professor, Department of Inorganic and Physical Chemistry, Indian Institute of Science,

Bangalore 560012, atanub@iisc.ac.in

Our interest in viewing chemical reactions with optical pulses at ever-increasingly

shorter time scale (microsecond to femtosecond) has given birth to the modern ultrafast

science. Flash photolysis and Femtochemistry are two representative milestones in the

history of ultrafast science.1 Having followed reactions through their transition state

ultimately in the femtosecond time domain, would a further improvement in the time

resolution of flash photolysis into the attosecond regime contribute to the molecular

chemical dynamics field with new discoveries of interest to general chemistry? The subject

of my seminar will revolve around this question while addressing meaning of attosecond

time scale, role of attosecond time scale in ionized weakly bound molecular clusters and

consequences of attosecond charge migration with the help of quantum molecular

dynamics simulation and high harmonic generation spectroscopy.2,3.

REFERENCES

1. A. Zewail, The Chemical Bond: Structure and Dynamics, Academic Press, Inc. 1992.

2. Sankhabrata Chandra and Atanu Bhattacharya, "Attochemistry of Ionized Halogen,

Chalcogen, Pnicogen, and Tetrel Non-Covalent Bonded Clusters" Journal of Physical

Chemistry A, Feature Article, 2016, 120, 10057-10071.

3. Sankhabrata Chandra, Irfana Ansari, Gopal Dixit, Franck Lepine and Atanu

Bhattacharya, "Experimental Evidence of Sensitivity of the High Harmonic Generation to

the Hydrogen Bonding" Journal of Physical Chemistry A, 2019, 123, 5144-5149.

87

Energy Transfer followed by Sequential Electron Transfer in a Supramolecular

Tetrad Composed of Phenothiazine, Zinc Porphyrin, Borondipyyromethene, and

Fullerene: Charge Stabilization in “Antenna-Reaction Center” Mimic

Kanika Jain,a Francis D’Souza,*b Raghu Chitta*a,c aDepartment of Chemistry, School of Chemical Sciences & Pharmacy, Central University of Rajasthan,

Kishangarh, Dist. Ajmer, Rajasthan-305817, India. bDepartment of Chemistry, University of North Texas, 1155 Union Circle, #305070, Denton, Texas 76203-

5017, United States cDepartment of Chemistry, National Institute of Technology Warangal, Hanamkonda, Warangal, Telangana

– 506004.

In natural photosynthesis sunlight is harvested via natural antenna complexes by

creating electronic excitations and the subsequent rapid excitation energy transfer to the

reaction center followed by multistep electron transfer reactions resulting into long lived

charge separated state.1 However, artificial photosynthesis calls for broad band capturing

of light to maximize the utilization and conversion of light energy. Generation of long-

lived charged sepd. states is also one of the important criteria in developing artificial

photosynthetic reaction centers.2

In the present work, we have utilized the antenna-reaction center and the electron

transfer-hole shift idea by designing a single model compound, (PTZ)3-ZnP-

BODIPY:C60Im, in which PTZ absorbs in the UV-visible region from 290-350 nm and acts

as an energy transfer antenna and also a hole shifting entity to ZnP, BODIPY absorbs in

the visible region from 350-520 nm and acts as the energy transfer antenna to ZnP, where

ZnP absorbs in the visible region from 400-610 nm and behaves as the electron donor when

axially ligated with C60Im as the electron acceptor. As integrating PTZ, BODIPY, and ZnP

moieties onto a single platform leads to the absorption of the wavelengths from 260-620

nm, this artificial photosynthetic model is expected to, not only exhibit antenna effect by

capturing broader spectrum of sunlight but also lead to charge separation along with charge

stabilization via hole shifting process. The outcome of these findings revealed by the

steady-state absorption, fluorescence emission studies, electrochemical, and

photochemical (from femtosecond and nanosecond transient spectroscopy) studies are

presented.

REFERENCES

1. F. D'Souza, P. M. Smith, M. E. Zandler, A. L. McCarty, M. Itou, Y. Araki, O. Ito, J. Am. Chem. Soc. 2004,

126, 7898-7907.

2. G. N. Lim, E. Maligaspe,; M. E. Zandler, F. D'Souza, Chem.: Eur. J. 2014, 20, 17089-17099.

88

Squaramide Based, “Turn-on” Schiff Base Multi-analyte Sensors for Zn2+ and Cd2+:

Influence of Acetate ion and Co-operativity

Lasitha P, a G.Naresh Patwari a a Department of Chemistry, IIT Bombay, Powai, India, naresh@chem.iitb.ac.in

Squaramide based sensors are well studied in recent past1 and these molecules are used mainly in the fields of organo-catalysis2, molecular recognition3, and self-assembly4. The 3d10 configuration makes both Zn2+ and Cd2+ ion spectroscopically silent and this chemical similarity of Zn2+ and Cd2+ ion makes the selective sensing of these metal ions difficult using a single sensor5. Due to these reasons an effective multi-analyte sensor with selective sensing ability for Zn2+ and Cd2+are still under way9. For this purpose, sensing technique based on fluorescence, especially “turn-on” fluorescence has an inherent advantage over other conventional techniques owing to its simplicity in operation, ease of handling, reliability of the data and good sensitivity6.

In this work, we have synthesized novel squaramide ligands following a Schiff base condensation reaction and studied for their sensing properties. The ligands consist of functional groups such as OH and –OCH3 were compared with ligand without any functional groups. Ligands show a feeble emission in DMSO and emission quantum yield increases an order of ten (from 0.0027 to 0.041) in the presence of zinc and cadmium producing a “turn-on” fluorescence effect. The selective emission responses for zinc and cadmium makes these ligands an efficient multi-analyte sensor. The role of anions is accounted in these studies and found that acetate ions play a major role in sensing by enhancing the complexation probability in a co-operative manner. Excited-state properties of ligand-metal complexes are characterized by TCSPC and up-conversion measurements. Better selectivity of cadmium ion was observed over zinc and the ligands also show sensing properties at 70/30, DMSO/water mixture under basic medium.

Figure 1: Proposed mechanism of complex formation (Photographs of a DMSO solution

of the ligand in presence of zinc and cadmium acetate showing different emission for

each metal)

REFERENCES

1. A. Rostami, C. J. Wei, G. Guérin and M.S. Taylor, Angew. Chem. Int. Ed., 2011, 50, 2059.

2. L. Kong, N. Li, S. Zhang, X. Chen, M. Zhao, Y. Zhang and X. Wang, Org. Biomol. Chem., 2014,

12, 8656.

3. X. Wu, N. Busschaert, N. J. Wells, Y. Jiang and P. A. Gale, J. Am. Chem. Soc., 2015, 137, 1476.

4. A. Portell, M. Font-Bardia and R. Prohen, Cryst. Growth Des., 2013, 13, 4200.

5. R. Purkait, S. Dey and C. Sinhaa, New J. Chem., 2018, 42, 16653.

6. S. J. Malthus, S. A. Cameron and S. Brooke, Inorg. Chem., 2018, 57, 2480.

89

Dynamics of Preferential Solvation of 5-Aminoquinoline in Hexane-Alcohol Solvent

Mixtures

Sharmistha Das, Anindya Datta* a Department of Chemistry, IIT Bombay, adutta@iitb.ac.in

Dynamics of formation of a polar solvation layer around a polar solvent in hexane-

alcohol mixtures has been studied, using 5-Aminoquinoline (5AQ) as a fluorescent probe,

whose dipole moment is increased significantly upon photoexcitation. Significant spectral

red shift, accompanied by severe fluorescence quenching, is observed, even in solvent

mixtures with as low as mole fraction 0.01 for alcohols. These solvatochromic shifts

deviate significantly from linear behaviour in their dependence on mole fraction, indicating

dipolar enrichment and making 5AQ a good candidate for study of dynamics of formation

of the solvation shell. Fluorescence decays are emission wavelength-dependent and exhibit

nanosecond rise times at red end of emission spectra, which indicate translational diffusion

of bulk polar molecules leading to dipolar enrichment of the solvation shell of 5AQ and

consequent preferential solvation. Electrostatic stabilization and hydrogen bonding

between dipolar excited state of 5AQ and polar alcohol molecules are major driving factors

here. Time evolution of emission spectra, from that in a predominantly hexane-like

environment to that in a predominantly alcohol-like environment, takes place in

nanosecond time scale and depends on the alcohol in the mixture. This in agreement with

calculations using an existing model.

REFERENCES

1. Singh, A. K.; Das, S.; Karmakar, A.; Kumar, A.; Datta, A. Phys. Chem. Chem. Phys. 2018, 20,22320.

2. Molotsky, T.; Huppert, D. J. Phys. Chem. A 2003, 107, 2769. 3. Lerf, C.; Suppan, P. J. Chem. Soc. Faraday Trans. 1992, 88, 963.

4. Hazra, M. K.; Bagchi, B. J. Chem. Phys. 2019, 151, 084502.

5. Królicki, R.; Jarzȩba, W.; Mostafavi, M.; Lampre, I. J. Phys. Chem. A 2002, 106, 1708.

90

Excited State Dynamics of Fluorogenic Molecules

Soumyadipta Rakshit,a Souradip Dasgupta,a Anindya Datta a* a Department of Chemistry, Indian Institute of Technology Bombay, Mumbai, Maharashtra 400076,

adutta@iitb.ac.in

Fluorogenic molecules have attracted significant attention due to their potential in

chemical sensing and organic electronics. Here, we report our work on two classes of such

fluorogenic molecules.

As a first of its kind, we report a nonionic surfactant TX-100 induced unidirectional

aggregated growth of a fluorophore, Dimethyl-2,5-bis(4-

methoxyphenylamino)terephthalate (DBMPT) to produce highly luminescent nanorods.

Pure aqueous phase white light emission with CIE coordinate (0.33, 0.36) from the

DBMPT nanorods was achieved through a unique Fröster Resonance Energy Transfer

(FRET) platform with Perylene-3,4,9,10-tetracarboxylic Acid Dianhydride with a potential

light harvesting ability. This work is in collaboration with the group of Prof. Anil Kumar.

Schiff bases constitute the second class of fluorogenic molecules of our interest.

Torsional motion coupled with rapid proton transfer have been predicted to be the major

non radiative pathways contributing to the very low lifetime as well as emission intensity

of these class of molecules. In this work we have tried to hinder the rapid Excited State

Intramolecular Proton Transfer (ESIPT) of a Schiff base by complexation with Zn+2 and

Al+3. In order to have a better understanding of intramolecular quenching interactions

between the metal centres we have meticulously prepared bi and trinuclear complexes

complexes with the same ligand and went on with their ultrafast studies. The complex

interplay of torsional motion, ESIPT alongside density of states has been evoked to

rationalize these observations though further experimental findings are still on in order to

completely quantify and understand this phenomenon.

REFERENCES

1. Khan, T.; Datta, A. J. Phys. Chem. C 2017, 121 (4), 2410.

2. K. Pal, V. Sharma and A. L. Koner, Chem. Commun. 2017, 53, , 7909.

91

Efficient Generation of Ultrahigh-Contrast High-Intensity Laser Pulses

C. Aparajit a, Kamalesh Jana a, Amit D. Lad a, Yash Ved a, G. Ravindra Kumar a

a Tata Institute of Fundamental Research, 1 Homi Bhabha Road, Mumbai 400 005, India

The last few decades have seen a rapid progress in generating laser pulses with peak

intensities exceeding 1022 W/cm2. These laser pulses are used for a variety of

applications, e.g., laser-driven electron or ion acceleration, generation of high-energy x-

rays and shock waves, and laboratory astrophysics.

Most of these applications would strongly benefit or even ultimately require laser pulses

with a well-known temporal structure and a temporal intensity contrast as high as

possible. Improvement of the temporal pulse quality could be realized after the pulse

compression, e.g., with plasma mirrors, plasma shutters or by generating the second

harmonic. Compared to plasma mirrors, or plasma shutter, generation of second-

harmonic pulses is simple to work with as it requires less optical components. The last

few decades has seen a lot of interest and progress in second-harmonic generation, but

not with femtosecond (fs) pulses of high intensities (of the order of terawatt (TW)/𝑐𝑚2)

using 800 nm fundamental pulses.

We present here experimental results of second-harmonic generation (SHG) of 150 TW,

chirped-pulse amplification (CPA) based laser system, centered at 800 nm and with a

pulse duration of about 25 fs, using a 2 mm thin, 70 mm diameter, lithium triborate

(LBO) type-I SHG-crystal. For the first time, we could achieve second-harmonic

conversion efficiencies as high as 70 percent, which is really promising and opens doors

to study high intensity laser-matter interactions with ultra-high temporal contrast laser

pulses.

REFERENCES

1. Marco Hornung et. al., Appl. Sci. 2015, 5, 1970-1979.

2. David Hillier et. al., Appl. Opt. 2013, 52, 4258-4263

3. Kurumi Mori, Yusuke Tamaki, Minoru Obara, and Katsumi Midorikawa, Journal

of Applied Physics 1998, 83, 2915

4. Ildar A. Begishev, Mikhail Kalashnikov, Vladimir Karpov, Peter Nickles, and

Horst Schonnagel, J. Opt. Soc. Am. B, Vol. 21, No. 2, 2004

5. Andrew M. Weiner, Ultrafast Optics, Wiley Publication, 2008

R. W. Boyd, Nonlinear Optics, Academic Press, San Diego, CA, 2nd edition, 2003

92

Enhanced Two-Photon Activity with Extended Molecular Conjugation

Habib Ali,a Debabrata Goswamib

a Department of Chemistry, IIT Kanpur, hali@iitk.ac.in b Faculty of Chemistry, IIT Kanpur, dgoswami@iitk.ac.in

The absorption of two photons of identical or different frequencies in order to excite

a molecule from its ground to its excited state is two-photon absorption. The measured

laser intensity through a sample during two-photon absorption process follows the relation:

I(z, 𝜆) =𝐼0(𝜆)

1+𝛽(𝜆)𝐼0(𝜆)𝑧.1 Here, I0(𝜆) is the incident Gaussian laser beam profile, z is the

propagation length in medium, β(λ) is the two-photon coefficient, which is related to the

two-photon cross-section (𝜎2) as, 𝜎2 (𝜆) = 𝛽ℎ𝑣 × 103/𝑁𝐴𝑐 and is reported in GM units

that correspond to 10-50 cm4s. We use 120fs laser pulses at 800nm with 600mW average

power from a commercial Ti:Sapphire oscillator (Mira-900F) to excite various azepine

samples dissolved in dichloromethane. The samples were made to flow through a 1 mm

closed circulating cuvette to ensure that there were no cumulative pulse-to-pulse effects.

It has been conjectured that extended molecular conjugation is more favored towards two-

photon absorption.2 In this work we specifically show that two azepine like molecules

having cis-trans conjugated structures (Fig. 1) show a drastic change in their two-photon

absorption (TPA) characteristics. Conformer (a) in Fig. 1 has more extended conjugation

as compared to conformer (b) and find a strong correlation between the TPA signal and the

molecular conjugation.

(a) (b)

Figure 1: Cis-Trans isomers of the important segments of the azepine based

moieties that show drastic difference in TPA.

REFERENCES

1. K. Makhal, P. Mathur, S. Maurya, D. Goswami, J. Appl. Phys., 2017, 121, 053103.

A. Nag, D. Goswami, J Photo. Chem. Photo. Bio. A, 2009, 206, 188.

N N

93

Femtosecond time resolved, micrometer space resolved two dimensional velocity

mapping of an ultraintense laser driven solid plasma

Kamalesh Jana a*, Amit D. Lad a, Yash M. Ved a, Alex P.L. Robinson c, John Pasley b, G.

Ravindra Kumar a

a Tata Institute of Fundamental Research Dr. Homi Bhabha Road, Colaba, Mumbai-400005; b York Plasma Institute, University of York, Heslington, York YO10 5DQ, United Kingdom; cRutherford-

Appleton Laboratory, Chilton, Didcot OX11 0QX, United Kingdom

When an ultraintense, femtosecond laser pulse interacts with solid matter, it

produces high temperature, near solid-density, plasma. The hot dense plasma created via

different laser absorption mechanisms evolves on an ultrafast timescale. It is very important

to know the temporal evolution of the plasma density profile during a laser-plasma

interaction for better understanding of the interaction process [1]. The dynamics of the

plasma can be influenced by different processes including shock compression, rarefactions

and instabilities which in turn depend on the parameters of the interacting laser pulse like

duration, polarization, intensity etc. In recent years, efforts have been made by us and

others to get to grips with the femtosecond evolution of these plasmas [2,3,4]. All these

efforts however lacked transverse spatial information. It is well known that the transverse

evolution of the plasma is a crucial feature in intense laser-matter interaction. We present

an advance on mapping the ultrafast variation of the transverse evolution of the plasma.

Specifically, we obtain micron scale resolved velocity maps of the plasma on femtosecond

timescales. We believe that our study opens a new vista in understanding several issues

crucial for ultrafast laser excited solid plasmas. Interpretation of the results and an

appropriate model will be presented.

REFERENCES

1. R. P. Drake, High Energy Density Physics (Springer-Verlag, Berlin, Heidelberg, 2006).

2. S. Mondal et al., Phys. Rev. Lett. 105, 105002 (2010).

3. K. Jana et al., Phys. Plasmas 25, 013102 (2018).

K. Jana et al., Appl. Phys. Lett. 114, 254103 (2019).

94

Design and Development of a new High Harmonic Generation (HHG) setup and

XUV beamline

Pranav Bhardwaj* ,Madhusudan*, Rituparna Das*, Pooja Chandravanshi*, Swetapuspa

Soumyashree* and Rajesh Kumar Kushawaha* * Atomic, Molecular, and Optical Physics Division, Physical Research Laboratory, Ahmedabad

bhardwaj@prl.res.in

kushawaha@prl.res.in

Design and development of a new High Harmonic Generation setup and XUV

beamline at PRL, Ahmedabad has been initiated for femtosecond and attosecond research.

The simulation has been performed in Zemax. Preliminary simulation and experimental

results will be presented at this conference.

The HHG setup comprises two vacuum chambers. One vacuum chamber is

dedicated to the HHG in which the Even-Lavie valve has been installed for generating a

pulsed atomic/molecular beam. PRL's femtolaser (25fs, 1Khz and 10mJ) pulses are focused

on the molecular beam. The HHG beam is passed through an XUV grating and HHG

spectrum is recorded using an Andor XUV camera. Optimization of laser power, gas and

phase matching has been performed to get intense XUV light. For XUV pump-IR probe

experiments, an XUV beamline has been proposed. The design and simulation results of

this beamline will be reported.

REFERENCES

1. Crane, J. K., Perry, M. D., Herman, S., & Falcone, R. W. High-field harmonic generation in

helium. Optics letters 1992, 17(18), 1256-1258.

2. Kelkensberg, F., Lefebvre, C., Siu, W., Ghafur, O., Nguyen-Dang, T. T., Atabek, O., ... & Remetter, T.

Molecular dissociative ionization and wave-packet dynamics studied using two-color XUV and IR pump-

probe spectroscopy. Physical review letters, 2009 103(12), 123005.

95

Towards Light Induced Carbocation Generation in a Supramolecular Cavity

Sunandita Paul,a and Jyotishman Dasguptaa a Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai

The timescale of primary structural changes associated with carbocation formation,

a two-electron removed transient carbon-centered intermediate, is of fundamental interest

to synthetic organic chemistry. In order to structurally track the formation of carbocations

and the subsequent equilibrating solvation timescale, ultrafast activation in confinement is

imperative. We tried to address this problem by choosing an all aromatic substrate,

tetrathiafulvalene(TTF) which has stable one-electron and two-electron oxidation states.1

TTF was confined inside a Pd6L4 12+ (where L= 2,4,6-tris(4-pyridyl)-1,3,5-triazine)

nanocage2 and the ground state of the molecule in confinement was characterized using

steady state optical spectroscopy. Neutral TTF molecule changes its molecular structure

from boat shape to form a planar aromatic TTF cation radical state. To stabilize and isolate

the radical cation form of TTF, neutral TTF powder was mixed with an aqueous solution

of Pd6L4 12+ nanocage at room temperature. Formation of a colored solution was

immediately observed which was characterized by steady state absorption, 1H NMR, EPR

and Raman spectroscopy. All the spectral features matched with literature reported TTF

radical cation3 thereby confirming that the compatible redox potentials of TTF and PdEn

cage led to the formation of a ground state radical cation in confinement. On exciting the

TTF radical cation by femtosecond pulsed laser the formation of cationic state was

observed at ~2ps which lived for around ~10ps. Further using time-resolved Raman

spectroscopy will help us unravel the timescale of the structural changes during TTF cation

generation.

REFERENCES

1. Nazario Martı´n Chem. Comm., 49, 7025, (2013)

2. Makoto Fujita Nature, 378 469, (1995)

3. J. B. Torrance Phy Rev.B Vol 19, 730 (1979)

96

High order harmonic generation from noble gases using annular laser beam

H. Singhala,b*, M. Kumara,b, A. Ansaria, and J. A. Chakeraa,b

a Homi Bhabha National Institute, Anushaktinagar, Mumbai, Maharashtra, 400 94 India. b Raja Ramanna Centre for Advanced Technology, Indore 452013, India Email *himanshu@rrcat.gov.in

Generation of high order harmonics of femtosecond laser pulses from their interaction with

gas cell is a well-established method to generate attosecond pulses. In this regard the

generation and optimization of high order harmonics from annular beam is highly

desirable, as the use of annular beams for high order harmonic generation (HHG) provides

an easy way to separate the high order harmonic radiation from the fundamental beam

without the use of any material filter. High order harmonic generation and optimization

from annular beams is not well studied, only a few reports exists in this field1,2 which

studied the HHG from annular beams in thin gas sheets1 or gas jets2. Here we report the

comparative study of HHG from the interaction of annular and Gaussian laser beams with

gas cells filled with Ar, Ne and He gases.

High order harmonics of a Ti:sapphire laser operating at 800 nm central wavelength, 1 kHz

repetition rate, 6.5 mJ energy and 45 fs pulse duration was generated by its interaction with

various gases filled in gas cell. The laser was focussed using a 750 mm focal length plano-

convex lens. Generated harmonics are then focussed using a grazing incidence toroidal

mirror and then dispersed by a flat field grating spectrograph. These harmonic orders are

then detected by a micro channel plate detector coupled with CCD camera. High order

harmonics in the range of 15th to 51st order were detected. The laser has beam diameter of

~20 mm (1/e2 intensity), annular laser beams are generated by reflecting the laser pulse

from a mirror with a circular hole of 5 mm diameter in centre.

The intensity of high order harmonics generated from the interaction of annular laser pulse

with Ar, Ne, and He gases varies between ~ 0.5x to 5x compared to the HHG from non-

annular beams. The intensity ratio between HHG from non-annular beams and annular

beams strongly depends on the laser propagation through the gas cell.

REFERENCES 1. J. Peatross, J. L. Chaloupka, and D. D. Meyerhofer Opt. Lett. 1994, 942, 19..

R. Klas, A. Kirsche, M. Tschernajew, J. Rothhardt, and J. Limpert Opt. Express 2018, 19318, 26.

97

Femtosecond Transient Absorption Dynamics of 𝝅-Extended Thioalkyl

Substituted Tetrathiafulvalene Sensitizers on TiO2 Thin Films

Chinmoy Biswas,1 K. Krishnakanth,2 N. Duvva,3 L. Giribabu,3 S. Venugopal Rao,2 Sai

Santosh Kumar Raavi1* 1 Ultrafast Photophysics and Photonics Laboratory, Department of Physics, Indian

Institute of Technology Hyderabad, Kandi 502285, Telangana 2Advanced Centre of Research in High Energy Materials (ACRHEM), University of

Hyderabad, Hyderabad 500046, Telangana, India 3 Polymers & Functional Materials Division, CSIR-Indian Institute of Chemical Technology, Tarnaka,

Hyderabad-500007, India.

Author e-mail address: sskraavi@iith.ac.in

Abstract: The excited state and electron injection dynamics of two new

organic 𝜋-extended sensitizers have been studied using femtosecond

transient absorption spectroscopy in visible region with 400 nm excitation.

The measurements were carried out for the two dyes in predominantly

neutral form in film on glass and bound on nanocrystalline mesoporous

TiO2 thin films. This study provides evidence for formation of radical

cations in dye-sensitized TiO2 films.

Keywords: Transient absorption Spectroscopy, dye-sensitized solar cell,

ultrafast charge recombination

Introduction Dye-sensitized solar cells (DSSCs) composed of a dye adsorbed on a wide band gap

semiconductor (typically TiO2 or ZnO) absorbing in the visible spectral region, are one of

the emerging solar technologies offering low production cost, easy fabrication and low

environmental impact to conventional silicon solar cells. However, a considerable progress

toward the improvement of device efficiency and stability can still be achieved through

better understanding and optimization of the fundamental charge-transfer processes[1]. In

a working DSSC, a variety of kinetically competing charge-transfer mechanisms take

place[2]. The most fundamental process in DSSCs, after the absorption of light by the dye

molecules, is the electron injection from the dye’s excited state to the conduction band of

the semiconductor[3].

Femtosecond transient absorption (TA) is a most valuable tool to observe charge

transfer dynamics taking place in liquid as well as in solid-state DSSCs. TA measurements

allow us to identify the generation of dye cations formed after injection of electrons from

the dye’s excited state to the conduction band of the semiconductor[3]. In this paper, we

present investigation of two new thioalkyl substituted tetrathiafulvalene sensitizers, G1 and

G3 by using fs-TA spectroscopy in the visible region. The structures of the sensitizers G1

and G3, their synthetic procedures and spectroscopic characterizations are reported in

literature[4]. This study provides an insight into the dynamics of the excited state, the

electron injection, and the photoinduced radical cation generation. The studies are focused

on (a) a comparison of the photodynamics in the different environments and (b) a

comparison of the photodynamics of the two dyes in order to predict which structure seems

more suitable for solar cell applications.

98

Experimental Section

In the visible region the electronic TA setup has been described in detail in literature[5].

The 800 nm and 70 fs output pulses (FWHM) of an amplified Ti:sapphire system were split

into two parts. One part was used for white light generation, from 420 to 780 nm, after

focusing into a 3 mm thick sapphire window. The other fraction was frequency doubled to

generate 400 nm excitation beam. The fluence of the excitation beam at the sample was

approximately 0.1 mJ/cm2, and its polarization was at magic angle with respect to the

probe beam. TA measurement were performed from -2 up to 4000 ps. The solid samples

were placed in a holder, which was constantly moved randomly, on a plane perpendicular

to the excitation beam. The liquid samples were measured in a 1 mm quartz cell. The TA

spectra were corrected for the chirp of the white-light probe pulses. The exponential fitting

routine did not account for wavelength dependent IRF or dispersion. Therefore, the first

ca. 300 fs were excluded from analysis, to avoid artifacts arising from the IRF.

Results and Discussion The TA spectra of the sensitizers G1 and G3 were measured on plane glass and mesoporous

substrates upon excitation at 400 nm. The Decay Associated Spectra (DAS) obtained after

a multiexponential global analysis along with the multiexponential fit of the principle

kinetic obtained from Single Value Decomposition (SVD) in global analysis of TA data

are reported in Figure 1. DASs for dye on glass film are shown in Figure 1(a) and 1(c) for

G1 and G3 respectively. While the DASs for dye on TiO2 layers are shown in Figure 1(b)

and 1(d) for G1 and G3 respectively. Figure 1(e) and 1(g) show the bi-exponential fitting

of the principal kinetics for G1 and G3 dye on glass film respectively while Figure 1(f) and

1(h) represents the 3-exponential fitting of the principal kinetics for dye on mesoporous

TiO2 layers respectively. The parameters of the TA dynamics obtained after the global

fitting are along with the UV-VIS absorption maxima of dye on TiO2 films are summarized

in Table 1. The early TA spectra on glass and TiO2 substrate are composed of a small

negative band below 550 nm, due to the bleach of the ground state population (GSB) and

a broad positive band above 550 nm which can be ascribed to excited state absorption.

With time the ESA band decreases as well as shifts to longer wavelengths. The time

evolution of the TA spectra for dye on TiO2 film could be reproduced using the sum of a

three exponential functions with 6.616, 226, and > 1700 ps time constants for G1 and 2.26,

52.56 and > 1900 ps time constants for G3 respectively. The first two shorter components

are possible associated with the decay of unrelaxed excited states, and in a more specific

way the latter could also be associated with the decay of the cation band due to fast

99

recombination of the injected electrons with the dye cations. The longest ns components

could be associated with a slow decay of the cation band.

Table 1: Parameters of TA Dynamics for the Two Sensitizers in Different Environments

upon Excitation at 400 nm obtained after multiexponential global analysis.

Conclusions

The Photophysics and electron injection dynamics of three novel D-𝝅-A organic dye have

been examined using femtosecond transient absorption spectroscopy in visible region. The

transient absorption spectra upon excitation at 400 nm provides enough evidence for the

generation of dye radical cations. The radical cations are long lived in TiO2 because of

slow back electron transfer.

References

[1] B.E. Hardin, H.J. Snaith, M.D. McGehee, Nature photonics 6 (2012) 162.

[2] A. Listorti, B. O’Regan, J.R. Durrant, Chemistry of Materials 23 (2011) 3381.

[3] S.G. Bairu, E. Mghanga, J. Hasan, S. Kola, V.J. Rao, K. Bhanuprakash, L. Giribabu,

G.P. Wiederrecht, R. da Silva, L.G. Rego, The Journal of Physical Chemistry C 117

(2013) 4824.

[4] L. Giribabu, N. Duvva, S.P. Singh, L. Han, I.M. Bedja, R.K. Gupta, A. Islam,

Materials Chemistry Frontiers 1 (2017) 460.

[5] S. Bhattacharya, C. Biswas, S.S.K. Raavi, J. Venkata Suman Krishna, N. Vamsi

Krishna, L. Giribabu, V.R. Soma, The Journal of Physical Chemistry C 123 (2019)

11118.

Dye 𝜆𝑎𝑏𝑠 𝑚𝑎𝑥 (for dye on glass)

Dye on Glass Dye on mesoporous TiO2 layers

𝜏1 (ps) 𝜏2(ps) 𝜏1(ps) 𝜏2(ps) 𝜏3(ps)

G1 431 nm 27.59 𝑝𝑠 ±4.7 𝑝𝑠

371.9 𝑝𝑠 ± 8 𝑝𝑠

6.616 𝑝𝑠 ±0.945 𝑝𝑠

226 𝑝𝑠 ± 8 𝑝𝑠

1795 𝑝𝑠 ±3𝑝𝑠

G3 464 nm 35.34 𝑝𝑠 ±4.36 𝑝𝑠

481.8 𝑝𝑠 ± 5 𝑝𝑠

2.266 𝑝𝑠 ±0.280 𝑝𝑠

52.56 𝑝𝑠 ±5𝑝𝑠

1900𝑝𝑠 ±3𝑝𝑠

Figure 1: Left panel-Decay associated spectra obtained from multi-exponential global

analysis: (a) and (b) for G1 dye and (c) and (d) for G3 dye on plane glass substrate and

mesoporous TiO2 layers respectively. Right panel- multi-exponential fit of principle SVD

component: (e) and (f) for G1 dye and (c) and (d) for G3 dye on plane glass and mesoporous

TiO2 layers respectively.

100

Effect of charge state on the ultrafast dynamics of molecular rotor

Sukriti Santra,a,b Aruna K Mora,a Sukhendu Natha a Radiation & Photochemistry Division, Bhabha Atomic Research Center, Mumbai-400085

b Center for Excellence for Basic Sciences, Kalina campus, Mumbai

9-(2-carboxy-2-cyanovinyl)julolidine (CCVJ), a well known ultrafast molecular

rotor (UMR), is extensively used to measure the microviscosity of complex chemical and

biological samples.1,2 We have investigated the detailed excited state dynamics of CCVJ

in molecular solvents to understand its excited state torsional dynamics that is primarily

responsible for its viscosity sensing behaviour. Due to the presence of carboxylic group,

CCVJ can present either in the anionic or neutral form depending on the pH of the solution.

Our detailed studies show that the excited state dynamics of neutral CCVJ is significantly

different from the anionic form. The emission quantum yield of neutral form is

significantly lower than anion. Further the excited state lifetime is relatively shorter for

neutral CCVJ than its anion (cf. figure 1A). Detailed emission wavelength dependent

excited state dynamics have been performed for both prototropic forms of CCVJ using

femtosecond upconversion technique. From time resolved emission spectra (TRES) of

these two forms of CCVJ it is observed that the excited state torsional dynamics is

significantly faster for neutral CCVJ than its anionic counterpart. This result indicates that

neutral form of CCVJ is better molecular rotor as compared to the anionic form. Hence,

the modulation of the emission intensity due to the change in the viscosity of the medium

is relatively stronger for neutral CCVJ than anionic form. Forster-Hoffmann analysis of the

viscosity dependent excited state lifetime results in the viscosity coefficient values of 0.62

and 0.46 for neutral and anionic CCVJ, respectively (cf. figure 1B). Higher viscosity

coefficient value clearly indicates that the neutral form of CCVJ is much better viscosity

sensor than its anionic form.

Figure 1A. Fluorescence spectra of CCVJ in anionic and neutral form Inset: Fluorescence intensity decays

of CCVJ in both prototropic forms. B. Emission transients of neutral CCVJ in acetonitrile-ethylene glycol

mixtures. Inset: Forster-Hoffmann plot of CCVJ for anionic and neutral forms.

REFERENCES

1. Haidekker, M. A.; Theodorakis, E. A. Molecular Org. Biomol. Chem. 2007, 5, 1669-1678.

2. Iwaki, T.; Torigoe, C.; Noji, M.; Nakanishi, M. Biochemistry 1993, 32, 7589-7592

101

High-Harmonic generation from spin-polarised defects in solids

Mrudul M S,a Nicolas Tancogne-Dejean,b Angel Rubio,b and Gopal Dixit a a Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai 400076 b Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, 22761

Hamburg, Germany

Generation of high-order harmonics in gases enabled to probe the attosecond

electron dynamics in atoms and molecules with unprecedented resolution. Extending the

techniques developed originally for atomic and molecular gases to solid state materials

requires a fundamental understanding of the physics at place that has been recently only

partially addressed theoretically. Here we employ time-dependent density-functional

theory to investigate how the electron dynamics resulting in high-harmonic emission in

monolayer hexagonal boron nitride is affected by the presence of vacancies. We show how

these realistic spin-polarised defects modify the harmonic emission, and demonstrate that

important differences exist between harmonics from a pristine solid and a defected-solid.

In particular, we found that the different spin channels are affected differently because of

the presence of the spin-polarised point defect, and that localisation of the wavefunction,

the geometry of the defect and the electron-electron interaction are all important

ingredients to describe high-harmonic generation in defected-solids.

REFERENCES

1. Mrudul M S et. al, arXiv preprint, arXiv:1906.10224 (2019).

102

Probing molecular chirality via laser-induced electronic fluxes

Sucharita Giri,a ,b Alexandra Maxi Dudzinski,b,c

Jean Christophe Tremblay,b,d and Gopal Dixit a

a Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076 India b Institut für Chemie und Biochemie, Freie Universität Berlin, 14195 Berlin, Germany c Institut NEEL CNRS/UGA UPR2940, 38042 Grenoble cedex 9, France d Laboratoire de Physique et Chimie Théoriques, CNRS-Université de Lorraine, 57070 Metz, France

The present work focuses on understanding the conditions required to modify

the chirality during ultrafast electronic motion by bringing enantiomers out-of-

equilibrium. Different kinds of ultrashort linearly-polarised laser pulses are used to drive

an ultrafast charge migration process by the excitation of a small number of low-lying

excited states from the ground electronic state of S- and R-epoxypropane.

Control over chiral electron dynamics is achieved by choosing the different orientations

of the linearly polarised pulse. We find that chirality breaking electric fields are only

possible in oriented molecules, and that charge migration remains chiral when the

polarisation of the field lies in the mirror plane defining the enantiomer pair, or when it is

strictly perpendicular to it. Ultimately, the presence or the absence of a mirror symmetry

for the enantiomer pair in the external field

determines the chiral properties of the charge migration process.

REFERENCES

1. S. Giri, A. M. Dudzinsky, J. C. Tremblay, and G. Dixit, arXiv preprint arXiv:1909.10740 (2019).

103

Characterizing Laguerre-Gaussian pulses using Angle-resolved Attosecond

Streaking

Irfana Neyaz Ansaria and Gopal Dixitb a Department of Physics, Indian Institute of Technology Bombay, Mumbai, India, irfana@phy.iitb.ac.in b Department of Physics, Indian Institute of Technology Bombay, Mumbai, India, gdixit@phy.iitb.ac.in

Photons can carry orbital angular momentum, along with the spin angular momentum, due

to their spatial structure. The presence of this extra angular momentum has been exploited

extensively such as for nanoparticle trapping, quantum state engineering in Bose-Einstein

condensates, and chiral recognition in molecules. Here, we have proposed a strategy to

directly characterize the orbital angular momentum of the Laguerre-Gaussian (LG) pulse.

The technique, called as attosecond streaking, involves photo-emission of an electron from

the hydrogen atom by XUV- LG pulse, which are then deflected in angular spatial

directions by circularly polarized IR pulse. We have shown that the units of orbital angular

momentum present in LG pulse is directly reflected in the angle-resolved streaking spectra.

104

The curious case of warfarin photophysics Sushil S. Sakpal,a Deborin Ghosh,b Sayan Bagchi* c

a SRF,CSIR-NCL,Pune.

b SERB-NPDF, CSIR-NCL,Pune.

c Principal Scientist, Physical and Materials chemistry division, CSIR-NCL Pune, s.bagchi@ncl.res.in

Warfarin is an important oral anticoagulant drug that explores the diversity of its

surrounding environment.Warfarin binds to a specific site of Human Serum Albumin

(HSA) and acts as a probe in the competitive binding of other drugs to the HSA.In the

earlier reports of warfarin in organic solvents and aqueous based environments, multiple

UV-visible absorption peaks were assigned to different structural conformations of

warfarin. Here, we report a systematic study of warfarin and its different derivatives using

spectroscopic measurements and quantum chemical calculations to demonstrate that the

multiple absorption peaks do not arise from different isomers. We show that coumarin

moiety of warfarin is majorly responsible for the absorption spectrum, where transition

involving higher excited states give rise to the multiple absorption peaks. As coumarin

moiety is present in a variety of drugs, our study will be helpful to understand the

interaction of warfarin and other coumarin based drugs in the different drug-receptor

complex.

105

IR-IR control of High Harmonic Generation

Ankur Mandal,a Kamal P. Singhb a Department of Physical Sciences, Indian Institute of Science Education and Research Mohali, India,

ankur@iisermohali.ac.in b Department of Physical Sciences, Indian Institute of Science Education and Research Mohali, India,

kpsingh@iisermohali.ac.in

We numerically investigate IR-IR time delayed pulse on the control of HHG. We

observe a very rich variety of structures in HHG yield with respect to harmonic order and

delay. We isolate different effects such as effect of intensity and identify trajectories of

electron corresponding to each structure and identify the effect of quantum path

interference in HHG. We observe a tilt in the near cut-off harmonics, splitting towards

lower orders. This demonstrates an all optical control of HHG. 1

REFERENCES:

1. Carsten Winterfeldt, C. Spielmann, G. Gerber, Rev. Mod. Phys. 2008, 80, 117.

106

Temporal evolution of radiative rate reveals the localization of holes in

CuInS2-based quantum dots Arpita Mukherjee, Biswajit Bhattacharyya and Anshu Pandey

Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore-560012, India

In recent years the study of ternary (I − III − VI2) chalcopyrite nanocrystals have

gained increasing attentions due to their low toxicity compared to Cd and Pb based

quantum dots. Furthermore the bulk band gap (1.5eV), size-dependent tunable emission

from visible to NIR region, long exciton-lifetime (generally in hundreds of nanoseconds)

make them promising in various applications especially in photovoltaics. In addition, these

materials possess broad photoluminescence emission spectra and there is a large stoke-shift

between the emission and absorption maxima. The aforesaid properties of these

nanocrystals suggest a strong localization of the charge carriers in intra-gap states. Here

we investigate the hole localization dynamics in CuInS2/ CdS quantum dot ensembles

using time-resolved up-conversion luminescence (UPL) and transient absorption (TA)

spectroscopy. Although the TA data suggest that the electron remains in the conduction

band, the temporal evolution of the spontaneous lifetime evaluated from UPL

measurements (from 46 ns to 294 ns) infers the collapse of the hole wave function. We

further investigate the hole localization dynamics in these QDs using a model based on

simple harmonic oscillator in configuration space. Using the model, the absorption and

emission characteristics of these systems are analyzed. We compute that the transfer rate

of hole from the valence band to the defect states (~1012 s-1). The model explains the defect-

related emission broadening and the stokes shift. We also evaluate the evolution in

emission lifetimes, which is consistent with the experimental data.

REFERENCES:

1. Arpita Mukherjee, Biswajit Bhattacharyya and Anshu Pandey, Nano Futures, 2018, 2, 045007

2. under preparation