Energy and Electron Transfer in Ethynylene Bridged Perylene Diimide

Multichromophores

Cristina Flors, Ingo Oesterling, Tobias Schnitzler, Eduard Fron, Gerd Schweitzer, Michel Sliwa, Andreas Herrmann, Mark van

der Auweraer, Frans C. de Schryver, Klaus Mullen, and Johan Hofkens

J.Phys.Chem.C. 2007, 111, 4861-4870

Kou ITOHMIYASAKA Lab.

Contents

● Background

● Method – explanation of measurement technique time-resolved spectroscopy (ensemble) single-molecule spectroscopy

● Results and discussion　　 Steady-state measurement　　 Florescence decay measurement 　　 Femtosecond transient absorption spectroscopy　　 Single-Molecule detection

● Conclusion

Background

Novel photonic devices consisting of molecular systems ● single photon source ● artificial light-harvesting system etc.

single photon source artificial light-harvesting system

lightpulse

Singlephoton

light

energy

Chromophore :

J.P.C.B.2004,108,16686-16696 J.A.C.S.2007,129,3539-3544

Evaluation and understanding of the molecular photonic devices

Ensemble measurements Single molecule measurements

• Energy transfer• Electron transfer• Emission lifetime etc.

Dynamics, Efficiency of

• Ultra-high temporal resolution• Reliable average values

• Emission dynamics of individual molecular systems

• Photon antibunching

Enables us to evaluate single nanoscale photonic devices

Complementary use of both measuring methods can give us comprehensive understanding of the nanoscale-molecular devices

Method 1):ensemble time-resolved measurement

hν

fluorescenceS0

S1

Pump light

T

T: delay time

Wavelength/nmD

elt

a

ATransient absorption spectra

①

②

Probe light

Charge separation

Fluorescence decay

cou

nt

time/ns

sample

detector

Method 2): single-molecule spectroscopy

imaging

Fluorescence intensity trajectory

coun

ts

Time/s

Fluorescence decay

coun

ts

Time/ns

coincidence

Eve

nts

Delay/ns

Molecular structure of PDI derivatives

Perylene-3,4,9,10-tetracarboxdiimide(PDI)

:bay area

Ａ

B

CＰＤＩ０

Steady-state measurement

Compound A B C

λmax, 　 abs,nm

573 573 573

λmax, emi,nm

604 602 602

ΦF 0.99 1.00 1.00

Summery of the photophysical properties of Ａ－Ｃ in solution in toluene

in THF

: Diphenylacetylene group(electron donor)

A: blackB: redC: blue(in toluene)

Compound A B C

λmax, 　 abs,nm

569 568 589

λmax, emi,nm

601 601 600

ΦF 0.42 0.11 0.96

scheme

S1

S0

Charge Separation

B

A

Fluorescence decay measurement

A B C

Toluene τF[ns] 5.1 5.3 5.3

THF τF[ns] 1.0(14%)2.8(86% ）

1.1

5.6

B(THF)A(THF)

C(THF)

Ａ

B

tF: 1.0 ns

tF ~ 2.8 nsElectron transfer from a diphenylacetylene group

Through-space electron transfer

A B C

Toluene [ns] [ps]

3.1110

0.56---

THF [ns] [ps]

3.153

0.38---

Fluorescence decay (time constant)

Time-resolved fluorescence depolarization

C

oxygen

nitrogen

Femtosecond transient absorption spectroscopy ①

Transient absorption spectra in THF of PDI0(A)And B(B) at 2(black),10(red),50(green),100(blue)200(purple),and 400ps(brown).

PDI0

Compound B

Lifetime ＰＤＩ０ B

5ns 185ps,1ns

S1

S0

Radical anion

1.1ns(Slide 9)

185ps

1ns

Summary of the ensemble measurements

A B CToluene × × ×

THF ○ ○ ×

Electron Transfer

●Femtosecond transient absorption measurementThe dynamics of generation and decay about PDI radical

anion was revealed. (in more polar solvent)

Single-Molecule measurement : Results①

Channel A

Channel B

Single-molecule intensity trace of Ａ in PMMAChannel A (gray) and B (black) correspond toPolarization directions perpendicular in each other.

1:stepwise change → the emitting chromophoric site is changing with time.2:fluctuating trace → intersystem crossing from singlet to triplet by oxygen3:off time → influence of charge separation

APD2

APD1

fluorescence

Beam splitter

Offtime

NC

NLNL

NC/NL ~ 0.2

APD2

APD1

Repetition period ~ 125ns

APD1

APD2

Interphoton arrival time

　　 ： Photon

Coincidence

Single-photon emitting source 1 pulse → 1 photon

Single-photon emitting source 1 pulse → 1 photon

Antibunching

J.P.C.B 2004,108,16686-16696

Jpn.J.Appl.Phys 2007,46,268-270

Single-Molecule measurement (Coincidence)

NC/NL = 1 － ( 1 / M ) 　

NC : number of central positionNL : number of lateral positionsM : number of photons / 1 pulse

M NC/NL ratio

1 0

2 0.5

3 0.67

4 0.75

Fluorescence from the sample

sample

Single-Molecule measurement : results②

Compound A

J.Phys,:.Condens.Matter. 2007,19,445004Fluorescence trajectory of single-molecule (A)and fluctuation of Nc/NL ratio

S1-S1 annihilationS1-S1 annihilation

S1* + S1*　　→　　 So + S1*　

S ０

S １

S ０

S １

S ｎ

Conclusion

The authors synthesized a multichromophoric system as a candidate for single photon source and measured the property of the emission.

Steady state and time-resolved ensemble measurement revealed that charge transfer can take place in the multi-chromophoric compound in relatively polar environment; polarity affects the emission property of compound A.

The time-resolved measurement also suggested that energy-migration as well as the charge transfer.

The efficient energy migration was confirmed by measuring the photon-antibunching of compound; the compound worked as “single photon emitter”.