Functionalized quantum dots and Functionalized quantum dots and IMA Workshop“IMA Workshop“Scientific Challenges in Solar Energy Conversion and Storage”, Scientific Challenges in Solar Energy Conversion and Storage”, MinneapolisMinneapolis November 1, 2008November 1, 2008

qqconjugated polymers for light harvesting conjugated polymers for light harvesting

applications: Theoretical insightsapplications: Theoretical insightsapplications: Theoretical insightsapplications: Theoretical insightsSergei TretiakSergei Tretiak

Group homepage:Group homepage: http://t12www.lanl.gov/home/serghttp://t12www.lanl.gov/home/serg serg@lanl.govserg@lanl.gov

Center for Integrated Nanotechnologies (CINT)Center for Integrated Nanotechnologies (CINT)g g ( )g g ( )Center for Nonlinear Studies (CNLS)Center for Nonlinear Studies (CNLS)

Theoretical DivisionTheoretical Division

Rough overview of typical molecular modelingRough overview of typical molecular modelingGiven is a molecule composed from nuclei and electrons bound byGiven is a molecule composed from nuclei and electrons bound byGiven is a molecule composed from nuclei and electrons bound by Given is a molecule composed from nuclei and electrons bound by

Coulomb interactionsCoulomb interactions

Separate electronic (fast) from nuclei (slow) motion (adiabatic or Separate electronic (fast) from nuclei (slow) motion (adiabatic or p ( ) ( ) (p ( ) ( ) (BornBorn--Oppenheimer approximation)Oppenheimer approximation)

Assign finite basis size (lattice) Assign finite basis size (lattice) –– Gaussian (Gaussian, Turbomole, Gaussian (Gaussian, Turbomole, QQ Ch t ) l i (VASP t ) Sl t (ADF t )Ch t ) l i (VASP t ) Sl t (ADF t )

Solve Solve

QQ--Chem, etc.) or plain waves (VASP, etc.) or Slater (ADF, etc.)Chem, etc.) or plain waves (VASP, etc.) or Slater (ADF, etc.)

for molecular electronic Hamiltonian:for molecular electronic Hamiltonian:

MethodMethod HamiltonianHamiltonian WavefunctionWavefunction CostCostAb initioAb initio(e.g. CAS(e.g. CAS--CI, CCCI, CC--EOM)EOM)

ExactExact ApproximateApproximate(All electronic correlations)(All electronic correlations)

LargeLarge(~10 atoms)(~10 atoms)

Density Functional Density Functional (e g TDDFT)(e g TDDFT)

Approximate, F(Approximate, F(ρρ),),(All electronic correlations)(All electronic correlations)

Fixed Fixed (Kohn(Kohn--Sham system)Sham system)

Significant Significant (~100 atoms)(~100 atoms)(e.g. TDDFT)(e.g. TDDFT) (All electronic correlations)(All electronic correlations) (Kohn(Kohn--Sham system)Sham system) (~100 atoms)(~100 atoms)

SemiempiricalSemiempirical(e.g. INDO/S(e.g. INDO/S--CIS)CIS)

Approximate,Approximate,(Some electronic correlations)(Some electronic correlations)

ApproximateApproximate(Some electronic correlations)(Some electronic correlations)

LowLow(~1000 atoms)(~1000 atoms)

TimeTime--Dependent Density Functional Theory &Dependent Density Functional Theory &TimeTime--Dependent Dependent HartreeHartree--FockFock formalismformalismTimeTime Dependent Dependent HartreeHartree FockFock formalismformalism

TD equation of motion:TD equation of motion:A B

L ξ Ω ξ

X XA

-B

B

-AΩ

X

Y

X

Y

K2

Electronic normal modes Electronic normal modes or transition densitiesor transition densities

K2

A, X - CIS (particle-hole) part

or transition densitiesor transition densities

Scaling of computational effort:Scaling of computational effort:Krylov space algorithms Krylov space algorithms Scaling of computational effort:Scaling of computational effort:•• Time ~Time ~NN33

•• Memory ~Memory ~NN22

(e.g. Davidson, Lanczos)(e.g. Davidson, Lanczos)

TDHF: Dirac, Pines, Bartlett, SchmittTDHF: Dirac, Pines, Bartlett, Schmitt--Rink, Rink, e o ye o y NNCost/per excited state is smaller Cost/per excited state is smaller than SCF ground state effortthan SCF ground state effort

Jorgensen, McKoy, Fukotome ….Jorgensen, McKoy, Fukotome ….

TDDFT: Runge, Gross, Casida, Perdew, Becke, TDDFT: Runge, Gross, Casida, Perdew, Becke, Yang, Burke, Furche …. Yang, Burke, Furche ….

TDDFT example (luminescent TDDFT example (luminescent oligomersoligomers))Accuracy about 0.1Accuracy about 0.1--0.2 0.2 eVeVyyStill limited by NStill limited by N33 expense expense

(~500(~500--1000 atoms)1000 atoms)

J. Tao, S. Tretiak, and J.J. Tao, S. Tretiak, and J.--X. Zhu, J. Phys. Chem. B, (2008, in press)X. Zhu, J. Phys. Chem. B, (2008, in press)

Energy funneling effects in Energy funneling effects in dendrimersdendrimers

S. Tretiak, V. Chernyak, and S. Mukamel, J. Phys. Chem. B, 102, 3310 (1998)S. Tretiak, V. Chernyak, and S. Mukamel, J. Phys. Chem. B, 102, 3310 (1998)

MultiscaleMultiscale modeling of electronic excitations: modeling of electronic excitations: ExcitonExciton Scattering (ES) model for Scattering (ES) model for supramoleculessupramoleculesg ( )g ( ) pp

Electronic excitations areexcitations are standing waves

1200 years old tree

•• Delocalized Delocalized excitonicexcitonic (generically many(generically many­­electron) excited states in large treeelectron) excited states in large tree­­like quasilike quasi­­oneone­­dimensional structure can be represented as standing waves;dimensional structure can be represented as standing waves;

•• These result from These result from excitonexciton scattering at the molecular ends  joints  and scattering at the molecular ends  joints  and These result from These result from excitonexciton scattering at the molecular ends, joints, and scattering at the molecular ends, joints, and branching vertices;branching vertices;

•• This model is asymptotically exact in the limit of the This model is asymptotically exact in the limit of the excitonexciton size being short size being short compared to the linear segment lengths;compared to the linear segment lengths;

C. Wu, S. C. Wu, S. MalininMalinin, S. Tretiak, and V. Chernyak, Nature Phys., 2, 631 (2006), S. Tretiak, and V. Chernyak, Nature Phys., 2, 631 (2006)

•• Any branching canter can be treated as a scattering center with  an Any branching canter can be treated as a scattering center with  an appropriate unitary frequencyappropriate unitary frequency­­dependent scattering matrix.dependent scattering matrix.

How to apply the How to apply the ExcitonExciton Scattering modelScattering model1) U i t h i t t h i d t i it t1) Using quantum-chemistry techniques determine exciton spectrum ω(k) (dispersion curve) in long linear segments and determine exciton scattering matrices Γ(ω) for every branching center.2) For a given supramolecular nanostructure (‘molecular network’) solve exciton scattering system of linear equations to find electronic spectrum. Assume standing wave approximation for excitonic wavefunctionAssume standing wave approximation for excitonic wavefunction

C. Wu, S. C. Wu, S. MalininMalinin, S. , S. Tretiak, and V. Tretiak, and V. Ch k N tCh k N tChernyak, Nature Chernyak, Nature Phys., 2, 631 (2006)Phys., 2, 631 (2006)

Spectrum k(Spectrum k(ωω) ) TD-DFT, BHandHLYP/6-31G

4.2ω (eV) Calculated dispersion

Fit A (k )

TD DFT, BHandHLYP/6 31G

3.8

4.0 Fit: Acos(k+φ)+Ω0

3.6

3.8

N

3.4

3.0

3.2

2.8 kk-π π0

C. Wu, S. C. Wu, S. MalininMalinin, S. Tretiak, and V. Chernyak, Phys. Rev. , S. Tretiak, and V. Chernyak, Phys. Rev. LettLett. 100, 057405 (2008). 100, 057405 (2008)

Phases Phases φφ00((ωω),), φφ((ωω), ), θθ((ωω))TD-DFT, BHandHLYP/6-31GTD DFT, BHandHLYP/6 31G

ФФ00 increases with increases with ωω, , which deviates from the which deviates from the ideal reflection (ideal reflection (ππ). ). OOФФde e ec o (de e ec o ( ).). OOФФand and OOθθ are around ideal are around ideal transmission (transmission (--π/2π/2 and and 00), which indicates the ), which indicates the ),),orthoortho--joint is to some joint is to some extent transparent to extent transparent to excitonsexcitons. . MMθθ is around is around ideal reflection value ideal reflection value ((π/π/2) and 2) and MMФФ is is approximately approximately ФФ00 shifted shifted by 2by 2ππ, indicating , indicating similarity of metasimilarity of meta--joint joint and molecule ends.and molecule ends.

C. Wu, S. C. Wu, S. MalininMalinin, S. Tretiak, and V. Chernyak, Phys. Rev. , S. Tretiak, and V. Chernyak, Phys. Rev. LettLett. 100, 057405 (2008). 100, 057405 (2008)

Accuracy of ES model Accuracy of ES model TD-DFT, BHandHLYP/6-31G

2 5 3 0 3 5 4 0 4 520

2.5 3.0 3.5 4.0 4.5

M15-1510

15

V)

M3-3

M7-3

mnMn-m

0

5

-ΩTD

DFT

(eV

O15-15m

m

-10

-5

ΔΩ=Ω

ES-

O7-3

O3-3n

On-m

20

-15

10

P30

10Pn

3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8-20

Ω (eV)

Error does not exceed Error does not exceed 20 20 meVmeV compared to compared to the ‘exact’ calculationsthe ‘exact’ calculations!

ES model

P10n

P4 Exact the exact calculationsthe exact calculations! 2.5 3.0 3.5 4.0 4.5

Ω (eV)C. Wu, S. C. Wu, S. MalininMalinin, S. Tretiak, V. Chernyak, , S. Tretiak, V. Chernyak, Phys. Rev. Phys. Rev. LettLett. 100, 057405 (2008). 100, 057405 (2008)

Different structures… Different structures… TD-DFT, BHandHLYP/6-31G

The larger the The larger the molecule, the better ES molecule, the better ES

d l k !d l k !model works!model works!

Error does not exceed 10 meV compared to the ‘exact’ calculationscalculations.

C. Wu, S. C. Wu, S. MalininMalinin, S. Tretiak, and V. Chernyak, , S. Tretiak, and V. Chernyak, Phys. Rev. Phys. Rev. LettLett. 100, 057405 (2008). 100, 057405 (2008)

Different superDifferent super--structures… structures… Bu

BuS

BuBu

S

BuBu

S

BuBu

S

BuBu

Bu

B Bu

BuS

BuBu

S

BuBu

S

BuBu

S

BuBu

Bu

B

NN

NN

Zn

NMeN

B

S Bu

Bu

S

Bu

BuS

Bu

BuS

BuS

S

Bu

S

Bu

Bu

S

Bu

Bu

S

Bu

Bu

H

H

H

H

S

Bu Bu

S

Bu Bu

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BuBu

S

BuBu

S

Bu

BuSBu

BuS

BuBu S

BuBu

S

Bu Bu

HH

H

H S

Bu Bu

S

Bu Bu

S

BuBu

BuBuS

BuBu S

Bu Bu

HH

S

Bu Bu BuBuBu

BuB

S Bu

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BuS

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Bu

Bu

S

Bu

Bu

S

Bu

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H

H

H

H

S

Bu Bu

S

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BuBu

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BuBu

S

Bu

BuSBu

BuS

BuBu S

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S

Bu Bu

HH

H

H S

Bu Bu

S

Bu Bu

S

BuBu

BuBuS

BuBu S

Bu Bu

HH

S

Bu Bu BuBuBu

Bu

NN

N NZn

NMeN

N

NN

NN

Zn

MeNN

NNN

N ZnNN N

NZn

MeN

N

MeNN

NN

NNZn

NMe

N

C9H19 C9H19

C9H19

C9H19C9H19

C9H19 C9H19

S

Bu

Bu

S

Bu

Bu

SBu

Bu

S

Bu

Bu

S

Bu

Bu

SBu

BuH

HH

S

Bu

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SBu

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S Bu

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Bu S Bu

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Bu

S Bu

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S BuBu

SS

S

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Bu

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HH

SS

Bu

SBu

Bu

SBuBu

S BuBu

SBu

BuS

BuBu

S

BuBu

SBu

Bu

SBuBu

SBuBu

SBu

H

H

H

H 12mer

S

Bu

Bu

S

Bu

Bu

SBu

Bu

S

Bu

Bu

S

Bu

Bu

SBu

BuH

HH

S

Bu

Bu

SBu

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S Bu

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SBu

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Bu S Bu

SBu

Bu

S Bu

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S BuBu

SS

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Bu

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Bu

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HH

SS

Bu

SBu

Bu

SBuBu

S BuBu

SBu

BuS

BuBu

S

BuBu

SBu

Bu

SBuBu

SBuBu

SBu

H

H

H

H 12mer NN

N NZn

NMeN

NN

N NZn

NMeN

N N

NNZn

MeN N

N N

NN Zn

MeN N

C9H19C9H19

C9H19

C9H19

SS

S

Bu

S

Bu

Bu

S

Bu

Bu

S

Bu

BuSBu

Bu

SBu

Bu

SBu

Bu S

Bu

HH

H

S Bu

BuS

BuBuS

BuBu

S

BuBu

S

BuBu

S

BuBu

S

BuBu

S

BuBu

S

Bu

BuH

HH

H

SBu

BuSBuBu

S

BuBu

S

BuBu

S

BuBu

H

H

18mer

24mer

30merS

S

S

Bu

S

Bu

Bu

S

Bu

Bu

S

Bu

BuSBu

Bu

SBu

Bu

SBu

Bu S

Bu

HH

H

S Bu

BuS

BuBuS

BuBu

S

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S

BuBu

S

BuBu

S

BuBu

S

BuBu

S

Bu

BuH

HH

H

SBu

BuSBuBu

S

BuBu

S

BuBu

S

BuBu

H

H

18mer

24mer

30mer

N N

NNZn

MeNN

NN

NZn

NN

NNZn

NMeN

NN N

NZnNNN

NZn

NMe

N

NMeN

NN

NN Zn

MeN

N

C9H19C9H19

C9H19C9H19

C9H19C9H19

S

BuBu

S

Bu Bu

S

Bu BuBu

Bu

BuBu

Bu

H

HS

BuBu

S

Bu Bu

S

Bu BuBu

Bu

BuBu

Bu

H

H N NN

Zn

MeNN

n

Rhomb Super L Hexagon Super Meta

m-1

n-1 n-1

m-1Super Triangle Structures

C. Wu, S. C. Wu, S. MalininMalinin, S. Tretiak, and V. Chernyak, (2008, in preparation), S. Tretiak, and V. Chernyak, (2008, in preparation)

Vision for the Vision for the ExcitonExciton Scattering Approach Scattering Approach In real timeIn real time

StructuresStructures SpectraSpectra

de

PPV(10)

urie

r am

plitu

d

5 10 15 20 25 30 35 40 45 50

Fo

T (fs)

Conjugated polymers for solar cells Conjugated polymers for solar cells

Complexity of electronic structure of Complexity of electronic structure of conjugated polymers and carbon conjugated polymers and carbon nanotubesnanotubesconjugated polymers and carbon conjugated polymers and carbon nanotubesnanotubesMobile π-electron system leads to interesting photochemical, spectroscopic, and transport phenomena

BandBand--gap (lowestgap (lowest--excited state) energyexcited state) energy ~2~2 eVeVBandBand gap (lowestgap (lowest excited state) energy excited state) energy 2 2 eVeVExcitonExciton binding energy (electronic correlations) binding energy (electronic correlations) ~0.2~0.2--1 1 eVeVElectronElectron--phonon (coupling to vibrations) interaction phonon (coupling to vibrations) interaction ~0.2~0.2--1 1 eVeV

Diversity of electronic phenomenaDiversity of electronic phenomenaLocalization, Delocalization, Peierls distortion, Disorders and traps Localization, Delocalization, Peierls distortion, Disorders and traps Excitons, Polarons, BiExcitons, Polarons, Bi--polarons, Solitons, Breathers, Etc.polarons, Solitons, Breathers, Etc.

Charge Charge mobilitiesmobilities in devicesin devicesElectron and hole are Electron and hole are generated at gatesgenerated at gatesThey recombineThey recombine

+ OLEDThey recombine They recombine radiativelyradiatively

-

Light creates an Light creates an excitonexciton

+excitonexcitonExcitonExciton produces produces charged speciescharged species -

PhotovoltaicsPhotovoltaics

Structure of Structure of phenylenephenylene--vinylenevinylene (PPV) materials(PPV) materialsPPVPPV

C

CC

CC

C C

HH

C

H

PPVPPVNN

C CC

HHH

C

N

M l l d i i l ti f thM l l d i i l ti f thChains are not perfect in the materialChains are not perfect in the material Molecular dynamics simulation of the Molecular dynamics simulation of the polymer packing in the materialpolymer packing in the material

Electrons and holes hop from one Electrons and holes hop from one chain to anotherchain to another

ee

Teach your old dog the new tricksTeach your old dog the new tricksMATPIG (2 units)

PFO (4 units)

S. Kilina, P. Yang, E. Batista, S. Tretiak, S. Kilina, P. Yang, E. Batista, S. Tretiak, R.L. Martin, and D. Smith, ACS R.L. Martin, and D. Smith, ACS NanoNano, , 2, 1381 (2008)2, 1381 (2008)

PFO with 2(C H ) side chains:

Disordered PFO material (5u/8mol)Disordered PFO material (5u/8mol)PFO backbone chains only:PFO with 2(C8H17) side chains: PFO backbone chains only:

2776 atoms; density=1.041 g/mL 8x107=856 atoms; Distance between C‐rings ~ 3.5‐3.7 A

density = 0.441 g/mLS. Kilina, P. Yang, E. Batista, S. Tretiak, R.L. Martin, S. Kilina, P. Yang, E. Batista, S. Tretiak, R.L. Martin, D. Smith, ACS D. Smith, ACS NanoNano, 2, 1381 (2008), 2, 1381 (2008)

Crystal structure vs. amorphous materialCrystal structure vs. amorphous material

P. Yang, E. Batista, A. P. Yang, E. Batista, A. SaxenaSaxena, R.L. Martin, S. Tretiak, D.L. Smith Phys. Rev. B, 76, 241201 (2007)., R.L. Martin, S. Tretiak, D.L. Smith Phys. Rev. B, 76, 241201 (2007).

DOS: intermolecular DOS: intermolecular vsvs conformational disorder (VASP)conformational disorder (VASP)

P. Yang, E. Batista, A. P. Yang, E. Batista, A. SaxenaSaxena, R.L. Martin, S. Tretiak, D.L. Smith Phys. Rev. B, 76, 241201 (2007)., R.L. Martin, S. Tretiak, D.L. Smith Phys. Rev. B, 76, 241201 (2007).

Participation Ratio (PR) in a crystalParticipation Ratio (PR) in a crystalMost delocalized 

(over 12 molecules)

Molecular 

orbitals

Most 

orbitals

localized  (VASP) calculations PW91 l f

Energy, eV

PW91, ultrasoft potentials

Participation Ratio (PR) in amorphous materialParticipation Ratio (PR) in amorphous materialS Kilina S Tretiak R L Martin ES Kilina S Tretiak R L Martin EThe most delocalizedS. Kilina, S. Tretiak, R.L. Martin, E. S. Kilina, S. Tretiak, R.L. Martin, E. Batista, D. Smith (2007, in preparation)Batista, D. Smith (2007, in preparation)

LUMO (localized)

The most delocalizedThe most popular partially delocalized states

(VASP) calculationscalculations PW91, ultrasoft

HOMO (localized)

ultrasoft potentials

Energy, eV

PRs of disordered PFO material (5u/8 mol)PRs of disordered PFO material (5u/8 mol)

Compared to semiconductor maerials

d h iliand amorphous silicon, PR shows that the band formation is essentially suppressed in polymeric materials

S. Kilina, P. Yang, E. Batista, S. Tretiak, R.L. Martin, D. Smith , ACS S. Kilina, P. Yang, E. Batista, S. Tretiak, R.L. Martin, D. Smith , ACS NanoNano, 2, 1381 (2008), 2, 1381 (2008)

Electronic effects in carbon Electronic effects in carbon nanotubesnanotubes

A. Gambetta, C. Manzoni, E. A. Gambetta, C. Manzoni, E. MennaMenna, M. , M. MeneghettiMeneghetti, G. , G. CerulloCerullo, S. Tretiak, A. , S. Tretiak, A. Piryatinski, A. Piryatinski, A. SaxenaSaxena, R.L. Martin, A. R. Bishop and G. Lanzani, Nature Phys. 2, , R.L. Martin, A. R. Bishop and G. Lanzani, Nature Phys. 2, 515 (2006);515 (2006);S. Tretiak, S. Kilina, A. Piryatinski, A. S. Tretiak, S. Kilina, A. Piryatinski, A. SaxenaSaxena, R.L. Martin and A. R. Bishop, , R.L. Martin and A. R. Bishop,

108 (200 )108 (200 )Nano Letters, 7, 108 (2007)Nano Letters, 7, 108 (2007);;A.P. Shreve, E.H. Haroz, S.M. Bachilo, R.B. Weisman, S.K. Doorn, S. Kilina, S. A.P. Shreve, E.H. Haroz, S.M. Bachilo, R.B. Weisman, S.K. Doorn, S. Kilina, S. Tretiak, Phys. Rev. Lett., 98, 037405 (2007);Tretiak, Phys. Rev. Lett., 98, 037405 (2007);P.T. Araujo, S.K. Doorn, S. Kilina, S. Tretiak, S. Maruyama, H. Chacham, M.A. P.T. Araujo, S.K. Doorn, S. Kilina, S. Tretiak, S. Maruyama, H. Chacham, M.A. Pimenta, A. Jorio, Phys. Rev. Lett., 98, 067401 (2007);Pimenta, A. Jorio, Phys. Rev. Lett., 98, 067401 (2007);, , y , , ( );, , y , , ( );S. Tretiak S. Tretiak NanoNano LettLett. . 7, 2201 (2007);7, 2201 (2007);G.D. G.D. ScholesScholes, S. Tretiak, W. Metzger, C. , S. Tretiak, W. Metzger, C. EngtrakuEngtraku, G. Rumbles, M.J. , G. Rumbles, M.J. HebenHeben, J. , J. Chem. Phys. C Chem. Phys. C 111, 11139 (2007);111, 11139 (2007);S. Kilina and S. Tretiak, Adv. S. Kilina and S. Tretiak, Adv. FuncFunc. Mat. . Mat. 17, 3405 (2007);17, 3405 (2007);

DNA strand wrapped around DNA strand wrapped around nanotubenanotube (exp.)(exp.)8

6

8

t

FFT shows DNA wrapping period along the tube

2

4

Cou

nt

2.5 3.0 3.5 4.0 4.5 5.0 5.50

2

P i d l CNT ( )

3.3 A period determined from STMPeriod along CNT (nm)

D. D. YarotskiiYarotskii, S. Kilina, O.V. Prezhdo, S. Tretiak, A. Taylor, A.V. Balatsky, (2008, submitted), S. Kilina, O.V. Prezhdo, S. Tretiak, A. Taylor, A.V. Balatsky, (2008, submitted)

STM images from MPA/CINT lab

DNA strand wrapped around DNA strand wrapped around nanotubenanotube (Th.)(Th.)

Classical MD simulations show that wrapping period of DNA around the tube isDNA around the tube is closely related to the tube chirality

D.D. YarotskiiYarotskii, S. Kilina, O.V. Prezhdo,, S. Kilina, O.V. Prezhdo,D. D. YarotskiiYarotskii, S. Kilina, O.V. Prezhdo, , S. Kilina, O.V. Prezhdo, S. Tretiak, A. Taylor, A.V. Balatsky, S. Tretiak, A. Taylor, A.V. Balatsky, (2008, submitted)(2008, submitted)

Colloidal quantum dotsColloidal quantum dotsR = 10 50 Å δR/R= 2 5%R = 10—50 Å, δR/R= 2—5%

Carrier multiplication effects

V. I. V. I. KlimovKlimov, , AnnuAnnu. . RevRev. Phys. . Phys. ChemChem. 58 635 (2007); A. J. . 58 635 (2007); A. J. NozikNozikh ( )h ( ) S h llS h ll lili hhPhys. E 14 115 (2002); R. D. Phys. E 14 115 (2002); R. D. SchallerSchaller , V. I. , V. I. KlimovKlimov Phys. Phys. RevRev. .

LettLett. 92,186601(2004); R. J. . 92,186601(2004); R. J. EllingsonEllingson, M. C. , M. C. BeardBeard, J. C. , J. C. Johnson, P. R. Johnson, P. R. YuYu, O. I. , O. I. MicicMicic, A. J. , A. J. NozikNozik, A. , A. ShabaevShabaev, A. L. , A. L. EfrosEfros, Nano , Nano LettLett. 5, 865 (2005).. 5, 865 (2005).

LigatedLigated and ‘bare’ Cdand ‘bare’ Cd3333SeSe3333 model model nanocrystalsnanocrystals• ‘Bare’ Cd33Se33 dot;33 33 ;

• Dot + 9 ligands (double coordination sites););

• Dot + 21 ligands (double and single coordination gsites);

• NH2Me and OPMe2 are 2 2model ligands for ptimary amines and TOPO,

Cd33Se33 dot species with diameter D=1.6nm have been observed in mass-spectra: A. Kasuya, et al. Nature Mat. 3, 99 (2004)

S. Kilina, S. S. Kilina, S. IvanovIvanov, and S. Tretiak, , and S. Tretiak, (2008, submitted)(2008, submitted)

(2004)

Analysis of DOS and molecular Analysis of DOS and molecular orbitalsorbitals

• Molecular orbitals close to the edges of valence and conduction bands are localized on the QD bulk;

• A significant number of ‘h b idi d’ f t t‘hybridized’ surface states appears upon ligation;

• Amine (NH Me) ligands• Amine (NH2Me) ligands mostly modify the valence band of QDs;

• Phosphine oxide (OPMe3) ligands mostly modify the conduction band of QDs.conduction band of QDs.

S. Kilina, S. S. Kilina, S. IvanovIvanov, and S. Tretiak, , and S. Tretiak, (2008, submitted)(2008, submitted)

Decomposition of the absorption spectraDecomposition of the absorption spectra4 contributions of the transition4 contributions of the transition dipole have been separated:

• Surface ‘hybridized’ states are mostly inactive in theare mostly inactive in the absorption spectra;

• Surface absorption appear p ppat energies > 6eV;

• Ligand absorption appear i Vat energies > 7.5 eV;

S. Kilina, S. S. Kilina, S. IvanovIvanov, and S. Tretiak, , and S. Tretiak, (2008, submitted)(2008, submitted)

Decomposition of DOSDecomposition of DOS• Surface ‘hybridized’ states yare appear from energies 2Ebulk gap ~ 4eV;

‘H b idi d’ l• ‘Hybridized’ states couple to the high frequency molecular vibrations on ligands (~0.1-0.25 eV);

•• This may provide efficient This may provide efficient ib iib i h l (‘h l (‘vibronicvibronic channels (‘common channels (‘common

molecular view’) of molecular view’) of relaxation of highrelaxation of high--frequency frequency photoexcitationsphotoexcitations in in ligatedligatedQDs.QDs.

S. Kilina, S. S. Kilina, S. IvanovIvanov, and S. Tretiak, , and S. Tretiak, (2008, submitted)(2008, submitted)

Conclusions and future outlook: Conclusions and future outlook: •• Compared to semiconductor Compared to semiconductor maerialsmaerials and amorphous silicon, and amorphous silicon, the band formation is suppressed in polymeric materials;the band formation is suppressed in polymeric materials;•• NearNear--gap trap states can substantially modify charge gap trap states can substantially modify charge mobilitiesmobilities. . CarefullCarefull molecular engineering needs to be done;molecular engineering needs to be done;•• Surface and organic Surface and organic ligandsligands may substantially modify valence may substantially modify valence and conduction band in QDs;and conduction band in QDs;

A i ifi t b f ‘h b idi d’ f /A i ifi t b f ‘h b idi d’ f /li dli d l t il t i•• A significant number of ‘hybridized’ surface/A significant number of ‘hybridized’ surface/ligandligand electronic electronic states appears upon ligation, starting at ~2Eg;states appears upon ligation, starting at ~2Eg;•• LigandsLigands substantially increase relaxation rates of high energysubstantially increase relaxation rates of high energy•• LigandsLigands substantially increase relaxation rates of high energy substantially increase relaxation rates of high energy photoexcitationsphotoexcitations >3Eg (internal conversion);>3Eg (internal conversion);•• Substantial electronic coupling is observed for dyeSubstantial electronic coupling is observed for dye--sensitizedsensitized•• Substantial electronic coupling is observed for dyeSubstantial electronic coupling is observed for dye--sensitized sensitized QDs QDs –– hopes for efficient charge extraction;hopes for efficient charge extraction;•• The value of atomisticThe value of atomistic abab initioinitio simulations will likely increasesimulations will likely increaseThe value of atomistic The value of atomistic abab initio initio simulations will likely increase simulations will likely increase in the future. in the future.

AcknowledgmentsAcknowledgmentsQuantum dotsQuantum dotsPolymers/Polymers/nanotubesnanotubes::Svetlana Kilina (LANL)Svetlana Kilina (LANL)Artem Masunov (UCF)Artem Masunov (UCF)Oleg Prezhdo (UW)Oleg Prezhdo (UW)

yySvetlana Kilina (LANL)Svetlana Kilina (LANL)Avadh Saxena (LANL)Avadh Saxena (LANL)Richard Martin (LANL)Richard Martin (LANL) Oleg Prezhdo (UW)Oleg Prezhdo (UW)

Ping Yang (PNNL)Ping Yang (PNNL)Victor Albert (U. Florida)Victor Albert (U. Florida)Sergei Ivanov (LANL)Sergei Ivanov (LANL)

Richard Martin (LANL)Richard Martin (LANL)Enrique Batista (LANL)Enrique Batista (LANL)Darryl Smith (LANL)Darryl Smith (LANL)Ping Yang (LANL)Ping Yang (LANL) g ( )g ( )

Milan Sykora (LANL)Milan Sykora (LANL)Victor Klimov (LANL)Victor Klimov (LANL)ExcitonExciton scatteringscattering

g g ( )g g ( )Antoinette J. Taylor (LANL)Antoinette J. Taylor (LANL)Sasha Balatsky (LANL)Sasha Balatsky (LANL)Normand Modine (SNL)Normand Modine (SNL) gg

Vladimir Chernyak (Wayne) Vladimir Chernyak (Wayne) Sergey Sergey MalininMalinin (Wayne)(Wayne)Chao Wu (Wayne)Chao Wu (Wayne)

Alec Alec TalinTalin (SNL)(SNL)Dzmitry Yarotski (LANL)Dzmitry Yarotski (LANL)

Group homepage: http://t12www.lanl.gov/home/serg serg@lanl.govGroup homepage: http://t12www.lanl.gov/home/serg serg@lanl.govCenter for Integrated Nanotechnologies (CINT)Center for Integrated Nanotechnologies (CINT)

Chao Wu (Wayne)Chao Wu (Wayne)

Center for Nonlinear Studies (CNLS)Center for Nonlinear Studies (CNLS)LDRD program at LANL, DOE BESLDRD program at LANL, DOE BES