Excited state calculations for polyene and PPV systems

Chao Wu

Contents

• Introduction

• Computational method

• Results and Discussion

• Difficulty met

• Future work

Introduction• Conjugated molecules have potential a

pplications in optoelectronic devices, photo dynamic therapy and biological imaging, etc. because of their optical properties

• Polarizability, conformational change, electronic density variations, etc. can not be studied by experimental methods only as they all involve coupled electron-nuclear structure dynamics.

• The connection between electronic structure and the optical properties of these compounds forms a complex and fundamental problem.

Introduction

• These optical properties involve time dependent photochemical process with non-adiabatic excitation/relaxation

• Ground state adiabatic calculation is not enough

• Aiming at excited states energy calculation, this project provides a basis training for the future work in this area

Introduction

• The systems for calculation are polyacetylene(n=2~6) and poly phenylene vinylene (PPV, n=2~5) oligomers which are both promising photonics materials under intensive investigation.

Computational method

egge ˆ2

2

3

2

e

mf

ge

ge

Age 2

Computational method

• Gaussian03(both on local PC & Grid)

• For polyacetylenes:• HF/3-21G CIS/3-21G and TDHF/3-21G• B3LYP/3-21GTDB3LYP/3-21G• B3LYP/6-31+GTDB3LYP/6-31+G• AM1ZINDO

• For PPV:• HF/3-21G CIS/3-21G• AM1ZINDO

Results and Discussion

• For polyacetylene system,• The optimized structures (ground state)

are trans-planar. (C2h symmetry).

• The excitation energy calculation, we used singlet spin and 10 states for investigation.

• We got transition dipole moment, oscillator strengths, and vertical excitation energies.

Molecule level Osc. Stren. Transition energy (eV)

Butadiene

CIS/3-21G 1.2214 7.2413

TDHF/3-21G 0.9189 6.8280

TDB3LYP/3-21G 0.6669 6.2564

TDB3LYP/6-31+G 0.6701 5.6542

ZINDO 0.9081 5.4016

Hexatriene CIS/3-21G 1.7949 6.1503

TDHF/3-21G 1.4032 5.8137

TDB3LYP/3-21G 1.0600 5.0336

TDB3LYP/6-31+G 1.0970 4.6648

ZINDO 1.2886 4.4703

Octatetraene CIS/3-21G 2.3481 5.4623

TDHF/3-21G 1.9052 5.1763

TDB3LYP/3-21G 1.4707 4.2716

TDB3LYP/6-31+G 1.5211 4.0038

ZINDO 1.6603 3.9226

Decapentaene CIS/3-21G 2.8727 4.9980

TDHF/3-21G 2.4141 4.7469

TDB3LYP/3-21G 1.8832 3.7427

TDB3LYP/6-31+G 1.9407 3.5311

ZINDO 2.0166 3.5643

Dodecahexene CIS/3-21G 3.3725 4.6683

TDHF/3-21G 2.9244 4.4411

TDB3LYP/3-21G 2.2910 3.3523

TDB3LYP/6-31+G 2.3543 3.1746

ZINDO 2.3579 3.3144

Polyacetylene

S. M. Smith et al., J. Phys. Chem. A 2004, 108, 11063-11072.

Dodecahexene HOMO

Dodecahexene LUMO

PPV

• For PPV system, the optimized structures are not planar: librational motion also pertubation (impurity and intermolecular interaction)

• Verified by experimental results

PPV5 non-planar ground state geometry optimized at AM1

Molecule Level Osc. Stren. Transition Energy(eV)

PPV2 CIS/3-21G 1.1900 5.1883

ZINDO 0.8975 4.0902

PPV3 CIS/3-21G 1.8463 4.6044

ZINDO 1.7585 3.4727

PPV4 CIS/3-21G * *

ZINDO 2.4457 3.2885

PPV5 CIS/3-21G * *

ZINDO 2.8725 3.5141

* Result not got yet

PPV

S. Tretiak, A. Saxena, R. L. Martin, A. R. Bishop, Phys. Rev. Lett., 89, 9, 097402-1~4.

Difficulty

• Limited experience on calculation

• Limited calculation resource on local computer

• For excited state calculation, the RWF is too big and sometimes hard to predict

Future work• Finish planned calculation• Optimize PPV excited state geography• Compare PPV excited state bond length• Calculate PPV excited state reorganizatio

n energy and fluorescence frequency (can calculate stoke shift)

• Calculate polarizability and other optical properties

Acknowledgement

• Dr. Smriti Anand

• Dr. Schlegel

• Dr. Chernyak

• Ph.D. students:

Stanley M. Smith

Jie Li

Thank you

Q & A