Excited state calculations for polyene and PPV systems

1
Excited state calculations for polyene and PPV
systems

• Chao Wu

2
Contents

• Introduction
• Computational method
• Results and Discussion
• Difficulty met
• Future work

3
Introduction

• Conjugated molecules have potential applications
  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.

4
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

5
Introduction

• The systems for calculation are
  polyacetylene(n26) and poly phenylene vinylene
  (PPV, n25) oligomers which are both promising
  photonics materials under intensive
  investigation.

6
Computational method
7
Computational method

• Gaussian03(both on local PC Grid)
• For polyacetylenes
• HF/3-21G ?CIS/3-21G and TDHF/3-21G
• B3LYP/3-21G?TDB3LYP/3-21G
• B3LYP/6-31G?TDB3LYP/6-31G
• AM1?ZINDO

• For PPV
• HF/3-21G ?CIS/3-21G
• AM1?ZINDO

8
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.

9
(No Transcript)
10
Polyacetylene
S. M. Smith et al., J. Phys. Chem. A 2004, 108,
11063-11072.
11
Dodecahexene HOMO
12
Dodecahexene LUMO
13
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
14
Result not got yet
15
PPV
S. Tretiak, A. Saxena, R. L. Martin, A. R.
Bishop, Phys. Rev. Lett., 89, 9, 097402-14.
16
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

17
Future work

• Finish planned calculation
• Optimize PPV excited state geography
• Compare PPV excited state bond length
• Calculate PPV excited state reorganization energy
  and fluorescence frequency (can calculate stoke
  shift)
• Calculate polarizability and other optical
  properties

18
Acknowledgement

• Dr. Smriti Anand
• Dr. Schlegel
• Dr. Chernyak
• Ph.D. students
• Stanley M. Smith
• Jie Li

19
Thank you

• Q A