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Excited state calculations for polyene and PPV systems

Excited state calculations for polyene and PPV systems. Chao Wu. Contents. Introduction Computational method Results and Discussion Difficulty met Future work. Introduction.

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Excited state calculations for polyene and PPV systems

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  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(n=2~6) and poly phenylene vinylene (PPV, n=2~5) 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/6-31+GTDB3LYP/6-31+G • 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. Polyacetylene S. M. Smith et al., J. Phys. Chem. A2004, 108, 11063-11072.

  10. Dodecahexene HOMO

  11. Dodecahexene LUMO

  12. 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

  13. * Result not got yet

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

  15. 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

  16. 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

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

  18. Thank you Q & A

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