Presentation on theme: "Excited state calculations for polyene and PPV systems Chao Wu."— Presentation transcript:
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 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.
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.
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
Results and Discussion For polyacetylene system, The optimized structures (ground state) are trans-planar. (C 2h 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.
PPV For PPV system, the optimized structures are not planar: librational motion also pertubation (impurity and intermolecular interaction) Verified by experimental results PPV 5 non-planar ground state geometry optimized at AM1
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 reorganization 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