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Excited state calculations for polyene and PPV systems Chao Wu

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Contents Introduction Computational method Results and Discussion Difficulty met Future work

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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.

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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

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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.

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Computational method

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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

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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.

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Molecule levelOsc. Stren.Transition energy (eV) Butadiene CIS/3-21G 1.22147.2413 TDHF/3-21G 0.91896.8280 TDB3LYP/3-21G 0.66696.2564 TDB3LYP/6-31+G 0.67015.6542 ZINDO 0.90815.4016 Hexatriene CIS/3-21G 1.79496.1503 TDHF/3-21G 1.40325.8137 TDB3LYP/3-21G 1.06005.0336 TDB3LYP/6-31+G 1.09704.6648 ZINDO 1.28864.4703 Octatetraene CIS/3-21G 2.34815.4623 TDHF/3-21G 1.90525.1763 TDB3LYP/3-21G 1.47074.2716 TDB3LYP/6-31+G 1.52114.0038 ZINDO 1.66033.9226 Decapentaene CIS/3-21G 2.87274.9980 TDHF/3-21G 2.41414.7469 TDB3LYP/3-21G 1.88323.7427 TDB3LYP/6-31+G 1.94073.5311 ZINDO 2.01663.5643 Dodecahexene CIS/3-21G 3.37254.6683 TDHF/3-21G 2.92444.4411 TDB3LYP/3-21G 2.29103.3523 TDB3LYP/6-31+G 2.35433.1746 ZINDO 2.35793.3144

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

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Dodecahexene HOMO

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Dodecahexene LUMO

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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

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MoleculeLevelOsc. Stren.Transition Energy(eV) PPV 2 CIS/3-21G 1.19005.1883 ZINDO 0.89754.0902 PPV 3 CIS/3-21G 1.84634.6044 ZINDO 1.75853.4727 PPV 4 CIS/3-21G ** ZINDO 2.44573.2885 PPV 5 CIS/3-21G ** ZINDO 2.87253.5141 * Result not got yet

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

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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

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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

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

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Thank you Q & A

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