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Vibronic Fine-structure In The S0â†'S1Absorption Spectrum Of Zinc Porphyrin And Porphin: A Franck-condon Simulation Incorporating The Duschinsky Effect And Herzberg-Teller Theory

Posted on:2013-03-24Degree:MasterType:Thesis
Country:ChinaCandidate:H B LiFull Text:PDF
GTID:2231330371972420Subject:Physical chemistry
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In the present work, we calculated the equilibrium geometries and vibrational frequencies of zinc porphyrin (ZnP) and porphin using the DFT and TDDFT methods (B3LYP, BHandHLYP and PBEO functionals) and then simulated the S0â†'S1absorption spectrum of ZnP using the FC simulation with and without the HT and Duschinsky contributions. Furthermore, we tentatively assigned the fundamental vibrational lines of the spectral profile by taking into account the contributions from all interrelated normal modes.1. S0â†'S1Absorption Spectrum of ZnPAlthough zinc porphyrin is suitable object for the study of electronic structure and fine optical spectra of large molecules, few theoretical investigations were performed to simulate the high resolved spectra and assign the vibrational bands. In the frameworks of density functional theory and its TD extension, the S0â†'S1absorption spectrum (that is, the Q band) of zinc porphyrin was simulated using the Franck-Condon (FC) approximation including both the Herzberg-Teller (HT) and Duschinsky contributions to the electronic transition dipole moments. Our theoretical results provided a good description of the optical spectrum, which was in nice agreement with experimental observations. The spectral profile of the Q band of zinc porphyrin is primarily described by the transition of the vibrational normal modes v8, v18, v49, v56, v57, v63, v64and v87. Comparison of the FC and FCHT spectra with the experimental results revealed that the S0â†'S1absorption spectrum of zinc porphyrin is mainly induced by the HT mechanism. This result indicated that for the vibronically allowed or very weak transitions, such as those of the Q band in zinc porphyrin, the HT effect is more dominant than the FC contribution. We also tentatively assigned the vibrational lines in the simulated absorption spectrum. The results were compared with the available experimental spectrum and most of the dominant transitions were reproduced correctly.2. Qx Band Absorption/Fluorescence Spectra of PorphinThe Qx band (that is, the S0â†'S1absorption band) of Porphine is studied using the density functional theory with the B3LYP functional. The results indicate that the all kind of structural parameters, vertical excitation energies, oscillator strengths and frequencies of porphine agree well with the previous experimental and theoretical results. Moreover, we also simulated the absorption spectrum of porphine in the Qx-band region using the Franck-Condon (FC) approximation with the Herzberg-Teller (HT) and Duschinsky contributions. The results indicate that the high resolved spectral profile of porphine is primarily described by the Herzberg-Teller mechanism, while the Franck-Condon contributions are negligible, the FCHT spectrum accurately reproduce most of the dominant transitions, and the fluorescence and absorption spectra show mirror symmetry.
Keywords/Search Tags:zinc porphyrin, porphin, absorption spectrum, vibronic bands, Herzberg-Teller, Duschinsky
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