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A Theoretical Study Of Electronic Absorption Spectrum Of Photochomic Materials

Posted on:2008-03-02Degree:MasterType:Thesis
Country:ChinaCandidate:P XieFull Text:PDF
GTID:2121360215956817Subject:Physical chemistry
Abstract/Summary:PDF Full Text Request
Dithienylethene macrocycle attract much attention for their optically switching capability. The switching is caused by their ring-opening/closing photoisomerization. In general, the ring-closing photoisomers are thermally unstable and return to the initial ring-opening photoisomers in the visible light. We can change the molecule's structure to recognize or release the molecule by controlling the light. These will have a far-reaching impact on the supramolecular field.The advanced technique applied in experiments greatly promotes the development of modern computational chemistry. On one hand, the comparison between calculation and experiment can test the reliability and accuracy of electronic structure theory, showing the dependence of theory on experiment; on the other hand, to develop the electronic structure theory is to support and/or supplement the known experimental results, and further to predict the potential results, indicative of theoretical forward looking and independence.In this paper, we systematically studied dithienylethene macrocycle 30 and its photoisomers' (1C+20, 2C+10, 3C) ground-state geometries, electronic absorption spectrum, and obtained the following main results:Molecular geometries of the molecule 30, 1C+20, 2C+10, 3C in the ground state are optimized using the semiempirical molecular orbits theory, Austin Model 1 (AM1) method. On the basis of the optimized geometries, the electronic spectra, the electronic transition energies and oscillator strengths of the molecules are calculated by standard semiempirical Zerner's Intermediate Neglect of Differential Overlap/Spectroscopy (ZINDO/S) method for single excitations from 10 highest occupied to 10 lowest unoccupied molecular orbits, then the assignments of the spectrum are successfully made. All these calculation were elaborated using Gaussian 03 program package. The result showed that, when the 300 nm UV light is irradiated, the ring-closing photoisomerization occurs in the dichloromethane solution. There are molecule 1C+2O and 2C+1O in the solution, molecule 3C can hardly be produced. At the same time, we applied density functional theory (DFT) B3LYP/6-31G in program ADF2005 to optimize molecular geometries of the molecule 30, 1C+2O, 2C+1O, 3C in the ground state. The results show that DFT method is more accurate than AM1 method by comparing with experimental data. On the basis of the optimized geometries, the electronic spectra, the electronic transition energies and oscillator strengths of the molecules are calculated by time-dependent density functional theory (TDDFT) method for single excitations, then the assignments of the spectrum are made too. The results show that the results of TDDFT agree with the results of ZINDO/S well.
Keywords/Search Tags:Dithienylethene macrocycle, Electronic absorption spectrum, AM1, ZINDO, DFT, TDDFT
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