Fluorescence and absorption spectra of oligophenylenevinylenes: Vibronic coupling, band shapes, and solvatochromism
Fluorescence and absorption spectra of oligophenylenevinylenes: Vibronic coupling, band shapes, and solvatochromism
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DOI：
10.1063/1.1469612
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发表时间：
2002-05-15
影响因子：
4.4
通讯作者：
Oelkrug, D
中科院分区：
文献类型：
--
作者：
Gierschner, J;Mack, HG;Oelkrug, D
本文从实验和理论上研究了苯乙烯基对苯乙炔nPV的荧光发射和激发光谱随温度和溶剂极化率的变化。在低温下，S-0 S-1发射带和激发带的电子振动结构是镜像对称的，具有可忽略的0-0能隙。突出的振动模式的频率被分配到整个分子的第二纵向声学声子模式和本地化的碳-碳伸缩振动。在假设平面C-2 h分子对称性的情况下，在从头算Hartree-Fock（HF/6- 311 G（*））和限制构型相互作用单（RCIS/6- 311 G（*））理论水平上计算了光谱的完整振动结构。理论预测的光谱与实验符合得很好。在室温下，第一能带最大值之间的0-0能隙打开，并且吸收和发射之间的镜像对称性丧失。结合低温谱的高斯展宽和指数展宽，成功地模拟了电子振动带形和0-0带隙。指数项反映了S-0和S-1电子态中苯基-乙烯基扭转模式的热布居的差异。温度和溶剂的变化时的光谱位移定量解释的环境中的折射率的变化。从外推的实验数据的低聚物在真空中的垂直和绝热跃迁能，并比较RCIS和半经验量子化学计算，分别。(C)2002年美国物理学会。
Fluorescence emission and excitation spectra of para-phenylene vinylenes nPV with n=1-4 styryl units are investigated experimentally and theoretically as a function of the temperature and the polarizability of the solvent. At low temperatures, the vibronic structures of the S-0S-1 emission and excitation bands are mirror symmetrical with negligible 0-0 energy gaps. The frequencies of the prominent vibrational modes are assigned to the second longitudinal acoustic phonon modes of the entire molecules and to localized carbon-carbon stretching vibrations. The complete vibronic structures of the spectra are calculated at the ab initio Hartree-Fock (HF/6-311G(*)) and restricted configuration interaction singles (RCIS/6-311G(*)) levels of theory assuming planar C-2h molecular symmetry. The theoretically predicted spectra are in good agreement with the experiments. At room temperature, a 0-0 energy gap between the first band maxima opens, and the mirror symmetry between absorption and emission is lost. The vibronic band shapes and 0-0 band gaps are successfully simulated with a combination of Gaussian and exponential broadening of the low temperature spectra. The exponential term reflects the differences in thermal population of the phenyl-vinyl torsional modes in the S-0 and S-1 electronic states. Spectral shifts upon changes in temperature and solvents are quantitatively explained by changes in the refractive index of the environment. From extrapolation of the experimental data the vertical and adiabatic transition energies of the oligomers in vacuo are obtained and compared to RCIS and semiempirical quantum chemical calculations, respectively. (C) 2002 American Institute of Physics.