Hefei National Laboratory for Physical Science at Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei, P R China.
J Phys Chem B. 2011 Mar 31;115(12):2699-708. doi: 10.1021/jp107449v. Epub 2011 Mar 8.
We have recently presented a theoretical study on the temperature-dependent absorption and photoluminescence spectroscopy of rubrene multichromophores by combining the time-dependent long-range-corrected density functional theory with the Frenkel exciton model (Gao; et al. J. Phys. Chem. A2009, 113, 12847). The spectra of rubrene multichromophores up to heptamers have been calculated and the effects of exciton-phonon coupling and temperature on the photophysical properties of both H- and J-aggregated oligomers were addressed. However, in that work the contribution of intermolecular charge-transfer excitons (CTEs) to vibronic spectra was not addressed. Here we take into account the effect of CTEs for the absorption and emission spectra of the aggregated perylene bisimide (PBI) oligomers in order to have a quantitative explanation to the experimental absorption and emission spectra of the PBI dyes. The role of intermolecular CTEs is discussed for different intermolecular orientations and distances. The simulations demonstrate that the contribution of CTEs becomes significant when the intermolecular distance is less than 4.5 Å for the π-π stacked PBI aggregates, and the mixed exciton model is prerequisite to explain the experimentally observed red-shift of the absorption spectra in this case. The large Stokes shift of the emission spectra can be reproduced by our model, and it is induced by the asymmetric nature of the lowest excitonic state of the H-aggregated oligomers. The experimentally observed broad emission bands come from two species with different conformations. As for J-aggregated PBI oligomers, the interactions of FEs induce the red-shift and the increase of the relative intensity of 0-0 peak of the absorption spectra with more aggregated units.
我们最近结合含时密度泛函理论和福井激子模型（Gao 等人，J. Phys. Chem. A，2009，113，12847），对并五苯多色团的温度依赖吸收和光致发光光谱进行了理论研究。计算了多达七聚体的并五苯多色团的光谱，并研究了激子-声子耦合和温度对 H 和 J 聚集低聚物光物理性质的影响。然而，在这项工作中，没有考虑分子间电荷转移激子（CTEs）对振子光谱的贡献。在这里，我们考虑了 CTEs 对聚集的苝二酰亚胺（PBI）低聚物吸收和发射光谱的影响，以便对 PBI 染料的实验吸收和发射光谱进行定量解释。讨论了不同分子间取向和距离对分子间 CTEs 的作用。模拟表明，对于π-π堆积的 PBI 聚集体，当分子间距离小于 4.5 Å 时，CTEs 的贡献变得显著，在这种情况下，混合激子模型是解释实验观察到的吸收光谱红移的前提。我们的模型可以重现发射光谱的大斯托克斯位移，这是由 H 聚集低聚物最低激子态的不对称性质引起的。实验观察到的宽发射带来自两种具有不同构象的物质。对于 J 聚集的 PBI 低聚物，FEs 的相互作用导致吸收光谱的红移和 0-0 峰相对强度的增加，随着聚集单元的增加而增加。
