Lukes Vladimír, Aquino Adélia Justina Aguiar, Lischka Hans, Kauffmann Harald-Friedrich
Department of Chemical Physics, Slovak University of Technology, Radlinského 9, SK-81 237 Bratislava, Slovakia.
J Phys Chem B. 2007 Jul 19;111(28):7954-62. doi: 10.1021/jp068496f. Epub 2007 Jun 26.
A systematic characterization of excited-state properties of para-phenylene oligomers constructed from two to eight aromatic rings is presented using density functional theory (DFT) and the coupled-cluster singles and doubles (CC2) method. Geometry optimizations have been performed for the ground state and for the electronically excited state. Vertical excitations and the fluorescence transitions have been calculated. Time-dependent DFT (TDDFT) method underestimates excitation and fluorescence energies systematically in comparison with experimental results. The computed TDDFT lifetime for the polymer limit (0.43 ns) is in agreement with the experimental value of 0.55 ns. The TDDFT torsional potential curves were investigated for biphenyl, terphenyl, and quarterphenyl oligomers in their electronic ground and excited states. Our calculations show an increase in the separation of the lowest excited state (S1) to the next higher one with increasing molecular size. No indication is found for state crossings of the S1 state with higher ones from planar structures up to torsional angles of 60 degrees to 70 degrees. Thus, an adiabatic description of the dynamics of the S1 state might significantly simplify any dynamics simulations of torsional broadenings.
利用密度泛函理论（DFT）和耦合簇单双激发（CC2）方法，对由2至8个芳环构成的对亚苯基低聚物的激发态性质进行了系统表征。对基态和电子激发态进行了几何优化。计算了垂直激发和荧光跃迁。与实验结果相比，含时密度泛函理论（TDDFT）方法系统性地低估了激发能和荧光能。计算得到的聚合物极限的TDDFT寿命（0.43纳秒）与0.55纳秒的实验值相符。研究了联苯、三联苯和四联苯低聚物在电子基态和激发态下的TDDFT扭转势曲线。我们的计算表明，随着分子尺寸的增加，最低激发态（S1）与下一个更高激发态之间的间距增大。从平面结构到60度至70度的扭转角，均未发现S1态与更高激发态发生态交叉的迹象。因此，对S1态动力学的绝热描述可能会显著简化扭转展宽的任何动力学模拟。
