He Rong-Xing, Duan Xiao-Hui, Li Xiang-Yuan
College of Chemical Engineering, Sichuan University, Chengdu 610065, People's Republic of China.
J Phys Chem A. 2005 May 12;109(18):4154-61. doi: 10.1021/jp045999h.
The excited states of a donor-bridge-acceptor (DBA) model system have been investigated using time-dependent density-functional theory (TD-DFT) in vacuo and in solution. It is found that the MPW1PW91 functional always gives higher excitation energies than those with a B3LYP functional. Results from both TD-B3LYP and TD-MPW1PW91 are found consistent with the experimental observations. The two most intense absorptions of the DBA system, one resulting from the local excitation of catechol moiety and the other from that of dicyanoethylene, possess the pipi* transition feature. It seems that the solvent polarity does not remarkably influence the positions of absorption peaks. The spectroscopic properties of isolated donor, acceptor, and bridge and the donor-bridge compound have been investigated at the TD-B3LYP/6-31+G* and TD-MPW1PW91/6-31+G* levels. Results indicate that the donor and the acceptor are weakly coupled with the bridge. Therefore, it is more likely that the electron transfer takes place through a superexchange mechanism. In addition, we calculate the electronic coupling matrix elements according to the generalized Mulliken-Hush theory, and the detailed analyses also predict that the strong absorptions are due to the local excitation of the DBA system.
已采用含时密度泛函理论（TD-DFT）在真空和溶液中研究了供体-桥-受体（DBA）模型体系的激发态。发现MPW1PW91泛函给出的激发能总是高于B3LYP泛函给出的激发能。TD-B3LYP和TD-MPW1PW91的结果均与实验观测结果一致。DBA体系的两个最强吸收峰，一个源于儿茶酚部分的局域激发，另一个源于二氰基乙烯的局域激发，具有ππ跃迁特征。溶剂极性似乎对吸收峰位置没有显著影响。已在TD-B3LYP/6-31+G和TD-MPW1PW91/6-31+G*水平上研究了孤立的供体、受体、桥以及供体-桥化合物的光谱性质。结果表明供体和受体与桥的耦合较弱。因此，电子转移更有可能通过超交换机制发生。此外，我们根据广义穆利肯-赫什理论计算了电子耦合矩阵元，详细分析也预测强吸收是由于DBA体系的局域激发。
