Li Junfeng, Rinkevicius Zilvinas, Cao Zexing
State Key Laboratory of Physical Chemistry of Solid Surfaces and Fujian Provincial Key Lab of Theoretical and Computational Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, People's Republic of China.
Division of Theoretical Chemistry and Biology, School of Biotechnology, Royal Institute of Technology, SE-106 91 Stockholm, Sweden.
J Chem Phys. 2014 Jul 7;141(1):014306. doi: 10.1063/1.4885845.
Time-dependent density-functional theory (TD-DFT) and complete active space multiconfiguration self-consistent field (CASSCF) calculations have been used to determine equilibrium structures and vibrational frequencies of the ground state and several singlet low-lying excited states of coumarin. Vertical and adiabatic transition energies of S1, S2, and S3 have been estimated by TD-B3LYP and CASSCF/PT2. Calculations predict that the dipole-allowed S1 and S3 states have a character of (1)(ππ*), while the dipole-forbidden (1)(nπ*) state is responsible for S2. The vibronic absorption and emission spectra of coumarin have been simulated by TD-B3LYP and CASSCF calculations within the Franck-Condon approximation, respectively. The simulated vibronic spectra show good agreement with the experimental observations available, which allow us to reasonably interpret vibronic features in the S0→S1 and S0→S3 absorption and the S0←S1 emission spectra. Based on the calculated results, activity, intensity, and density of the vibronic transitions and their contribution to the experimental spectrum profile have been discussed.
含时密度泛函理论（TD-DFT）和完全活性空间多组态自洽场（CASSCF）计算已被用于确定香豆素基态和几个单重态低激发态的平衡结构及振动频率。通过TD-B3LYP和CASSCF/PT2估算了S1、S2和S3的垂直和绝热跃迁能量。计算预测，允许偶极矩跃迁的S1和S3态具有(1)(ππ*)特征，而禁阻偶极矩跃迁的(1)(nπ*)态对应于S2。分别在弗兰克-康登近似下通过TD-B3LYP和CASSCF计算模拟了香豆素的电子振动吸收和发射光谱。模拟的电子振动光谱与现有的实验观测结果吻合良好，这使我们能够合理地解释S0→S1和S0→S3吸收以及S0←S1发射光谱中的电子振动特征。基于计算结果，讨论了电子振动跃迁的活性、强度和密度及其对实验光谱轮廓的贡献。
