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采用量子化学密度泛函理论在B3LYP/6-311G~(**)水平对标题化合物可能存在的A、B、C三类互变异构体进行全优化,采用AIM 2000程序包计算了分子内氢键及相应的成键临界点电荷密度和关键原子的电荷;在计算的基础上,分析了异构体几何构型、相对稳定性和电荷分布,讨论分子内质子转移的难易程度.采用含时密度泛函理论在相同水平上对其进行了电子吸收光谱研究.为模拟真实条件,计算还考虑了水溶液对电子结构和光谱性质的影响.研究结果表明:烯胺式B为最稳定结构,三个异构体稳定性为B>A>C.A、B、C的λ_(max)均来源于分子的π→π~*跃迁,且存在明显的分子内电荷转移现象.异构体A、B之间易通过分子内质子转移进行互变,质子转移的能垒较低;质子供体和受体之间的电荷转移可能是通过共轭体系的π电子跃迁产生的.水溶液中A、B电子光谱的λ_(max)发生红移,振子强度增大,吸收增强;而C的λ_(max)基本不改变,振子强度减小,吸收减弱.
Quantum chemical density functional theory (DFT) was used to optimize the three classes of tautomers A, B and C at B3LYP / 6-311G ~ (**). AIM 2000 package was used to calculate intramolecular Hydrogen bond and the corresponding critical charge density of the bond formation and the charge of the key atom. Based on the calculations, the geometrical configuration, relative stability and charge distribution of the isomers were analyzed and the intramolecular proton transfer was discussed. Time-dependent density functional theory (EDF) was used to study the electron absorption spectra at the same level.In order to simulate the real conditions, the influence of aqueous solution on the electronic structure and spectral properties was also considered.The results showed that enamine B was the most stable structure , The three isomers have the stability of B> A> CA, and the λ max of B and C are all derived from the π → π ~ * transition of the molecule with obvious intramolecular charge transfer. Isomers A, B is easily interconverted by intramolecular proton transfer, and the proton transfer energy barrier is low. The charge transfer between the proton donor and acceptor may be caused by the π electron transition of the conjugated system. A, B in aqueous solution The red shift of λ_ (max) in the electron spectrum increases the oscillator strength , And the absorption increases; while the λ_ (max) of C basically does not change, the oscillator strength decreases, and the absorption decreases.