Zhao Jinfeng, Dong Hao, Zheng Yujun
School of Physics, Shandong University , Jinan 250100, China.
J Phys Chem A. 2018 Feb 8;122(5):1200-1208. doi: 10.1021/acs.jpca.7b10492. Epub 2018 Jan 24.
As the most important component of deep red pigments, alkannin is investigated theoretically in detail based on time-dependent density functional theory (TDDFT) method. Exploring the dual intramolecular hydrogen bonds (O1-H2···O3 and O4-H5···O6) of alkannin, we confirm the O1-H2···O3 may play a more important role in the first excited state than the O4-H5···O6 one. Infrared (IR) vibrational analyses and subsequent charge redistribution also support this viewpoint. Via constructing the S-state potential energy surface (PES) and searching transition state (TS) structures, we illuminate the excited state double proton transfer (ESDPT) mechanism of alkannin is the stepwise process that can be first launched by the O1-H2···O3 hydrogen bond wire in gas state, acetonitrile (CHCN) and cyclohexane (CYH) solvents. We present a novel mechanism that polar aprotic solvents can contribute to the first-step proton transfer (PT) process in the S state, and nonpolar solvents play important roles in lowering the potential energy barrier of the second-step PT reaction.
作为深红色色素的最重要成分，紫草素基于含时密度泛函理论（TDDFT）方法进行了详细的理论研究。通过探究紫草素的双分子内氢键（O1-H2···O3和O4-H5···O6），我们证实了在第一激发态中，O1-H2···O3可能比O4-H5···O6发挥更重要的作用。红外（IR）振动分析及随后的电荷重新分布也支持这一观点。通过构建S态势能面（PES）并搜索过渡态（TS）结构，我们阐明了紫草素的激发态双质子转移（ESDPT）机制是一个逐步过程，在气态、乙腈（CHCN）和环己烷（CYH）溶剂中，该过程可首先由O1-H2···O3氢键链引发。我们提出了一种新机制，即极性非质子溶剂可促进S态的第一步质子转移（PT）过程，而非极性溶剂在降低第二步PT反应的势能垒方面发挥重要作用。
