School of Electrical Engineering, University of South China, Hengyang 421001, PR China; Institute of Molecular Sciences and Engineering, Shandong University, Qingdao 266235, PR China.
Institute of Molecular Sciences and Engineering, Shandong University, Qingdao 266235, PR China.
Spectrochim Acta A Mol Biomol Spectrosc. 2020 Apr 15;231:117800. doi: 10.1016/j.saa.2019.117800. Epub 2019 Nov 16.
Time-dependent density functional theory (TDDFT) method was used to study the different excited states proton transfer mechanism of DPP in cyclohexane (CHE) and Methanol (MeOH). The results indicate that the concerted mechanism and the stepwise mechanism coexist in the double proton transfer process of DPP dimer in the aprotic solvent CHE, the stepwise mechanism predominates. The stepwise mechanism can only carry out single proton transfer (DPP-SPT), the second proton cannot be transferred because it is hindered by high energy barriers. The concerted mechanism produces a double proton transfer (DPP-DPT). The potential energy surface of the DPP dimer was calculated and the double fluorescence phenomenon of DPP dimer observed by Chou et al. (P.T. Chou, Y.I. Liu, H.W. Liu, W.S. Yu, Dual Excitation behavior of double proton transfer versus Charge Transfer in 4-(N-Substituted Amino)-1H-pyrrolo[2,3-b]pyridines tuned by dielectric and hydrogen-bonding perturbation, J. Am. Chem. Soc., 123 (2001) 12119-12120) was explained. In view of the protonic solvent effect of methanol, the potential energy curve of the DPP/MeOH cluster was constructed. The fluorescence quenching process of DPP/MeOH clusters was elucidated. The proton transfer pathways of DPP/MeOH clusters are revealed in two different concerted ways (Type A: protons transfer from DPP molecules to MeOH solvent molecules; Type B: protons transfer from MeOH solvent to DPP molecules). The ESPT process of DPP molecules in the protic solvent MeOH was found to be more prone to Type B. The results can help to better understand the intermolecular hydrogen bonding mechanism of DPP molecules.
采用含时密度泛函理论（TDDFT）方法研究了 DPP 在环己烷（CHE）和甲醇（MeOH）中不同激发态质子转移的机理。结果表明，在非质子溶剂 CHE 中 DPP 二聚体的双质子转移过程中存在协同机制和分步机制，分步机制占主导地位。分步机制只能进行单质子转移（DPP-SPT），由于高能垒的阻碍，第二个质子不能转移。协同机制产生双质子转移（DPP-DPT）。计算了 DPP 二聚体的势能面，并解释了 Chou 等人观察到的 DPP 二聚体的双荧光现象（P.T. Chou, Y.I. Liu, H.W. Liu, W.S. Yu, Dual Excitation behavior of double proton transfer versus Charge Transfer in 4-(N-Substituted Amino)-1H-pyrrolo[2,3-b]pyridines tuned by dielectric and hydrogen-bonding perturbation, J. Am. Chem. Soc., 123 (2001) 12119-12120）。考虑到甲醇的质子溶剂效应，构建了 DPP/MeOH 团簇的势能曲线。阐明了 DPP/MeOH 团簇的荧光猝灭过程。揭示了 DPP/MeOH 团簇中两种不同协同方式（A 型：质子从 DPP 分子转移到 MeOH 溶剂分子；B 型：质子从 MeOH 溶剂转移到 DPP 分子）的质子转移途径。发现 DPP 分子在质子溶剂 MeOH 中的 ESPT 过程更倾向于 B 型。这些结果有助于更好地理解 DPP 分子的分子间氢键机理。
