氨硼烷激发态物理化学性质及脱氢机理的理论研究

As a kind of potential solid hydrogen storage material, ammonia borane, which contains dihydrogen bonding, can realize the hydrogen storage and release. The dehydrogenation mechanism of ammonia borane and its derivatives in the ground state has been widely investigated, while the properties and dehydrogenation mechanism in the excited state are not clear. The excited state is the foothold of this project. The density functional theory (DFT) and time-dependent density functional theory (TDDFT) are adopted: (1) To reveal the changes of dihydrogen, charge distribution, frontier molecular orbital, etc. through the photo-excited process. (2) To explore the role of dihydrogen bond in the excited state dehydrogenation process and reveal excited state dehydrogenation mechanism of the ammonia borane. (3) To research the effect of the change of dihydrogen bond and other physical and chemical parameters through the photo-excited on the excited state dehydrogenation kinetics of ammonia borane. The change of the physical and chemical parameters will obtain through the research. The energy profile of the excited state dehydrogenation process and the function of key bond length changes over time will be constructed to describe the energy barrier and rate of the dehydrogenation process. The influencing factors of excited state dehydrogenation process will be found through the analysis of the change rule of the physical and chemical parameters and dehydrogenation mechanism at different electronic states. The research of this project can open a new train of thought for synthesizing more efficient ammonia borane hydrogen storage material.

氨硼烷是一种极具潜力的固态储氢材料，分子中含有独特的双氢键，可以实现氢气的储存和释放。氨硼烷及其衍生物在基态的脱氢机理被广泛研究，但激发态下氨硼烷的性质及脱氢机理并不明确。本项目以激发态为出发点，采用密度泛函和含时密度泛函理论：（1）揭示氨硼烷双氢键、电荷分布、前线轨道等参数在光激发过程中的变化情况；（2）探究氨硼烷双氢键在激发态脱氢过程中的作用并揭示氨硼烷激发态脱氢机理；（3）研究光激发过程中双氢键及其它物理化学参数的变化对氨硼烷激发态脱氢动力学过程的影响。通过研究获得氨硼烷在光激发过程中物理化学参数的变化情况；构建出激发态脱氢过程的能量过程图及关键键长随时间变化的函数，直观的给出氨硼烷激发态脱氢过程的能垒和速率；通过不同电子态氨硼烷物理化学参数及脱氢机理的变化规律，找到影响氨硼烷激发态脱氢动力学过程难易程度的主要因素。本项目的研究能为人们合成更加高效的氨硼烷类储氢材料打开一个新的思路。

本项目选取氨硼烷衍生物二甲基胺硼烷和苯酚形成的双氢键复合物为研究对象，采用密度泛函和含时密度泛函理论方法探究了氢键和二氢键键长、键角、方向等构型参数在光激发过程中的变化情况；除了构型参数以外，还对苯酚-二甲基胺硼烷复合物的红外振动光谱、电荷分布、前线轨道等物理化学参数进行了研究，对比分析了这些参数在不同电子态的变化情况。通过基态和激发态稳定构型的柔性扫描，构建了苯酚-二甲基胺硼烷基态和激发态脱氢过程的势能曲线，分析了基态和激发态的脱氢机理以及羟基裂解、构型异变现象，并通过关键物理化学参数在不同电子态的变化情况解释了激发态脱氢过程比基态更容易发生的原因。对后续含有二氢键的分子体系的研究具有一定的指导意义。同时我们还研究了氟取代对体系氢键强度的影响以及荧光分子的激发态双质子转移机理和多荧光特性，揭示了轨道跃迁、电荷转移、质子转移以及荧光发射等光物理过程。为氢键以及二氢键等分子体系的研究提供了理论基础。