【作者】 韩萍；

【导师】 郝策；

【作者基本信息】 大连理工大学 ， 分析化学（专业学位）， 2020， 硕士

【摘要】 氢键是聚集体中最普遍、最基本和最重要的相互作用。由于其高度的取向性和丰富的形式,被称为“聚集体中的万能作用”,又被称为“弱作用,强效应”。氢键不仅支配着基态的性质,也支配着电子激发态的性质。然而,人们对激发态氢键的行为了解甚少。激发态氢键的行为不仅能够影响反应体系的发光性质还能影响体系的光物理、光化学过程。因此激发态氢键在不同反应体系中的作用机制成为亟待解决的科学问题。HHTP-DPB COF与NH₃之间通过氢键结合。氢键会对COF的发光机理产生影响。通过比较激发态与基态之间氢键键长、特征键的红外振动频率、氢键键能、¹H-NMR及非共价相互作用分析描述了激发态下氢键的行为。通过能隙法则分析发现激发态氢键增强会导致NH₃与HHTP-DPB COF之间的电子耦合增强,从而使激发态到基态的内转换速率增强,提高非辐射跃迁速率,使荧光速率系数从1.04×10⁸ s^-1降到8.57×10⁷ s^-1,导致荧光减弱,进而通过荧光强度的变化检测NH₃。在光催化还原CO₂体系中,催化剂与CO₂和H₂O之间存在着丰富的氢键。通过构建催化剂与CO₂和H₂O的氢键复合物来研究激发态氢键在体系中的作用机制。在TiO₂光催化还原CO₂体系中,以氢键复合物模型为基础,采用DFT/TDDFT方法计算得到了完整的光物理和光化学反应机理。通过比较各个过程的速率系数找到反应的速控步骤为C=O键的断裂,该步活化能需要40.1 kcal/mol,反应速率仅为2.72×10^-1717 s^-1。结合电荷和自旋密度分析了反应中氢键诱导的电子转移及质子转移。从理论上预测在TiO₂中掺杂金属Mg可以改进速控步骤,使得反应活化能降低5.5 kcal/mol。并通过实验进行了验证,发现Mg的加入使得CO产率较纯TiO₂提高了3.6倍。g-C₃N₄光催化还原CO₂体系中,通过理论与实验相结合的方法,考察了体系的光物理和光化学过程,探究了激发态氢键诱导的电子转移和质子转移,找到光化学反应中C=O键断裂为反应的速控步骤,该步活化能需要38.7 kcal/mol。从理论上针对性地筛选出Cr对g-C₃N₄催化剂改性,改性后的催化剂可使速控步骤活化能降低5.9 kcal/mol。在实验中加入Cr使得反应活性大幅提升,产率为原来的2倍左右。更多还原

【Abstract】 Hydrogen bond is the most common,basic and important interaction in aggregates.Because of its strong orientation and various forms,it is called"the universal interaction in the aggregate",also known as"weak interaction,strong effect".Hydrogen bond not only dominates the properties of ground state,but also the properties of excited state.However,little is known about the behavior of excited state hydrogen bonds.The behavior of excited state hydrogen bonds can affect not only the luminescence properties of the reaction system,but also the photophysical and photochemical processes of the system.Therefore,the mechanism of excited state hydrogen bond in different reaction systems has become an urgent scientific problem to be solved.HHTP-DPB COF and NH₃ are combined by hydrogen bond.Hydrogen bond can affect the luminescence mechanism of COF.The behavior of hydrogen bond in excited state is described by comparing the length of hydrogen bond between excited state and ground state,infrared vibration frequency of characteristic bond,hydrogen bond energy,¹H-NMR and noncovalent interaction.It is found that the enhanced hydrogen bonding in the excited state leads to the enhanced electronic coupling between NH₃ and HHTP-DPB COF by energy gap rule analysis,which enhances the internal conversion rate from the excited state to the ground state,increases the non-radiative transition rate,makes the fluorescence conversion rate dcreased from 1.04×10⁸ s^-11 to 8.57×10⁷ s^-1,and leads to the weakening of fluorescence,and then detects NH₃ by the change of fluorescence intensity.In the system of photocatalytic reduction of CO₂,there are abundant hydrogen bonds between the catalyst,CO₂ and H₂O.The mechanism of excited state hydrogen bond in the system was studied by modeling the hydrogen bond complex of catalyst with CO₂ and H₂O.In the system of photocatalytic reduction of CO₂ by TiO₂,based on the hydrogen bond complex model,the complete photophysical and photochemical reaction mechanism was calculated by DFT/TDDFT method.By comparing the rate coefficients of each steps,it is found that the rate-controlling step of the reaction is the breaking of the C=O bond and the activation energy of this step needs 40.1 kcal/mol which reaction rates is 2.72×10^-1717 s^-1.The hydrogen bond-induced electron transfer and proton transfer in the reaction were analyzed by combining charge and spin density.Theoretically predict that the doped metal Mg in TiO₂ can improve the rate-controlling step which reduces the activation energy by 5.5kcal/mol.In validation experiments,it is found that CO yield increased by 3.6 times compared with that of pure TiO₂ with the addition of Mg.In the system of g-C₃N₄ photocatalytic reduction of CO₂,the photophysical and photochemical processes of the system were investigated by theoretical and experimental methods,and the excited state hydrogen bond induced electron transfer and proton transfer were studied.It is found that the C=O bond breaking in photochemical reaction is the rate-controlling step of the reaction and the activation energy of this step needs 38.7 kcal/mol.The modification of g-C₃N₄ catalyst by Cr was selected in theory,and Cr was added in the experiment greatly increased the activity of the reaction which reduces the activation energy by 5.9kcal/mol,and makes the CO yield increased by 2 times compared with that of g-C₃N₄.更多还原