乙二醇的分子间氢键结构动力学的飞秒非线性红外光谱

Intermolecular Hydrogen Bonding Structural Dynamics in Ethylene Glycol by Femtosecond Nonlinear Infrared Spectroscopy

利用稳态线性红外光谱和飞秒泵浦-探测红外光谱技术,研究了在乙腈(Me CN)、丙酮(AC)、四氢呋喃(THF)和二甲基亚砜(DMSO)溶剂中乙二醇(EG)的结构和羟基(―OH)伸缩振动动力学.结果表明,乙二醇的―OH伸缩振动的频率位置、峰宽以及振动弛豫动力学都表现出强烈的溶剂依赖性.乙二醇溶液中至少存在两种形式的分子间氢键,一种是溶质-溶剂团簇的分子间氢键,另一种是溶质-溶质团簇的分子间氢键.量子化学计算预测的―OH伸缩振动频率的溶剂依赖性与我们的红外光谱实验观测结果一致.进一步,我们发现在乙腈中参与形成溶质-溶剂团簇氢键的乙二醇―OH伸缩振动具有最慢的弛豫动力学,丙酮和四氢呋喃次之,而最快的弛豫动力学过程发生在二甲基亚砜中.在每一溶剂条件下,乙二醇/乙二醇溶质团簇中―OH伸缩振动弛豫都更快一些.本文结果有助于认识在溶质-溶质、溶质-溶剂分子团簇共存的体系中不同分子间氢键的结构动力学特性.

In this work, we examined the structural and―OH stretching vibrational dynamics of ethylene glycol （EG） solvated in acetonitrile （MeCN）, acetone （AC）, tetrahydrofuran （THF）, and dimethylsulfoxide （DMSO） using steady-state linear infrared （IR） spectroscopy and ultrafast pump-probe IR spectroscopy. The results suggested that the frequency position, bandwidth, and vibrational relaxation of the―OH stretching vibration that participate in the formation of intermolecular hydrogen bonds （IHBs） were strongly influenced by the type of solvent. At least two types of IHBs were detected in the EG solution including clustered solute-solute IHBs and solute-solvent IHBs. Quantum chemical calculations predicted a similar solvent dependence of the―OH stretching vibrational frequency to that observed in the IR experiments. Furthermore, we found that the IHB-involved―OH stretching mode in the case of solute-solvent clusters displayed the slowest population relaxation dynamics in the case of EG in MeCN. The relaxation became slightly faster in AC and even faster in THF. The fastest dynamics was observed in the case of EG in DMSO. However, in each solvent environment examined, the IHB-involved―OH stretching mode in the solute-solute cluster displayed the fastest population relaxation. The results obtained in this study provide further insights into different IHB structural dynamics in co-existing solute-solute and solute-solvent clusters.