Intramolecular Vibrational Energy Relaxation of CO 2 in Cross-Linked Poly(ethylene glycol) Diacrylate-Based Ion Gels
Intramolecular Vibrational Energy Relaxation of CO 2 in Cross-Linked Poly(ethylene glycol) Diacrylate-Based Ion Gels
复制标题
交联聚乙二醇二丙烯酸酯基离子凝胶中 CO 2 的分子内振动能量弛豫
DOI：
10.1021/acs.jpcb.0c06685
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Garrett-Roe, Sean
中科院分区：
文献类型：
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作者：
Kelsheimer, C. J.;Garrett-Roe, Sean
采用超快二维红外光谱（2D-IR）和傅里叶变换红外光谱（FTIR）测量了1-乙基-3-甲基咪唑双（三氟甲基磺酰基）酰亚胺（[emim][Tf 2N]）、交联低分子量聚乙二醇二丙烯酸酯（PEGDA）和由50 vol %的两者共混物组成的离子凝胶中的二氧化碳（CO2）。CO2的反对称伸缩振动的中心频率ν3随聚合物含量的增加单调地向较低的波数移动，在离子凝胶中具有最大的线宽（6 cm-1）。增加聚合物含量会减慢光谱扩散和振动能量弛豫（VER）速率。在交联PEGDA的2D-IR中由于VER从反对称拉伸到弯曲模式ν2而出现意外的激发态吸收峰。需要32个响应函数来描述在2D-IR光谱中观察到的特征。非线性最小二乘拟合提取光谱扩散和VER率。在离子凝胶中，CO2表现出介于纯化合物之间的光谱扩散动力学。VER的动力学反映了与离子液体（IL）类似的弯曲模式的快速激发和去激发，以及与交联聚合物类似的缓慢的整体振动布居弛豫。类离子液体和聚合物的动力学表明，CO2驻留在离子凝胶中的两个组件的界面。
Ultrafast two-dimensional infrared spectroscopy (2D-IR) and Fourier transform infrared spectroscopy (FTIR) were used to measure carbon dioxide (CO2) in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf2N]), cross-linked low-molecular-weight poly(ethylene glycol) diacrylate (PEGDA), and an ion gel composed of a 50 vol % blend of the two. The center frequency of the antisymmetric stretch, ν3, of CO2shifts monotonically to lower wavenumbers with increasing polymer content, with the largest line width in the ion gel (6 cm–1). Increasing polymer content slows both spectral diffusion and vibrational energy relaxation (VER) rates. An unexpected excited-state absorbance peak appears in the 2D-IR of cross-linked PEGDA due to VER from the antisymmetric stretch into the bending mode, ν2. Thirty-two response functions are necessary to describe the observed features in the 2D-IR spectra. Nonlinear least-squares fitting extracts both spectral diffusion and VER rates. In the ion gel, CO2exhibits spectral diffusion dynamics that lie between that of the pure compounds. The kinetics of VER reflect both fast excitation and de-excitation of the bending mode, similar to the ionic liquid (IL), and slow overall vibrational population relaxation, similar to the cross-linked polymer. The IL-like and polymer-like dynamics suggest that the CO2resides at the interface of the two components in the ion gel.