Elucidating the mechanism behind the infrared spectral features and dynamics observed in the carbonyl stretch region of organic carbonates interacting with lithium ions
Elucidating the mechanism behind the infrared spectral features and dynamics observed in the carbonyl stretch region of organic carbonates interacting with lithium ions
复制标题
DOI：
10.1063/5.0049742
复制
发表时间：
2021-06-21
影响因子：
4.4
通讯作者：
Kuroda, Daniel G.
中科院分区：
文献类型：
--
作者：
Fulfer, Kristen D.;Galle Kankanamge, Susith R.;Kuroda, Daniel G.
超快红外光谱已成为研究溶液结构和超快动力学的重要工具。特别是，它最近已被应用于研究分子间的相互作用和锂盐在有机碳酸酯中的运动。然而，从这些光谱中得到的光谱特征和动力学的分子解释存在差异。因此，使用线性和非线性光谱工具以及共溶剂稀释策略进一步研究了羰基伸缩区域中出现的光谱特征背后的机制。高氯酸锂在碳酸二甲酯（DMC）和四氢呋喃的二元混合物中被用作稀释策略的一部分，以确定第一溶剂化壳层中的碳酸酯的数量的光谱特征的变化，因为这两种溶剂具有类似的相互作用能量与锂离子。实验表明，即使在低浓度的碳酸二甲酯中，锂离子的溶剂化结构中也总是有一个以上的碳酸酯参与。此外，温度依赖性研究表明，在室温下，配位锂离子的溶剂分子的交换是不可热接近的。此外，时间分辨红外光谱实验证实了存在的振动耦合羰基拉伸之间的协调DMC分子，并表明，这一过程显着改变通过限制在锂离子溶剂化壳的碳酸酯分子的数量。总体而言，所提出的实验结果强烈支持振动能量转移的机制背后的非对角线功能出现在2S光谱的锂盐在有机碳酸盐的溶液。
Ultrafast infrared spectroscopy has become a very important tool for studying the structure and ultrafast dynamics in solution. In particular, it has been recently applied to investigate the molecular interactions and motions of lithium salts in organic carbonates. However, there has been a discrepancy in the molecular interpretation of the spectral features and dynamics derived from these spectroscopies. Hence, the mechanism behind spectral features appearing in the carbonyl stretching region was further investigated using linear and nonlinear spectroscopic tools and the co-solvent dilution strategy. Lithium perchlorate in a binary mixture of dimethyl carbonate (DMC) and tetrahydrofuran was used as part of the dilution strategy to identify the changes of the spectral features with the number of carbonates in the first solvation shell since both solvents have similar interaction energetics with the lithium ion. Experiments showed that more than one carbonate is always participating in the lithium ion solvation structures, even at the low concentration of DMC. Moreover, temperature-dependent study revealed that the exchange of the solvent molecules coordinating the lithium ion is not thermally accessible at room temperature. Furthermore, time-resolved IR experiments confirmed the presence of vibrationally coupled carbonyl stretches among coordinated DMC molecules and demonstrated that this process is significantly altered by limiting the number of carbonate molecules in the lithium ion solvation shell. Overall, the presented experimental findings strongly support the vibrational energy transfer as the mechanism behind the off-diagonal features appearing on the 2DIR spectra of solutions of lithium salt in organic carbonates.