In this work we demonstrate the use of the push–pull model system 4-(dimethylamino)benzonitrile (DMABN) as a convenient molecular probe to investigate the local solvation structure and dynamics by means of time-resolved infrared spectroscopy (TRIR). The photochemical features associated with this system provide several advantages due to the high charge separation between the ground and charge transfer states involving the characteristic nitrile bond, and an excited state lifetime that is long enough to observe the slow solvation dynamics in organic solvents and ionic liquids. The conversion from a locally excited state to an intramolecular charge transfer state (LE–ICT) in ionic liquids shows similar kinetic lifetimes in comparison to organic solvents. This similarity confirms that such conversion depends solely on the intramolecular reorganization of DMABN in the excited state, and not by the dynamics of solvation. In contrast, the relative shift of the ν(CN) vibration during the relaxation of the ICT state reveals two distinct lifetimes that are sensitive to the solvent environment. This study reveals a fast time component which is attributed to the dipolar relaxation of the solvent and a slower time component related to the rotation of the dimethylamino group of DMABN.

中文翻译：

---

通过时间分辨的红外光谱研究4-（二甲氨基）苄腈的离子液体中的溶剂化结构和动力学

在这项工作中，我们证明了使用推挽模型系统4-（二甲基氨基）苄腈（DMABN）作为方便的分子探针，通过时间分辨红外光谱（TRIR）研究局部溶剂化结构和动力学。与该系统相关的光化学特征具有多种优势，这归因于基态和电荷转移态之间的高电荷分离（涉及特征性的腈键）以及激发态寿命，该寿命足以观察有机溶剂和离子液体中缓慢的溶剂化动力学。与有机溶剂相比，离子液体中从局部激发态到分子内电荷转移态（LE–ICT）的转换显示出相似的动力学寿命。这种相似性证实，这种转化仅取决于处于激发态的DMABN的分子内重组，而不取决于溶剂化的动力学。相比之下，ICT状态松弛期间的ν（CN）振动揭示了对溶剂环境敏感的两个不同的寿命。这项研究揭示了归因于溶剂的偶极弛豫的快速时间成分和归因于DMABN的二甲基氨基基团旋转的较慢的时间成分。