Raman spectroscopic study on the solvation of N,N-dimethyl-p-nitroaniline in room-temperature ionic liquids.
Raman spectroscopic study on the solvation of N,N-dimethyl-p-nitroaniline in room-temperature ionic liquids.
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N,N-二甲基对硝基苯胺在室温离子液体中溶剂化的拉曼光谱研究。
DOI：
10.1021/jp072020u
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发表时间：
2007
期刊：
影响因子：
--
通讯作者：
M. Terazima
中科院分区：
文献类型：
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作者：
Y. Kimura;T. Hamamoto;M. Terazima
测量了N，N-二甲基对硝基苯胺（DMPNA）在从超临界流体（SCF）的类气态状态到高极性室温离子液体（RTIL）的各种流体中的电子吸收光谱和拉曼光谱。我们发现DMPNA在RTIL中的S 0-S1吸收带中心主要由离子的摩尔浓度决定。另一方面，吸收光谱的带宽并不遵循从一个简单的介电连续模型的预期。特别是在SCF中，吸收光谱的带宽随着溶剂密度的增加而减小，这表明分子内重组能是溶剂密度的递减函数。NO2伸缩模式的拉曼位移已被证明是溶剂极性的良好指示剂;即，NO2伸缩模式的振动频率从在大部分非极性溶剂如乙烷中的1340 cm-1变化到在水中的1300 cm-1。吸收带中心和NO2模式的振动频率之间的线性关系，这在先前的论文（Fujisawa，T.; Terazima，M.; Kimura，Y. J.Chem.Phys.2006，124，184503），对于包括SCF和RTIL在内的所有流体几乎保持良好。另一方面，振动带宽与吸收带中心并不存在简单的关系。RTIL中的振动带宽通常比具有类似极性尺度的常规液体中的振动带宽大。在我们研究的RTIL中，振动带宽与阴离子的分子大小松散相关。对于吸收光谱的带宽，也观察到对阴离子尺寸的类似依赖性。我们还研究了RTIL中NO2伸缩模的拉曼位移与激发波长的关系。在所有流体中的激发波长的依赖程度是很好地与振动带宽。
Electronic absorption spectra and Raman spectra of N,N-dimethyl-p-nitroaniline (DMPNA) have been measured in various fluids from the gaseous-like conditions in supercritical fluids (SCFs) to highly polar room-temperature ionic liquids (RTILs). We found that the S0-S1 absorption band center of DMPNA in RTILs is mostly determined by the molar concentrations of ions. On the other hand, the bandwidth of the absorption spectrum does not follow the expectation from a simple dielectric continuum model. Especially in SCFs, the bandwidth of the absorption spectrum decreases with increasing solvent density, suggesting that the intramolecular reorganization energy is a decreasing function of the solvent density. The Raman shift of the NO2 stretching mode has been proven to be a good indicator of the solvent polarity; i.e., the vibrational frequency of the NO2 stretching mode changes from 1340 cm-1 in mostly nonpolar solvent such as ethane to 1300 cm-1 in water. The linear relationship between the absorption band center and the vibrational frequency of the NO2 mode, which was observed for conventional liquids in a previous paper (Fujisawa, T.; Terazima, M.; Kimura, Y. J. Chem. Phys. 2006, 124, 184503), holds almost well for all fluids including SCFs and RTILs. On the other hand, the vibrational bandwidth does not show a simple relationship with the absorption band center. The vibrational bandwidths in RTILs are generally larger in comparison with those in conventional liquids with similar polarity scales. Among the RTILs we investigated, the vibrational bandwidth loosely correlates with the molecular size of the anion. A similar dependence on the anion size is also observed for the bandwidth of the absorption spectrum. We have also investigated the excitation wavelength dependence of the Raman shift of the NO2 stretching mode in RTILs. The extent of the dependence on the excitation wavelength in all fluids is well correlated with the vibrational bandwidth.