Osawa K, Hamamoto T, Fujisawa T, Terazima M, Sato H, Kimura Y
Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
J Phys Chem A. 2009 Apr 2;113(13):3143-54. doi: 10.1021/jp8111606.
Raman spectra of the C[triple bond]N stretching vibration of p-aminobenzonitrile (ABN) have been investigated in water, methanol, and cyclohexane under sub- and supercritical conditions, and in acetonitrile under subcritical condition. In all solvent fluids covering the supercritical region, the vibrational frequency of the C[triple bond]N stretching mode decreased with increasing solvent density from the gaseous region to the medium density region rho(r) approximately = 2, where rho(r) is the reduced density by the critical density of the solvent. However, from the medium density region to the higher density region, the vibrational frequency turned to increase with the solvent density. The temperature-induced low frequency shift of the C[triple bond]N stretching Raman band was also ascertained by the measurement of the temperature dependence of Raman spectrum of ABN vapor above 543 K. The electronic absorption spectra in the UV region of ABN were also measured under the same experimental conditions. The absorption peak energies decreased with an increase of the solvent density, except in water above rho(r) = 2.8. The vibrational frequency shift in cyclohexane was explained by a sum of contributions of the repulsive interaction, the mean field attractive interaction, and the pure temperature effect probably due to the hot-band contribution. The residual frequency shift after the subtraction of the repulsive and temperature effects in water and methanol showed the low frequency shift with increasing solvent density from rho(r) congruent with 0 to 2.8. However, above rho(r) congruent with 2.8 in water, the residual shift showed a high frequency shift with increasing solvent density. The electronic state calculations based on the PCM model using the density functional theory (DFT) indicated that the solvent polarity change caused the low frequency shift of the C[triple bond]N stretching mode, which was also correlated with the shift of the electronic absorption spectrum. The results of the DFT calculations on the cluster of ABN with water molecules and the molecular dynamics simulations indicated that the high frequency shift of the C[triple bond]N stretching mode in water above rho(r) congruent with 2.8 could be due to the hydrogen bonding between water and ABN.
对对氨基苯甲腈（ABN）中C≡N伸缩振动的拉曼光谱，已在亚临界和超临界条件下的水、甲醇和环己烷中，以及亚临界条件下的乙腈中进行了研究。在覆盖超临界区域的所有溶剂流体中，C≡N伸缩模式的振动频率随着溶剂密度从气态区域增加到中等密度区域ρr≈2（其中ρr是溶剂临界密度下的折合密度）而降低。然而，从中等密度区域到更高密度区域，振动频率随溶剂密度增加而升高。通过测量543K以上ABN蒸汽拉曼光谱的温度依赖性，也确定了C≡N伸缩拉曼带的温度诱导低频位移。在相同实验条件下，还测量了ABN在紫外区域的电子吸收光谱。除了在ρr = 2.8以上的水中，吸收峰能量随溶剂密度增加而降低。环己烷中的振动频率位移可通过排斥相互作用、平均场吸引相互作用以及可能由于热带贡献的纯温度效应的贡献之和来解释。扣除水和甲醇中的排斥和温度效应后的残余频率位移表明，随着溶剂密度从ρr≈0增加到2.8，频率发生低频位移。然而，在水中ρr≈2.8以上时，残余位移随着溶剂密度增加而呈现高频位移。基于密度泛函理论（DFT）使用PCM模型的电子态计算表明，溶剂极性变化导致C≡N伸缩模式的低频位移，这也与电子吸收光谱的位移相关。对ABN与水分子簇的DFT计算结果和分子动力学模拟表明，在水中ρr≈2.8以上时，C≡N伸缩模式的高频位移可能是由于水与ABN之间的氢键作用。
