Center for Functional Materials and Nanomolecular Science, Jacobs University , Campus Ring 1, D-28759 Bremen, Germany.
J Am Chem Soc. 2014 Apr 23;136(16):6136-41. doi: 10.1021/ja502527y. Epub 2014 Apr 15.
Femtosecond time-resolved coherent anti-Stokes Raman scattering (CARS) is used as a probe for monitoring the vibrational dynamics of room temperature ionic liquids (ILs). The experiments are performed on a series of 1,3-dialkylimidazolium ILs containing the bis(trifluoromethylsulfonyl)imide [NTf2] anion. The effect of methylation of the cationic C2 position on the dephasing time is studied analyzing [NTf2]-ILs of 1-ethyl-3-methylimidazolium [EMIM], 1-ethyl-2,3-dimethylimidazolium [EMMIM], 1-butyl-3-methylimidazolium [BMIM], and 1-butyl-2,3-dimethylimidazolium [BMMIM]. Raman coherences are excited around ∼1400 cm(-1), and the vibrational dephasing of the modes in the fingerprint region is monitored as a function of time. The results indicate that vibrational energy transfer occurs governed by the interionic interactions. This is suggested by mode beating involving vibrations beyond the excitation spectrum as well as systematic differences in the temporal dephasing behavior. In contrast, the length of the cationic alkyl side chain has a negligible impact on the vibrational dynamics.
飞秒时间分辨相干反斯托克斯拉曼散射（CARS）被用作监测室温离子液体（ILs）振动动力学的探针。实验在一系列含双（三氟甲烷磺酰基）亚胺 [NTf2] 阴离子的 1,3-二烷基咪唑 ILs 上进行。通过分析 1-乙基-3-甲基咪唑 [EMIM]、1-乙基-2,3-二甲基咪唑 [EMMIM]、1-丁基-3-甲基咪唑 [BMIM] 和 1-丁基-2,3-二甲基咪唑 [BMMIM] 的 [NTf2]-ILs，研究了阳离子 C2 位置甲基化对退相时间的影响。在 ∼1400cm(-1) 附近激发拉曼相干，作为时间函数监测指纹区域模式的振动退相。结果表明，振动能量转移是由离子间相互作用控制的。这是通过涉及激发光谱之外的振动的模式拍频以及时间退相行为的系统差异来表明的。相比之下，阳离子烷基侧链的长度对振动动力学几乎没有影响。
