Radiation & Photochemistry Division, Bhabha Atomic Research Centre , Trombay, Mumbai 400 085, India.
J Phys Chem B. 2013 Oct 10;117(40):12261-7. doi: 10.1021/jp4078079. Epub 2013 Sep 26.
Rotational diffusion of a nonpolar solute 9-phenylanthracene (9-PA) and a cationic solute rhodamine 110 (R110) has been examined in a series of 1-alkyl-3-methylimidazolium (alkyl = octyl, decyl, dodecyl, tetradecyl, hexadecyl, and octadecyl) bis(trifluoromethylsulfonyl)imides to understand the influence of alkyl chain length on solute rotation. In this study, reorientation times (τr) have been measured as a function of viscosity (η) by varying the temperature (T) of the solvents. These results have been analyzed using the Stokes-Einstein-Debye (SED) hydrodynamic theory along with the ones obtained for the same solutes in 1-alkyl-3-methylimidazolium (alkyl = methyl, ethyl, propyl, butyl, and hexyl) bis(trifluoromethylsulfonyl)imides (Gangamallaiah and Dutt, J. Phys. Chem. B 2012, 116, 12819-12825). It has been noticed that the data for 9-PA and R110 follows the relation τr = A(η/T)(n) with A being the ratio of hydrodynamic volume of the solute to the Boltzmann constant and n = 1 as envisaged by the SED theory. However, upon increasing the alkyl chain length from methyl to octadecyl significant deviations from the SED theory have been observed especially from the octyl derivative onward. From methyl to octadecyl derivatives, the value of A decreases by a factor of 3 for both the solutes and n by a factor of 1.4 and 1.6 for 9-PA and R110, respectively. These observations have been rationalized by taking into consideration the organized structure of the ionic liquids, whose influence appears to be pronounced when the number of carbon atoms in the alkyl chain attached to the imidazolium cation exceeds eight.
非极性溶质 9-苯基蒽（9-PA）和阳离子溶质罗丹明 110（R110）在一系列 1-烷基-3-甲基咪唑（烷基=辛基、癸基、十二烷基、十四烷基、十六烷基和十八烷基）双（三氟甲烷磺酰）亚胺中的旋转扩散已被研究，以了解烷基链长度对溶质旋转的影响。在这项研究中，通过改变溶剂的温度（T），测量了重取向时间（τr）作为粘度（η）的函数。这些结果已经使用 Stokes-Einstein-Debye（SED）流体动力学理论进行了分析，同时还对相同溶质在 1-烷基-3-甲基咪唑（烷基=甲基、乙基、丙基、丁基和己基）双（三氟甲烷磺酰）亚胺（Gangamallaiah 和 Dutt，J. Phys. Chem. B 2012, 116, 12819-12825）中获得的结果进行了分析。已经注意到，9-PA 和 R110 的数据遵循关系 τr = A(η/T)(n)，其中 A 是溶质的流体力学体积与玻尔兹曼常数的比值，n = 1，正如 SED 理论所设想的那样。然而，随着烷基链长度从甲基增加到十八烷基，特别是从辛基衍生物开始，观察到与 SED 理论的显著偏差。对于两种溶质，从甲基到十八烷基衍生物，A 的值降低了 3 倍，n 分别降低了 1.4 和 1.6 倍。这些观察结果通过考虑离子液体的组织结构得到了合理化，当连接到咪唑阳离子的烷基链中的碳原子数超过八个时，离子液体的影响似乎更为显著。
