CLARITY: Centre for Sensor Web Technologies, National Centre for Sensor Research, Dublin City University, Dublin 9, Ireland.
Phys Chem Chem Phys. 2010 Feb 28;12(8):1895-904. doi: 10.1039/b920580b. Epub 2010 Jan 6.
Investigations into the extent of structuring present in phosphonium based ionic liquids (ILs) have been carried out using photochromic molecular probes. Three spiropyran derivatives containing hydroxyl (BSP-1), carboxylic acid (BSP-2) and aliphatic chain (C(14)H(29)) (BSP-3) functional groups have been analysed in a range of phosphonium based ionic liquids and their subsequent physico-chemical interactions were reported. It is believed that the functional groups locate the probe molecules into specific regions based upon the interaction of the functional groups with particular and defined regions of the ionic liquid. This structuring results in thermodynamic, kinetic and solvatochromic parameters that are not predictable from classical solvent models. BSP-1 and BSP-2 exhibit generally negative entropies of activation ranging from -50 J K(-1) mol(-1) to -90 J K(-1) mol(-1) implying relatively low solvent-solute interactions and possible anion interactions with IL polar functional groups. Higher than expected activation energies of 60 kJ mol(-1) to 100 kJ mol(-1) obtained for polar probes maybe be due to IL functional groups competing with the charged sites of the merocyanine (MC) isomer thus reducing MC stabilisation effects. Differences in thermal relaxation rate constants (2.5 x 10(-3) s(-1) in BSP-1 and 3 x 10(-4) s(-1) in BSP-2 in [P(6,6,6,14)][dbsa]) imply that while the polar probe systems are primarily located in polar/charged regions, each probe experiences slightly differing polar domains. BSP-3 entropies of activation are positive and between 30 J K(-1) mol(-1) to 66 J K(-1) mol(-1). The association of the non-polar functional group is believed to locate the spiropyran moiety in the interfacial polar and non-polar regions. The thermal relaxation of the MC form causes solvent reorientation to accommodate the molecule as it reverts to its closed form. Slow thermal relaxation rate constants were obserevd in contrast to high activation energies (5 x 10(-4) s(-1) and 111.91 kJ mol(-1) respectively, for BSP-3 in [P(6,6,6,14)][dbsa]). This may be due to steric effects arising from proposed nano-cavity formation by the alkyl chains in phosphonium based ILs.
已经使用光致变色分子探针对磷鎓基离子液体（ILs）中存在的结构进行了研究。分析了三种含有羟基（BSP-1）、羧酸（BSP-2）和脂肪链（C(14)H(29)）（BSP-3）官能团的螺吡喃衍生物，在一系列磷鎓基离子液体中的理化相互作用。据信，根据官能团与离子液体特定和定义区域的相互作用，官能团将探针分子定位到特定区域。这种结构导致了热力学、动力学和溶剂化颜色参数，这些参数不能从经典溶剂模型中预测。BSP-1 和 BSP-2 表现出一般为负的活化熵，范围为-50 J K(-1) mol(-1) 至-90 J K(-1) mol(-1)，这表明溶剂-溶质相互作用相对较低，可能存在与 IL 极性官能团的阴离子相互作用。对于极性探针，获得的高于预期的活化能为 60 kJ mol(-1) 至 100 kJ mol(-1)，这可能是由于 IL 官能团与内消旋体（MC）的带电位点竞争，从而降低了 MC 稳定化效应。在 [P(6,6,6,14)][dbsa] 中，BSP-1 中的热弛豫速率常数为 2.5 x 10(-3) s(-1)，BSP-2 中的热弛豫速率常数为 3 x 10(-4) s(-1)，这表明虽然极性探针系统主要位于极性/带电区域，但每个探针经历的极性域略有不同。BSP-3 的活化熵为正，范围为 30 J K(-1) mol(-1) 至 66 J K(-1) mol(-1)。非极性官能团的缔合被认为将螺吡喃部分定位在界面极性和非极性区域。MC 形式的热弛豫导致溶剂重新取向以适应分子，因为它恢复到其闭合形式。与高活化能（分别为 5 x 10(-4) s(-1) 和 111.91 kJ mol(-1)，BSP-3 在 [P(6,6,6,14)][dbsa] 中）相比，观察到较慢的热弛豫速率常数。这可能是由于在基于磷鎓的 IL 中，烷基链形成拟纳米腔引起的空间位阻效应。
