This study explores the excited state prototropic behavior of the fluorophore, 7-hydroxy-4-methylcoumarin (7H4MC), in the [C_nmim][BF₄] (n = 2, 4, 6, 8, 10) series of ionic liquid (IL)–water mixtures at low water contents. In pure IL media, 7H4MC exists in the neutral form in both ground and excited states. However, on addition of water to the ILs, the excited neutral form of the dye is gradually converted to the anionic and the tautomeric species, leading to characteristic changes in the emission spectra. The similarity in the spectral features of 7H4MC in the IL–water system with that in a conventional reverse micelle system rather than with organic solvent–water mixtures, suggests that in the presence of water, the ILs are organized into reverse micelle-like structures with the consequent formation of confined water pockets. The results further suggest that formation of water nanoclusters and the ensuing changes in excited state prototropic behavior of the dye, is facilitated by increase in the alkyl chain length of the IL cation. These propositions are supported by time-resolved fluorescence studies. To the best of our knowledge this is the first report on proton transfer reaction in IL–water mixtures at low water contents. Considering that ILs are useful as solvents and surfactants, and IL–water mixtures in particular have applications in chemical extractions and biocatalysis, an understanding of the structural organization and water pool formation in these systems is quite important. The insights obtained from the prototropic transformations of 7H4MC are significant not only for fundamental self-assembly studies, but also for the development of ILs as chemical reaction media.

中文翻译：

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[C _n mim] [BF ₄ ]系列离子液体-水混合物中7-羟基-4-甲基香豆素的激发态原质性：类似于胶束状水纳米团簇形成的见解†

这项研究探索了荧光团7-羟基-4-甲基香豆素（7H4MC）在[C _n mim] [BF ₄ ]（n= 2、4、6、8、10）系列离子液体（IL）–低水含量的水混合物。在纯IL介质中，7H4MC以中性形式存在，既处于基态又处于激发态。但是，在IL中加水后，染料的激发中性形式逐渐转变为阴离子和互变异构物质，从而导致发射光谱发生特征性变化。IL-水系统中7H4MC的光谱特征与常规反胶束系统（而不是有机溶剂-水混合物）中的7H4MC光谱特征相似，这表明在水的存在下，ILs呈反胶束状结构，具有结果形成了承压水袋。结果进一步表明，水纳米团簇的形成以及随之而来的染料激发态质子行为的变化，IL阳离子的烷基链长度的增加促进了β-内酰胺基的形成。这些命题得到了时间分辨荧光研究的支持。据我们所知，这是低水含量的IL-水混合物中质子转移反应的第一份报告。考虑到ILs可用作溶剂和表面活性剂，尤其是IL-水混合物可用于化学提取和生物催化，因此了解这些系统的结构组织和池形成非常重要。从7H4MC的质子化转化中获得的见解不仅对于基础自组装研究具有重要意义，而且对于将IL作为化学反应介质的发展也具有重要意义。据我们所知，这是低水含量的IL-水混合物中质子转移反应的第一份报告。考虑到ILs可用作溶剂和表面活性剂，尤其是IL-水混合物可用于化学提取和生物催化，因此了解这些系统的结构组织和池形成非常重要。从7H4MC的质子化转化中获得的见解不仅对于基础自组装研究具有重要意义，而且对于将IL作为化学反应介质的发展也具有重要意义。据我们所知，这是关于低水含量的IL-水混合物中质子转移反应的第一份报告。考虑到ILs可用作溶剂和表面活性剂，尤其是IL-水混合物可用于化学提取和生物催化，因此了解这些系统的结构组织和池形成非常重要。从7H4MC的质子化转化中获得的见解不仅对于基础自组装研究具有重要意义，而且对于将IL作为化学反应介质的发展也具有重要意义。尤其是IL-水混合物在化学提取和生物催化中具有应用，了解这些系统中的结构组织和水池形成非常重要。从7H4MC的质子化转化中获得的见解不仅对于基础自组装研究具有重要意义，而且对于将IL作为化学反应介质的发展也具有重要意义。尤其是IL-水混合物在化学提取和生物催化中具有应用，了解这些系统中的结构组织和水池形成非常重要。从7H4MC的质子化转化中获得的见解不仅对于基础自组装研究具有重要意义，而且对于将IL作为化学反应介质的发展也具有重要意义。