Majhi Debashis, Sahu Prabhat Kumar, Seth Sudipta, Sarkar Moloy
School of Chemical Sciences, National Institute of Science Education and Research, Bhubaneswar P.O. Jatni, Khurda 752050, Odisha, India.
School of Chemistry, University of Hyderabad, Hyderabad - 500046, India.
Phys Chem Chem Phys. 2016 Aug 10;18(32):22343-54. doi: 10.1039/c6cp03006h.
The rotational diffusion of two organic solutes, 4-(azitidine-1-yl)-7-nitrobenzo[1,2,5]oxadi-azole (ANBD) and 7-nitrobenzo[1,2,5]oxadiazole-4-amine (HNBD), has been examined in 1-ethyl-3-methylimidazolium alkyl sulfate (alkyl = ethyl, hexyl and octyl) ionic liquids with the aim of understanding intermolecular interactions among solute and solvent molecules. Solute-solvent interaction has also been investigated by employing fluorescence, NMR and fluorescence correlation spectroscopy (FCS). The ionic liquids (ILs) having a fixed cationic moiety are chosen to monitor the roles of the alkyl chain length as well as the solute-anion (sulfate) interactions in the rotational diffusion of the solutes in the given ILs. In the present study, two chemically distinguishable solutes with structural similarity in their fluorophore unit are employed so that the difference in the rotational behavior of the solutes, if any, can be correlated with the solute-solvent interactions, and not with other factors like the size of the solutes etc. The steady state absorption and emission data indicate that HNBD and ANBD exist in different microenvironments in both ILs. The rotational diffusion data for both the solutes have been analyzed in light of hydrodynamic and quasi hydrodynamic theories. Interestingly, the rotational dynamics of ANBD is observed to be relatively fast and shows slip hydrodynamics, whereas HNBD exhibits hindered rotation with superstick behavior. The hindered rotation of HNBD as compared to that of ANBD in both ILs has been explained by considering the strong hydrogen bonding interactions between the two N-H groups of HNBD and sulfate anions of ILs. The faster rotation of ANBD with the increasing anion chain length has been explained by invoking quasi hydrodynamic theory. The presence of a specific hydrogen bonding interaction between solute (HNBD) and solvent (ILs) molecules has been confirmed by (1)H-NMR experiments. FCS measurements have independently demonstrated the relatively strong association of HNBD with the present ILs as compared to that of ANBD.
为了理解溶质与溶剂分子之间的分子间相互作用，研究了两种有机溶质4-(氮杂环丁烷-1-基)-7-硝基苯并[1,2,5]恶二唑（ANBD）和7-硝基苯并[1,2,5]恶二唑-4-胺（HNBD）在1-乙基-3-甲基咪唑烷基硫酸盐（烷基 = 乙基、己基和辛基）离子液体中的旋转扩散。还通过荧光、核磁共振和荧光相关光谱（FCS）研究了溶质 - 溶剂相互作用。选择具有固定阳离子部分的离子液体（ILs）来监测烷基链长度以及溶质 - 阴离子（硫酸盐）相互作用在给定离子液体中溶质旋转扩散中的作用。在本研究中，使用了两种在荧光团单元结构上相似但化学性质可区分的溶质，以便溶质旋转行为的差异（如果有的话）可以与溶质 - 溶剂相互作用相关联，而不是与溶质大小等其他因素相关联。稳态吸收和发射数据表明，HNBD和ANBD在两种离子液体中都存在于不同的微环境中。根据流体动力学和准流体动力学理论分析了两种溶质的旋转扩散数据。有趣的是，观察到ANBD的旋转动力学相对较快，并表现出滑移流体动力学，而HNBD表现出受阻旋转和超粘性行为。通过考虑HNBD的两个N - H基团与离子液体的硫酸根阴离子之间的强氢键相互作用，解释了在两种离子液体中HNBD与ANBD相比旋转受阻的现象。通过准流体动力学理论解释了随着阴离子链长度增加ANBD旋转更快的现象。通过¹H - NMR实验证实了溶质（HNBD）与溶剂（离子液体）分子之间存在特定的氢键相互作用。FCS测量独立地证明了与ANBD相比，HNBD与当前离子液体的缔合相对较强。
