Mahapatra Amita, Chakraborty Manjari, Barik Sahadev, Sarkar Moloy
School of Chemical Sciences, National Institute of Science Education and Research, HBNI, P.O. Jatni, Khurda, 752050, Bhubaneswar, Odisha, India.
Phys Chem Chem Phys. 2021 Sep 29;23(37):21029-21041. doi: 10.1039/d1cp02790e.
With an aim to understand the difference in the behaviour of imidazolium and pyrrolidinium-based dicationic ionic liquids (DILs) in terms of the intermolecular interactions, microscopic-structure and dynamics, two DILs, the imidazolium-based 1,9-bis(3-methylimidazolium-1-yl)nonane bis(trifluoromethanesulfonyl)imide and the pyrrolidinium-based 1,9-bis(1-methylpyrrolidinium-1-yl)nonane bis(trifluoromethanesulfonyl)imide, have been synthesized and subsequently investigated by exploiting combined steady sate and time resolved fluorescence, electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) spectroscopic techniques. Data obtained for DILs have also been compared with their corresponding mono-cationic counterpart (MILs) to evaluate and understand the distinctive characteristics of the DILs in contrast with the corresponding MILs. Steady state emission and EPR data have revealed that the pyrrolidinium-based DIL is slightly less polar than the imidazolium-based DIL. Temperature-dependent fluorescence anisotropy decay of two probes, perylene and MPTS (8-methoxypyrene-1,3,6-trisulfonate), has been measured in DILs as well as in MILs. Solute-solvent coupling constants obtained from the experimentally measured rotational correlation times with the aid of Stokes-Einstein-Debye hydrodynamic theory have indicated appreciable differences in the dynamics of both the solutes on going from MILs to DILs. More interestingly, the outcome of the NMR study has suggested that the alkyl spacer chain in the imidazolium-based DIL exists in the folded form, but the pyrrolidinium-based DIL remains in the straight chain conformation. Inherently, the outcomes of all of these studies have depicted that the microscopic structural organisations in imidazolium and pyrrolidinium-based DILs are different from each other as well as from their respective mono-cationic counterparts.
为了从分子间相互作用、微观结构和动力学方面理解咪唑鎓基和吡咯烷鎓基双阳离子离子液体（DILs）行为的差异，合成了两种DILs，即咪唑鎓基的1,9 - 双（3 - 甲基咪唑鎓 - 1 - 基）壬烷双（三氟甲磺酰）亚胺和吡咯烷鎓基的1,9 - 双（1 - 甲基吡咯烷鎓 - 1 - 基）壬烷双（三氟甲磺酰）亚胺，随后利用稳态和时间分辨荧光、电子顺磁共振（EPR）和核磁共振（NMR）光谱技术对其进行了研究。还将DILs获得的数据与其相应的单阳离子对应物（MILs）进行了比较，以评估和理解DILs与相应MILs相比的独特特性。稳态发射和EPR数据表明，吡咯烷鎓基DIL的极性略低于咪唑鎓基DIL。在DILs以及MILs中测量了两种探针（苝和MPTS（8 - 甲氧基芘 - 1,3,6 - 三磺酸盐））的温度依赖性荧光各向异性衰减。借助斯托克斯 - 爱因斯坦 - 德拜流体动力学理论从实验测量的旋转相关时间获得的溶质 - 溶剂耦合常数表明，从MILs到DILs时，两种溶质的动力学存在明显差异。更有趣的是，NMR研究结果表明，咪唑鎓基DIL中的烷基间隔链以折叠形式存在，但吡咯烷鎓基DIL保持直链构象。本质上，所有这些研究的结果都表明，咪唑鎓基和吡咯烷鎓基DILs中的微观结构组织彼此不同，也与其各自的单阳离子对应物不同。
