Rotational Dynamics of Imidazolium-Based Ionic Liquids: Do the Nature of the Anion and the Length of the Alkyl Chain Influence the Dynamics?

Choline chloride and ethylene glycol based deep eutectic solvent (DES) versus hydroxyl functionalized room temperature ionic liquids (RTILs): assessing the differences in microscopic behaviour between the DES and RTILs

With the aim of understanding the differences in the behavior of deep eutectic solvents (DESs) and room temperature ionic liquids (RTILs) in terms of their structure, dynamics, and intra- and intermolecular interactions, three different ILs and one DES having similar functionalities (hydroxyl) have been investigated by using both ensembled average and single-molecule spectroscopic techniques. Specifically, for this purpose, a choline chloride based DES (ethaline) and three hydroxyl functionalized ILs (1-(2-hydroxyethyl)-3-imidazolium bis(trifluoromethanesulfonyl)imide ([OHEMIM][NTF₂]), N-(2-hydroxyl ethyl)-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([OHEMPy][NTf₂]), and N-(2-hydroxyethyl)-N,N-dimethylpropan-1-aminium bis(trifluoromethanesulfonyl)imide ([OHC3CH][NTf₂])) are employed and investigated by EPR, time-resolved fluorescence, NMR and FCS studies. Estimation of polarity through EPR spectroscopy has revealed that the hydroxyl ILs employed in these studies are hyper-polar (close to water) in nature, whereas the polarity of the DES is found to be close to those of aliphatic polyhydroxy-alcohols. Interestingly, both time-resolved fluorescence anisotropy and FCS studies on these systems have suggested that the hydroxyl ILs are more dynamically heterogeneous than the DES. More interestingly, PFG-NMR measurements have indicated that the fluid structure of ethaline is relatively more associated as compared to those of the ILs despite the fact that all the cations have the same hydroxyl functionalities. All these investigations have essentially demonstrated that, despite having similar functionalities, both the DES and hydroxyl ILs employed in the present study exhibit microscopic behaviours that are significantly different from each other, indicating the interplay of various intermolecular interactions within the constituent species in governing the behaviours of these solvent systems.

Understanding the Behavior of Monocationic and Dicationic Room-Temperature Ionic Liquids through Resonance Energy-Transfer Studies

The present work has been undertaken with an objective to understand the differences in the local structural organization of imidazolium-based monocationic ionic liquids (MILs) and dicationic ionic liquids (DILs) through resonance energy-transfer (RET) studies. In this study, a neat IL is used as a donor and a charged species rhodamine 6G (R6G) is used as an acceptor unit because of the fact that they satisfy the spectroscopic criteria that are needed for an RET event to take place. Additionally, R6G, being a charged species, is expected to facilitate the electrostatic interactions with the ILs which are also charged. Specifically, two imidazolium-based germinal DILs and their monocationic counterparts are used for the present investigations. Additionally, the studies are carried out in some selected MILs where the lengths of the alkyl side chains are kept unchanged for MILs and DILs. Interestingly, the present data reveal that the RET interaction is more favorable for DILs than for MILs, even though the DILs are relatively bulkier than their monocationic counterparts. More interestingly, the RET interaction is also found to be more favorable for DILs than for MILs, where the length of the alkyl group is kept fixed for MILs and DILs. The result of the present study delineates that the alkyl chain length on the cation is not the sole factor contributing to the RET outcomes for DILs and MILs but the local structure of DILs also contributes significantly to the same. The current investigation clearly indicates that DILs have a more compact local structure than that of MILs. Essentially, the current study highlights that a cost-effective, noninvasive technique such as RET is quite effective in capturing the differences in the nanostructural organization of MILs and DILs.

Capturing the effect of [PF3(C2F5)3]−vs. [PF6]−, flexible anion vs. rigid, and scaled charge vs. unit on the transport properties of [bmim]+-based ionic liquids: a comparative MD study

Effect of [PF₃(C₂F₅)₃]⁻vs. [PF₆]⁻, flexible anion vs. rigid, and scaled charge vs. unit on the transport properties of ILs.

Probing the microscopic structural organization of neat ionic liquids (ILs) and ionic liquid-based gels through resonance energy transfer (RET) studies

With the aim to understand the role of the ionic constituents of ionic liquids (ILs) in their structural organization, resonance energy transfer (RET) studies between ionic liquids (donor) and rhodamine 6G (acceptor) have been investigated.