Abstract
Abstract: Steady state and time-resolved fluorescence behavior of coumarin153(C153) in bis(1-methyl-1H-imidazol-3-ium-3-yl)dihydroborate cation containing room temperature ionic liquid and its mixture with dimethylformamide (DMF) has been investigated. Density functional calculations on the present ionic liquid have been carried out to have ground state structural information of this system. C-H···N and C-H···O hydrogen bonding interactions between cationic and anionic moiety of the present ionic liquid has been observed. Steady state absorption and emission spectral profiles of C153 are found not to be influenced by the polar cosolvent. Time-resolved fluorescence anisotropy experiments show that the rotational motion of the probe becomes faster in presence of DMF. During time dependent dynamic Stokes shift measurements in ionic liquid-DMF mixtures, the average solvation time is found to decrease with the addition of DMF to the ionic liquid. The decrease in both average solvation and rotational time of probe molecule upon gradual addition of polar organic co-solvent is attributed to the lowering of bulk viscosity of the medium.
Highlights
In recent years, room-temperature ionic liquids (RTILs) have drawn great attention due to its versatile applications in the fields of chemical, material and biological sciences [1, 2]
Over the past few years, mixed ionic liquid-cosolvent systems are found to be extremely useful in several new applications, such as organic synthesis [14], catalysis [15], polymerization processes [16], extraction of solutes from solvent [17, 18] etc
Keeping in mind the uses of RTIL-cosolvent systems in new potential applications, it is of paramount importance to have thorough understanding of the roles of cosolvents that they play in governing the properties of RTILs
Summary
Room-temperature ionic liquids (RTILs) have drawn great attention due to its versatile applications in the fields of chemical, material and biological sciences [1, 2]. It may be mentioned that Sarkar and coworkers’ [8,9,10,11] have studied the effects of polar solvents such as, acetonitrile, water and methanol on the dynamics of solvation of ammonium and imadazolim-based ionic liquids These studies have demonstrated that addition of cosolvents in RTILs affects both the solvent relaxation as well as solute rotation. We would like to take a note here that, RTIL-cosolvent systems are known to be micro-heterogeneous [34,35,36,37] In this regard, it would be an interesting study to find a relationship between average solvation and rotational time and medium viscosity. For G-factor calculation, the same procedure was adopted, but with 5 cycles and horizontal polarization of the exciting laser beam
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