Dynamics of solvent and rotational relaxation of coumarin-153 in room-temperature ionic liquid 1-butyl-3-methyl imidazolium tetrafluoroborate confined in poly(oxyethylene glycol) ethers containing micelles

We have investigated solvent and rotational relaxation of coumarin 153 (C-153) in room-temperature ionic liquid (RTILs) 1-butyl-3-methyl-imidazolium tetrafluoroborate ([bmim][BF4]) and the ionic liquid confined in alkyl poly(oxyethylene glycol) ethers containing micelles. We have used octaethylene glycol monotetradecyl ether (C14E8) and octaethylene glycol monododecyl ether (C12E8) as surfactants. In the [bmim][BF4]-C14E8 micelle, we have observed only a 22% increase in solvation time compared to neat [bmim][BF4], whereas in the [bmim][BF4]-C12E8 system, we have observed similar to 57% increase in average solvation time due to micelle formation. However, the slowing down in solvation time on going from neat RTIL to RTIL-confined micelles is much smaller compared to that on going from water to water confined micellar aggregates. The 22-57% increase in solvation time is attributed to the slowing down of collective motions of cations and anions in micelles. The rotational relaxation times become faster in both the micelles compare to neat [bmim][BF4].