Photophysics and rotational dynamics of Nile red in room temperature ionic liquid (RTIL) and RTIL-cosolvents binary mixtures

Abstract

The photophysics and rotational dynamics of nile red (NR) have been studied in neat room-temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl)imide ([emim]+[Tf2N]ˉ) and RTIL-cosolvents binary mixtures with the variation of temperature from 278K to 333K. We have used methanol, acetonitrile, and benzene as a cosolvents. The fluorescence lifetime values of the nile red in RTIL and RTIL-cosolvent binary mixtures are gradually decreased on increasing of temperature in a regular manner. The rotational dynamics of nile red in neat RTIL and RTIL-cosolvents binary mixtures were analyzed using Stokes-Einstein-Debye (SED) hydrodynamic theory and GW-quasihydrodynamic model. We observed that in all cases experimental values of rotational reorientation time exhibits sub-slip behaviour. We have also carried out fluorescence lifetime imaging microscopy (FLIM) study to observed the distribution of lifetime of nile red on the surface of RTIL and RTIL-cosolvents binary mixtures.