Solvation dynamics of Nile Red in a room temperature ionic liquid using streak camera

Time-resolved fluorescence behavior of Nile Red (NR) has been studied using a streak camera in a room temperature ionic liquid, [bmim]PF6. Wavelength dependent fluorescence decay and time dependent fluorescence Stokes shift have been observed. The time-correlated spectral shift function, C(t), indicator for solvation dynamics of NR in [bmim]PF6, is found to be biexponential with two well-separated time constants: 0.13 and 1.25 ns. The short and the long component of the dynamics have been explained in terms of the translational motion of the anion and a collective motion of the cation and anion, respectively. The effect of two different conformers of the cation of this room temperature ionic liquid, as revealed in the recent studies, on the long time constant is also discussed.