Molecular reorientation dynamics of polar dye probes in tertiary-butyl alcohol-water mixtures

The rotational motion of the four dye probe molecules-nile blue and thionine (monocations), resorufin (monoanion), and nile red (polar but neutral) have been investigated in aqueous mixtures of tertiary-butyl alcohol using picosecond fluorescence depolarization spectroscopy. The simple hydrodynamic theory due to Stokes-Einstein-Debye is unable to describe the entire profile of the plot of rotational reorientation time vs viscosity, but is adequate in the water rich region (low viscosity). If the dielectric friction theory proposed for pure solvents is considered, then it is possible to mimic the bivalued profile seen in the alcohol rich region (high viscosity). The inability to produce a satisfactory fit over the entire composition range possibly demands a suitable dielectric friction theory for binary mixtures