Fluorescence anisotropy of ketocyanine dyes in homogeneous and heterogeneous media. Estimation of micellar microviscosity

Abstract

Fluorescence anisotropies (r) of two ketocyanine dyes have been determined in homogeneous solvents (pure and mixed binary) and in micellar media. For pure solvents the rotational reorientation times have been calculated and compared with the values calculated using the modified Stokes–Einstein–Debye equation. The discrepancy between the two values has been discussed in terms of dielectric factors. Ethanol–water and ethanol–octan-1-ol binary mixtures exhibit ideal solvation behaviour and the anisotropy values are well represented by Perrin's equation. For a protic–aprotic solvent mixture, non-ideal solvation behavior is observed which has been explained as due to solute–solvent as well as solvent–solvent interaction for the two component solvents. The microviscosity around a micellar region and the related activation energy has been measured from the r values in these media at various temperatures.