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

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 c ompared with the values calculated using the modified Stokes-Einstein-Debye equation. The discrepancy between the two values has been discussed in ter ms of dielectric factors. Ethanol-water and ethanol-octan-1-ol binary mixtu res exhibit ideal solvation behaviour and the anisotropy values are well re presented by Perrin's equation. For a protic-aprotic solvent mixture, non-i deal solvation behavior is observed which has been explained as due to solu te-solvent as well as solvent-solvent interaction for the two component sol vents. The microviscosity around a micellar region and the related activati on energy has been measured from the r values in these media at various tem peratures.