Excitation Energy Transport and Concentration Depolarization of Donor Fluorescence in Two-Component Viscous Solutions

The concentration depolarization of the fluorescence of rhodamine B (donor) in the presence of malachite green (acceptor) was investigated in a glycerol-ethanol mixture with constant ratios of the reduced concentrations of the donor and acceptor (system I: γD/γA = 1, system II: γD/γA = 19). A marked effect of the configuration of the active molecules surrounding the successively excited donors upon the emission anisotropy was found in system I, having strong fluorescence quenching and weak migration, whereas in system II, with strong migration and weak fluorescence quenching, this effect is smaller. The results are discussed based on the up-to-date theories of the concentration depolarization of fluorescence.