Investigations of the excitation energy transport mechanism in donor-acceptor systems.

Measurements of fluorescence quantum yield ηD/ηoD of Na-fluorescein (donor; D) versus concentration of rhodamine B (acceptor; A) in viscous solutions have been carried out. The donor concentration in these solutions was as follows:C D=2·10(-2) M (system I), 1.5·10(-2) M (II), 10(-2) M (III), 3·10(-3) M (IV), and 5·10(-5) M (V). The experimental results have been compared with current theories of nonradiative electronic energy transfer (NEET). In the case of very strong migration (systems I, II, and III), a significant influence of correlations (between configurations of D and A molecules in the surroundings of successively excited donors) on quantum yield ηD/ηoD has been determined. Experimental values have been found to be clearly higher in comparison with those predicted theoretically. The influence of possible factors on the decrease in the effectiveness of excitation energy transport to traps-acceptors in systems of very strong migration has been discussed.