Direct and reverse energy transport in systems of monomers and imperfect traps: Monte Carlo simulations

A Monte Carlo simulation of the concentration dependence of the fluorescence quantum yield _M and emission anisotropyr _M of a system containing dye molecules in the form of monomers M and clusters T (statistical pairs and trimers) playing the role of the imperfect traps for nonradiative excitation energy transfer (NET) has been carried out. The simulation has been made for determined values of Förster critical distancesR ₀ ^MM andR ₀ ^MT and for several values ofR ₀ ^TM andR ₀ ^TT , assuming that the energy may be transferred from M^* to T as well as from T^* to M (reverse nonradiative energy transfer, RNET). It was shown that the RNET process in the range of high concentrations may strongly change the values ofr _M as well as those of _M. For emission anisotropyr _M an effect of repolarization was observed which decreases rapidly with increasingR ₀ ^TM andR ₀ ^TT . A very good agreement between the simulation results of _M and the theoretical model with no adjustable parameters was found. In the model, the RNET process and influence of correlation between active molecules on energy migration among monomers were taken into account.