Exciton Percolation, Tunneling and ThermaIization

Abstract

New experimental data are presented for triplet and singlet naphthalene exciton transport in ternary molecular crystals: isotopic mixed guest-host systems with a small added amount of sensor (supertrap). The focus is on the effects of the following parameters: Time, temperature, concentration and energy denominators (for guest-host, guest-guest, and guest-sensor energy levels). We find that, under the proper conditions, both singlet and triplet measurements are consistent with a dynamic exciton percolation model, i.e. where a guest cluster is defined by the extent of long-range exciton-superexchange (tunneling) interactions, and where the interaction cut-off is determined by the overall time available for transport (i.e., the lifetime of the excitation). The roles of temperature, lattice heterogeneity, and suggested models involving an Anderson-Mott mobility edge are discussed. We also emphasize the distinction between intra and inter-domain energy transfer and discuss the localization vs. delocalization dichotomy as well as dynamic vs. static percolation.