RATE EXPRESSIONS FOR EXCITATION TRANSFER .4. ENERGY MIGRATION AND SUPEREXCHANGE PHENOMENA

General microscopic mechanisms of electronic excitation (energy) trans fer (EET) in multichromophoric assemblies are investigated. Aspects of superexchange-mediated EET and energy migration (EM) and their contri bution to the efficiency of donor-to-trap energy transport processes i n macromolecules are discussed from a quantum mechanical viewpoint. Th e possibility of superexchange pathways for EM via higher excited stat es of the intermediate chromophores is introduced. The role of quasico herent EM pathways, and how they are manifested in the quantum mechani cal rate expression, is investigated and the significance of contribut ions to the rate arising through quantum mechanical interference betwe en pathways is elucidated. The theory indicates conditions under which coherent EM pathways may significantly increase the efficiency of ene rgy transport and trapping and the applications to natural and synthet ic light-harvesting systems are outlined. (C) 1995 American Institute of Physics.