Dexter energy transfer pathways

Significance Controlling the dynamics of excitons—including their transport, fission, fusion, and free carrier generation—presents a central challenge in energy science, optoelectronics, and photobiology. We develop a coupling-pathway theory for triplet energy transfer, a process controlled by the structure of the medium between donor and acceptor sites, and find two competing coupling pathway mechanisms. At shorter distances or high tunneling gaps, the electron and hole move sequentially from donor to acceptor, accessing donor–acceptor charge-transfer exciton virtual states; at longer distances or lower tunneling gaps, virtual exciton states of the bridge mediate the transport. Molecular design strategies can leverage these competing mechanisms and their distinctive dependences on molecular structure.