Tuning Exciton Diffusion in Organic Semiconductors through Hybridization with Charge-Transfer Excitations

The interplay between Frenkel (FE) excitons and charge-transfer (CT) states crucially impacts exciton transport in organic molecular aggregates. Using large-scale nonadiabatic surface hopping dynamics on Holstein-type Hamiltonians parametrized for realistic systems, we here show that exciton diffusion strongly depends on the FE-CT energy offset (Δ<i>E</i>) and the sign pattern of excitonic and electronic couplings. Hybridization at the bottom of the exciton band (H_- and J₊) promotes delocalized states with moderate CT character (30-50%), boosting diffusion coefficients by up to an order of magnitude. In contrast, hybridization at the top of the band (H₊ and J_-) leads to stronger localization and reduced transport. These trends persist even under strong vibronic coupling, where band-based descriptions fail, highlighting robust design principles for enhancing exciton mobility in organic materials.