Intersystem Crossing in Acceptor–Donor–Acceptor Type Organic Photovoltaic Molecules Promoted by Symmetry Breaking in Polar Environments

The intramolecular electron push-pulling effect has been widely applied to manipulate the excited states in organic photovoltaic (OPV) molecules toward efficient photocurrent generation in working devices with bias fields. However, the effect of field induced polar environments on the excited-state dynamics remains largely unexplored. Here, we investigate the polar environment effect on excited dynamics in acceptor-donor-acceptor type OPV molecules dissolved in solvents with different polarities. By combining ultrafast transient absorption spectroscopy and quantum chemical computation, we observe the stabilization of excited states induced by symmetry breaking in the polar solvent in the molecules exhibiting strong electron push-pulling effects. The stabilized excited states undergo faster intersystem crossing processes with reduced singlet-triplet energy gaps. The findings suggest that the dynamics of charge generation and recombination may be controlled by manipulating the polar environment and electron push-pulling effect to improve the device performance.