Ground State Orbital Analysis Predicts S1 Charge Transfer in Donor–Acceptor Materials

Donor-acceptor (D-A) materials, such as D-A co- crystals and D-A copolymers, can exhibit a wide range of unique photophysical properties with applications in next-generation optoelectronics. The properties of D-A dimer models, computed with electronic structure calculations, are often employed to predict properties of D-A materials. One of the most important D-A dimer quantities is the degree of charge transfer (DCT) in the S1 state, which correlates with properties such as fluorescence lifetimes and intersystem crossing rates. Predictive metrics of the S1 DCT generally require an excited state quantum chemistry calculation. Presented here is a novel metric for predicting the degree of charge transfer (DCT) in the S1 electronic state of D-A materials, computed solely with ground state orbital analysis. This metric computes the average of two quantities: (1) the degree of similarity between the highest occupied molecular orbital (HOMO) in the donor molecule and the D-A complex and (2) the degree of similarity between the lowest occupied molecular orbital (LUMO) in the acceptor molecule and the D-A complex. A linear relationship between this similarity metric and the DCT in the S1 state (HOMO → LUMO transition) is demonstrated for a data set of 31 D-A dimers. The integration of this novel orbital structure- function relationship into high-throughput screening methods is discussed alongside best practices for choosing molecular geometries and quantifying the DCT.