In this work we test a recently developed method for correlating ground state orbital characteristics with degree of S1 CT in CT co-crystals in the pursuit of uncovering orbital structure-function relationships. We quantify the orbital similarity between donor HOMO and D-A HOMO as well as acceptor LUMO and D-A LUMO to predict the degree of S1 CT in HOMO à LUMO dominated electronic transitions, finding that the degree of orbital similarity positively correlates with degree of CT in the S1 state.