A Density Functional Theory Study of an Exciplex II: Benzene and Tricyanobenzene

The exciplex of benzene–tricyanobenzene was theoretically investigated at the levels of density functional theory (DFT) and its time‐dependent variation within Tamm–Dancoff approximation (TDA‐DFT) using ωB97X functional and 6–311++G(d,p) basis set. Unlike the benzene and pyridine system studied previously, the charge transfer (CT) character from benzene, the electron donor to tricyanobenzene, the electron acceptor, is observed to be significant in a few low‐lying singlet excited states. Via the crossing and mixing between the states of the same symmetry, however, we also observe the mixed characters between the CT and local excitation (LE) as the intermolecular distance decreases. In the comparison to the benzene–pyridine complex, the enriched CT characters in the low‐lying singlet states stem from the significant energy offsets between the frontier molecular orbitals of benzene and tricyanobenzene, which suppresses their molecular orbital interactions and hence their delocalization.