A Density Functional Theory Study of an Exciplex: Pyridine and Benzene

Abstract

An exciplex formation of pyridine and benzene complex in cofacial configuration was investigated at time-dependent density functional theory level within Tamm–Dancoff approximation using ωB97X functional in conjunction with 6–311++G(d,p) basis sets. Unlike the benzene excimer, calculated potential energy surfaces for the lowest-lying singlet excited states for this complex show double minima, corresponding to a simple excited complex and an exciplex, respectively. While the former is associated with the localized exciton characterized as the n–π* transition of pyridine, the latter is linked to the significant electronic coupling between the π–π* transitions of constituting individual molecules. Despite its obvious presence, the net charge transfer character from benzene to pyridine is not such significant as expected; wave function delocalization of exciton and hence reduced orbital energy gap are found to play more pivotal role in the exciplex formation of this complex.