Anilino-Substituted Multicyanobuta-1,3-diene Electron Acceptors: TICT Molecules with Accessible Conical Intersections

A theoretical investigation based on DFT, TD-DFT, and CASSCF/CASPT2 methods has been carried out to elucidate the photophysics of two anilino-substituted pentacyano- and tetracyanobuta-1,3-dienes (PCBD and TCBD, respectively). These molecules exhibit exceptional electron-accepting properties, but their effective use in multicomponent systems for photoinduced electron transfer is limited because they undergo ultrafast (∼1 ps) radiationless deactivation. We show that the lowest-energy excited states of these molecules have a twisted intramolecular charge-transfer character and deactivate to the ground state through energetically accessible conical intersections (CIs). The topology of the lowest-energy CI, analyzed with a linear interpolation of the two branching-space vectors (g and h), indicates it is a sloped CI, ultimately responsible for the ultrafast deactivation of this class of compounds.