A theoretical study of the intramolecular charge transfer in 4-(dimethylamino)benzethyne

Abstract

We have investigated the non-adiabatic relaxation processes occurring in the singlet manifold of 4-(dimethylamino)benzethyne (DMABE), a molecule isoelectronic with 4-(dimethylamino)benzonitrile (DMABN) but lacking its characteristic dual fluorescence, using multireference perturbation theory methods. The results obtained point out to the existence of a two-fold decay mechanism in which the population of the initially accessed L_a state bifurcates towards a locally excited (LE) and a πσ* state. Further relaxation to an emitting intramolecular charge transfer (ICT) state is impeded due to the presence of pronounced energy barriers along their associated potential energy surfaces. These results provide further evidence of the role of πσ* states in the non-adiabatic relaxation processes of dialkylaminobenzonitriles.