Solvent effect dependence of the dual fluorescence of N,N-dimethylbenzodiazepine

N,N-dimethylbenzodiazepine exhibits two fluorescence emission (Fa and Fn) bands in protic solvents and one (Fn band) in aprotic solvents. These bands are assigned on the basis of the absorption, emission solvent effects and lifetimes and yield quantum fluorescence. The abnormal fluorescence (Fa) observed in protic solvents is attributed to an intermolecular interaction between solute and solvent molecules in the excited state (exciplex formation). Experimental results show a dipole moment difference between the ground and the Sn and Sa exited states levels from which the molecule emits the two fluorescence.