Dual fluorescence of diphenyl carbazide and benzanilide: effect of solvents and pH on electronic spectra.

The absorption and fluorescence spectra of benzanilide (BA) and diphenyl carbazide (DPC) in solvents of different polarities and pH have been analysed. The spectral characteristics of DPC and BA are compared with diphenyl amine molecule. In water and methanol, a dual fluorescence is observed for both DPC and BA molecules. The normal stokes shifted emission originates from a locally excited pi* electronic state and the large stokes shifted band is due to emission from a twisted intramolecular charge transfer (TICT) state. pH studies show that both monocations and monoanions are non-fluorescent. The excited state acidity constants determined by fluorimetric titration and Förster cycle methods, have been reported and discussed.