ANOMALOUS DUAL FLUORESCENCE OF BENZANILIDE

The absorption and fluorescence spectra of benzanilide and N-methylben zanilide have been investigated in solution and low-temperature glasse s and assigned with the aid of ZINDO calculations. The anomalous dual fluorescence observed by previous workers has been assigned to the two lowest singlet states of benzanilide. The lower energy n,pi state is populated by excitation in the long-wavelength tail of the absorption band. Its fluorescence is readily detected in low-temperature glasses and at room temperature in aromatic solvents. Large NMR solvent-induc ed shifts provide evidence for ground-state complex formation of benza nilide with aromatic solvents. The higher energy iz,.pi,pi state is p opulated by excitation of an allowed transition. It undergoes twisting about the amide C-N bond to form a fluorescent twisted intramolecular charge-transfer state with a maximum of 520 nm in benzene solution. I n rigid glasses twisting to form the twisted charge-transfer state can not occur, and the pi,pi state undergoes internal conversion to the l ower energy n,pi state.