Solvent-dependent intramolecular exciplex formation of N-benzyl-N-methylamine and N,N-dibenzylamine

The fluorescence properties of N-benzyl-N-methylamine (BMA) and N,N-dibenzylamine (DBA) have been studied in several solvents of different polarities to examine the nature of the intramolecular interaction between phenyl and amino groups. BMA shows the fluorescence of the phenyl group and DBA shows the fluorescence of the phenyl group and the intramolecular excimer emission in non-polar solvents. New fluorescence bands appeared in the long-wavelength region for BMA and DBA in certain polar solvents. These bands showed red-shifts with increasing solvent polarity. Upon the addition of trichloroacetic acid to the BMA solution in acetonitrile (AN) the intensity of the long-wavelength band decreased and the intensity of the fluorescence of the phenyl group increased. The intensity of the long-wavelength band was low and that of phenyl group fluorescence was high in alcohols compared with those in THF and AN. These findings are caused by the loss of the electron-donation ability of the amino group owing to the protonation and hydrogen-bonding with the alcohol molecule. Similar spectral changes were observed for DBA. These results indicate that the long-wavelength bands can be attributed to the intramolecular exciplexes between phenyl and amino groups. The formation of the complex between the exciplex and a dipolar molecule was observed in THF-AN mixtures.