Unusual luminescence characteristics of aminobiphenyls

Analysis of fluorescence solvatochromic shifts of ortho, meta and para aminobiphenyls reveals that the change in dipolemoment of m-aminobiphenyl on excitation is more when compared to other isomers. This change is due to the resonance interaction of unsubstituted phenyl ring with NH 2 group at meta position in the excited singlet state. The fluorimetric titration curves of three aminobiphenyls are found to be different from each other. The stretched sigmoidal curves obtained for m-aminobiphenyl indicates that the rates of proton transfer in S 1 state are comparable to the rates of fluorescence.