PHOTOLUMINESCENCE OF 4,4'-DIAMINOBIPHENYL

Fluorescence solvatochromic shifts of 4,4'-diaminobiphenyl (DABP) were found to be less than those of 4-aminobiphenyl and the difference mai nly occured in hydrogen bonding solvents. This shows that the net effe ct of hydrogen bonding interactions of two amino groups is less than t hat of one amino group. The unusual fluorescence red-shift observed fo r the monocation of DABP relative to the neutral form is not because o f the amino group becoming more basic, but because of a large solvent relaxation in aqueous media. As the entire molecule becomes planar upo n excitation, its behavior is found to be similar to that of 2,7-diami nofluorene in the S-1 state. pK(a) values for various prototropic reac tions in the S-0 and S-1 states were determined and are discussed.