SOLVENT EFFECT ON THE EXCITED-STATE BEHAVIOR OF DONOR-ACCEPTOR-SUBSTITUTED BIARYLS

The fluorescence properties of two biaryl donor-acceptor compounds (4- dimethylamino-4'-cyanobiphenyl (DMACNB) and 4-dimethylanilino-1-cyanon aphthalene (DMACNN)) were compared in solvents of different polarity. Low temperature, steady state spectra were also studied in non-polar a nd polar media. The transient Stokes shifts measured with 30 ps excita tion in 1-propanol and 1-hexanol at room temperature show that the cha rge transfer process is controlled by the dynamics of solvation. A lar ge decrease in the radiative rate constant as a function of the solven t polarity and as a function of time in 1-hexanol solution was observe d for DMACNN, whereas this effect was not significant in the case of D MACNB. These differences have been related to the larger steric hindra nce to coplanarity in the phenylnaphthalene derivative with respect to that in the substituted biphenyl.