Model studies of spectral and photophysical characteristics of donor-acceptor-polyenes: dimethylamino-cyano-diphenylbutadiene

4-Dimethylamino-4′-cyano-1,4-diphenylbutadiene (DCB) and 4-dimethylamino-2,6-dimethyl-4′-cyano-1,4-diphenylbutadiene (DMDCB) have been photophysically characterized. Quantum chemical calculations were performed for comparison. The fluorescence quantum yields increase with increasing solvent polarity and decreasing temperature. It is concluded that the lowest excited state is a strongly allowed and highly dipolar π,π* state in polar solvents, and nonradiative deactivation is reduced. This occurs similarly in both compounds. More specifically, the two methyl groups in DMDCB do not enhance the nonradiative decay. This suggests that neither a fluorescent nor a nonfluorescent TICT state is involved in DCB and DMDCB.