Electronic structure of donor or acceptor substituted linear polyenes

Vibrationally resolved optical spectra, fluorescence decay times, and fluorescence quantum yields have been measured for all-trans diphenyloctatetraene and all-trans diphenyloctatetraene substituted in the para position(s) of the phenyl ring(s) with an electron donor (MeO) or (and) and electron acceptor (CN). The electronic excitation energies, S0–S1 and S0–S2 transition dipoles and vibrational properties of the spectra provide a detailed picture of the effects of donor–acceptor substitution on the S0, S1, and S2 states. The electronic excitation energies are well fit by a simple parametrized quantum-mechanical model for polyene electronic structure which is used to estimate substituent-induced shifts in π-electron density in the S0, S1, and S2 states.