s-cis octatetraene: Photoproduction and spectroscopic properties

Irradiation of solutions of all-trans octatetraene in n-octane and cyclohexane at temperatures below 10 K efficiently produces a photoproduct whose fluorescence and absorption spectra are shifted ∼1200 cm−1 to lower energy than the corresponding features in the all-trans precursor. High resolution excitation and fluorescence spectra and fluorescence lifetimes for this product have been determined. These data establish that the photoproduct is a noncentrosymmetric octatetraene isomer. The spectroscopic properties and thermal lability of this isomer are consistently interpreted if it is assumed that the photoproduct is generated from all-trans octatetraene by isomerization about one of the single bonds.