Photochemistry of substituted cycloheptatrienes XIII: The dependence of quantum yields for sigmatropic hydrogen shifts on the excitation energy

Abstract

The partial quantum yields in a substituted cycloheptatriene reversible system were measured to determine the dependence on the excitation energy. The quantum yields decrease significantly with increasing excitation wavelength. This is in accordance with the prediction from orbital symmetry considerations for a sigmatropic hydrogen shift. The chemical deactivation from higher excited states is able to compete with internal conversion processes. Furthermore the wavelength dependence of the partial quantum yields is interpreted with two different pericyclic minima in the excited state. The participation of conformers as a possible origin for the wavelength dependence of quantum yields is excluded.