Photoreduction of polycyclic DBO-type azoalkanes with amines to hydrazine products

The n,pi*-singlet-excited polycyclic, alpha-substituted DBO-type azoalkanes 1 are reduced by amines to form the corresponding hydrazines 2 as photored uction products in competition to denitrogenation to the bicyclo[2.2.0]hexa ne photoproducts 3. The photophysical, photochemical, and electrochemical p roperties of the azoalkane determine the product ratio of the hydrazine 2 v ersus the bicyclo[2.2.0]hexane 3. The quantum yields of the photoreduction are quite low (<0.1), for which efficient deactivation of the singlet excit ed state through charge transfer is postulated. The charge transfer in the exciplex between the azoalkane and the amine promotes the hydrogen abstract ion of the alpha-CH bond from the amine by the azoalkane and, thus, facilit ates its photoreduction, a general photochemical process applicable to sing let- as well as triplet-excited azoalkanes.