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.