Abstract The 9, 10-dicyanoanthracene (DCA)-sensitized photooxygenation of Ar 2 C= CH (CH 2) n CH= CAr 2 in acetonitrile was studied. When Ar= 4-CH 3 OC 6 H 4, n= 3 and 4, bicyclic peroxides were obtained via 1, 4-radical cations that are generated by intramolecular interaction between two ethenyl moieties of the alkadienes.