Photocycloaddition of 9,10-dichloroanthracene to 1,3-Cyclohexadiene

Article abstract of DOI:10.1021/ja00341a040

Irradiation of 9,10-dichloroanthracene (DCA) in the presence of 1,3-cyclohexadiene (CHD) gives three major adducts corresponding to <2 + 2> addition of CHD to the 1,2-positions of DCA and <4 + 4> addition of CHD to the 9,10- and 1,4-positions of DCA.The previously undetected <2 + 2> adduct is the major primary photoadduct in toluene, benzene, acetonitrile, or pyridine, provided that it is protected from shorter wavelength exciting light.The dependence of emission and product quantum yields on demonstrates that interaction between the first excited singlet state of DCA with CHD is the first step of these reactions.The product distributions are not entirely consistent with a recently proposed algorithm for prediction of reactivity in allowed <2 + 2> and <4 + 4> photocycloadditions.DCA*CHD exciplex emission was not detected, but involvement of a singlet exciplex in the cycloadditions is suggested by (a) the inverse temperature dependence of Stern-Volmer plot slopes for CHD quenching of DCA fluorescence and (b) the marked decrease of adduct quantum yields in the presence of pyridine, a known exciplex-specific quencher.