External heavy atom effects have been studied for the photoreaction of phthalazine in 2- propanol. Addition of bromine containing compounds alters the product distribution in the dual photoreactions occurred simultaneously. The results can be interpreted in terms of enhancement of the intersystem crossing from the triplet radical pair to the singlet radical pair, including the spin inversion within the solvent cage.
[Inoue, Hiroyasu; Sakurai, Tadamitsu; Tomiyama, Koichi; Sano, Ryo; Oshio, Masahiro; et al. Bulletin of the Chemical Society of Japan, 1988 , vol. 61, p. 893 - 898]