Photoinduced electron transfer from tetraphenyl-substituted 1,2-digermacyclohexa-3,5-dienes and related compounds to C-60

The irradiation of benzene-benzonitrile solutions of 3,4,5,6-tetraphenyl-substituted 1,2-digermacyclohexa-3,5-dienes and related compounds in the presence of C-60 afforded the corresponding ring-contracted products, namely 1-germacyclopenta-2,4-dienes, with the extrusion of germylene and ring-expanded oxadigerma compounds, namely 1-oxa-2,7-digermacyclohepta-3,5-dienes. The laser flash photolysis of a benzene-benzonitrile solution of 1,2-digermacyclohexa-3,5-dienes in the presence of C-60 showed that the transient absorption band of the C-60 triplet state (C-T(60)*) appeared immediately at 730 nm. With the decay of C-T(60)*, the absorption bands of the radical anion of C-60 .(-) appeared at 1060 nm, showing that an electron transfer takes place from 1,2-digermacyclohexa-3,5-dienes to C-T(60)*. The formation of cyclic oxadigerma compounds was explained by processes of both the photooxidation of 1,2-digermacyclohexa-3,5-dienes in the absence of C-60 with singlet oxygen and oxidation of the cation radical of 1,2-digermacyclohexa-3,5-dienes with triplet oxygen.