Light harvesting phthalocyanine/subphthalocyanine system: Intermolecular electron-transfer and energy-transfer reactions via the triplet subphthalocyanine

Photoinduced electron transfer from the electron-donating zinc tetra-tert-butylphthalocyanine, ZnTBPc, to the electron-accepting dodecafluorosubphthalocyanine, SubPcF₁₂, in the polar benzonitrile has been investigated with nanosecond laser photolysis method. The examined ZnTBPc/SubPcF₁₂ mixture absorbs the light in a wide section of the UV/vis/NIR spectra. Owing to the particular electronic properties of both entities, such combination seems to be perfectly suited for the study of intermolecular electron-transfer process in the polar solvents via the triplet-excited state of SubPcF₁₂. Upon excitation of SubPcF ₁₂ with 570 nm laser light in polar benzonitrile (ε_s = 25.2), the electron transfer from ZnTBPc to the triplet-excited state of SubPcF₁₂ was confirmed by observing the transient absorption bands of ZnTBPc radical cation and SubPcF₁₂ radical anion in the visible and near-IR region. On addition of an appropriate electron acceptor with excellent electron-accepting properties, namely dicyanoperylene-3,4,9,10- bis(dicarboximide) (PDICN₂), the anion radical of SubPcF₁₂ transfers to the PDICN₂ yielding the PDICN₂ radical anion. These observations confirm the photosensitized electron-transfer/ electron-mediating cycle of ZnTBPc/SubPcF₁₂/PDICN₂ system. In non-polar toluene (ε_s = 2.2), the energy-transfer process from the triplet-excited state of SubPcF₁₂ to the low-lying triplet state of ZnTBPc was confirmed by the consecutive appearance of the triplet ZnTBPc.