Photophysical properties of benzoannelated metal-free phthalocyanines

Symmetrically (1–4) and unsymmetrically (5–7) benzoannelated metal-free porphyrazines bearing tert-butyl substituents have been investigated in regard to their photophysical properties and their splitting behavior of the Q-band. Q-band splitting in the series of symmetrical tetraazaporphyrine (1), tetrabenzoporphyrazine (2), tetranaphthoporphyrazine (3), is decreased from ΔQ ∼2000 to ∼0 cm−1 while the tetraanthraporphyrazine system (4) shows a low splitting of about ΔQ=265 cm−1 again. In the unsymmetrically substituted series in going from tribenzomononaphthoporphyrazine (6) (ΔQ=903 cm−1) to tribenzomonoanthraporphyrazine (7) (ΔQ=875 cm−1) Q-band splitting is very similar while tribenzoporphyrazine (5) (ΔQ=2073 cm−1) exhibits a drastic increase. In the series 1–4, fluorescence lifetimes 2.6, 5.5, 3.0, 0.5 ns, fluorescence quantum yields 0.17, 0.44, 0.19, 0.01 and singlet oxygen quantum yields 0.53, 0.21, 0.03, <10−4 were determined. Fluorescence lifetimes of 5–7 are in the range 3.1–4.7 ns. The absorption- and fluorescence spectra as well as the fluorescence lifetimes of the separated isomers of 5 do not differ.