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 Δ Q =265 cm −1 again. In the unsymmetrically substituted series in going from tribenzomononaphthoporphyrazine ( 6 ) (Δ Q =903 cm −1 ) to tribenzomonoanthraporphyrazine ( 7 ) (Δ Q =875 cm −1 ) Q -band splitting is very similar while tribenzoporphyrazine ( 5 ) (Δ Q =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, −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.