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 DeltaQ similar to2000 to similar to0 cm(-1) while the tetraanthraporphyrazine system (4) shows a low splitting of about DeltaQ = 265 cm(-1) again. In the unsymmetrically substituted series in going from tribenzomorionaphthoporphyrazine (6) (DeltaQ = 903 cm(-1)) to tribenzomonoanthraporphyrazine (7) (DeltaQ = 875 cm(-1)) Q-band splitting is very similar while tribenzoporphyrazine (5) (DeltaQ = 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 us. The absorption- and fluorescence spectra as well as the fluorescence lifetimes of the separated isomers of 5 do not differ. (C) 2004 Elsevier B.V. All rights reserved.