Photophysics and photochemistry of tetraanthraporphyrazines; attempts to obtain a new generation of photosensitizers

Linearly benzo-annulated copper porphyrazines, such as octaphenyltetraanthraporphyrazinato-copper and octapentoxytetranaphthoporphyrazinato-copper, with absorption maxima at about 880 nm, were synthesized. These compounds exhibit very low-lying triplets with an energy below the activation energy of singlet oxygen. Therefore they do not generate singlet oxygen. The transient absorption spectra of the T₁—T_x transition were measured. The solvent dependence of the photophysical parameters in the triplet manifold is discussed. On irradiation in the presence of CBr₄, π-cation radicals are formed.