Photophysical properties of neutral and cationic tetrapyridinoporphyrazines.

We describe the synthesis and photophysical properties of a series of neutral and cationic 3,4-tetrapyridinoporphyrazines, potential lead photosensitizers for photodynamic inactivation of bacteria. Tetracationic TPyPzs exist essentially as monomers in aqueous systems, but the presence of trialkylated compounds due to incomplete quaternization of the outer nitrogen atoms induces severe aggregation. The absorption, fluorescence, triplet, and singlet oxygen quantum yields for both the neutral and cationic compounds are comparable to those of the related phthalocyanines.