The synthesis and characterization of novel unsymmetrical azaphthalocyanines containing one carboxylic group

Unsymmetrical zinc and magnesium complexes of azaphthalocyanines with one carboxylic group were synthesized using statistical condensation of 5,6-bis(tert-butylsulfanyl)pyrazine-2,3-dicarbonitrile (A) and 3-(5,6-dicyano-3-methylpyrazin-2-ylsulfanyl)propionic acid (B) or 6-(3-tert-butylsulfanyl-5,6-dicyanopyrazine-2-ylamino)hexanoic acid (C); unsymmetrical AAAB or AAAC azaphthalocyanines were isolated from the mixture. During preparation of Mg complexes of AAAC type, the precursor C had to be esterified before cyclotetramerization and the final azaphthalocyanine was hydrolyzed to yield AAAC of higher purity. The synthesized compounds were characterized using IR, NMR, MS and UV–vis spectroscopy; singlet oxygen quantum yields were measured using DPBF decomposition method. The zinc AAAB complex showed good photodynamic properties indicating that it may be suitable as a third generation photosensitizer.