Photodynamically active phthalocyanine building blocks for click chemistry

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Synthesis of symmetrical and unsymmetrical zinc phthalocyanines from two different precursors 4,5-bis(tert-butylsulfanyl)phthalonitrile (A) and N-(3-azidopropyl)-2,3-dicyanoquinoxaline-6-carboxamide (B) is described. Congeners of AAAA, AAAB, ABAB and AABB type were isolated by a chromatographic technique, however, the congener of BBBB type had to be prepared in a separate reaction. The adjacent and opposite isomers were also separated and fully characterized. Isolated phthalocyanines contained different number of azide groups, a substrate for highly efficient Cu(I) -catalyzed azide-alkyne 1,3-dipolar cycloaddition ("click chemistry"). All phthalocyanines absorbed strongly (ε over 150 000 M-1.cm-1) over 700 nm. Their singlet oxygen quantum yields were determined in DMF and ranged from 0.63 to 0.79, fluorescence quantum yields in DMF were considerably lower in the range 0.03–0.06. All these properties make them suitable building blocks for a simple modification and a synthesis of phthalocyanines with better tuned properties for photodynamic therapy.