Photosensitized transformation of 4-chlorophenol in the presence of aggregated and non-aggregated metallophthalocyanines

The photosensitizing properties of various water-soluble zinc and aluminum phthalocyanines towards the phototransformation of 4-chlorophenol (4-Cp) are presented. The complexes studied are the zinc (ZnPcS4) and aluminum (AlPcS4) tetra-sulfophthalocyanines; the zinc and aluminum complexes containing a mixture of differently substituted sulfophthalocyanines (represented as zinc (ZnPcSmix) and aluminum (AlPcSmix), respectively); the zinc (ZnOCPc) and aluminum (AlOCPc) octacarboxy phthalocyanines. The AlPcSmix and ZnPcSmix, complexes showed the best photocatalytic activity towards the transformation of 4-Cp. The values of singlet oxygen quantum yields of the sensitizers were obtained, and it was found that the rates of 4-Cp photooxidation, in general, follow the efficiency of singlet oxygen photosensitization by the phthalocyanine complexes. At 4-Cp concentration below 10(-4) mol l(-1) photooxidation by singlet oxygen is the dominating mechanism of substrate photodegradation, while at 4-Cp concentration above 10(-3) mol l(-1) the role of Type I mechanism increases. Kinetic analysis indicates that interaction of 4-Cp with singlet oxygen mainly results in "physical" quenching with (k(q) + k(r)) = (13.5 +/- 3) x 10(8) mol(-1) l s(-1) and k(r) = (2.7 +/- 0.3) x 10(8) mol(-1) l s(-1) for the phenolate form of 4-Cp, which significantly limits the rates and quantum yields of 4-Cp photooxidation. (C) 2001 Published by Elsevier Science B.V.