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

Abstract 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 (ZnPcS 4 ) and aluminum (AlPcS 4 ) tetra-sulfophthalocyanines; the zinc and aluminum complexes containing a mixture of differently substituted sulfophthalocyanines (represented as zinc (ZnPcS mix ) and aluminum (AlPcS mix ), respectively); the zinc (ZnOCPc) and aluminum (AlOCPc) octacarboxy phthalocyanines. The AlPcS mix and ZnPcS mix 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)×10 8  mol −1  l s −1 and k r =(2.7±0.3)×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.

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