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.