Photosensitizing activity of phthalocyanine derivatives dispersed on nanostructured amberlyst 15: Free base vs. metal complexes

A major problem with the use of peripherally unsubstituted metal-free phthalocyanine (H2Pc) and the corresponding metal complexes with Co(II), Zn(II) and Ni(II) as catalysts or photocatalyts is their extensive aggregation in most organic solvents and water. In order to overcome the aggregation of phthalocyanine compounds, metal-free phthalocyanine (H2Pc) and the corresponding metal complexes with Co(II), Zn(II) and Ni(II) dispersed on porous nano-structured amberlyst 15 (nanoAmbSO3H) were synthesized and used as efficient photosensitizers in the aerobic oxidation of methyl phenyl sulfide under aqueous and non-aqueous conditions. The polymer supported photosensitizers, H2Pc@nanoAmbSO3H, ZnPc@nanoAmbSO3H, CoPc@nanoAmbSO3H and NiPc@nanoAmbSO3H, were characterized by diffuse reflectance UV–Vis spectroscopy (DRS), FESEM/EDX-Mapping, AFM, IR, TGA and BET. The singlet oxygen quantum yield (φΔ) of the photosensitizers was determined through the oxidation of 1,3-diphenylisobenzofuran as a specific quencher of singlet oxygen. Solution UV–vis and DRS studies showed the lack of metal leaching from the metal complexes but significant red shift of the absorption bands upon exposure to sulfuric acid and the acidic conditions caused by the –SO3H groups of the strongly acidic polymer. A particle size less than 50 nm was determined for the almost spherical nanocomposites. In contrast to the metallophthalocyanines, the incorporation of H2Pc into the polymer structure led to a remarkable decrease in the thermal stability of the polymer. The immobilized photosensitizers were much more efficient than the non-immobilized counterparts (CoPc, ZnPc, NiPc and H2Pc), although no catalyst degradation was observed for the both series. In the present study, the interaction of the –SO3H groups of a nanostructured mesoporous polymer with phthalocyanines and its metal complexes was used to design new photosensitizers with red shifted absorption bands and high stability under oxidative conditions. Also, the insoluble photosensitizers, effectively dispersed on the polymer support showed remarkably increased photocatalytic activity relative to that of their non-immobilized counterparts. [Display omitted] •Phthalocyanine-amberlyst 15 nanocomposites as new photosensitizers.•Dispersion of insoluble photosensitizers into a nanostructured polymer.•Significantly enhanced photocatalytic activity of phthalocyanines and its metal complexes.•Comparable photocatalytic activity of the free base and metal