Stabilization of cationic zinc phthalocyanine monomers by adsorption on clay nanosheet colloid and photogeneration of singlet oxygen

To determine the optimal conditions for the stabilization of cationic zinc phthalocyanine (ZnPc4+) monomers within an aqueous medium, the adsorption behavior of ZnPc4+ on the surface of an anionic clay nanosheet was investigated. It was determined that ZnPc4+ could be adsorbed as a monomer on the surface of an anionic clay nanosheet dispersed in an aqueous medium, containing up to 0.9 ZnPc4+ per cationic exchange site on the clay nanosheet. It was observed that the concentration of ZnPc4+ monomers in the aqueous solution was negligible when the concentration of ZnPc4+ was low. When ZnPc4+ monomers - after having been adsorbed on the surface of the anionic clay nanosheet - were photoexcited by visible light (690 nm) in the presence of 9,10-antracenediyl-bis(methylene) dimolonoic acid (ADMA), the typical absorbance of ADMA at 398 nm decreased with an increase in irradiation time. This is indicative of the photogeneration of a singlet oxygen in aqueous ZnPc4+, due to a highly stabilized ZnPc4+ monomer on anionic clay nanosheet surface. The external quantum yield of decomposed ADMA in the presence of the anionic clay nanosheet colloid in aqueous medium was measured to be 2.62 x 10(-5).