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

Abstract

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 × 10−5.