Photoinduced Electron Transfer of ZnS–AgInS₂ Solid-Solution Semiconductor Nanoparticles: Emission Quenching and Photocatalytic Reactions Controlled by Electrostatic Forces

The electron transfer between the fluorescent ZnS–AgInS 2 solid-solution (ZAIS) nanoparticles (NPs) and redox species is investigated in an aqueous solution in terms of chemosensors and photocatalysts. In a case where the ZAIS NPs and quenchers are oppositely charged, very efficient photoluminescence (PL) quenching ( K S ≈ 10 6 M –1 ) is observed because of the specific adsorption of quenchers on particles. The quenching magnitude increases with the potential gap between the photoexcited NPs and quenchers. Methyl viologen (MV 2+ ) shows the largest quenching behavior; i.e., it is revealed to quench most of PL by the adsorption of only a single molecule. In such a case, the linearity of quenching magnitude is lost, and distribution of the quencher adsorption on NPs should be considered to clarify the quenching mechanism. In the opposite case where both the ZAIS NPs and quenchers are negatively charged, although the quenching efficiency is two to three orders of magnitude lower than that in the aforementioned adsorption case, electron transfer occurs from the NPs to redox species. The efficiency of photoreduction is investigated in association with the charge repulsion between both species.