Redox Modification of CdSe-ZnS-Polymer Quantum Dots: Photoassisted Fluorescence Quenching and Recovery

Commercial CdSe-ZnS-polymer quantum dots (QDs) were shown to be readily quenched by strong oxidants such as potassium permanganate. When exposed to permanganate solution of millimolar concentration for hours, damage was severe and the QDs would be permanently bleached. When oxidant concentration was micromolar and reaction time was minutes, oxidation would be mild and bleached QDs could recover their fluorescence if the oxidant was removed and the QDs subsequently irradiated. Light was essential in activating the fluorescence recovery. Light could also transform mild oxidations into severe ones if administered with the oxidant simultaneously. A model of the bleaching and recovery was proposed. It was based on the oxidative attack of the Zn-ligand bond and its repair. The model helped explain the critical role that light played and was consistent with all the experimental observations. By means of photocatalyzed oxidation of single QDs, a redox probe of high spatial and temporal resolution was demonstrated.