Efficient fluorescence quenching in carbon dots by surface-doped metals--disruption of excited state redox processes and mechanistic implications.

The carbon dots in this study were small carbon nanoparticles with the particle surface functionalized by oligomeric poly(ethylene glycol) diamine molecules. Upon photoexcitation, the brightly fluorescent carbon dots in aqueous solution served the function of excellent electron donors to reduce platinum(IV) and gold(III) compounds into their corresponding metals to be deposited on the dot surface. The deposited metals even in very small amounts were found to have dramatic quenching effects on the fluorescence emission intensities, but essentially no effects on the observed fluorescence decays. The obviously exclusive near-neighbor static quenching could be attributed to the disruption of electron-hole radiative recombinations (otherwise responsible for the fluorescence emissions in carbon dots). The results provide important evidence for the availability of photogenerated electrons that could be harvested for productive purposes, which in turn supports the current mechanistic framework on fluorescence emission and photoinduced redox properties of carbon dots.