Polymer Precursor Strategy Toward the Precise Synthesis of Uniform Hairy Carbon Dots with Tunable Sizes and Size Effects over Their Fluorescence

A polymeric precursor strategy was developed toward precise synthesis of uniform and size-tunable hairy fluorescent carbon dots (C-dots, CDs). The strategy was achieved by (i) the synthesis of core-shell 6-arm starlike block copolymers of PGMA-b-PMMA (poly(glucosyl methyacrylate), PGMA; poly-(methyl methacrylate), PMMA), serving as a precursor using atom transfer radical polymerization (ATRP) and (ii) selective carbonization of the inner PGMA chains to generate hairy C-dots with PMMA blocks attaching on the surfaces. The resultant C-dots with tunable sizes showed blue to green fluorescence depending on the excitation, size, and concentration. The large size of the C-dots led to a significant red shift of fluorescence emission, which was attributed to enhanced intra-C-dot Forster resonance energy transfer (FRET) between the emitter homologues in a single C-dot. In addition, the FRET effect between C-dots was further confirmed by the aggregation-caused quenching characteristics and red shift of emission at high concentrations. Interestingly, different from the traditional fluorophores with photobleaching characteristics, C-dots showed recoverable photoabsorption capacity and enhanced fluorescence after the long-time exposure to UV light.