Exploring Solvent-Related Reactions and Corresponding Band Gap Tuning Strategies for Carbon Nanodots Based on Solvothermal Synthesis

The role of the solvent in the solvothermal synthesis of carbon nanodots (CDs) is a long-standing puzzle for comprehensively understanding the CD formation mechanism and the relevant band gap tuning phenomenon. The controversy regarding solvent effect continues, largely because the importance of solvent-related reactions (SRs) has been ignored. In this Letter, we report that the SRs, i.e., oxidation-assisted solvent-involved dehydration and solvent-promoted oligomerization of phenylene/pyridinediamine (PD/PyD), are observed and dominate the formation of corresponding CDs by producing highly C2H4/C2H4O-featured species of precursors and PEG-like oligomer chains, which is very different from previously proposed theories. Moreover, our findings reveal that the photoluminescence (PL) of as-synthesized CDs originates from fluorophores formed by SRs and can be tailored by fluorophore engineering. Based on the SRs theory, three strategies for PL band gap tuning have been demonstrated.