Catalyst regulation of o-phenylenediamine-based carbon dots to achieve single red emission

Red fluorescence is of great significance in biomedicine because of its high tissue penetration and low photodamage to organisms. While the carbon dots (CDs) obtained from o-phenylenediamine (oPD) mainly emit yellow fluorescence in a single reaction system, which greatly limits its development in long-wavelength applications. Here, we design a strategy to control the color of oPD-based CDs by only adding catalyst without changing the materials and conditions. The addition of the catalyst made the mass proportion of the obtained red CDs from less than 1% to 95.6%, and the conversion rate was up to 61.7%. The red CDs with a photoluminescence quantum yield of 29.99% have been successfully applied to live cell imaging. It is well known that catalysts can selectively change the reaction pathway and improve the reaction activity. In the process of oPD-based CD formation, we propose that the catalyst can activate the amino functional group, further accelerate the dehydrogenation and polymerization process, thus effectively increasing the sp2-conjugated domain and graphitic N content, which finally realizes the conversion of mixed CDs to single red CDs. This work provides a new idea for how to regulate the fluorescence of CDs without changing the materials and conditions in the future.