The Surface Modification Strategy Toward Long Wavelength Emission of Carbon Dots

Carbon dots (CDs), as an important carbon-based nanomaterial, have been widely used in fluorescence (FL) detection, bioimaging, photocatalysis, light-emitting devices (LEDs) and many other fields, owing to their excellent optical properties. Regulating the fluorescent properties of carbon dots (CDs) in a controlled manner has been a fundamental research goal. Herein, solvent-dependent CDs (N-CDs) are synthesized through the solvothermal reaction of o-phenylenediamine (OPD) in ethanol. When N-CDs are dispersed in solvents of different polarities, the emission wavelength only turned 39nm red-shift. While, the O-CDs are obtained by modifying the surface of N-CDs with 1,2,4-benzenetricarboxylic acid (TMA). O-CDs show four obvious FL emission peaks in the yellow, orange and red regions at 554nm, 604nm, 650nm and 712nm with a tail extending to 750nm, even entering into near-infrared-I (NIR-I) region. Thus, according to the special structure of CDs, this work provides a novel donor-pi-acceptor (D-pi-A) strategy for preparing long wavelength emissive CDs. Finally, the N-CDs and O-CDs are successfully applied to cellular imaging.