Mechanisms behind multicolor tunable Near-Infrared triple emission in graphene quantum dots and ratio fluorescent probe for water detection

Developing environmental-friendly and low-cost strategies of synthesizing red-emission graphene quantum dots (R-GQDs) is a considerable challenge. Herein, we present the green and facile preparation of R-GQDs by using o-phenylenediamine (o-PD) and catechol as precursors via oxidation/polymerization and Schiff base reaction at low temperature (80 °C) for 3 hrs. Results show that the prepared R-GQDs exhibit triple fluorescence emissions, which is enabled by the introduce of different nitrogen (pyrrolic N, pyridinic N, and amino N) species on the surface of R-GQDs. Moreover, the R-GQDs are implemented to detect the moisture in different organic solvent. A highly sensitive ratiometric sensing of water in organic solvents is achieved, and the relationship between the change of fluorescence signal caused by moisture and the corresponding internal emission site is also determined. In the end, the multicolor light emissions of R-GQDs are realized by simply adjusting the polarity of surrounding solvents. And based on the solvatochromism of R-GQDs, the multicolor solid fluorescent powder and ink are prepared for illumination application. All in all, the above research work presents a novel R-GQDs for wide application in detecting and illumination.