Unveiling Unconventional Luminescence Behavior of Multicolor Carbon Dots Derived from Phenylenediamine

Fluorescence regulation of carbon dots (CDs) during theirpreparationhas become a hot research topic. In this work, multicolor fluorescentCDs with unconventional luminescence behavior are prepared by using o-, m-, or p-phenylenediamine(o-PD, m-PD, or p-PD, respectively) and 2,3-dihydroxynaphthalene with rich hydroxylgroups as reaction precursors. Tunable multicolor fluorescent CDswith bright blue, yellow, and red colors can be obtained by a solvothermalmethod under the joint action of ethanol and hydrochloric acid. Thefluorescence emission of the synthesized CDs follows a rule of o-PD to m-PD to p-PD fromblue to red, which is contrary to most previously reported results(the luminescence from blue to red following an order of m-PD to o-PD to p-PD). Our resultsreveal that the differences in the polymerization, surface states,functional groups, and graphite N content of CDs might be the mainreasons for the unconventional luminescence behavior. In addition,these multicolor CDs have good applications in the fields of light-emittingdiode lighting and anticounterfeiting.