Unveiling Unconventional Luminescence Behavior of Multicolor Carbon Dots Derived from Phenylenediamine

Fluorescence regulation of carbon dots (CDs) during their preparation has become a hot research topic. In this work, multicolor fluorescent CDs 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 hydroxyl groups as reaction precursors. Tunable multicolor fluorescent CDs with bright blue, yellow, and red colors can be obtained by a solvothermal method under the joint action of ethanol and hydrochloric acid. The fluorescence emission of the synthesized CDs follows a rule of o-PD to m-PD to p-PD from blue 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 results reveal that the differences in the polymerization, surface states, functional groups, and graphite N content of CDs might be the main reasons for the unconventional luminescence behavior. In addition, these multicolor CDs have good applications in the fields of light-emitting diode lighting and anticounterfeiting.