Synthesis of carbon nitride oligomer as a precursor of melon with improved fluorescence quantum yield

Carbon nitride (CN) compounds have attracted significant attention as new photocatalysts capable of decomposing water and producing hydrogen upon irradiation using visible light. To date, many studies have focused on their applications as photocatalysts. Melon, a typical CN polymer, is a semiconductor with a direct energy gap, because of which it cannot exhibit high photocatalytic activity without a cocatalyst. However, melon shows high potential as a blue-light-emitting material with high color purity, and the basic physical characteristics of melon are worth clarifying. Additionally, the synthesis of melon during thermal polymerization remains unclear. In this study, the polymerization of melon is investigated by varying the thermal polymerization conditions, and new CN compounds with optical properties similar to those of melon are examined. Characterization of the products prepared under different conditions allowed the identification of a new CN compound, a likely precursor of melon, at temperatures slightly below the calcination temperature of melon. This new compound, which consists of oligomers with four melem units, is very stable in air and shows improved optical properties compared to those of melon.