Regulation of the unconventional luminescence behaviors of phenylenediamine-based carbon dots with high PLQY values

Phenylenediamine has become a classic material for synthesizing carbon dots (CDs) due to its nitrogen doping, conjugated aromatic structure, low cost, and easy availability. Typically, the CDs obtained from m-phenylenediamine (mPD), o-phenylenediamine (oPD) and p-phenylenediamine (pPD) exhibit fluorescence that follows a rule from blue to red. However, their photoluminescence quantum yield (PLQY) is low, and the spectral coverage is relatively small, which greatly limits their application and development in high-quality white LEDs. Herein, we selected a simple and environmentally friendly succinic acid (SA) to regulate the luminescence properties, which achieve unconventional luminescent behaviors with high PLQY values (68 %, 60 %, and 72 %) and wide spectral coverage. The PL emission of the obtained CDs followed the rule of pPD, mPD, and oPD from deep-blue to red, which is different from most previously reported results. Additionally, The SA molecules altered the polymerization structure and led to changes in the conjugated domain and surface C=O and –COOH groups, achieving this unconventional luminescence with high PLQY values. Finally, high-quality white LEDs were fabricated with the CIE coordinates of (0.34, 0.33), close to the (0.33, 0.33) of pure white light. R-CDs with an absolute PLQY value of up to 72 % were also used in bioimaging. We use the same small organic acid to regulate the phenylenediamine isomer and obtain CDs with fluorescence in different shift directions. This work will provide a new idea for luminescence regulation with high PLQY values and wide spectral coverage.