Chemical modification with m-phenylenediamine on the purified carbon nano dots for remarkable enhancement of quantum yields and red-shift of fluorescent emission

Photoluminescence (PL) was the core of carbon nano dots (CDs). However, there were different opinions about origin of the PL. Also, the cause for enhanced PL performance via nitrogen doping was still obscure occasionally. However, the fluorophore certification provided an easier understanding on the PL and the surface group ascertainment facilitated nitrogen doping on CDs via surface modification. Imaginably, if CDs were purified in the first place discussions on the PL would be more convincing. Herein, CDs were obtained by hydrothermal treatment on glucose solution and were purified successively via an extraction of ethyl acetate (represented with gCDs). Nitrogen doping was accomplished successfully via the reaction between amine of m-phenylenediamine and the carboxyl of gCDs (the product was represented with N-gCDs). That realized the notable red-shift of the emission with remarkable enhancement of fluorescence quantum yield. Experiments revealed that aldehyde was the fluorophore and C = C bonds constructed the fluorescent skeleton of gCDs or N-gCDs, which were also supported by ab initio calculations on the fluorescent models for gCDs and N-gCDs. Cellular imaging experiment indicated N-gCDs could penetrate cytomembrance of MCF-7 successfully and stained cytoplasm and nucleus effectively during the cell cultivation, which excelled several nitrogen-doped CDs in this aspect.