A novel type of fluorescence modulation mechanism of carbon dots derived from the competition of photoinduced electron transfer and fluorescence

A series of nitrogen-doped carbon dots (N-CDs) are prepared under different solvent conditions from citric acid and different nitrogen sources, and a novel principle for modulating their fluorescence (FL) properties has been proposed. The nitrogen-doped carbon core can act as a fluorophore, causing diverse FL properties of N-CDs to a certain extent restricting electron delocalization. The solvent effect experiments show that the FL originates from the local emission (LE) of the carbon core. Significantly, the electron-rich substituents linked directly to the carbon core can act as electron donors, which lead N-CDs to undergo a normal "surface substituents-excited" photoinduced electron transfer (S-PET) or a nontypical "carbon core-excited" PET (C-PET) under alkaline or acidic conditions, respectively, causing an uncommon pH-sensitivity FL quenching of N-CDs. Since C-PET or SPET dominated by pH could further regulate the surface charges of N-CDs, unseparated dual-channel specific recognition and the "AND" logic gate detection for Cu2+ and Chlorpromazine hydrochloride (CPH) in neutral conditions have been established.