Intermolecular hydrogen bond-mediated fluorescence enhancement mechanism of nitrogen-doped carbon quantum dots in coexistence with bisphenolic compounds

Nitrogen-doped carbon quantum dots (NCQDs) possess tunable fluorescence in the presence of organic pollutants, but the mechanism by which bisphenol compounds (BPs) regulate NCQDs’ fluorescence via intermolecular interactions remains unclear. Herein, we systematically investigated the fluorescence responses of NCQDs induced by three typical BPs (BPA, BPS, BPAF) in aqueous environments and the concentration-fluorescence correlation. Results showed all three BPs significantly enhanced NCQDs’ fluorescence, with a clear linear relationship between their low concentrations (0.2–100 μg/L) and fluorescence intensity. DFT calculations revealed that the hydrogen bonding energies between NCQDs and BPA/BPS/BPAF are much higher than those with water, indicating NCQDs form more stable complexes with BPs via hydrogen bonding. Natural transition orbital analysis demonstrated that hydrogen bonds formed by NCQDs’ surface carboxyl groups shift the S 1 state transition mode from dominant 1(n + π, π*) to 1(π, π*), triggering fluorescence intensity changes and emission spectral shifts. Additionally, hole-electron distribution analysis showed hydrogen bonds effectively inhibit electron transfer from NCQDs’ carbon skeleton to surface carboxyl groups, confirming hydrogen bonds play a pivotal role in regulating NCQDs’ electron transition processes.