Solvent-induced switching between static and dynamic fluorescence quenching of N, S Co-doped carbon dots in sensing of Crotonaldehyde: A detailed systematic study

Blue emissive N, S co-doped carbon dots (NSCDs) (quantum yield = 12%) have been synthesized via one-pot microwave-assisted pyrolysis of optimal mole ratios of tartaric acid and thioacetamide and they are devised as a novel fluorescent probe for assessing the sensitive and selective detection of Crotonaldehyde (CH₃CH=CHCHO, CT) in aqueous and ethanol solution. In the presence of CT, the fluorescence of NSCDs was observed to switch between static and dynamic quenching in the two solvents – water and ethanol, although both exhibited a positive deviation from the linearity in the Stern-Volmer (SV) plots. The positive deviation in the SV plots in the aqueous medium has been attributed to a combination of static and dynamic quenching mechanisms, while the deviation in the ethanol medium followed the static quenching model. The LOD values in water and ethanol medium are estimated to be 50 μM and 30.8 μM in the CT concentration range of 0–6 mM and 0–8 mM respectively. The fluorescence quenching mechanism in the two solvents have been differentiated and validated through fluorescence lifetime measurement using time-resolved fluorescence spectroscopy, shifting in absorption maxima using UV–Vis spectroscopy and energy level calculations. The energy level calculations of NSCDs have been carried out using cyclic voltammetry (CV) measurement and that of CT from density functional theory (DFT) calculations.