In situ one-pot synthesis of graphitic carbon nitride quantum dots and its 2,2,6,6-tetramethyl(piperidin-1-yl)oxyl derivatives as fluorescent nanosensors for ascorbic acid.

Graphitic carbon nitride quantum dots (gCNQDs) when alone or containing embedded 4-amino-2,2,6,6-tetramethyl(piperidin-1-yl)oxyl) (4-AT) (gCNQDs-4-AT(embedded)) were synthesized via low temperature in situ one-pot process from diaminomaleonitrile (DAMN). The blue emission of both gCNQDs and gCNQDs-4-AT were excitation wavelength-dependent with very high fluorescence quantum yields of 43 and 51%, respectively. Further, the gCNQDs were covalently linked to 4-AT via an amide bond to give (gCNQDs-4-AT (linked)). gCNQDs were also non-covalently linked to 2,2,6,6-etramethyl(piperidin-1-yl)oxyl (TEMPO, not containing amino groups) derivatized zinc phthalocyanine (ZnPc) to form gCNQDs-TEMPO-ZnPc(π-π). The TEMPO-derivatized gCNQDs (gCNQDs-4-AT(embedded)), gCNQDs-4-AT(linked), or gCNQDs-TEMPO-ZnPc(π-π) were found to be highly sensitive and selective fluorescent probes for ascorbic acid (AA) detection with limits of detection (LOD) in the nanomolar range. Hence, 4-AT (or TEMPO) functionality introduced into the gCNQDs (or ZnPc) afforded the derivation of selective and sensitive AA probes. Real samples were evaluated by the designed probes and satisfactory recoveries further confirmed the analytical applicability of the gCNQDs-based probes.