N-doped carbon dots with tunable emission for multifaceted application: solvatochromism, moisture sensing, pH sensing, and solid state multicolor lighting.

• Novel N-doped green-emitting carbon dots with high QYs (17.36%–48.4%) were synthesized for multifaceted application. • N-GCDs exhibited strict solvent polarity-dependent switchability (solvatochromism). • Solvatochromism technique was utilized to detect moisture content in acetone and THF with LOD 0.37% and 0.38%, respectively. • N-GCDs were utilized to detect pH in the range of 3.8–6.2 with good linear relationship (R2 = 0.99). • Multicolor-emissive N-GCD/polymer films were prepared demonstrating the application of N-GCDs for solid-state lighting. Novel N-doped green-emitting carbon dots (N-GCDs) that were responsive to various external stimuli and had high quantum yields (QYs) for multifaceted applications were synthesized from β-resorcylic acid and ethylenediamine using a hydrothermal process followed by a reflux method. The QYs of the N-GCDs were in the range of 17.36%–48.4% and were associated with different photoluminescent color emission in different solvents. Interestingly, the as-synthesized N-GCDs exhibited strict solvent polarity-dependent switchability (solvatochromism) and multicolor excitation-wavelength-independent emission in different solvents. Sensing of an analyte based on the switching of the photoluminescence (PL) emission maxima (λ max) is always preferred over that based on fluorescence quenching to avoid complexity and confusion regarding the initial fluorescence intensity (I 0) and thus make the sensing process simple, rapid, ordered, and reliable. The N-GCDs exhibited blue emission in low-polarity organic solvents, but with the increase of the trace water content in the system, the PL emission peak gradually shifted to a higher wavelength (bathochromic shift) at a single-wavelength excitation. Thus, the N-GCDs are sensitive visual probes for the fluorescence detection of the trace water content in organic solvents without sophisticated processes. They also indicate the pH-response behavior. When the pH decreased from 7.6 to 2.4, the fluorescence emission intensity decreased, with a particularly good linear relationship (R2 = 0.990) in the range of 3.8–6.2. Moreover, the polarity-dependent-emission property was observed in the solid state polymer matrices. Multicolor-emissive N-GCD/polymer films were prepared by integrating N-GCDs with the polymer matrices of different polarity, demonstrating the application of carbon dots for solid-state lighting. [ABSTRACT FROM AUTHOR]