Solvatochromism of high-efficient and long-wavelength emissive carbon dots for wide-range water-sensing in organic solvents

A novel solvent-dependent fluorescent CDs (R-CDs) were prepared by solvothermal method from neutral red and urea precursors. The multicolor emissions ranging from blue to red from R-CDs could be achieved by tuning the solvents polarity. The highest quantum yield of 61.11% is achieved in R-CDs acetone solution with bright yellow emission at 565 nm. The solvent-dependent fluorescence is ascribed to the variation of CDs’ band-gap and surface potential, which are induced by polarity. R-CDs were used as a quantitative fluorescent sensor for detecting water in different solvents. An excellent linear relationship between water content (0–90%) and emission intensity is found in ethanol, methanol, acetonitrile, isopropanol, DMSO, and acetone. The limit of detection (LOD) is 1.55%, the recoveries range from 95% to 110%, and the relative standard deviations (RSD) are 0.15%–5.43%. All results indicate that our R-CDs for water sensing exhibit good linear relationship and accuracy.