Preparation and characterization of chiral carbon dots with red emission

Methods for the synthesis of chiral carbon dots (CDs) possessing bright long-wavelength emission are highly desirable. Here, we develop red-emissive chiral CDs from hydrothermal treatment of L-/D-lysine and o-phenylenediamine (OPD). Pure chiral CDs are obtained by filtration and dialysis. Ultraviolet-visible (UV–vis) absorption spectra, photoluminescence (PL) spectra, PL quantum yield (QY), and PL decay of the chiral CDs are thoroughly studied. The chiral CDs exhibit bright red fluorescence with PL QY in the range of 26.6%–42.2% in different solvents. Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) indicate that the chiral CDs have a mean particle size of 2.7 nm, and consist of graphite-like carbons and abundant functional groups at their surfaces. Circular dichroism spectroscopy shows new Cotton bands at about 300 and 610 nm for chiral CDs differed from those of L-/D-lysine, revealing the generation of optical chirality for CDs. Then transparent optical resins made of CDs/epoxy resin composites are prepared, possessing red fluorescence and circular dichroism, broadening potential applications of solid materials with chiroptical properties. Finally, we discuss the possible origins of chirality and fluorescence of the CDs. The exploitation of highly red-emissive chiral CDs may promote the development and application of chiral CDs.