Solid-State Luminescence in Self-Assembled Chlorosalicylaldehyde-Modified Carbon Dots

Carbon dots (CDs) have excellent optical properties with broad potential applications. However, obtaining CDs with multicolor emission in the solid state remains a great challenge. Four chlorosalicylaldehyde-functionalized CDs with solid-state fluorescence were prepared here via molecular self-assembly. Their emission wavelengths were 456, 494, 556, and 584 nm, ranging from blue to yellow. Experimental results and theoretical calculations indicated that the different positions (para-, meta-, and ortho-position) of Cl on the aromatic core of chlorosalicylaldehyde affect the coplanarity and degree of conjugation of the CDs, thereby changing their molecular orbital energy levels and adjusting the emission. The self-assembly showed distinct isomeric effects: with changing positioning of the Cl, three-dimensional to one-dimensional self-assembled morphologies appeared in turn. The multicolor luminescence of the CDs makes them potentially useful in light-emitting diodes and fluorescent films. Their fat solubility and strong ultraviolet absorption characteristics allow them to be applied in fingerprint detection.