N,S-Codoped Carbon Dots with Red Fluorescence and Their Cellular Imaging.

The emergence of carbon dots (C-dots) has aroused increasing attention owing to their excellent chemical and physical properties, such as favorable biocompatibility and an outstanding fluorescence (FL) property. Most reported C-dots show blue emission, which hinders their applications in the biomedical field due to the strong FL background of biosamples. Therefore, strategies for the achievement of long-wavelength fluorescent C-dots are urgently needed. Herein, red emissive biocompatible C-dots were prepared from polythiophene (PTh) through chemical cutting by nitric acid. Various methods were utilized to shed light on the luminescence mechanism of the C-dots. The results demonstrated that FL emission of the prepared C-dots was mainly dominated by sp domains. The C-dots were well-applied in in vitro imaging. This work prepared red fluorescent C-dots from the perspective of the structure of C-dots, which would benefit the regulation of the FL of C-dots.