Rational Design of Far-Red to Near-Infrared Emitting Carbon Dots for Ultrafast Lysosomal Polarity Imaging.

Carbon dots (CDs) have been widely studied for their excellent properties. However, most of the prepared CDs only show strong emission in the blue to green region, which greatly limits the application of CDs in the biomedical field. In this report, a new design strategy of long-wavelength CDs was reported. The orange phenyl-CDs with good optical properties and biocompatibility were successfully prepared by changing the substituted group of the o-phenylenediamine and the main emission band of phenyl-CDs was in the far-red region. With the increase of polarity, the wavelength of phenyl-CDs red-shifts and the fluorescence intensity decreases, demonstrating their sensitive polarity response function. In addition, phenyl-CDs can achieve ultrafast target imaging of lysosome within 40 s through clathrin-mediated endocytosis. Finally, phenyl-CDs were successfully applied for monitoring lysosomal polarity induced by drugs, which is helpful in getting a better understanding of the physiological and pathological processes of lysosomes. This report provides an important theoretical basis for the rational design and precise synthesis of long-wavelength fluorescent CDs.