Rational synthesis of highly efficient ultra-narrow red-emitting carbon quantum dots for NIR-II two-photon bioimaging

Despite the growing research interest in highly bio-compatible carbon quantum dots (CQDs) for bioimaging, the synthesis of red-emitting CQDs with high photoluminescence efficiency and a sharp emission spectrum remains a formidable challenge in this field. Herein, we established a rational strategy for the synthesis of highly efficient ultra-narrow red-emitting CQDs by adopting a conjugated aromatic amine precursor (tris(4-aminophenyl)amine, TAPA) and introducing oxidative radical reagents. The resultant CQDs, T-CQDs featured red PL (615 ± 2 nm) with a high photoluminescence quantum yield (84 ± 5%) and a narrow emission linewidth (FWHM = 27 ± 1 nm), which together represented one of the highest levels in the field of CQDs so far. The T-CQDs were then further analyzed from the spectral and structural aspects, and the repeatability and universality of this strategy have also been discussed. Finally, the T-CQDs were successfully applied for both one-photon imaging and two-photon imaging with various bio-samples, both in vitro and in vivo.