Near‐Infrared Carbonized Polymer Dots for NIR‐II Bioimaging

Carbon dots (CDs) or carbonized polymer dots (CPDs) are an emerging class of optical materials that have exceptional applications in optoelectronic devices, catalysis, detection, and bioimaging. Although cell studies of CPDs have produced impressive results, in vivo imaging requires available CPDs to fluoresce in the near‐infrared‐II (NIR‐II) window (1000−1700 nm). Here, a two‐step bottom‐up strategy is developed to synthesize NIR‐CPDs that provide bright emissions in both NIR‐I and NIR‐II transparent imaging windows. The designed strategy includes a hydrothermal reaction to form a stable carbon core with aldehyde groups, followed by the Knoevenagel reaction to tether the molecular emission centers. This procedure is labor‐saving, cost‐efficient, and produces a high yield. The NIR‐CPDs enable high‐performance NIR‐II angiography and real‐time imaging of the disease degree of colitis noninvasively. This technology may therefore provide a next‐generation synthesis strategy for CPDs with rational molecular engineering that can accurately tune the absorption/emission properties of NIR‐emissive CPDs. Carbonized polymer dots (CPDs) are remarkable optical materials with low preparation cost, high biocompatibility, and excellent optical properties. The emission wavelengths of current CPDs are limited in the visible to NIR‐I range, impeding their applications in the transparent NIR‐II window. A new series of NIR‐CPDs is reported through a two‐step hydrothermal/Knoevenagel reaction with adjustable absorption/emission wavelength for NIR‐II bioimaging.