Development of Polyene-Bridged Hybrid Rhodamine Fluorophores for High-Resolution NIR-II Imaging

This work presents a polyene bridging strategy on Rhodamine-type dye analogues (Rh824, Rh926, and Rh1029) for tuning absorption and emission wavelengths from the first near-infrared window (NIR-I; 750–900 nm) to the unprecedented second near-infrared window (NIR-II; 1000–1700 nm). Phosphatidylcholine (PC) enclosures of the dyes improve water solubility and triple the fluorescent quantum yields. The representative NIR-II fluorophore Rh1029-PC presents significantly higher spatial resolution, compared to NIR-I fluorophore Rh824-PC, when performing in vivo vascular imaging. We construct a mouse vascular hemorrhage model and apply Rh1029-PC as the angiography agent in NIR-II window for the first time. The images show superior clarity of the hemorrhage positions in the NIR-II window, suggesting the successful application of the hybrid Rhodamine-derived dye in NIR-II fluorescent bioimaging.