Indocyanine Green–Inspired Polymeric Chromophores With Intrinsic Photostability for Near‐Infrared Imaging

Indocyanine green (ICG), the only FDA-approved near-infrared (NIR) dye, is widely used in bioimaging but suffers from rapid photobleaching and nonspecific biodistribution. Here we introduce KR-NIR-P, a polymerized form of ICG that preserves its NIR fluorescence while markedly enhancing stability. Under continuous illumination, KR-NIR-P retained ∼66% of its initial fluorescence at 200 s, compared to ∼40% for free ICG within the first 50 s. The polymer was efficiently internalized into immortalized cancer cells (HeLa, HSC-3) and primary human dermal fibroblasts (HDFs), exhibiting predominant cytosolic localization with >90% cell viability even at 20 µM, confirming excellent biocompatibility. The inclusion of both immortalized and primary cells underscores the polymer's broad compatibility across physiologically diverse models. This straightforward polymerization strategy provides a robust and durable NIR imaging platform, overcoming the key drawbacks of ICG and broadening its utility for advanced biomedical research and clinical translation.