Boron Cluster Renders Organic Radicals Water-Stable for Photothermal Anti-Infections

Water-stable organic radicals are promising photothermal conversion candidates for photothermal therapy (PTT). However, organic radicals are usually unstable in biological environments, which greatly hinders their wide application. Here, we have developed a chaotropic effect-based and photoinduced water-stable supramolecular radical (MB₁₂-2) for efficient antibacterial PTT. The supramolecular radical precursor MB₁₂-1 was constructed by the chaotropic effect between closo-dodecaborate cluster (B₁₂H₁₂^2-) and N,N'-dimethylated dipyridinium thiazolo [5,4-d] thiazole (MPT²⁺). Subsequently, with triethanolamine (TEOA) serving as an electron donor, MB₁₂-1 could transform to its radical form MB₁₂-2 through photoinduced electron transfer (PET) under 435-nm laser irradiation. The N₂ adsorption-desorption analysis confirmed that MB₁₂-2 was tightly packed through the introduction of B₁₂H₁₂^2-, which effectively enhanced its stability via a spatial site-blocked effect. Moreover, the half-life of MB₁₂-2 in water was calculated through ultraviolet-visible light (UV-vis) absorption spectra results for periods as long as 20 days. In addition, in the skin infection model, MB₁₂-2, as a wound dressing, showed remarkable photothermal antibacterial activity (>97%) under 660-nm laser irradiation and promoted wound healing. This study presents a simple method for designing long-term water-stable supramolecular radicals, offering a novel avenue for noncontact treatments for bacterial infections.