Stabilizing\nDye-Sensitized Upconversion Hybrids by\nCyclooctatetraene

Lanthanide-doped upconversion nanoparticles (UCNPs) can\nconvert\nlow-energy near-infrared (NIR) light into high-energy visible light,\nmaking them valuable for broad applications. UCNPs often suffer from\npoor light-harvesting capabilities, which can be significantly improved\nby incorporating organic dye antennas. However, the dye-sensitized\nupconversion systems are prone to severe photobleaching in an ambient\natmosphere. Here, we present a synergistic approach to mitigate photobleaching\nby introducing triplet state quencher cyclooctatetraene (COT). COT\neffectively suppresses the generation of singlet oxygen by quenching\nthe triplet states of the dye and consumes the existing singlet oxygen\nthrough oxidant reactions. The inclusion of COT extends the half-life\nof IR806 by 4.7-times by preventing the oxidation of its poly(methylene)\nchains. Without significantly affecting emission intensity and dynamics,\nCOT effectively stabilized dye-UCNPs, demonstrating a notable 3.9-fold\nincrease in half-life under continuous laser irradiation. Our findings\nsuggest a new strategy to enhance the photostability of near-infrared\ndyes and dye-sensitized upconversion nanohybrids.