Near-Infrared to Visible Photon Upconversion with Gold Quantum Rods and Aqueous Photo-Driven Polymerization

Converting near-infrared (NIR) photons into visible light via triplet-triplet annihilation upconversion (TTA-UC) is a promising strategy for advancing energy, biomedical, and materials science. However, the development of efficient NIR sensitizers remains a major challenge. Here, we report an atomically precise gold quantum rod, Au₄₂(PET)₃₂ (PET = 2-phenylethanethiolate), as a high-performance photosensitizer for NIR-to-visible TTA-UC. Paired with TES-ADT as an annihilator, the system exhibits a 6.7% quantum yield, a 0.5 eV anti-Stokes shift, and a low threshold intensity of 90 mW/cm². To enable aqueous compatibility, the upconversion nanodroplets are encapsulated with a silica shell, yielding Au₄₂/TES-ADT@SiO₂ nanoparticles (NPs) capable of driving efficient photoinduced atom-transfer radical polymerization (photo-ATRP) and forming hydrogels in water. This system offers a versatile platform for the next generation photopolymerization with NIR light, solar energy utilization and noninvasive biomedical applications.