Photon upconversion with indium phosphide quantum dots enables high-energy photoreactions using visible light

Photochemical reactions that rely on high-energy photons are limited by low solar abundance in the UV region and undesired photodecomposition. Photon upconversion processes, particularly triplet-triplet annihilation-based upconversion (TTA-UC), provide an alternate pathway to enable the use of low-energy, abundant visible and near-infrared (NIR) light for chemical transformations that typically require high-energy UV light. In this context, quantum dot (QD)-sensitized TTA-UC systems offer distinct advantages with respect to a larger anti-Stokes shift, enhanced upconversion quantum yield, and superior photostability. However, the successful application of QD-sensitized upconversion energy in photocatalysis remains limited, especially for high-energy reactions requiring UV-active catalysts. Here, we report the use of upconversion energy from a QD-sensitized TTA-UC system in performing a high-energy-driven dehalogenation reaction with visible light. Indium phosphide (InP) QDs are used as the sensitizer and diphenylanthracene (DPA) as the annihilator molecule, which gave a green-to-blue TTA-UC with a normalized upconversion quantum yield of ∼8.2% and an apparent anti-Stokes shift of 0.55 eV. The upconversion energy from the InP QD-sensitized TTA-UC system is effectively used to drive a photoredox C-C coupling reaction <i>via</i> the dehalogenation of substituted aryl halides in excellent yields. TTA-UC is the sole driving force for this photoredox reaction, as the required potential is beyond the maximum achievable redox potential of InP-QDs. Further, the scope of the QD-sensitized TTA-UC system is extended towards the radical polymerization of methyl methacrylate (MMA), resulting in the production of industrially important polymethyl methacrylate (PMMA). Our work overcomes key limitations of traditional UV-based photochemistry and introduces a sustainable, low-energy pathway for enabling high-energy transformations.