Photon Upconversion Enhanced by Ag₂₉ Nanocluster Sensitizers and Multifunctional P(DPA)₃ Acting as Triplet Mediator, Annihilator, and Emitter

The [Ag₂₉(BDT)₁₂]^3- nanocluster (<b>Ag</b>_<b>29</b>, BDT = 1,3-benzenedithiolate) is renowned for its high stability, photoluminescence, and ability to accommodate up to four phosphine compounds as secondary ligands. Herein, the multichromophoric phosphine derivative P(DPA)₃, bearing three 9,10-diphenylanthracene (DPA) units, was employed to serve triple roles: triplet-energy mediator ligand, annihilator, and emitter. By adding an excess amount of P(DPA)₃ to <b>Ag</b>_<b>29</b>, a solution was prepared containing [Ag₂₉(BDT)₁₂[P(DPA)₃]_<i>n</i>]^3- (<b>Ag</b>_<b>29</b><b>PDPA</b>, <i>n</i> = 1-4) complexes coexisting with unbound (free) P(DPA)₃ molecules. This enabled efficient intra- and intermolecular triplet energy transfer from photoexcited <b>Ag</b>_<b>29</b>, first to the bound and then to the unbound P(DPA)₃. Under 532 nm excitation, the system achieved a green-to-blue UC internal quantum yield of 24.0% (48% normalized to the 100% maximum) and a significantly low threshold intensity of 2.0 mW cm^-2. Remarkably, this performance rivals that of the benchmark Pt(II)-octaethylporphine/DPA pair, establishing the <b>Ag</b>_<b>29</b><b>PDPA</b>/P(DPA)₃ combination as a high-performing green-to-blue UC system.