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 (Ag29, 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 Ag29, a solution was prepared containing [Ag29(BDT)12[P(DPA)3]n]3– (Ag29PDPA, n = 1–4) complexes coexisting with unbound (free) P(DPA)3 molecules. This enabled efficient intra- and intermolecular triplet energy transfer from photoexcited Ag29, 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 Ag29PDPA/P(DPA)3 combination as a high-performing green-to-blue UC system.