Binary Annihilator Systems for NIR-II Upconversion: Synergistic FRET and Hetero-TTA Enable Enhanced Upconversion Quantum Yield

High Resolution Image Download MS PowerPoint Slide Triplet–triplet annihilation upconversion (TTA-UC) in the near-infrared II region holds promise for beyond-silicon photovoltaics and deep-tissue imaging but remains inefficient due to stringent energetic requirements in single-annihilator systems, limiting design space to only a few viable materials. Mixed-annihilator systems provide a strategy to circumvent these constraints, yet the complex mechanistic pathways governing their enhanced performance lack a quantitative understanding. Here, we examine binary mixtures of rubrene, TES-ADT, and V79 sensitized by PbS quantum dots. Using time-resolved single-photon counting with spectral deconvolution, we quantify the relative contributions of singlet-mediated FRET and collectively triplet-mediated pathways involving interannihilator triplet transfer and hetero -TTA in mixed TES-ADT/V79 blends. Our analysis indicates that both singlet- and triplet-mediated pathways contribute substantially to the enhanced upconversion emission and act cooperatively to redistribute upconverted emission toward V79, reducing reabsorption losses, enhancing optical outcoupling, and yielding up to 2-fold enhancement in upconversion quantum yield at an optimal TES-ADT/V79 ratio of 31:1. These results establish a quantitative framework for evaluating singlet- and triplet-mediated contributions in multicomponent TTA systems and provide design principles for next-generation NIR-II upconversion.