Triplet-Mediated Photon Upconversion via Near-Infrared-II Excitation without Tetracene Derivatives.

Nearly all triplet-mediated near-infrared (NIR, over 800 nm) photon upconversion materials have traditionally relied on tetracene derivatives as surface ligands or annihilators. However, the inherent limitations of these compounds, such as poor stability and limited energy level tunability, have significantly impeded the development of NIR-excitable triplet-sensitized photon upconversion materials. In this work, we introduce a distyryl-substituted BODIPY (DS-BDP) derivative that exhibits exceptional stability and spectral tunability, enabling it to function dually as both a surface ligand and an annihilator in quantum dot-based photon upconversion with color-tunable emission under 1064 nm excitation. The incorporation of dicarboxylic acid anchoring groups not only enhances ligand exchange density and facilitates efficient triplet exciton transfer from quantum dots to surface ligands but also effectively suppresses excited-state energy losses caused by ligand conformational relaxation. This ensures high upconversion efficiency in NIR-II-excitable quantum dot-based upconversion materials, even at low surface ligand coverage. Our findings overcome the long-standing limitations associated with tetracene derivatives in photon upconversion and establish a robust material platform with excellent performance and stability for applications in nanophotonics, biophotonics, and photochemistry.