Efficient near-infrared-excitable quantum dot-based triplet–triplet annihilation upconversion with a record anti-Stokes shift via low coverage of mono-styryl-BODIPY ligands

Abstract

Ligands anchored on quantum dot surfaces with matched energy levels can significantly enhance triplet–triplet annihilation photon upconversion. In this study, we report a novel surface ligand (monosubstituted styryl-BODIPY) on near-infrared-absorbing lead sulfide quantum dots (PbS QDs) that achieves a high triplet exciton transfer efficiency of 65.4% as determined by femtosecond transient absorption spectroscopy, with an average of only seven ligands per quantum dot. Using rubrene as the annihilator, an upconversion efficiency of up to 16.8% ± 0.6% (normalized to 100%) is observed. Our newly developed BODIPY-derived ligand exhibits enhanced stability compared to widely reported tetracene-based surface ligands. Furthermore, its higher T₁ energy level allows coupling with the cyan-emitting annihilator 9,10-bis(phenylethynyl)anthracene, achieving a significant anti-Stokes shift from 808 nm excitation to 480 nm emission—an advancement not previously realized in NIR-excited QD-based TTA-UCs. This work provides a new opportunity, from the perspective of ligand design, to enhance quantum dot-based upconversion performance and expand the TTA-UC anti-Stokes shift using QDs into the cyan blue region, thereby advancing the development of efficient and stable upconversion materials.