Triplet–Triplet Annihilation Upconversion: From Molecules to Materials

Abstract

Photon upconversion, particularly triplet–triplet annihilation upconversion (TTA-UC), converts low-energy photons into higher-energy ones through multiphoton fusion, offering unique photophysical properties with broad applications. As a new generation of organic upconversion materials, TTA-UC shows great promise in biosensing, biomedicine, photoredox catalysis, and solar energy harvesting. For example, TTA-UC-based nanoprobes enable highly sensitive, background-free biomarker detection; TTA-UC nanoparticles act as phototransducers that extend optogenetic responses into the near-infrared region; their nonlinear luminescence supports high-resolution 3D printing; and they enhance photon utilization in photovoltaics. Although significant progress has been made in the past decade, challenges remain, including developing high-performance near-infrared TTA-UC pairs with ultralarge anti-Stokes shifts, creating general strategies for synthesizing water-dispersible and oxygen-resistant nanoparticles, and expanding biomedical applications to promote clinical translation.