Visible‐to‐UV Photon Upconversion: Recent Progress in New Materials and Applications

Ultraviolet (UV, λ400 nm) light to UV light. Among several mechanisms, UC based on triplet‐triplet annihilation (TTA‐UC) in particular has made remarkable progress in recent years. The development of new chromophores has enabled highly efficient conversion of low‐intensity visible light into UV light. In this review, we summarize the recent development of visible‐to‐UV TTA‐UC, from the development of chromophores and their production into films to their application in various photochemical processes such as catalysis, bond activation and polymerization. Finally, challenges and opportunities in future material development and applications will be discussed. This Review summarizes recent progress in photon upconversion from visible to ultraviolet light based on triplet‐triplet annihilation. The development of new chromophores, which have achieved high efficiency and low threshold excitation intensity, the material design for film formation, and their application in various photochemical processes are summarized, and the future challenges as an ultraviolet light source are discussed.