Π‐Radical Photosensitizer for Highly Efficient and Stable Near‐Infrared Photon Upconversion

Abstract Near‐infrared (NIR)‐to‐blue triplet–triplet annihilation upconversion (TTA‐UC) exhibits substantial potential for diverse applications, encompassing photovoltaics, photocatalysis, bioimaging, and photodynamic therapy. A major challenge in this field, however, is attaining high upconversion quantum yields (Φ_UC) without using transition metals as NIR photosensitizers. This research presents an innovative organic π‐radical photosensitizer (TTM‐TPA) featuring extended absorption in the NIR region (≈760 nm) that is capable of generating pronounced anti‐Stokes emissions when coupled with suitable triplet acceptors. By eliminating energy loss associated with intersystem crossing and promoting rapid doublet–triplet energy transfer processes, the binary TTM‐TPA/perylene system achieves Φ_UC values of up to 6.8% and an anti‐Stokes shift of 0.93 eV. Notably, the TTA‐UC system demonstrates exceptional stability when subjected to intense 733 nm laser irradiation (4 W cm⁻²), maintaining nearly constant upconversion intensity after 4 h. These findings underscore the considerable potential of doublet‐sensitized TTA‐UC for a broad array of practical applications.