Triplet–Triplet Annihilation Photon Upconversion Toward UVC Energy Generation Using TIPS‐Benzene and a Heptazine Derivative

Abstract UV energy generation via triplet‐triplet annihilation‐based photon upconversion (TTA‐UC) plays a pivotal role in enabling high‐energy photochemical reactions. However, generating UVB/UVC energy through TTA‐UC remains a significant challenge. In this work, the TTA‐UC from visible/UVA to UVB/UVC is demonstrated by combining (triisopropylsilyl)ethynyl benzene (TIPS‐benzene)‐based emitters with an organic sensitizer, a heptazine derivative. The heptazine derivative exhibits absorption in the visible/UVA region and has a triplet energy level high enough to sensitize the TIPS‐benzene‐based emitters. The introduction of bulky substituents into TIPS‐benzene suppresses the deactivation pathways of the excited triplet state that compete with TTA, thereby enhancing the TTA‐UC efficiency. This study demonstrates the direction of molecular design for the challenging generation of UVB/UVC energy.