Metal‐Free Organic Triplet Emitters with On–Off Switchable Excited State Intramolecular Proton Transfer

Metal-free organic triplet emitters are an emerging class of semiconducting material. Among them, molecules with tunable emission responsive to environmental stimuli have shown great potential in solid-state lighting, sensors, and anti-counterfeiting systems. Here, a novel excited-state intramolecular proton transfer (ESIPT) system is proposed showing the activation thermally activated delayed fluorescence (TADF) or room-temperature phosphorescence (RTP) simultaneously from both keto enol tautomers. The prototype ESIPT exhibit up 50% quantum yield. Their enol–keto tautomerization can be switched by controlling matrix acidity doped polymer films. Taking advantage these unique properties, “on-off” switchable systems controlled acid vapor annealing, as well photopatterning capable generating facile high-contrast emissive patterns, devised.