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

Abstract

Metal-free organic triplet emitters are an emerging class of organic 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 of thermally activated delayed fluorescence (TADF) or room-temperature phosphorescence (RTP) simultaneously from both keto and enol tautomers. The prototype ESIPT triplet emitters exhibit up to 50% delayed emission quantum yield. Their enol–keto tautomerization can be switched by controlling the matrix acidity in doped polymer films. Taking advantage of these unique properties, “on-off” switchable triplet emission systems controlled by acid vapor annealing, as well as photopatterning systems capable of generating facile and high-contrast emissive patterns, are devised.