Spiro‐Based Thermally Activated Delayed Fluorescence Emitters for Organic Light‐Emitting Diodes

Abstract Spiro structures, possessing unique π‐electron systems, large steric hindrance, high glass transition temperature, and chemical stability, serve as critical structural building blocks in constructing thermally activated delayed fluorescence (TADF) emitters. The incorporation of various heteroatoms such as oxygen, sulfur, and nitrogen in 9,9′‐spirobifluorene generates diverse spiro structures like spiro[fluorene‐9,9′‐xanthene], spiro[fluorene‐9,9′‐thioxanthene], and spiro[acridine‐9,9′‐fluorene]. Based on the charge transfer characteristics, TADF emitters built upon spiro structures can be classified into various types, including twisted intramolecular charge transfer, through‐space charge transfer, multiresonance, and exciplex‐type TADF emitters. This review systematically highlights the recent progress in the research on TADF emitters comprised of spiro‐structured aromatics. It intricately explores the molecular design strategies, material synthesis methods, understanding of photophysical attributes, and analysis of organic light‐emitting diode performance. Concurrently, it sketches out the challenges faced in the commercial application stage while providing an outlook for potential research trajectories.