Rational Design of Color‐Pure Blue Organic Emitters by Poly‐Heteroaromatic Omni‐Delocalization

Abstract Current research on organic light emitters which utilize multiple resonance‐induced thermally activated delayed fluorescence (MR‐TADF) materials is gaining significant interest because of the materials’ ability to efficiently generate color‐pure blue emission. However, the underlying reasons for high color purity remain unclear. It is shown here that these emitters share a common electronic basis, which is deduced from resonance structure considerations following Clar's rule, and which is termed as “poly‐heteroaromatic omni‐delocalization” (PHOD). The simple and clear design rules derived from the PHOD concept allow extending the known chemical space by new structural motifs. Based on PHOD, a set of novel high‐efficiency color‐pure emitters with brilliant deep‐blue hue is specifically designed.