Thermally Activated Delayed Fluorescence and Room‐Temperature Phosphorescence in Sulfidoazatriangulene‐Based Materials and their S‐oxides

Abstract Structural constraint is an emerging strategy for improving the photoluminescence quantum yield, molar absorptivity, and color purity of luminescent materials. In this report, emitters displaying thermally activated delayed fluorescence (TADF) are achieved for the first time using the planarized donor sulfidotetramethyazatriangulene (SMAT). Compared to non‐planarized phenothiazine (PTZ) donors, the enhanced rigidity of SMAT contributes to improved color purity and photoluminescence quantum yield, with up to 90% quantum yield observed for donor–acceptor compounds in toluene solution. Planarized SMAT‐based emitters also offer up to tenfold enhancement in two‐photon absorption cross‐section compared to analogous PTZ‐based materials. Oxidation of sulfur‐containing donors to sulfoxide and sulfone derivatives is demonstrated as a simple and generalizable means of tuning the electron‐donating ability of sulfur‐containing moieties. SMAT‐TRZ and SOMAT‐TRZ both exhibit TADF, with green and blue emission, respectively, while SO 2 MAT‐TRZ displays blue room temperature phosphorescence. Overall, this work demonstrates that SMAT and its S‐oxides can be used to design high‐performance luminescent materials with emergent properties such as TADF or room‐temperature phosphorescence.