Gong, X.X.GongLu, C.-H.C.-H.LuLee, W.-K.W.-K.LeeLi, P.P.LiHuang, Y.-H.Y.-H.HuangChen, Z.Z.ChenZhan, L.L.ZhanCHUNG-CHIH WUGong, S.S.GongYang, C.C.Yang2021-03-262021-03-262021https://www.scopus.com/inward/record.url?eid=2-s2.0-85089582726&partnerID=40&md5=5e4edb4f43be1529ac771ce3a77397a4https://scholars.lib.ntu.edu.tw/handle/123456789/555319Red thermally activated delayed fluorescence (TADF) emitters underperform their blue and green counterparts, largely due to their low photoluminescence quantum efficiency and isotropic orientation. Here, we designed two rigid and strong electron-rich donor moieties, 3-methyl-13H-spiro[benzo[4,5]thieno[3,2-c]acridine-5,9′-fluorene] (MSTA) and 3-phenyl-13H-spiro[benzo[4,5]thieno[3,2-c]acridine-5,9′-fluorene] (PSTA), by fusing benzothiophene unit on a spiro-acridine framework. Combined with a rigid, linear, and planar acenaphtho[1,2-b]quinoxaline-9,10-dicarbonitrile (ANQDC) acceptor, two red emitters, ANQDC-MSTA and ANQDC-PSTA, were synthesized and characterized. In virtue of high rigidity and linear donor–acceptor (D-A) molecular skeleton, both emitters showed distinct TADF nature, high photoluminescence quantum efficiencies and high horizontal ratios of emitting dipole orientation of ≈85%. Consequently, the ANQDC-PSTA-based OLEDs realized high external quantum efficiency (EQE) of 24.7% at an electroluminescence peak (ELpeak) of 622 nm, together with Commission Internationale de l'Eclairage 1931 (CIE1931) coordinates of (0.61, 0.38). Furthermore, with the modulation of the microcavity effect on the device architecture, we delivered a 19.1% EQE in a deep-red EL region, with an ELpeak of 646 nm and favorable CIE1931 coordinates of (0.64, 0.36). These efficiencies are on par with the highest EL performance for red TADF OLEDs in the similar color gamut. © 2020 Elsevier B.V.Electron donor; Emitting dipole orientation; Organic light-emitting diodes; Red emitters; Thermally activated delayed fluorescence[SDGs]SDG7Efficiency; Electroluminescence; Fluorescence; Molecular orientation; Organic light emitting diodes (OLED); Photoluminescence; Thiophene; Device architectures; Dipole orientation; External quantum efficiency; High-efficiency; Microcavity effects; Molecular skeleton; Photoluminescence quantum efficiency; Thermally activated delayed fluorescences; Quantum efficiencyjournal article10.1016/j.cej.2020.1266632-s2.0-85089582726