Spiro−type TADF emitters based on acridine donors and anthracenone acceptor. (January 2022)

• Record Type: Journal Article
• Authors: Yang, Dongwook; Huh, Jin-Suk; Hong, Jong-In
• Is Part Of: Dyes and pigments. Volume 197(2022)
• Publication Date: 2022-01
• Subjects: Organic light emitting diodes -- Thermally activated delayed fluorescence -- Spiro-type TADF -- D-σ-A structure; Dyes and dyeing -- Periodicals; Pigments -- Periodicals; 667.2
• DOI: 10.1016/j.dyepig.2021.109873
• Languages: English
• ISSNs: 0143-7208

Abstract

Abstract: Two rigid spiro-type TADF emitters (CBZANQ, PXZANQ) were designed and synthesized via a two-step route. CBZANQ and PXZANQ both contain an anthracenone acceptor along with a carbazole‒acridine-fused donor and a phenoxazine‒acridine-fused donor, respectively, where each donor and acceptor are linked by a spiro bridge to form D-σ-A structures with an orthogonal arrangement. Both CBZANQ and PXZANQ have the difference between the singlet and triplet energy values (ΔEST ) of 0.05 eV and 0.03 eV, respectively, which are sufficiently small for efficient triplet harvesting. CBZANQ with a weak electron donor (carbazole) exhibited a weak intramolecular charge transfer (ICT) character, resulting in a low photoluminescence quantum yield (PLQY) of 18%. On the other hand, when combined with a strong electron donor (phenoxazine), PXZANQ exhibited a strong ICT character, resulting in a high PLQY of 71%. Organic light-emitting diode (OLED) devices based on CBZANQ emitter and bis[2-(diphenylphosphino)phenyl] ether oxide (DPEPO) host exhibited sky-blue electroluminescence (EL) at 492 nm with a low external quantum efficiency (EQE) of 6.7%. Conversely, the OLED devices fabricated using PXZANQ emitter and DPEPO host exhibited green emission at 528 nm, along with a high EQE of 22.1%. Additionally, the efficiency of PXZANQ-based devices remained high at high luminance, indicating relatively small efficiency roll-off (13.9% EQE under 500 cd/m 2 ). Graphical abstract: Image 1 Highlights: We synthesized spiro−type thermally activated delayed fluorescence (TADF) emitters, CBZANQ and PXZANQ . σ-Bonding between electron donor and electron acceptor barely allowed π delocalization from D to A resulting in small ΔEST . CBZANQ-based device shows a maximum quantum efficiency (EQE) of 6.7% due to low photoluminance quantum yield (PLQY) of 18%. PXZANQ -based device shows EQE of 22.1%, which is the highest EQE among D-σ-A type TADF emitters reported so far.