Steric Rooted Multi‐Resonant Thermally Activated Delayed Fluorescent Emitters for Pure Blue Organic Light Emitting Diodes with Ultralow Efficiency Roll‐Off

• Published in: Advanced functional materials Vol. 33; no. 35
• Main Authors: Ravindran, Ezhakudiyan, Baek, Ho Eon, Son, Hee Won, Park, Ji Hyun, Kim, Yun‐Hi, Suh, Min Chul
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.08.2023
• Subjects: Dipoles; Efficiency; Emission spectra; Emitters; Fluorescence; fused and extended π‐skeletons; Materials science; meta‐xylene substituents; multiple resonance effect; Narrowband; narrowband pure blue emission; Organic light emitting diodes; Photoluminescence; Quantum efficiency; Steric hindrance; ultralow efficiency roll‐off; Xylene
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.202213461

Multi‐resonant thermally activated delayed fluorescent (MR‐TADF) materials are blooming for high‐resolution organic light‐emitting diodes (OLEDs). However, boron/nitrogen (B/N)‐integrated MR‐TADF emitters suffer severe efficiency roll‐off from their strong inter‐molecular π–π interactions. Herein, versatile narrowband pure blue emitters (mono‐mx‐CzDABNA and tri‐mx‐CzDABNA) are demonstrated featuring a ring‐fused extended π‐skeleton: a classic steric hindrance and rigidity accessed by integrating with meta‐xylene (mx) rotors. tri‐mx‐CzDABNA shows a narrowband (FWHM, 26 nm) pure blue emission (λmax, 462 nm) with substantial hypsochromic shift (12 nm) while maintaining MR‐TADF characteristics. The key solid‐state analyses conclude that they conceivably suppress the non‐radiative energy loss, thus improving the photoluminescence quantum yield (PLQY > 90%) and rate of reverse intersystem crossing (RISC) (kRISC ≈2.85 × 105 s−1). The integration of tri meta‐xylene significantly leads to an enhanced horizontal dipole ratio (HDR) from 65% to 85%. Hyperfluorescent‐OLEDs are fabricated using designed MR‐TADF as terminal emitter, achieving a narrowband (FWHM, 34 nm) pure blue electroluminescence (λmax, 472 nm) and maximum external quantum efficiency (EQEmax) of 26.97% with magnificently suppressed efficiency roll‐off (7.8%) at 1000 cd m−2. So, it is believed that regulation of internal efficiencies and high color purity can amplify the route to achieving a narrowband pure blue emission through new synthetic MR‐TADF approaches. The architecture of the ring fuses and extends π‐skeleton based on high‐order B/N‐embedded steric rooted and structurally rigid hypsochromic‐shifted narrow‐band pure blue multi‐resonant thermally activated delayed fluorescent emitter for efficient and ultralow‐efficiency roll‐off hyperfluorescent‐organic light‐emitting diodes.