Ultrafast Triplet–Singlet Exciton Interconversion in Narrowband Blue Organoboron Emitters Doped with Heavy Chalcogens. (15th June 2022)

• Record Type: Journal Article
• Authors: Park, In Seob; Min, Hyukgi; Yasuda, Takuma
• Is Part Of: Angewandte Chemie. Volume 134:Number 31(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-06-15
• Subjects: Narrowband Emission -- Organic Light-Emitting Diodes -- Organoboron Compounds -- Spin-Orbit Coupling -- Superimposed Fluorescence; Chemistry -- Periodicals; 540
• DOI: 10.1002/ange.202205684
• Languages: English
• ISSNs: 0044-8249

Abstract

Abstract: Narrowband emissive organoboron emitters featuring the multi‐resonance (MR) effect have now become a critical material component for constructing high‐performance organic light‐emitting diodes (OLEDs) with pure emission colors. These MR organoboron emitters are capable of exhibiting high‐efficiency narrowband thermally activated delayed fluorescence (TADF) by allowing triplet‐to‐singlet reverse intersystem crossing (RISC). However, RISC involving spin‐flip exciton upconversion is generally the rate‐limiting step in the overall TADF; hence, a deeper understanding and precise control of the RISC dynamics are ongoing crucial challenges. Here, we introduce the first MR organoboron emitter (CzBSe ) doped with a selenium atom, demonstrating a record‐high RISC rate exceeding 10 8 s −1, which is even higher than its fluorescence radiation rate. Furthermore, the spin‐flip upconversion process in CzBSe can be accelerated by factors of ≈20000 and ≈800, compared to those of its oxygen‐ and sulfur‐doped homologs (CzBO and CzBS ), respectively. Unlike CzBO and CzBS, the photophysical rate‐limiting step in CzBSe is no longer RISC, but the fluorescence radiation process; this behavior is completely different from the conventional time‐delaying TADF limited by the slow RISC. Benefitting from its ultrafast exciton spin conversion ability, OLEDs incorporating CzBSe achieved a maximum external electroluminescence quantum efficiency as high as 23.9 %, accompanied by MR‐induced blue narrowband emission and significantly alleviated efficiency roll‐off features. Abstract : A selenium‐doped polycyclic organoboron emitter exhibits ultrafast triplet–singlet exciton interconversion ability in addition to strong narrowband blue emission. Its spin‐flip reverse intersystem crossing (RISC) rate exceeds 10 8 s −1 (100 million times spin inversion per second), enabling superimposed fluorescence with full exciton utilization. This breakthrough shatters the stereotypical physicochemical views of conventional thermally activated delayed fluorescence limited by slow RISC.