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A novel class of o‐carboranyl luminophores, 2CB‐BuDABNA (1) and 3CB‐BuDABNA (2) is reported, in which o‐carborane moieties are incorporated at the periphery of the B,N‐doped multi‐resonance thermally activated delayed fluorescence (MR‐TADF) core. Both compounds maintain the inherent local emission characteristics of their MR‐emitting core, exhibiting intense MR‐TADF with high photoluminescence quantum yields in toluene and rigid states. In contrast, the presence of the dark lowest‐energy charge transfer state, induced by cage rotation in THF, is suggested to be responsible for emission quenching in a polar solvent. Despite the different arrangement of the cage on the DABNA core, both 1 and 2 show red‐shifted emissions compared to the parent compound BuDABNA (3). By utilizing 1 as the emitter, high‐efficiency blue organic light‐emitting diodes (OLEDs) are achieved with a remarkable maximum external quantum efficiency of 25%, representing the highest reported efficiency for OLEDs employing an o‐carboranyl luminophore as the emitter. [ABSTRACT FROM AUTHOR]

Designing multi‐resonance (MR) emitters that can simultaneously achieve narrowband emission and suppressed intermolecular interactions is challenging for realizing high color purity and stable blue organic light‐emitting diodes (OLEDs). Herein, a sterically shielded yet extremely rigid emitter based on a triptycene‐fused B,N core (Tp‐DABNA) is proposed to address the issue. Tp‐DABNA exhibits intense deep blue emissions with a narrow full width at half maximum (FWHM) and a high horizontal transition dipole ratio, superior to the well‐known bulky emitter, t‐DABNA. The rigid MR skeleton of Tp‐DABNA suppresses structural relaxation in the excited state, with reduced contributions from the medium‐ and high‐frequency vibrational modes to spectral broadening. The hyperfluorescence (HF) film composed of a sensitizer and Tp‐DABNA shows reduced Dexter energy transfer compared to those of t‐DABNA and DABNA‐1. Notably, deep blue TADF‐OLEDs with the Tp‐DABNA emitter display higher external quantum efficiencies (EQEmax=24.8 %) and narrower FWHMs (≤26 nm) than t‐DABNA‐based OLEDs (EQEmax=19.8 %). The HF‐OLEDs based on the Tp‐DABNA emitter further demonstrate improved performance with an EQEmax of 28.7 % and mitigated efficiency roll‐offs. [ABSTRACT FROM AUTHOR]

Doubly boron‐doped thermally activated delayed fluorescence (TADF) emitters based on a 9,10‐diboraanthracene (DBA) acceptor decorated with ortho‐donor groups (Cz2oDBA, 2; BuCz2oDBA, 3; DMAC2oDBA, 4) are prepared to realize high‐efficiency green‐to‐red organic light‐emitting diodes (OLEDs). X‐ray diffraction analyses of 2 and 4 reveal the symmetrical and highly twisted ortho‐donor–acceptor–donor (D‐A‐D) structure of the emitters. The twisted conformation leads to a very small energy splitting (ΔEST <0.08 eV) between the excited singlet and triplet states that gives rise to strong TADF, as supported by theoretical studies. Depending on the strength of the donor moieties, the emission color is fine‐tuned in the visible region from green (2) to yellow (3) to red (4). Carbazole‐containing 2 and 3 exhibit high photoluminescence quantum yields (PLQYs) approaching 100 %, whereas DMAC‐substituted 4 is moderately emissive (PLQY=44 %) in a doped host film. Highly efficient green‐to‐red TADF‐OLEDs are realized with the proposed ortho‐D‐A‐D compounds as emitters. The green and yellow OLEDs incorporating Cz2oDBA (2) and BuCz2oDBA (3) emitters exhibit high external quantum efficiencies (EQEs) of 26.6 % and 21.6 %, respectively. In particular, the green device shows an excellent power efficiency above 100 lm W−1. A red OLED fabricated with a DMAC2oDBA (4) emitter exhibits a maximum EQE of 10.1 % with an electroluminescence peak at 615 nm. [ABSTRACT FROM AUTHOR]

[Display omitted] • Rigid TADF emitters based on a spiro-fluorenyl B -heterotriangulene acceptor were prepared. • The emitters exhibit narrowband blue emissions (FWHM = 52 nm) with unitary PLQYs in doped host films. • Fast RISC (∼106 s−1) is achieved by the strong SOC between the T 2 (3LE) and S 1 (1CT) states. • The doped host films exhibit excellent horizontal transition dipole orientation ratios of ∼0.90. • Blue TADF-OLEDs demonstrate a state-of-the-art EQE of 36.4% with supressed roll-off. The design of robust thermally activated delayed fluorescence (TADF) emitters is crucial in realizing highly efficient and stable blue TADF-organic light-emitting diodes (OLEDs). Here boron-based donor–acceptor-type blue TADF compounds incorporating a triply-bridged, spiro-type boron acceptor; namely, spiro-fluorenyl B -heterotriangulene, and 9,9-diphenyl-9,10-dihydroacridine (DPAC, 1) or 10 H -spiro[acridine-9,9′-fluorene] (sAC, 2) donors are presented. Their doped host films show blue emissions with narrow full width at half maximum values of 52 nm (0.29 eV) and unitary photoluminescence quantum yields. The compounds exhibit short-lived delayed fluorescence (τ d = 1.8–2.7 μs) and undergo fast reverse intersystem crossing with the rate constants of ∼106 s−1 in the film state. These are attributable to the small singlet–triplet energy splitting of ∼40 meV and the effective spin–orbit coupling between the singlet (1CT, S 1) and local triplet (3LE, T 2) excited states. From outstanding horizontal transition dipole orientation ratios of 0.89 and 0.90 for the host films of 1 and 2 , respectively, high-efficiency blue TADF-OLEDs showing maximum external quantum efficiencies (EQEs) of over 30% are realized. Notably, the device with the fully spiro 2 achieves a state-of-the-art EQE max of 36.4% and a suppressed efficiency roll-off, with a high EQE of 26.3% even at 1,000 cd/m2, highlighting the synergistic effect between the spiro-structure and the B -heterotriangulene acceptor skeleton. [ABSTRACT FROM AUTHOR]

Two pairs of para -donor-appended triarylboron compounds that are derived from 9,9-dialkylacridine (9,9-dimethylacridine (DMAC) or 9,9-diphenylacridine (DPAC)) donors and boryl (9-boraanthryl (BA) or dimesitylboryl (BMes 2)) acceptors are prepared and characterized. X-ray diffraction studies reveal that the BA ring is nearly orthogonal to the phenylene linker, whereas the BMes 2 moiety is tilted by ca. 60°. The BA-containing compounds exhibit blue thermally activated delayed fluorescence (TADF) in both the solution and film states. In contrast, BMes 2 -containing compounds display normal blue fluorescence in solution, while TADF is induced in their films. The small Δ E ST values (<0.1 eV) and high k RISC (ca. 106 s−1) of the doped films of the BA-containing compounds support the strong TADF character with the short-lived delayed fluorescence (τ d = 1.6–2.0 μs). The theoretical studies along with the experimental results reveal that the electronic transitions in the BA-containing compounds proceed by the stronger charge transfer from the donor to the acceptor moieties than the BMes 2 -containing compounds. Pure to deep blue TADF-OLEDs are realized with all compounds as the dopants. The devices employing the DMAC donor-based emitters exhibit high device performance with a maximum external quantum efficiency (EQE) of 21.3%. However, lower EQEs (<12.8%) and severe efficiency roll-off are observed for the devices with the DPAC donor-based emitters. Image 1 • Para -acridine-appended triarylboron compounds with cyclic boryl (BA) and diarylboryl (BMes 2) acceptors were prepared. • All compounds exhibited pure to deep blue thermally activated delayed fluorescence in the film states. • BA-containing emitters underwent strong charge transfer transitions. • The blue OLED devices based on the emitters exhibited high external quantum efficiencies of over 20%. [ABSTRACT FROM AUTHOR]