Extending the π‐Skeleton of Multi‐Resonance TADF Materials towards High‐Efficiency Narrowband Deep‐Blue Emission

Abstract

Multi-resonance TADF (MR-TADF) emitters are promising for high-resolution OLEDs, but the concurrent optimization of excited-state dynamics and color purity remains a tough challenge. Herein, three deep-blue MR-TADF compounds (BN1-BN3) featuring gradually enlarged ring-fused structures and increased rigidity are accessed by lithiumfree borylation in high yields from the same precursor, with all the emitters possessing CIE y coordinates below 0.08. Structure-property investigations demonstrate a strategic improvement of the oscillator strength (f osc ) and acceleration of the reverse intersystem crossing (RISC) process by extending the π-skeleton, where BN3 realizes a maximum external quantum efficiency (EQE) of 37.6 % and reduced roll-off, thus showing the best efficiency reported for deep-blue TADF OLEDs. The internal regulation of the efficiency and color purity of these compounds validate the general effectiveness to achieve advanced deep-blue narrowband emitters with higher-order boron/nitrogen-based MR motifs.

Narrowband Emissive Thermally Activated Delayed Fluorescence Materials

“…As a result, the TADF‐OLED using NBNP exhibited a high EQE max of 28.0% based on a narrowband green EL (λ EL = 502 nm and FWHM EL = 33 nm), together with a low efficiency roll‐off. Almost simultaneously, Yang and co‐workers reported a series of deep‐blue MR‐TADF materials, BN1 , BN2 , and BN3 [ 69 ] (Figure 4, see Section 3.3 for BN3 ), with fused π‐extended MR skeletons. Owing to its increased rigidity and π‐extension, BN2 exhibited red‐shifted emission with λ PL of 464 nm and a narrower FWHM PL of 15 nm relative to BN1 (λ PL = 454 nm and FWHM PL = 18 nm in toluene).…”

Boron‐Based Narrowband Multiresonance Delayed Fluorescent Emitters for Organic Light‐Emitting Diodes

“…In 2022, Yang et al reported three deep blue MR‐TADF emitters ( BN1 , BN2 , and BN3 ) by extending the π ‐skeleton by increasing the number of phenyl rings from 7 to 13. [ 95 ] The designed emitters were synthesized by a one‐pot lithium‐free cyclization method. All three emitters exhibited high PLQY of over 90%, with increased k RISC from BN1 to BN3 .…”

Boron‐, Sulfur‐ andNitrogen‐DopedTridecacyclic Aromatic Emitters with Multiple Resonance Effect for Narrowband Red Emission†

“…For instance, by employing boron (B) and nitrogen (N) as electron‐deficient and electron‐rich atoms, respectively, [ 23 ] B, N‐doped PAH MR‐TADF emitters are developed to exhibit both narrowband emission and high photoluminescence quantum yield (PLQY) near unity. [ 24‐32 ] Recently, carbonyl, nitrogen (C=O, N)‐doped PAH MR‐TADF emitters were designed by inserting carbonyl and nitrogen atoms as electron‐deficient and electron‐rich atoms in PAH skeletons, [ 33‐38 ] giving narrowband emissions with external quantum efficiency (EQE) over 20%. Lately, we have developed boron, sulfur (B, S)‐doped PAH as a kind of nitrogen‐free MR‐TADF emitter by incorporating B and S atoms in PAH skeleton, where S atoms not only serve as electron donors to generate MR effect with B atoms, but also play crucial roles in enhancing SOC and promoting RISC process by heavy‐atom effect.…”