Steric Modulation of Spiro Structure for Highly Efficient Multiple Resonance Emitters

Abstract

A multiple resonance thermally activated delayed fluorescence (MR-TADF) molecule with a fused, planar architecture tends to aggregate at high doping ratios, resulting in broad full width at half maximum (FWHM), redshifting electroluminescence peaks, and low device efficiency. Herein, we propose a mono-substituted design strategy by introducing spiro-9,9'-bifluorene (SBF) units with different substituted sites into the MR-TADF system for the first time. As a classic steric group, SBF can hinder interchromophore interactions, leading to high device efficiency (32.2-35.9 %) and narrow-band emission ( � 27 nm). Particularly, the shield-like molecule, SF1BN, seldom exhibits a broadened FWHM as the doping ratio rises, which differs from the C3-substituted isomer and unhindered parent emitter. These results manifest an effective method for constructing highly efficient MR-TADF emitters through a spiro strategy and elucidate the feasibility for steric modulation of the spiro structure in π-framework.

Highly efficient pure-blue organic light-emitting diodes based on rationally designed heterocyclic phenophosphazinine-containing emitters

“…The EQEs of BNCz-NPO and BNCz-NPS maintain a high level of 21.7% and 23.5% (EQE 100 ) at a display relevant luminance of 100 cd m -2 , over 12.9% of BNCz without functionalization. 49 The alleviated e ciency roll-offs in our devices can be attributed to the enhanced RISC of BNCz-NPO and BNCz-NPS, effectively mitigating triplet-involved exciton quenching. Voltage measured at 1 cd m − 2 ; b) maximum luminance; c) maximum current e ciency; d) maximum power e ciency; e) external quantum e ciency at maximum, 100, 1000 cd m − 2 , respectively; f) EL peak; g) full width at half maximum of EL spectrum; h) recorded at 4 V.…”

High-Efficiency Narrowband Multi-Resonance TADF Emitters via the Introduction of Bulky Adamantane Unit

“…Device with 30 wt% doped BN-CP1 in the emission layer presented the EQE max of 33.3% with the FWHM of 25 nm. Jiang [26] employed 9,9'-spirobi[fluorene] to resist ACQ effect that the OLED using SF1BN obtained the EQE max of 27.1% with the FWHM of 28 nm at 15 wt% doping ratios. Until now, there are limited examples reported.…”

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.…”