Constructing Organic Electroluminescent Material with Very High Color Purity and Efficiency Based on Polycyclization of the Multiple Resonance Parent Core

Abstract

Multiple resonance thermally activated delayed fluorescence (MR-TADF) compounds have set off an upsurge of research because of their tremendous application prospects in the field of wide color gamut display. Herein, we propose a novel MR-TADF molecular construction paradigm based on polycyclization of the multiple resonance parent core, and construct a representative multiple resonance polycyclic aromatic hydrocarbon (MR-PAH) based on the para-alignment of boron and nitrogen atoms into a six-membered ring (p-BNR). Through the retrosynthesis analysis, a concise synthesis strategy with wide applicability has been proposed, encompassing programmed sequential boron esterification, Suzuki coupling and Scholl oxidative coupling. The target model molecule BN-TP shows green fluorescence with an emission peak at 523 nm and a narrow full-width at half-maximum (FWHM) of 34 nm. The organic light-emitting diode (OLED) employing BN-TP as an emitter exhibits ultrapure green emission with Commission Internationale de L'Eclairage (CIE) coordinates of (0.26, 0.70), and achieves a maximum external quantum efficiency (EQE) of 35.1 %.

Achieving highly efficient narrowband sky-blue electroluminescence with alleviated efficiency roll-off by molecular-structure regulation and device-configuration optimization

“…15 In the Franck-Condon transition, this highly rigid framework is endowed with unique excitonic characteristics like a narrow fullwidth at half-maximum (FWHM), large extinction coefficient, giant oscillator strength (f) and near-unity photoluminescence quantum yield (PLQY), which provide great opportunities for the fabrication of high-performance OLEDs with extraordinary color purity. [16][17][18][19][20][21][22][23][24][25][26][27] Although such compounds can achieve effective TADF characteristics, they still have a relatively large DE ST value, which leads to the fairly long duration of delayed fluorescence, about tens of ms. [28][29][30][31][32] Consequently, the efficiency roll-offs of MR-TADF emiter-based devices are usually sharp, resulting from frequent bimolecular quenching events, such as triplet-triplet annihilation (TTA) or triplet-polaron annihilation (TPA) triggered by sluggish triplet exciton dynamics. 33 Therefore, how to alleviate the intrinsic efficiency roll-off and maintain excellent device efficiency under high brightness has imposed a formidable challenge to be addressed urgently.…”

Confining donor conformation distributions for efficient thermally activated delayed fluorescence with fast spin-flipping

“…Moreover, these emitters with fast spin-ipping can also be the assistant host for MR-TADF emitters with narrow-band emission to extend the color gamut. We selected TBN-TPA 54 and BN-TP 55 as blue and green MR-TADF terminal emitters, which possess narrow band emissions and high PLQYs but long excited state lifetimes (Supplementary Fig. 13).…”

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

“…Later Wang et al reported interesting approach by fusing MR core with polycyclic aromatic phenylene unit, BN-TP, featuring para-aligned B and N into the six-membered ring (Figure 6). [114] The photophysical properties revealed that the BN-TP showed a very intense absorption band at 506 nm corresponding to the ICT transition and vivid green emission with a peak wavelength of 523 nm. The observed small Stokes shift %22 nm and narrow FWHM % 34 nm indicates the structural rigidity of BN-TP in the excited state.…”