Carbazole‐Based DABNA Analogues as Highly Efficient Thermally Activated Delayed Fluorescence Materials for Narrowband Organic Light‐Emitting Diodes

Abstract

Carbazole‐based DABNA analogues (CzDABNAs) were synthesized from triarylamine by regioselective one‐shot single and double borylation. The reaction proceeded selectively at the ortho position of the carbazolyl group, where the highest occupied molecular orbital is mainly localized owing to the difference in the electron‐donating abilities of the diarylamino and carbazolyl groups. The facile and scalable method enabled synthesis of CzDABNAs, exhibiting narrowband thermally activated delayed fluorescence with emission spectra ranging from deep blue to green. The organic light‐emitting diode devices employing these products as emitters exhibited deep‐blue, sky‐blue, and green emission with high external quantum efficiencies of 19.5, 21.8, and 26.7 %, respectively.

Molecular design of thermally activated delayed fluorescent emitters for narrowband orange–red OLEDs boosted by a cyano-functionalization strategy

“… 8 The multi-resonance (MR) effect of nitrogen and boron atoms induces the localization of frontier molecular orbitals (FMOs), which significantly reduces the broadening of emission bands and thus enables excellent color purity. 9 However, the realization of red-shifted emission for MR-induced TADF (MR-TADF) materials is intrinsically difficult because of the rigid heterocyclic structure, and thus MR-TADF materials have flourished only in the emission color of the blue region. 6 b ,10 Recently, the twisted D–A molecular structure in the MR-skeleton has been introduced to develop green (519 nm) and yellow (549 nm) MR-TADF materials, while the fusion of an additional MR-skeleton via para B–π–B and N–π–N linkage has been proven to be an effective method to realize a red (615 nm) MR-TADF material.…”

A Deep Blue Strong Microcavity Organic Light‐Emitting Diode Optimized by a Low Absorption Semitransparent Cathode and a Narrow Bandwidth Emitter

“…Finally, all devices were encapsulated using glass cover and UV‐curable resin under nitrogen atmosphere. In this work, the 9‐[r‐(10‐phenylanthracene‐9‐yl)‐9H‐carbazole (PhPC), [ 43 ] BPPyA, [ 44 ] and DABNA‐NP‐TB [ 45,46 ] were synthesized using previously reported method. The BPPyA is a pyrene‐based fluorescent dopant and it has spectral peak of 460 nm and FWHM of 35 nm in film state.…”

Heavy-atom effect promotes multi-resonance thermally activated delayed fluorescence

“…6 Nonetheless, documented MR-TADF examples featuring promising electroluminescence remain sparse, and tactics to improve their efficiency are of great importance. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] Reverse intersystem crossing (RISC) process is a critical pathway for emitters to achieve TADF. [23][24][25][26][27] A fast rate constant of RISC (kRISC) of TADF emitter can efficient converted its T1 excitons to S1 state, promising high internal quantum efficiency (IQE), while inefficient RISC would conversely increase the concentration of triplet excitons to induce triplet-triplet annihilation (TTA) or other degradation events.…”