Four‐Coordinate Boron Emitters with Tridentate Chelating Ligand for Efficient and Stable Thermally Activated Delayed Fluorescence Organic Light‐Emitting Devices

Abstract

An ew class of four-coordinate donor-acceptor fluoroboron-containing thermally activated delayed fluorescence (TADF) compounds bearing atridentate 2,2'-(pyridine-2,6-diyl)diphenolate (dppy) ligand has been successfully designed and synthesized. Upon varying the donor moieties from carbazole to 10H-spiro[acridine-9,9'-fluorene] to 9,9dimethyl-9,10-dihydroacridine,these boron derivatives exhibit aw ide range of emission colors spanning from blue to yellow with alarge spectral shift of 2746 cm À1 ,with high PLQYs of up to 96 %i nt he doped thin film. Notably,v acuum-deposited organic light-emitting devices (OLEDs) made with these boron compounds demonstrate high performances with the best current efficiencies of 55.7 cd A À1 ,p ower efficiencies of 58.4 lm W À1 and external quantum efficiencies of 18.0 %. More importantly,l ong operational stabilities of the green-emitting OLEDs based on 2 with half-lifetimes of up to 12 733 hours at an initial luminance of 100 cd m À2 have been realized. This work represents for the first time the design and synthesis of tridentate dppy-chelating four-coordinate boron TADF compounds for long operational stabilities,s uggesting great promises for the development of stable boron-containing TADF emitters.The leap-forward development of thermally activated delayed fluorescence (TADF) materials that are capable to realize 100 %o fa ni nternal quantum efficiency (IQE) via reverse intersystem crossing (RISC) from the lowest triplet excited state (T 1 )t ot he lowest singlet excited state (S 1 )h as attracted al ot of research interests [1] since the first demonstration of highly efficient organic light-emitting devices (OLEDs) based on purely organic TADF materials by Adachi and co-workers in 2012. [2] From the molecular design viewpoint, as mall S 1 -T 1 energy gap (DE ST )a nd high photoluminescence quantum yield (PLQY) are the most important and closely associated physical parameters for efficient TADF emitters. [1] Generally,asmall DE ST can be achieved by spatially separating the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) through as imple donor-acceptor structure with atwisted conformation or anon-conjugated bridge. [1] A high PLQY can be accomplished by enhancing light absorption through increasing the oscillator strength, and the introduction of phenyl linkers,r igid structures,d ual emitting units and multiple donors. [1b] On the other hand, the nature of excited states and the heteroatom effect are found to play important roles in the RISC process,enabling efficient TADF to occur even with DE ST larger than 0.3 eV. [1d, 3] Forp ractical applications,o nly TADF emitters with chemical stability can provide the potential for realizing long lifetime of OLEDs. [1b] Considering all these factors,T ADF emitters based on the bipolar triazine-carbazole system have been attracting particular interests due to the ease of functionalization and good chemical stabilities of the triazine and carbazole moieties. [4] Highly efficient blue-, gr...

Through‐Space Charge‐Transfer Polynorbornenes with Fixed and Controllable Spatial Alignment of Donor and Acceptor for High‐Efficiency Blue Thermally Activated Delayed Fluorescence

“…Charge-transfer (CT) interactions between electron donors (D) and acceptors (A) are the basis of many functions of p-conjugated molecules and polymers, [1][2][3][4][5][6][7] Recently,thermally activated delayed fluorescence (TADF) polymers [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] with CT emission have attracted much attention because they can convert triplet excitons to singlet ones through reverse intersystem crossing (rISC) process to realize 100 %i nternal quantum efficiency (IQE), [28][29][30][31][32][33][34][35][36][37][38][39][40][41] providing ap romising approach for developing solution-processed OLEDs without use of precious metal complexes.…”

Luminescent hexagonal microtubes prepared through water-induced self-assembly of a polymorphic organoboron compound: formation mechanism and waveguide behaviour

“…28,29 Specifically, tetra-coordinated organoboron (TCOB) compounds with extended π-conjugation and structural rigidity exhibit notable Stokes shifts, improved fluorescence emission (both in solid and solution states) and offer a broad range of molecular diversity through chemical synthesis. 30 Hydroxyquinolate, 31,32 pyridylphenolate, 33,34 benzimidazolephenolate, 35 and similar bidentate heterocyclic ligands are often used to prepare TCOB complexes.…”

Highly efficient carbazolylgold(iii) dendrimers based on thermally activated delayed fluorescence and their application in solution-processed organic light-emitting devices

“…However, strong luminescence quenching was also observed in these dendrimers under aerated conditions, 20 similar to small molecule-based TADF emitters. [21][22][23][24][25][26] Since then, extensive research on TADF carbazole-anthracene-9,10-dione, 27 carbazole-phosphine oxide, 28 carbazole-sulfone 29 and carbazolecyanophenyl dendrimers [30][31][32] has been carried out to improve their luminescence properties. OLEDs based on these dendrimers exhibit extraordinary electroluminescence (EL) performance with a maximum external quantum efficiency (EQE) of 20.4%.…”