A new class of four‐coordinate donor‐acceptor fluoroboron‐containing thermally activated delayed fluorescence (TADF) compounds bearing a tridentate 2,2′‐(pyridine‐2,6‐diyl)diphenolate (dppy) ligand ...has been successfully designed and synthesized. Upon varying the donor moieties from carbazole to 10H‐spiroacridine‐9,9′‐fluorene to 9,9‐dimethyl‐9,10‐dihydroacridine, these boron derivatives exhibit a wide range of emission colors spanning from blue to yellow with a large spectral shift of 2746 cm−1, with high PLQYs of up to 96 % in the doped thin film. Notably, vacuum‐deposited organic light‐emitting devices (OLEDs) made with these boron compounds demonstrate high performances with the best current efficiencies of 55.7 cd A−1, power efficiencies of 58.4 lm W−1 and external quantum efficiencies of 18.0 %. More importantly, long 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−2 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, suggesting great promises for the development of stable boron‐containing TADF emitters.
Fine‐tuned emission: A new class of four‐coordinate fluoroboron‐containing thermally activated delayed fluorescence (TADF) emitters bearing a tridentate 2,2′‐(pyridine‐2,6‐diyl)diphenolate (dppy) ligand has been successfully designed and synthesized. Efficient vacuum‐deposited OLEDs with high EQEs of 18.0 % and long half‐lifetimes of 12 733 hours have been achieved.
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Gold(iii) complexes are attractive candidates as phosphorescent dopants in organic light-emitting devices for high-luminance full-colour displays. However, no data on the stability of such devices ...have been reported to date. Through rational molecular design and synthesis, we have successfully generated a new class of cyclometalated gold(iii) C^C^N complexes with tunable emission colours spanning from sky-blue to red. These complexes exhibit high photoluminescence quantum yields of up to 80% in solid-state thin films, excellent solubility and high thermal stability. Solution-processable and vacuum-deposited organic light-emitting devices based on these complexes operate with external quantum efficiencies of up to 11.9% and 21.6%, respectively, and operational half-lifetimes of up to 83,000 h at 100 cd m−2.Cyclometalated gold(iii) complexes are shown to offer tunable emission colours spanning from sky-blue to red and enable the fabrication of phosphorescent organic light-emitting devices with high external quantum efficiency and long lifetimes.
Phosphorescent dopants are promising candidates for organic light‐emitting diodes (OLEDs). Although it has been established that the out‐coupling efficiency and overall performances of ...vacuum‐deposited OLEDs can be significantly improved by a horizontal orientation of the dopants, no horizontally oriented gold(III) complexes have been reported to date. Herein, a novel class of tetradentate C^C^N^N ligand‐containing gold(III) complexes with a preferential horizontal orientation successfully generated through a one‐pot reaction is reported. These complexes demonstrate high photoluminescence quantum yields of 70 % and a high horizontal dipole ratio of 0.87 in solid‐state thin films. Green‐emitting OLEDs based on these complexes operate with a maximum external quantum efficiency of 20.6 % with an estimated out‐coupling efficiency of around 30 %. A promising device stability has been achieved in the vacuum‐deposited OLEDs, with operational half‐lifetimes of around 37 500 h at 100 cd m−2.
A novel class of tetradentate C^C^N^N ligand‐containing gold(III) complexes with a preferential horizontal orientation has been obtained through a one‐pot reaction. A high maximum external quantum efficiency of 20.6 % has been realized in the vacuum‐deposited gold(III)‐based OLEDs, with operational half‐lifetimes of around 37 500 h at 100 cd m−2.
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A new class of sky‐blue‐ to green‐emitting carbazolylgold(III) C^C^N complexes containing pyrazole or benzimidazole moieties has been successfully designed and synthesized. Through the judicious ...choice of the N‐heterocycles in the cyclometalating ligand and the tailor‐made carbazole moieties, maximum photoluminescence quantum yields of 0.52 and 0.39 have been realized in the green‐ and sky‐blue‐emitting complexes, respectively. Solution‐processed and vacuum‐deposited organic light‐emitting devices (OLEDs) based on the benzimidazole‐containing complexes have been prepared. The sky‐blue‐emitting device shows an emission peaking at 484 nm with a narrow full‐width at half‐maximum of 57 nm (2244 cm−1), demonstrating the potential of this class of complexes in the application of OLEDs with high color purity. In addition, high maximum external quantum efficiencies of 12.3 % and a long operational half‐lifetime of over 5300 h at 100 cd m−2 have been achieved in the vacuum‐deposited green‐emitting devices.
Blue skies over green fields: Sky‐blue to green emission has been realized in a new class of carbazolylgold(III) complexes with the judicious choice of N‐heterocycles in the C^C^N ligand. The complexes have been used to fabricate both vacuum‐deposited and solution‐processed organic light‐emitting devices, in which the green‐emitting devices realize a high maximum external quantum efficiency of 12.3 %, with an operational half‐life of over 5300 h at 100 cd m−2.
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To address and overcome the difficulties associated with the increased reactivity and susceptibility of blue emitters to deactivation pathways arising from the high-lying triplet excited states, we ...have successfully demonstrated an innovative strategy of harvesting triplet emission via the “thermally stimulated delayed phosphorescence” mechanism, where thermal up-conversion of excitons from the lower-energy triplet excited states (T1) to higher-energy triplet excited states (T1′) are observed to generate blue emission. The lower-lying T1 excited state could serve as a mediator to populate the emissive T1′ state by up-conversion via reverse internal conversion, which could enhance the photoluminescence quantum yield by over 20-folds. Organic light-emitting devices with respectable external quantum efficiencies of up to 7.7% and sky-blue emission with CIE coordinates of (0.17, 0.37) have been realized. The operational stability for the device based on complex 1 has also been explored, and the device is found to show fairly respectable lifetime. This work opens up a new avenue to the design and synthesis of blue phosphorescent emitters.
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A series of orange–red-emitting cyclometalating rhodium(III) complexes have been synthesized, characterized, and applied as phosphorescent dopants to fabricate solution-processed and ...vacuum-deposited organic light-emitting devices (OLEDs). Various substituents on different positions of 2,3-diphenylquinoxaline (dpqx) cyclometalating ligands were introduced. High external quantum efficiencies of 9.40% and good operational half-lifetimes of up to 17 322 h at 100 cd m–2 were achieved. The results revealed that the fluorine atoms might improve the electroluminescence performance in terms of device lifetime, demonstrating the potential suitable phosphorescent materials for OLED application.
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While the use of molecular materials having long‐lived triplet excited state(s) for harvesting solar energy could be an effective approach to boost up the power conversion efficiency (PCE) of organic ...solar cells (OSCs), the performances of this kind of OSCs as reported in the literature are low (< 2.9% PCE attained for the vacuum‐deposited OSCs). Herein is described the realization of high performance OSCs by using gold(III) 5,10,15‐triphenylcorrole (Au‐C1), gold(III) 10‐(p‐trifluoromethylphenyl)‐5,15‐diphenylcorrole (Au‐C2), and gold(III) 10‐(pentafluorophenyl)‐5,15‐diphenyl‐corrole (Au‐C3), as electron‐donors. These gold(III) corroles display excited state lifetimes of ≥ 25 μs and low emission quantum yields of < 0.15%. With the complexes Au‐C1, Au‐C2, and Au‐C3, vacuum‐deposited OSCs, which give PCEs of 2.7%, 3.0%, and 1.8%, respectively, are fabricated. The PCE can be further boosted up to 4.0% after thermal treatment of the OSC devices. Meanwhile, a solution‐processed OSC based on Au‐C2 with a high PCE of 6.0% is fabricated. These PCE values are among the best reported for both types of vacuum‐deposited and solution‐processed OSCs fabricated with metal‐organic complexes having long‐lived excited states as electron‐donor material. The underlying mechanism for the inferior performance of the reported OSCs is discussed.
High performance OSCs comprising gold(III) corroles as donors are demonstrated with 4.0% and 6.0% PCEs realized in optimized OSCs based on Au‐C2 via vacuum and solution‐processes. These PCEs are among the best reported for both types of devices with triplet photo‐absorber. Involvement of Au‐C2 with long excited‐state‐lifetime ≥ 25 μs and low Φ
PL < 0.15% may benefit to OSC performance.
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A series of luminescent cyclometalated rhodium(III) complexes have been designed and prepared. The improved luminescence property is realized by the judicious choice of a strong σ-donor ...cyclometalating ligand with a lower-lying intraligand (IL) state that would raise the d–d excited state and introduction of a lower-lying emissive IL excited state. These complexes exhibit high thermal stability and considerable luminescence quantum yields as high as up to 0.65 in thin film, offering themselves as promising light-emitting materials in OLEDs. Respectable external quantum efficiencies of up to 12.2% and operational half-lifetimes of over 3000 h at 100 cd m–2 have been achieved. This work demonstrates a breakthrough as the first example of an efficient rhodium(III) emitter for OLED application and opens up a new avenue for diversifying the development of OLED materials with rhodium metal being utilized as phosphors.
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A new class of charge neutral, strongly luminescent cyclometalated platinum(II) complexes supported by dianionic tetradentate ligand are synthesized. One of these platinum(II) complexes, Y‐Pt, ...displays a high photoluminescence quantum yield of 86% and electroluminescence efficacy (ηpower) of up to 52 lm W−1, and is utilized as a yellow phosphorescent dopant in the fabrication of white organic light‐emitting devices (WOLEDs). WOLEDs based on conventional structures with yellow emission from Y‐Pt in combination with blue emission from bis(4,6‐difluorophenyl‐pyridinato‐N,C2′) (picolinate) iridium(III) (FIrpic) show a total ηpower of up to 31 lm W−1. A two‐fold increase in ηpower by utilizing a modified WOLED structure comprising of a composite blue host is realized. With this modified device structure, the total ηpower and driving voltage at a luminance of 1000 cd m−2 can be improved to 61 lm W−1 and 7.5 V (i.e., 10 V for control devices). The performance improvement is attributed to an effectively broaden exciton formation‐recombination zone and alleviation of localized exciton accumulation within the FIrpic‐doped composite host for reduced triplet‐triplet annihilation, yielding blue light‐emission with enhanced intensity. The modified device structure can also adopt a higher concentration of Y‐Pt towards its optimal value, leading to WOLEDs with high efficiency.
An effective and simple approach for boosting the performance of white organic light‐emitting devices (WOLEDs) is demonstrated. A modified device structure consisting of a composite blue host that can significantly improve both device efficiency and efficiency roll‐off is developed. With the modified structure, a WOLED exhibiting twofold enhancement in the total efficacy from 31 up to 61 lm W−1 is realized.
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A new class of pyrazine-based carbazole-containing gold(III) complexes featuring thermally stimulated delayed phosphorescence (TSDP) properties has been designed and synthesized. The emission colors ...are found to be sensitive to the coordinating atom of the carbazolyl ligands at the gold(III) center, with emission energies spanning from green to red. The efficiency of TSDP can be enhanced by lowering the polarity of the solvent, as supported by the variable-temperature emission and computational studies. Interestingly, a significant spectral shift in electroluminescence with the change of Commission Internationale de L’Eclairage (CIE) coordinates from (0.35, 0.60) to (0.44, 0.54) has been achieved by simply changing the host material from CBP to TmPyPB. Solution-processable organic light-emitting devices (OLEDs) have also been fabricated, with maximum current efficiencies of up to 22.4 cd A–1 and maximum external quantum efficiencies (EQEs) approaching 7.0%. A higher current efficiency of 35.1 cd A–1 and EQE of 10.7% can be achieved for the vacuum-deposited device based on 1, representing the first demonstration of pyrazine-based tridentate ligand-containing gold(III) complexes as phosphorescent material for OLED application.
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