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Utilization of Ternary Europium Complex for Organic Electroluminescent Devices and as a Sensitizer to Improve Electroluminescence of Red-Emitting Iridium Complex
摘要： Two new lanthanide complexes [Ln(hfaa)3(Py-Im)] [hfaa = hexafluoroacetylacetone, Py-Im = 2-(2-pyridyl)benzimidazole and Ln = Eu(III) (1) and Tb(III) (2)] were synthesized and characterized. An X-ray crystal structure determination confirms that complex 1 is eight-coordinate with a distorted trigonal dodecahedral geometry. It shows typical vivid red Eu(III) emission in the solid state, in solution, and in a polymer matrix. The observed lifetime (τobs) of complex 1 in the solid state, in dichloromethane (DCM) solution, and in thin films is 833.01, 837.95, and 626.16?715.69 μs, respectively, with a photoluminescence quantum yield QEuL ≈ 33% in DCM solution. Complex 2 displays a yellowish-green emission in the solid state (τobs ≈ 36.99 μs), while a near white-light emission in solution (x; 0.2574: y; 0.3371) and in thin films. Therefore, it is a potential candidate for generating single-component white light-emitting materials for solid-state lighting applications. The kinetic scheme for modeling energy-transfer processes shows that the main donor state for 1 is the ligand triplet state (T1) and that energy transfer occurs to both the 5D1 (56.55%) and 5D0 (40.58%) levels. We fabricated a series of single- and double-layer organic light-emitting devices using complex 1. The luminance of the optimized double-layer electroluminescence (EL) device was 373 cd/m2 with very low turn-on voltage of ～4.2 V. Complex 1 was further utilized as a sensitizer to improve the EL of a red-emitting iridium complex PQ2Ir(dpm) (PQ = phenylquinoly-N,C2′, dpm = dipivaloylmethane). The codoped device achieved a maximum brightness and maximum current efficiency (ηc) of 93 224 cd/m2 and 36.38 cd/A, respectively.
关键词： electroluminescence,organic light-emitting devices,photoluminescence,energy transfer,lanthanide complexes
更新于2025-11-20 15:33:11
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Strategies towards rational design of gold(iii) complexes for high-performance organic light-emitting devices
摘要： 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.
关键词： operational stability,phosphorescent dopants,organic light-emitting devices,cyclometalated,gold(iii) complexes,C^C^N complexes
更新于2025-11-19 16:56:35
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Phenothiazine dioxide-containing derivatives as efficient hosts for blue, green and yellow thermally activated delayed fluorescence OLEDs
摘要： By conjugating 10-phenyl-10H-phenothiazine-5,5-dioxide (2PTO) with aromatic amine substituents (PhCz and DMACMN), three novel host materials namely 10-(9-phenyl-9H-carbazol-3-yl)-10H-phenothiazine 5,5-dioxide (3CzNPTO), (10-(4-(9H-carbazol-9-yl)phenyl)-10H-phenothiazine 5,5-dioxide (9CzNPTO) and 10-(4-(9,9-dimethylacridin-10(9H)-yl)-2,5-dimethylphenyl)-10H-phenothiazine 5,5-dioxide (DMACMNPTO) were designed and synthesized. DMACMNPTO with thermally activated delayed fluorescence (TADF) feature exhibited the bipolar characteristic resulting from the completely separated HOMO/LUMO distribution. Using DMACMNPTO as a host for TADF emitters, the devices showed a maximum external quantum efficiencies (EQEmax), current e?ciency (CEmax) and power e?ciency (PEmax) of 18.3%, 33.3 cd/A and 37.4 lm/W in the blue-emitting diode, 18.6%, 49.1 cd/A and 47.2 lm/W in the green-emitting diode, and 19.1%, 59.2 cd/A and 66.0 lm/W in the yellow-emitting diode, respectively. These results corroborated the potential of phenothiazine dioxide-containing derivatives as host materials in a sequence of colors TADF-OLEDs.
关键词： phenothiazine dioxide,Organic light-emitting devices,thermally activated delayed fluorescence,host
更新于2025-09-19 17:13:59
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Synthesis of acridone-naphthylamine derivative and its thermally-activated delayed fluorescence studies for application in OLEDs
摘要： Acridone (acceptor) and naphthylamine (donor) based Donor-Acceptor-Donor (D-A-D) compound (1) was synthesised, characterised and its thermally-activated delayed fluorescence (TADF) properties were studied in detail. Compound 1 is fluorescent and emits in the green region (550 nm). The energy gap between the ground and the lowest excited singlet (S1) state is estimated to be 2.55 eV. The energy gap between the CT singlet and triplet states (DEST) was found to be *0.3 eV. Small DES1-T1 is one of the important criteria for TADF to take place in a molecule and thus detailed photophysics has been studied. Transient lifetime measurements showed an increase in the fluorescence lifetime (s) on purging with N2, as compared with that in air-saturated solution, indicating the involvement of the triplet state in emission. Emission at 550 nm was also observed with a delay of 100 ls which corresponded to the delayed fluorescence in 1. The lifetime of TADF was found to be 176 ls. Applications of TADF materials in organic light-emitting devices (OLEDs) has gotten attention as TADF materials utilise the triplet excitons which helps in increasing internal quantum efficiency of device. Air-saturated based on 1 were fabricated and their intensity was found to be nearly as high as 17,000 Cd/m2 at 25 mA/cm2 which was comparable to many of the known TADF emitters.
关键词： Acridone,thermally activated delayed fluorescence,organic light-emitting devices
更新于2025-09-16 10:30:52
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Triarylboryl-substituted carbazoles as bipolar host materials for efficient green phosphorescent organic light-emitting devices
摘要： Two novel bipolar host materials based on carbazole and triarylborane moieties, i.e. B-2CZ and m-B-CZ, are synthesized and characterized. The spatially crowded compound B-2CZ exhibits a high thermal stability (Td > 340 °C) compared to the reported triarylboryl carbazoles, presumably due to the highly compact architecture. As a result, phosphorescent Ir(ppy)3 combined with both the borylated compounds is selected to construct a host-guest system. Devices A (B-2CZ) and B (m-B-CZ) achieve peak efficiencies of 19.3% (69.1 cd/A and 88.1 lm/W) and 19.1% (66.1 cd/A and 77.2 lm/W), respectively. The respective turn-on voltages of devices A and B are recorded at 2.4 and 2.6 V, which are much lower than that of device with the benchmark host (mCP, 3.3 V). In addition, at a higher practical luminance of 100 cd/m2 (1000 cd/m2), the external quantum efficiencies of devices A and B are still preserved at 19.1% (17.3%) and 18.2% (13.0%) with the mitigated efficiency drops of 1% (10%) and 5% (32%), suggesting the promising advantage for realizing efficient phosphorescent organic light-emitting devices.
关键词： Carbazole,Triarylborane,Bipolar host,Phosphorescent organic light-emitting devices
更新于2025-09-10 09:29:36
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Experimental Evidence for “Hot Exciton” Thermally Activated Delayed Fluorescence Emitters
摘要： Contradiction between no effective photophysical experiments and high device results causes the “hot exciton” thermally activated delayed fluorescence (TADF) mechanism to be still a controversial question. Here, the steady and transient photophysical characterization combined with theoretical calculation based on 4,7-bis(9,9-dimethyl-9H-fluoren-2-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole (2F-BTH-DMF), 4,7-bis(9,9-dimethyl-9H-fluoren-2-yl)benzo[c][1,2,5]thiadiazole (BTH-DMF), and 5,6-bis(9,9-dimethyl-9H-fluoren-2-yl)benzo[c][1,2,5] thiadiazole (o-BTH-DMF) demonstrate that all the emitters exhibit TADF via reverse intersystem crossing (RISC) from “hot exciton” triplet excited state. The fast RISC process “hot exciton” mechanism affords a very short delayed lifetime (1 μs). Organic light-emitting diodes (OLEDs) based on these emitters exhibit high exciton utilization over 25% and the best device shows a maximum current efficiency of 31.02 cd A?1, maximum power efficiency of 27.85 lm W?1, and external quantum efficiency of 9.13%, which are the highest performances for reported OLEDs with “hot exciton” mechanism. The experimental evidence for fast RISC process via “hot exciton” triplet state and short delayed lifetime highlights the TADF emitters with “hot exciton” mechanism for high-performance OLEDs with very low efficiency roll-off.
关键词： hot excitons,reverse intersystem crossing,thermally activated delayed fluorescence,organic light-emitting devices
更新于2025-09-04 15:30:14