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Dispirocycles: Novel Platforms for Construction of High-Performance Host Materials for Phosphorescent Organic Light-Emitting Diodes
摘要： Spirocycle compounds such as 9,9′-Spirobifluorene (SBF) are becoming more and more attractive for use as the host materials in organic optoelectronic devices. In this manuscript, two dispirocycles, namely dispiro[fluorene-9,9?-anthracene-10?,9??-fluorene] and 10,10??-diphenyl-10H,10??H-dispiro[acridine-9,9?-anthracene-10?,9??-acridine] were used for the construction of hosts materials (1, 2, 3, and 4). The attached triphenylamine group would determine the thermal, photophysical, electrochemical, and charge transport properties, and therefore they have different electroluminescence performances. The device based on dispiro[fluorene-9,9?-anthracene-10?,9??-fluorene] (2) and 10,10??-diphenyl-10H,10??H-dispiro[acridine-9,9?-anthracene-10?,9??-acridine] (3) molecular platforms exhibited a external quantum efficiency of over 21% with a very high power efficiency (~100 lm W-1). The results here demonstrate to us the potential of extending the possibilities of applying the dispirocyclic molecular platforms with inherent rigidity for developing highly efficient host materials for OLEDs.
关键词： Dispirocycles,OLEDs,Host materials,Phosphorescence,Triplet energy
更新于2025-11-19 16:56:42
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Red-Emitting Thermally Activated Delayed Fluorescence Polymers with Poly(fluorene- <i>co</i> -3,3′-dimethyl diphenyl ether) as the Backbone
摘要： A series of red-emitting thermally activated delayed ?uorescence (TADF) polymers have been designed and synthesized based on poly(?uorene-co-3,3′-dimethyl diphenyl ether) (PFDMPE) as the backbone. Compared with poly?uorene (PF, 2.16 eV), the introduction of 3,3′-dimethyl diphenyl ether into the main chain of PFDMPE leads to the increased triplet energy of 2.58 eV, which is higher enough than the tethered red TADF guest (2.13 eV) to prevent the unwanted triplet energy back-transfer. Meanwhile, there is a good overlap between the absorption spectrum of the red guest and the photoluminescence (PL) spectrum of the polymeric host, ensuring the e?cient energy transfer from host to guest. Consequently, the resultant polymers PFDMPE-R01 to PFDMPE-R10 in solid states show obvious red TADF properties with delayed ?uorescence lifetimes of 126?191 μs and PL quantum yields of 0.18?0.55. Among them, PFDMPE-R05 obtains the best device performance, revealing a bright red electroluminescence peaked at 606 nm and a promising current e?ciency of 10.3 cd/A (EQE = 5.6%). The results compete well with those of red phosphorescent polymers and indicate that PFDMPE other than PF is a suitable polymeric host for the construction of e?cient red TADF polymers.
关键词： PFDMPE,electroluminescence,polymers,poly?uorene,triplet energy,PF,energy transfer,red-emitting,thermally activated delayed ?uorescence,poly(?uorene-co-3,3′-dimethyl diphenyl ether)
更新于2025-09-23 15:21:01
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Impact of t-butyl group on the singlet-triplet energy gap via weak orbital overlap of [1,2,5]-thiadiazolo[3,4-C]pyridine based TADF emitters: Structural modification
摘要： We theoretically investigated the combination of D-A and D-spacer (phenyl ring) -A with an electron donating alkyl (t-butyl) group. The strategy of twisting the geometry of the molecule with the alkyl substituents exclusion of strong electron withdrawing or donating groups leads to gain efficient deep blue-blue TADF emitter through maintaining the band gap while the reduction of singlet-triplet energy gap (EST). The t-butyl group strongly twisted the conformation of molecules by the steric hindrance resulted in weak HOMO and LUMO overlap (IH/L) and efficient spatial separation of HOMO and LUMO (rH/L) in the S0 state. In contrast, designed molecules S1 state own large HOMO and LUMO overlap of excited singlet state (IS) and inefficient spatial separation of HOMO and LUMO. The computed results indicated that introducing alkyl group into the phenyl ring of the acceptor of the designed molecules cannot affect the ΔEST. The ΔEST is mainly related to the IH/L, which can be adjusted by tuning the orbital IH/L. The large modular orbital overlap at S1 and T1 excited states resulted large ΔEST occurs in the range of 0.38 to 0.59eV whose dominant contribution switches from charge transfer (CT) to local excitation (LE). Our studied results reiterate (10.1038/srep10923) that modular orbital overlap of IS, HOMO and LUMO overlap of excited triplet state IT, spatial separation of HOMO and LUMO in the excited singlet state (rS) and spatial separation of HOMO and LUMO in the excited triplet state (rT) are the essential factors to determine ΔEST when inconsistencies between ΔEST and IH/L. Increasing the dihedral angle between D and A from molecule 1-4 (9-12), decrease the transition dipole moment which lowering the oscillator strength. When changing the connection position between D and A, molecules 5-8, the oscillator strength reduced to half with respect to molecules 1-4 and 9-12. The present work provides a theoretical understanding of the impact of alkyl substituents on the overlap of HOMO-LUMO resulting to tuning the ΔEST, as well as its influence on the oscillator strength may be a reliable idea to design efficient TADF emitters.
关键词： [1,2,5]-thiadiazolo[3,4-C]pyridine,HOMO-LUMO orbital overlap,fluorescence radiative decay rate,TADF,singlet-triplet energy gap
更新于2025-09-23 15:21:01
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Direct vs Delayed Triplet Energy Transfer from Organic Semiconductors to Quantum Dots and Implications for Luminescent Harvesting of Triplet Excitons
摘要： Hybrid inorganic-organic materials such as quantum dots (QDs) coupled with organic semiconductors have a wide range of optoelectronic applications, taking advantage of the respective materials strengths. A key area of investigation in such systems is the transfer of triplet exciton states to and from QDs, which has potential applications in the luminescent harvesting of triplet excitons generated by singlet fission, in photocatalysis and photochemical upconversion. While the transfer of energy from QDs to the triplet state of organic semiconductors has been intensely studied in recent years, the mechanism and materials parameters controlling the reverse process, triplet transfer to QDs have not been well investigated. Here, through a combination of steady state and time-resolved optical spectroscopy we study the mechanism and energetic dependence of triplet energy transfer from an organic ligand (TIPS-tetracene carboxylic acid) to PbS QDs. Over and energetic range spanning from exothermic (-0.3 eV) to endothermic (+0.1 eV) triplet energy transfer we find that the triplet energy transfer to the QD occurs through a single step process with a clear energy dependence that is consistent with an electron exchange mechanism as described by Marcus-Hush theory. In contrast, the reverse process, energy transfer from the QD to the triplet state of the ligand does not show any energy dependence in the studied energy range, interestingly a delayed formation of the triplet state occurs relative to the quantum dots decay. Based on the energetic dependence of triplet energy transfer we also suggest design criteria for future materials systems where triplet excitons from organic semiconductors are harvested via QDs, for instance in light emitting structures or the harvesting of triplet excitons generated via singlet fission.
关键词： singlet fission,quantum dots,solar energy,photon multiplication,triplet energy transfer
更新于2025-09-23 15:19:57
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High triplet energy materials for efficient exciplex-based and full-TADF-based white OLEDs
摘要： Materials with high triplet energies have attracted great attention for their application in exciplex-based or thermally activated delayed fluorescence-based organic light-emitting diodes. To study the correlation between triplet energy and chemical structure, six compounds with typical donor-acceptor-donor structures were designed, synthesized, and characterized. Through the adjustment of molecular configuration by weakening the strengths of donors and increasing the angles between donors and acceptors, the triplet energies of the materials were gradually increased from 2.5 to 3.0 eV. Three exciplex-based organic light-emitting diodes containing one of the synthesized compounds were fabricated, which exhibited efficient blue, green-yellow, and white thermally activated delayed fluorescence. Blue and green-yellow organic light-emitting diodes exhibited the maximum external quantum efficiencies of 9.1% and 8.3%, respectively. White organic light-emitting diodes showed turn-on voltage of 4.8 V, high maximum luminance of 18474 cdm-2, and maximum external quantum efficiency of 10.6%. Maximum external quantum efficiencies of blue and white organic light-emitting diodes were close to the record values observed for all-exciplex-based blue and white organic light-emitting diodes.
关键词： full-TADF-based,exciplex-based,High triplet energy materials,white OLEDs
更新于2025-09-19 17:13:59
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Novel Carbazole/Fluorene-Based Host Material for Stable and Efficient Phosphorescent OLEDs
摘要： A novel host material of "M"-type carbazole/fluorene-based mDCzPF with a high triplet energy by utilizing meta-substituted phenyl groups as linkers was developed. It was demonstrated that the position of the substituents significantly affected the molecular configuration and dipole moment, which played a critical role in the device performances. Red phosphorescent OLED utilizing the "M"-type mDCzPF as the host represented a 10-fold operational lifetime improvement over the OLED using a "V"-type pDCzPF linked by para-substituted phenyl groups as the host because of the good charge transport ability of the mDCzPF. Additionally, the "M"-type mDCzPF host was also compatible with a blue emitting phosphorescent emitter PtNON. The PtNON-doped OLED using mDCzPF as the host exhibited a peak EQE of 18.3% with a small roll off, yet maintained an EQE of 13.3% at a high brightness of 5000 cd/m2. Thus, the novel "M"-type mDCzPF could be employed as stable host material for efficient OLED emitting across the whole visible spectrum. This study should provide a viable method for designing new host materials for the development of stable and efficient phosphorescent OLEDs.
关键词： operational lifetime,host material,blue device,OLED,high triplet energy
更新于2025-09-16 10:30:52
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Cyclohexane-cored dendritic host materials with high triplet energy for efficient solution-processed blue thermally activated delayed fluorescence OLEDs
摘要： Two dendritic host materials (CH-2D1 and CH-2D2) are developed by using non-conjugated cyclohexane core and two first/second generation carbazole dendrons, which show excellent solubility in organic solvents, high thermal stability and high triplet energy (ET) of 2.78–2.84 eV, making them suitable for fabrication of solution-processed blue thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs). Compared to CH-2D1 with the first-generation carbazole dendron which shows low-lying highest occupied molecular orbital (HOMO) energy level of (cid:0) 5.48 eV, CH-2D2 with the second-generation carbazole dendrons exhibits higher HOMO level of (cid:0) 5.37 eV, which is more favourable for hole injection from the anode to the emissive layers. Consequently, solution-processed blue TADF OLEDs utilizing CH-2D2 as host show promising device performance with a low turn-on voltage of 3.4 V, maximum external quantum efficiency of 17.8%, (cid:0) 1, which can compare with the most efficient solution-processed blue TADF OLEDs based on small-molecule and polymer hosts. These results indicate that dendritic host materials with well-defined chemical structure and good solubility are an attractive approach–beyond the soluble small-molecule hosts and polymer hosts–for the development of efficient solution-processed TADF OLEDs.
关键词： Thermally activated delayed fluorescence,Dendritic host materials,Organic light-emitting diodes,High triplet energy
更新于2025-09-12 10:27:22
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Decoration of Dibenzofuran Using Cyanocarbazole via 6‐ Position As a Molecular Design Approach for High Triplet Energy Bipolar Host Materials
摘要： In this study, two new dibenzofuran derivatives featuring one or two cyanocarbazole units, 6-(dibenzo[b,d]furan-4-yl)-9-phenyl-9H-carbazole-3-carbonitrile (mBFCzCN) and 6,6'-(dibenzo[b,d]furan-4,6-diyl)bis(9-phenyl-9H-carbazole-3-carbonitrile) (dBFCzCN), were developed as host materials for phosphorescent organic light emitting diodes (PhOLEDs). A new molecular design connecting the cyanocarbazole to the dibenzofuran using the cyanocarbazole 6-position instead of its 9-position was created, and the effects of number of cyanocarbazole units in the dibenzofuran building block on the photophysical and electroluminescence properties were investigated in detail. The mBFCzCN compound revealed high triplet energy (2.78 eV) than that of dBFCzCN (2.68 eV) and good bipolar charge transporting properties. The potential of these materials as hosts for blue and green PhOLEDs was investigated using bis(4,6-(difluorophenyl)pyridinato-N,C2’)picolinate iridium(III) (FIrpic) and tris(2-phenylpyridinato)iridium(III) (Ir(ppy)3) dopants, respectively. The results indicated that the mBFCzCN with one cyanocarbazole unit showed better device performance than the dBFCzCN with two cyanocarbazole units in the blue and green devices. High external quantum efficiencies of 19.0 and 21.2% were demonstrated in the blue and green PhOLEDs with the mBFCzCN host due to its high triplet energy and good bipolar charge transporting characteristics.
关键词： phosphorescent organic light emitting diodes,dibenzofuran,cyanocarbazole,host materials,bipolar charge transporting,triplet energy
更新于2025-09-09 09:28:46
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Photon Upconverted Circularly Polarized Luminescence via Triplet-Triplet Annihilation
摘要： Circularly polarized luminescent materials are of increasing attention due to their potential applications in advanced optical technologies, such as chiroptical devices and optical sensing. Recently, in all reported circularly polarized luminescent materials, high-energy excitation results in low-energy or downconverted circularly polarized luminescence (CPL) emission. Although photon upconversion—i.e., the conversion of low-energy light into higher-energy emission, with a wide variety of applications—has been widely reported, the integration of photon upconversion and CPL in one chiral system to achieve higher-energy CPL emission has never been reported. Herein, a brief review is provided of recent achievements in photon-upconverted CPL via the triplet–triplet annihilation mechanism, focusing on the amplified dissymmetry factor glum through energy transfer process and dual upconverted and downconverted CPL emission through chirality and energy transfer process.
关键词： triplet–triplet annihilation,photon upconversion,energy transfer,triplet energy migration,circularly polarized luminescence
更新于2025-09-04 15:30:14
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Catalytic deracemization of chiral allenes by sensitized excitation with visible light
摘要： Chiral compounds exist as enantiomers that are non-superimposable mirror images of each other. Owing to the importance of enantiomerically pure chiral compounds—for example, as active pharmaceutical ingredients—separation of racemates (1:1 mixtures of enantiomers) is extensively performed. Frequently, however, only a single enantiomeric form of a chiral compound is required, which raises the question of how a racemate can be selectively converted into a single enantiomer. Such a deracemization process is entropically disfavoured and cannot be performed by a conventional catalyst in solution. Here we show that it is possible to photochemically deracemize chiral compounds with high enantioselectivity using irradiation with visible light (wavelength of 420 nanometres) in the presence of catalytic quantities (2.5 mole per cent) of a chiral sensitizer. We converted an array of 17 chiral racemic allenes into the respective single enantiomers with 89 to 97 per cent enantiomeric excess. The sensitizer is postulated to operate by triplet energy transfer to the allene, with different energy-transfer efficiencies for the two enantiomers. It thus serves as a unidirectional catalyst that converts one enantiomer but not the other, and the decrease in entropy is compensated by light energy. Photochemical deracemization enables the direct formation of enantiopure materials from a racemic mixture of the same compound, providing a novel approach to the challenge of creating asymmetry.
关键词： chiral sensitizer,triplet energy transfer,deracemization,chiral compounds,visible light,enantiomers,photochemical
更新于2025-09-04 15:30:14