Highly efficient non-doped blue fluorescent OLEDs with low efficiency roll-off based on hybridized local and charge transfer excited state emitters

Designing a donor–acceptor (D–A) molecule with a hybridized local and charge transfer (HLCT) excited state is a very effective strategy for producing an organic light-emitting diode (OLED) with a high exciton utilization efficiency and external quantum efficiency. Herein, a novel twisting D–π–A fluorescent molecule (triphenylamine–anthracene–phenanthroimidazole; TPAAnPI) is designed and synthesized. The excited state properties of the TPAAnPI investigated through photophysical experiments and density functional theory (DFT) analysis reveal that its fluorescence is due to the HLCT excited state. The optimized non-doped blue OLED using TPAAnPI as a light-emitting layer exhibits a novel blue emission with an electroluminescence (EL) peak at 470 nm, corresponding to the Commission International de L''Eclairage (CIE) coordinates of (0.15, 0.22). A fabricated device termed Device II exhibits a maximum current efficiency of 18.09 cd A⁻¹, power efficiency of 12.35 lm W⁻¹, luminescence of ≈29 900 cd cm⁻², and external quantum efficiency (EQE) of 11.47%, corresponding to a high exciton utilization efficiency of 91%. Its EQE remains as high as 9.70% at a luminescence of 1000 cd m⁻² with a low efficiency roll-off of 15%. These results are among the best for HLCT blue-emitting materials involved in non-doped blue fluorescent OLEDs. The performance of Device II highlights a great industrial application potential for the TPAAnPI molecule.

A new pure fluorescent blue HLCT-emitter was designed and synthesized. Highly efficient non-doped blue OLEDs with low efficiency roll-off were achieved.     

Hermetic Seal of Organic Light Emitting Diode with Glass Frit

The components of OLED encapsulation with hermetic sealing and a 1026-day lifetime were measured by PXI-1033. The optimal characteristics were obtained when the thickness of the TPBi layer was 20 nm. This OLED obtained a maximum luminance (Lmax) of 25,849 cd/m² at a current density of 1242 mA/cm², an external quantum efficiency (EQE) of 2.28%, a current efficiency (CE) of 7.20 cd/A, and a power efficiency (PE) of 5.28 lm/W. The efficiency was enhanced by Lmax 17.2%/EQE 0.89%/CE 42.1%/PE 41.9%. The CIE coordinates of 0.32, 0.54 were all green OLED elements with wavelengths of 532 nm. The shear strain and leakage test gave results of 16 kgf and 8.92 × 10⁻⁹ mbar/s, respectively. The reliability test showed that the standard of MIL-STD-883 was obtained.     

Near-infrared electroluminescence beyond 940 nm in Pt(N^C^N)X complexes: influencing aggregation with the ancillary ligand X

We present a study of aggregate excited states formed by complexes of the type Pt(N^C^N)X, where N^C^N represents a tridentate cyclometallating ligand, and X = SCN or I. These materials display near-infrared (NIR) photoluminescence in film and electroluminescence in NIR OLEDs with λ^max_EL = 720–944 nm. We demonstrate that the use of X = SCN or I modulates aggregate formation compared to the parent complexes where X = Cl. While the identity of the monodentate ligand affects the energy of Pt–Pt excimers in solution in only a subtle way, it strongly influences aggregation in film. Detailed calculations on aggregates of different sizes support the experimental conclusions from steady-state and time-resolved luminescence studies at variable temperatures. The use of X = I appears to limit aggregation to the formation of dimers, while X = SCN promotes the formation of larger aggregates, such as tetramers and pentamers, leading in turn to NIR photo- and electroluminescence > 850 nm. A possible explanation for the contrasting influence of the monodentate ligands is the lesser steric hindrance associated with the SCN group compared to the bulkier I ligand. By exploiting the propensity of the SCN complexes to form extended aggregates, we have prepared an NIR-emitting OLED that shows very long wavelength electroluminescence, with λ^max_EL = 944 nm and a maximum EQE = 0.3 ± 0.1%. Such data appear to be unprecedented for a device relying on a Pt(ii) complex aggregate as the emitter.

The ancillary ligand X strongly influences the aggregates formed by complexes of the type Pt(N^C^N)X. X = I leads to a 4× increase in film PLQY and OLED EQE vs. X = Cl, while X = SCN yields very long wavelength electroluminescence, λ^max_EL = 944 nm.     

Phosphine Sulfide-Based Bipolar Host Materials for Blue Phosphorescent Organic Light-Emitting Diodes

Three phosphine sulfide-based bipolar host materials, viz CzPhPS, DCzPhPS, and TCzPhPS, were facilely prepared through a one-pot synthesis in excellent yields. The developed hosts exhibit superior thermal stabilities with the decomposition temperatures (T_d) all exceeding 350 °C and the melting temperatures (T_m) over 200 °C. In addition, their triplet energy (E_T) levels are estimated to be higher than 3.0 eV, illustrating that they are applicable to serve as hosts for blue phosphorescent organic light-emitting diodes (PhOLEDs). The maxima luminance, current efficiency (CE), power efficiency (PE), and external quantum efficiency (EQE) of 17,223 cd m⁻², 36.7 cd A⁻¹, 37.5 lm W⁻¹, and 17.5% are achieved for the blue PhOLEDs hosted by CzPhPS. The PhOLEDs based on DCzPhPS and TCzPhPS show inferior device performance than that of CzPhPS, which might be ascribed to the deteriorated charge transporting balance as the increased number of the constructed carbazole units in DCzPhPS and TCzPhPS molecules would enhance the hole-transporting ability of the devices to a large extent. Our study demonstrates that the bipolar hosts derived from phosphine sulfide have enormous potential applications in blue PhOLEDs, and the quantity of donors should be well controlled to exploit highly efficient phosphine sulfide-based hosts.     

Synthesis of pure blue emissive poly(2,7‐carbazole)s anchored by electron donor pendant

Three novel poly(2,7‐carbazole)s having hole injection and transporting pendent moieties of carbazole and triphenylamine at the N‐position were synthesized for achieving pure blue electroluminescence. The N‐pendants in the polymers correspond to N‐phenylcarbazol‐2‐yl ( P1 ), N,N‐diphenylamino‐N‐phenylcarabazol‐2‐yl ( P2) , and 4‐phenyl having a hydrocarbon chain with a triphenylamine terminal ( P3 ), respectively. Electronic, optical, and electroluminescence properties of these polymers were compared with those of a poly(2,7‐carbazole) directly connected with triphenylamine at the N‐position ( P0 ) having an aggregation‐induced emissive property. The photoluminescence (PL) spectra suggested that they could emit in the region of blue light in the film state. Especially, P2 that has the fixed and large diphenylaminocarbazolyl pendant showed a deep‐blue fluorescence with CIE(x, y) = (0.15, 0.07). The P0 , P2 , and P3 based light emitting diode devices showed maximum electroluminescence wavelengths in the range of 430–450 nm. The P2 device showed pure blue emission (CIE[x, y] = [0.18, 0.16]), high luminance (1130 cd/m²) and current density (628 mA/cm²) at 8 V, whereas low‐energy emissions around 500–600 nm were emerged at higher than 9 V. The P0 and P3 devices also showed a blue electroluminescence in the range of 8–11 V, but their luminance and efficiency were low. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2526–2534     

High‐Performance Blue OLEDs Based on Phenanthroimidazole Emitters via Substitutions at the C6‐ and C9‐Positions for Improving Exciton Utilization

Donor–acceptor (D–A) molecular architecture has been shown to be an effective strategy for obtaining high‐performance electroluminescent materials. In this work, two D–A molecules, Ph‐BPA‐BPI and Py‐BPA‐BPI, have been synthesized by attaching highly fluorescent phenanthrene or pyrene groups to the C6‐ and C9‐positions of a locally excited‐state emitting phenylamine–phenanthroimidazole moiety. Equipped with good physical and hybridized local and charge‐transfer properties, both molecules show high performances as blue emitters in nondoped organic light‐emitting devices (OLEDs). An OLED using Ph‐BPA‐BPI as the emitting layer exhibits deep‐blue emission with CIE coordinates of (0.15, 0.08), and a maximum external quantum efficiency (EQE), current efficiency (CE), and power efficiency (PE) of 4.56 %, 3.60 cd A^?1, and 3.66 lm W^?1, respectively. On the other hand, a Py‐BPA‐BPI‐based, sky‐blue OLED delivers the best results among nondoped OLEDs with CIE_y values of < 0.3 reported so far, for which a very low turn‐on voltage of 2.15 V, CIE coordinates of (0.17, 0.29), and maximum CE, PE, and EQE values of 10.9 cd A^?1, 10.5 lm W^?1, and 5.64 %, were achieved, respectively. More importantly, both devices show little or even no efficiency roll‐off and high singlet exciton‐utilizing efficiencies of 36.2 % for Ph‐BPA‐BPI and 39.2 % for Py‐BPA‐BPI.     

Synthesis and properties of oligofluorene-thiophenes as emissive materials for organic electroluminescent devices: color-tuning from deep blue to orange

A series of oligofluorene-thiophenes end-capped with 3,6-di-tert-butylcarbazole and pyrene were designed and synthesized for application as color tunable emissive materials for organic electroluminescent devices. They were characterized by ¹H NMR, ¹³C NMR, FT-IR, UV–vis, PL spectroscopy, and mass spectrometry. Theoretical calculations revealed that the carbazole moiety attached to the end of the molecule is nearly perpendicular to oligofluorene-thiophene-pyrene plane and π-electrons in the ground state delocalize over the entire molecule. Their optical, thermal, and electrochemical properties could be tuned by varying the number of thiophene units in the molecule. All were electrochemically and thermally stable molecules. OLED devices of these materials emitted brightly in various colors from deep blue to orange. Particularly, deep blue (CIE coordinates of 0.16, 0.14) and green (CIE coordinates of 0.27, 0.61) devices showed high color quality close to the NTSC standards with high luminance efficiencies of 1.14 and 11.15 cd/A, respectively.     

Efficient Nondoped Pure Blue Organic Light‐Emitting Diodes Based on an Anthracene and 9,9‐Diphenyl‐9,10‐dihydroacridine Derivative

Organic light‐emitting diodes (OLEDs) have been greatly developed in recent years owing to their abundant advantages for full‐color displays and general‐purpose lightings. Blue emitters not only provide one of the primary colors of the RGB (red, green and blue) display system to reduce the power consumption of OLEDs, but are able able to generate light of all colors, including blue, green, red, and white by energy transfer processes in devices. However, it remains a challenge to achieve high‐performance blue electroluminescence, especially for nondoped devices. In this paper, we report a blue light emitting molecule, DPAC‐AnPCN, which consists of 9,9‐diphenyl‐9,10‐dihydroacridine and p‐benzonitrile substituted anthracene moieties. The asymmetrically decoration on anthracene with different groups on its 9 and 10 positions combines the merits of the respective constructing units and endows DPAC‐AnPCN with pure blue emission, high solid‐state efficiency, good thermal stability and appropriate HOMO and LUMO energy levels. Furthermore, DPAC‐AnPCN can be applied in a nondoped device to effectively reduce the fabrication complexity and cost. The nondoped device exhibits pure blue electroluminescence (EL) locating at 464 nm with CIE coordinates of (0.15, 0.15). Moreover, it maintains high efficiency at relatively high luminescence. The maximum external quantum efficiency (EQE) reaches 6.04 % and still remains 5.31 % at the luminance of 1000 cd m^?2 showing a very small efficiency roll‐off.     

Imidazo[1,2-a]pyridine as an Electron Acceptor to Construct High-Performance Deep-Blue Organic Light-Emitting Diodes with Negligible Efficiency Roll-Off

Two novel bipolar deep-blue fluorescent emitters, IP-PPI and IP-DPPI, featuring different lengths of the phenyl bridge, were designed and synthesized, in which imidazo[1,2-a]pyridine (IP) and phenanthroimidazole (PI) were proposed as an electron acceptor and an electron donor, respectively. Both of them exhibit outstanding thermal stability and high emission quantum yields. All the devices based on these two materials showed negligible efficiency roll-off with increasing current density. Impressively, non-doped organic light-emitting diodes (OLEDs) based on IP-PPI and IP-DPPI exhibited external quantum efficiencies (EQEs) of 4.85 % and 4.74 % with CIE coordinates of (0.153, 0.097) and (0.154, 0.114) at 10000 cd m⁻², respectively. In addition, the 40 wt % IP-PPI doped device maintained a high EQE of 5.23 % with CIE coordinates of (0.154, 0.077) at 10000 cd m⁻². The doped device based on 20 wt % IP-DPPI exhibited a higher deep-blue electroluminescence (EL) performance with a maximum EQE of up to 6.13 % at CIE of (0.153, 0.078) and maintained an EQE of 5.07 % at 10000 cd m⁻². To the best of our knowledge, these performances are among the state-of-the art devices with CIE_y≤0.08 at a high brightness of 10000 cd m⁻². Furthermore, by doping a red phosphorescent dye Ir(MDQ)₂ (MDQ=2-methyldibenzo[f,h]quinoxaline) into the IP-PPI and IP-DPPI hosts, high-performance red phosphorescent OLEDs with EQEs of 20.8 % and 19.1 % were achieved, respectively. This work may provide a new approach for designing highly efficient deep-blue emitters with negligible roll-off for OLED applications.     

New cyclic aminals derived from rac-trans-1,2-diaminocyclohexane: synthesis and crystal structure of racemic 1,8,10,12-tetraazatetracyclo[8.3.1.1.8,1202,7] pentadecane and a route to its enantiomerically pure (R,R) and (S,S) isomers

New enantiomerically pure macrocyclic aminals (2R,7R)- and (2S,7S)-1,8,10,12-tetraazatetracyclo[8.3.1.1.^8,120^2,7]pentadecane (4a and 4b) were obtained by a three component reaction between their respective pure enantiomer of trans-1,2-diaminocyclohexane, ammonia, and formaldehyde. Additionally, the X-ray structure of the racemic compound 4 and the specific rotations of the racemic and optically pure compounds were determined. To further understand the synthetic utilities of enantiomers 4a and 4b, Mannich-type reactions with 1H-benzotriazole were performed, affording (3aR,7aR)- and (3aS,7aS)-1,1′-{[2,3,3a,4,5,6,7,7a-octahydro-1H-1,3-benzimidazole-1,3-diyl]bis(methylene)}bis-1H-benzotriazole (9 and 10) and allowing for new possibilities related to the preparation of chiral ligands for asymmetric catalysis.     

Novel thioxanthone host material with thermally activated delayed fluorescence for reduced efficiency roll-off of phosphorescent OLEDs

A symmetrical host material, 2,7-di(9,9-dimethyl-9H-fluoren-1-yl)-9H-thioxanthen-9-one (DMBFTX), with TADF property was firstly developed. The red phosphorescent OLED based on this TADF host displays a lower EQEs rolloff of 38.8% at a luminance of 10 000 cd/m² as compared to 71.2% of commercial mCP host, which is resulted from the upconversion of DMBFTX from triplet to singlet.     

Multi-Resonance Building-Block-Based Electroluminescent Material: Lengthening Emission Maximum and Shortening Delayed Fluorescence Lifetime

Multi-resonance thermally activated delayed fluorescence (MR-TADF) materials are considered a class of organic materials with exceptional electronic and optical properties, which make them promising for the applications in organic light-emitting diodes (OLEDs). In this study, we improved, synthesized, and characterized a multiple-resonance type emitter based on the assembly of MR-building blocks (MR-BBs). By optimizing the geometric arrangement of MR-BBs, we were able to generate narrowband emission in the longer wavelength region and shorten the delayed excited-state lifetime, resulting in improved emission efficiency compared to the parent molecule. Our proof-of-concept molecule, m-DBCz, exhibited narrowband yellowish-green TADF emission with a full width at half-maximum of 32 nm and a small singlet-triplet energy gap of 0.04 eV. The OLED developed using m-DBCz as the emitter demonstrated electroluminescence at 548 nm and achieved a high external quantum efficiency (EQE) of 34.9 %. Further optimization of the device resulted in a high external quantum efficiency of 36.3 % and extremely low efficiency roll-off, with EQE values of 30.1 % and 27.7 % obtained even at high luminance levels of 50 000 and 100 000 cd m⁻². These results demonstrate the full potential of MR-TADF materials for applications on ultrahigh-luminance OLEDs.     

An Insight into All Tested Small Molecules against Fusarium oxysporum f. sp. Albedinis: A Comparative Review

Bayoud disease affects date palms in North Africa and the Middle East, and many researchers have used various methods to fight it. One of those methods is the chemical use of synthetic compounds, which raises questions centred around the compounds and common features used to prepare targeted molecules. In this review, 100 compounds of tested small molecules, collected from 2002 to 2022 in Web of Sciences, were divided into ten different classes against the main cause of Bayoud disease pathogen Fusarium oxysporum f. sp. albedinis (F.o.a.) with structure–activity relationship (SAR) interpretations for pharmacophore site predictions as (δ⁻···δ⁻), where 12 compounds are the most efficient (one compound from each group). The compounds, i.e., (Z)-1-(1.5-Dimethyl-1H-pyrazole-3-yl)-3-hydroxy but-2-en-1-one 7, (Z)-3-(phenyl)-1-(1,5-dimethyl-1H-pyrazole-3-yl)-3-hydroxyprop-2-en-1-one 23, (Z)-1-(1,5-Dimethyl-1H-pyrazole-3-yl)-3-hydroxy-3-(pyridine-2-yl)prop-2-en-1-one 29, and 2,3-bis-[(2-hydroxy-2-phenyl)ethenyl]-6-nitro-quinoxaline 61, have antifungal pharmacophore sites (δ⁻···δ⁻) in common in N1---O4, whereas other compounds have only one δ⁻ pharmacophore site pushed by the donor effect of the substituents on the phenyl rings. This specificity interferes in the biological activity against F.o.a. Further understanding of mechanistic drug–target interactions on this subject is currently underway.     

Tri‐Spiral Donor for High Efficiency and Versatile Blue Thermally Activated Delayed Fluorescence Materials

Blue thermally activated delayed fluorescence (TADF) emitters that can simultaneously achieve high efficiency in doped and nondoped organic light‐emitting diodes (OLEDs) are rarely reported. Reported here is a strategy using a tri‐spiral donor for such versatile blue TADF emitters. Impressively, by simply extending the nonconjugated fragment and molecular length, aggregation‐caused emission quenching (ACQ) can be greatly alleviated to achieve as high as a 90 % horizontal orientation dipole ratio and external quantum efficiencies (EQEs) of up to 33.3 % in doped and 20.0 % in nondoped sky‐blue TADF‐OLEDs. More fascinatingly, a high‐efficiency purely organic white OLED with an outstanding EQE of up to 22.8 % was also achieved by employing TspiroS‐TRZ as a blue emitter and an assistant host. This compound is the first blue TADF emitter that can simultaneously achieve high electroluminescence (EL) efficiency in doped, nondoped sky‐blue, and white TADF‐OLEDs.     

Crystallography,Molecular Modeling,and COX-2 Inhibition Studies on Indolizine Derivatives

The cyclooxygenase-2 (COX-2) enzyme is an important target for drug discovery and development of novel anti-inflammatory agents. Selective COX-2 inhibitors have the advantage of reduced side-effects, which result from COX-1 inhibition that is usually observed with nonselective COX inhibitors. In this study, the design and synthesis of a new series of 7-methoxy indolizines as bioisostere indomethacin analogues (5a–e) were carried out and evaluated for COX-2 enzyme inhibition. All the compounds showed activity in micromolar ranges, and the compound diethyl 3-(4-cyanobenzoyl)-7-methoxyindolizine-1,2-dicarboxylate (5a) emerged as a promising COX-2 inhibitor with an IC₅₀ of 5.84 µM, as compared to indomethacin (IC₅₀ = 6.84 µM). The molecular modeling study of indolizines indicated that hydrophobic interactions were the major contribution to COX-2 inhibition. The title compound diethyl 3-(4-bromobenzoyl)-7-methoxyindolizine-1,2-dicarboxylate (5c) was subjected for single-crystal X-ray studies, Hirshfeld surface analysis, and energy framework calculations. The X-ray diffraction analysis showed that the molecule (5c) crystallizes in the monoclinic crystal system with space group P 2₁/n with a = 12.0497(6)Å, b = 17.8324(10)Å, c = 19.6052(11)Å, α = 90.000°, β = 100.372(1)°, γ = 90.000°, and V = 4143.8(4)ų. In addition, with the help of Crystal Explorer software program using the B3LYP/6-31G(d, p) basis set, the theoretical calculation of the interaction and graphical representation of energy value was measured in the form of the energy framework in terms of coulombic, dispersion, and total energy.     

Stable deep blue organic light emitting diodes with CIE of y < 0.10 based on quinazoline and carbazole units

Achieving stable deep blue organic light emitting diodes (OLEDs) with narrow full width at half maximum (FWHM) and color gamut in the range of the commission International de L’Eclairage (CIE) of y ≤ 0.10 is still challenging in display and lighting applications. In this investigation, three donor-acceptor (D-A) deep-blue emitters were designed and synthesized via integrating asymmetric quinazoline (PQ) acceptor with weak donating carbazole (Cz) donor. The effect of the position and number of Cz group in PQ unit are investigated, which is also first examples for systematic research about the effect of different position of asymmetric PQ as acceptor on deep OLEDs. Their bandgaps of 3.12∼3.19 eV and the singlet state energy levels of 3.12∼3.19 eV were found to be sufficiently large to achieve deep blue light. As expected, these emitters-based OLEDs exhibit deep blue emission with the maximum wavelength ≤ 450 nm and narrow FWHM ≈ 60 nm. Especially, a CIE of y = 0.080 was achieved for 4PQ-Cz-based OLED. Significantly, the deep blue electroluminescence (EL) spectra of these three emitters-based OLEDs are very stable and the corresponding CIE coordinates deviation (ΔCIE (x, y)) can be negligible under the applied voltage ranging from 5 V to 9 V.     

D–π–A polysulfones for blue electroluminescence

Donor–π–acceptor type fluorene‐based copolymers with a sulfone unit were designed and synthesized for application in efficient pure‐blue light emitting. The electroluminescence behaviors of these copolymers were investigated by fabricating light‐emitting diodes and electrochemical cell devices. The former device little functioned but the latter worked well. The electrochemical cell devices having a configuration of ITO/PEDOT:PSS/copolymer:ionic liquid/Al exhibited purplish blue electroluminescence with an emission maximum at 434 nm (CIE coordinates (x, y) = (0.17, 0.10)) measured at 7 V. The initial positive scan of the D–π–A polysulfone based light emitting electrochemical cell with a sweep rate of 0.1 V s^?1 afforded a maximum luminance of 1080 cd m^?2 with a current efficiency of 1.96 cd A^?1 at an operating voltage of 12.5 V. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3454–3461     

Copper coordination polymers from cavitand ligands: hierarchical spaces from cage and capsule motifs,and other topologies

The cyclotriveratrylene-type ligands (±)-tris(iso-nicotinoyl)cyclotriguaiacylene L1 (±)-tris(4-pyridylmethyl)cyclotriguaiacylene L2 and (±)-tris{4-(4-pyridyl)benzyl}cyclotriguaiacylene L3 all feature 4-pyridyl donor groups and all form coordination polymers with Cu^I and/or Cu^II cations that show a remarkable range of framework topologies and structures. Complex [Cu^I ₄Cu^II _1.5(L1)₃(CN)₆]·CN·n(DMF) 1 features a novel 3,4-connected framework of cyano-linked hexagonal metallo-cages. In complexes [Cu₃(L2)₄(H₂O)₃]·6(OTf)·n(DMSO) 2 and [Cu₂(L3)₂Br₂(H₂O)(DMSO)]·2Br·n(DMSO) 3 capsule-like metallo-cryptophane motifs are formed which linked through their metal vertices into a hexagonal 2D network of (4³.12³)(4².12²) topology or a coordination chain. Complex [Cu₂(L1)₂(OTf)₂(NMP)₂(H₂O)₂]·2(OTf)·2NMP 4 has an interpenetrating 2D 3,4-connected framework of (4.6².8)(6².8)(4.6².8²) topology with tubular channels. Complex [Cu(L1)(NCMe)]·BF₄·2(CH₃CN)·H₂O 5 features a 2D network of 6³ topology while the Cu^II analogue [Cu₂(L1)₂(NMP)(H₂O)]·4BF₄·12NMP·1.5H₂O 6 has an interpenetrating (10,3)-b type structure and complex [Cu₂(L2)₂Br₃(DMSO)]·Br·n(DMSO) 7 has a 2D network of 4.8² topology. Strategies for formation of coordination polymers with hierarchical spaces emerge in this work and complex 2 is shown to absorb fullerene-C₆₀ through soaking the crystals in a toluene solution.     

Triphenylamino or 9-phenyl carbazolyl-substituted pyrimidine-5-carbonitriles as bipolar emitters and hosts with triplet harvesting abilities

To obtain highly efficient organic semiconductors exhibiting fast emission decays, triplet-harvesting abilities and good bipolar charge-transporting properties for optoelectronic applications, compounds containing triphenylamine or 9-phenylcarbazole as donor moieties and pyrimidine-5-carbonitrile as electron-withdrawing unit were synthesised. Toluene solutions of the compounds demonstrated high photoluminescence quantum yields reaching 98%. As required for electroluminescent device applications, compound containing triphenylamino moiety showed high mobilities of both electrons and holes, which reached 4.4 × 10^?4 cm²/V × s and 7.3 × 10^?3 cm²/V × s, respectively at electric field of 3.6 × 10⁵ V/cm. This triplet-harvesting mechanism was confirmed by the theoretical and experimental studies including a femtosecond transient absorption pump?probe technique and time-resolved electroluminescence spectroscopy. Pure-blue and greenish-blue fluorescent organic light-emitting diodes (OLEDs) with external quantum efficiency (EQE) reaching 7% and 6%, corresposndingly, were obtained using the newly synthesised compounds as emitters. The operation time (T50) of ca. 650 h were observed for blue OLED and of ca. 3800 h for greenish-blue OLED until reaching the half initial brightness (100 cd/m²). EQE of more than 20% and T50 exceeding 20,000 h were observed for electroluminescent devices based on emitter characterised by triplet?triplet annihilation and thermally activated delayed fluorescence which was utilised to test hosting properties of the differently donor-substituted pyrimidine-5-carbonitriles.     

Highly Efficient Orange and Warm White Phosphorescent OLEDs Based on a Host Material with a Carbazole–Fluorenyl Hybrid

A new carbazole–fluorenyl hybrid compound, 3,3′(2,7‐di(naphthaline‐2‐yl)‐9H‐fluorene‐9,9‐diyl)bis(9‐phenyl‐9H‐carbazole) (NFBC) was synthesized and characterized. The compound exhibits blue‐violet emission both in solution and in film, with peaks centered at 404 and 420 nm. In addition to the application as a blue emitter, NFBC is demonstrated to be a good host for phosphorescent dopants. By doping Ir(2‐phq)₃ in NFBC, a highly efficient orange organic light‐emitting diode (OLED) with a maximum efficiency of 32 cd A^?1 (26.5 Lm W^?1) was obtained. Unlike most phosphorescent OLEDs, the device prepared in our study shows little efficiency roll‐off at high brightness and maintains current efficiencies of 31.9 and 26.8 cd A^?1 at a luminance of 1000 and 10 000 cd m^?2, respectively. By using NFBC simultaneously as a blue fluorescence emitter and as a host for a phosphorescent dopant, a warm white OLED with a maximum efficiency of 22.9 Lm W^?1 (21.9 cd A^?1) was also obtained.