11 research outputs found

    Two Host–Dopant Emitting Systems Realizing Four-Color Emission: A Simple and Effective Strategy for Highly Efficient Warm-White Organic Light-Emitting Diodes with High Color-Rendering Index at High Luminance

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    A four-color warm-white organic light-emitting diode employing a simple adjacent two-emitting-layer structure as a blue host–orange dopant/green host–red dopant has been fabricated, which exhibited a stable high electroluminescent performance: an external quantum efficiency of 23.3% and a power efficiency of 63.2 lm W<sup>–1</sup> at an illumination-relevant luminance of 1000 cd m<sup>–2</sup> with a high color-rendering index (CRI) of 92 and maintained high levels of 21.6% and 48.8 lm W<sup>–1</sup> with a CRI value of 93 at the extremely high luminance of 5000 cd m<sup>–2</sup>. To our knowledge, this should be the best result so far for a white-light organic light-emitting diode with CRI > 90, simultaneously exhibiting very high efficiencies based on a high luminance level for the solid-state lighting

    Growing Crystalline Zinc-1,3,5-benzenetricarboxylate Metal–Organic Frameworks in Different Surfactants

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    Six new zinc-1,3,5-benzenetricarboxylate-based metal–organic frameworks (MOFs) have been successfully synthesized using three different surfactants (PEG 400, octanoic acid, and hexadecyltributylphosphonium bromide) as reaction media. These surfactants with different characteristics, such as being neutral, acidic, and cationic, have been demonstrated to show strong effects on directing the crystals’ growth and resulted in different secondary building units (SBUs) including an unusual SBU unit [Zn<sub>4</sub>(μ<sub>4</sub>-O)­(CO<sub>2</sub>)<sub>7</sub>]. Our results clearly indicated that the surfactant–thermal method could offer exciting opportunities for preparing novel MOFs or other inorganic crystalline materials with diverse structures and interesting properties

    Rational Design and Characterization of Heteroleptic Phosphorescent Complexes for Highly Efficient Deep-Red Organic Light-Emitting Devices

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    Two new deep-red iridium­(III) complexes, (fpiq)<sub>2</sub>Ir­(dipba) (<b>fIr1</b>) and (f<sub>2</sub>piq)<sub>2</sub>Ir­(dipba) (<b>dfIr2</b>), comprising two cyclometaling ligands of fluorophenyl-isoquinoline derivatives (fpiq and f<sub>2</sub>piq) and a N-heterocyclic carbene (NHC)-based ancillary ligand of <i>N</i>,<i>N</i>′-diisopropylbenzamidinate (dipba) are designed, synthesized, and characterized. Given the unique four-membered Ir–N–C–N backbone built by the metal center and the ancillary ligand, both phosphors achieve significant improvement for their comprehensive optoelectronic characteristics. Density function theory (DFT) calculations and electrochemical measurements support the genuine pure red phosphorescent emission of <b>fIr1</b> and <b>dfIr2</b> based on their clearly distinct electron density distributions of the HOMO/LUMO orbitals compared with other red-emitting Ir­(III) derivatives. Both new phosphors show deep-red emission with λ<sub>max</sub> values in the region of 650–660 nm with high PLQYs and short excited-state lifetimes. The phosphorescent organic light emitting diodes (PhOLEDs) based on <b>fIr1</b> and <b>dfIr2</b> realize deep-red EL with the stable CIE<sub>x,y</sub> coordinates of (0.70, 0.30) and (0.69, 0.31), the peak EQE/PE values of 15.4%/9.3 lm W<sup>–1</sup> and 16.7%/10.4 lm W<sup>–1</sup>, respectively, which maintain such high levels as 10.6%/3.5 lm W<sup>–1</sup> and 10.8%/3.6 lm W<sup>–1</sup> at the practical luminance of 1000 cd m<sup>–2</sup>. They are the highest EL values reported for the OLEDs with such deep-red CIE coordinates

    Two-Dimensional Organic Single Crystals with Scale Regulated, Phase-Switchable, Polymorphism-Dependent, and Amplified Spontaneous Emission Properties

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    The successful preparation of two-dimensional (2D) single crystals can promote the development of organic optoelectronic devices with excellent performance. A Schiff base compound salicylidene­(4-dimethylamino)­aniline with aggregation induced emission (AIE) property was employed as the building block to fabricate 2D thin single crystal plates with scales from around 50 μm to 1.5 cm. Yellow and red emissive polymorphs were concomitantly obtained during crystallization. The single-crystal-to-single-crystal (SC-to-SC) transformation from yellow polymorph to red one was demonstrated. Furthermore, both polymorphs exhibited amplified spontaneous emission (ASE) properties. Interestingly, the red polymorph displayed size-dependent ASE characteristics. The larger red polymorph showed near-infrared ASE with maximum at 706 nm, whereas the smaller one presented red ASE with maximum at 610 nm. These results suggest that the different scale single crystalline thin films with perfect optoelectronic properties may be fabricated by using the organic molecules with 2D assembly feature

    Large π‑Conjugated Quinacridone Derivatives: Syntheses, Characterizations, Emission, and Charge Transport Properties

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    Two 11-ring-fused quinacridone derivatives, TTQA and DCNTTQA, have been synthesized by ferric chloride mediated cyclization and Knoevenagel reaction. Replacement of the carbonyl groups (in TTQA) with dicyanoethylene groups (in DCNTTQA) not only red-shifted the emission to the near-infrared region but also led to a nonplanar skeleton that significantly improved the solubility of DCNTTQA. Moreover, dicyanoethylene groups rendered DCNTTQA low-lying HOMO and LUMO levels. DCNTTQA-based solution-processed field-effect transistors showed a hole mobility up to 0.217 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>

    Single-Molecule-based White-Light Emissive Organic Solids with Molecular-Packing-Dependent Thermally Activated Delayed Fluorescence

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    White-light-emitting single molecules have attracted broad attention because of their great potential for use in flat-panel displays and future light sources. We report a unique molecule of 3-(diphenylamino)-9<i>H</i>-xanthen-9-one (3-DPH-XO), which was found to exhibit bright white-light emission in the solid state caused by the spontaneous formation of a mixture with different polymorphs. Single-crystal analyses demonstrate that noncovalent interactions (such as π···π stacking, hydrogen bonding, and C–H···π interactions) induce different stacking arrangements (polymorphs <b>A</b>, <b>B</b>, and <b>C</b>) with different photophysical properties in a molecular solid. In addition, crystals <b>B</b> and <b>C</b> with the acceptor···acceptor stacking feature show the thermally activated delayed fluorescence (TADF) characteristics, indicating that appropriate noncovalent interactions could enhance the reverse intersystem crossing process and consequently lead to delayed fluorescence. This discovery provides an effective strategy for the design of new white-light-emitting single molecules as well as TADF materials

    2‑(2-Hydroxyphenyl)benzimidazole-Based Four-Coordinate Boron-Containing Materials with Highly Efficient Deep-Blue Photoluminescence and Electroluminescence

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    Two novel four-coordinate boron-containing emitters <b>1</b> and <b>2</b> with deep-blue emissions were synthesized by refluxing a 2-(2-hydroxyphenyl)­benzimidazole ligand with triphenylborane or bromodibenzoborole. The boron chelation produced a new π-conjugated skeleton, which rendered the synthesized boron materials with intense fluorescence, good thermal stability, and high carrier mobility. Both compounds displayed deep-blue emissions in solutions with very high fluorescence quantum yields (over 0.70). More importantly, the samples showed identical fluorescence in the solution and solid states, and the efficiency was maintained at a high level (approximately 0.50) because of the bulky substituents between the boron atom and the benzimidazole unit, which can effectively separate the flat luminescent units. In addition, neat thin films composed of <b>1</b> or <b>2</b> exhibited high electron and hole mobility in the same order of magnitude 10<sup>–4</sup>, as determined by time-of-flight. The fabricated electroluminescent devices that employed <b>1</b> or <b>2</b> as emitting materials showed high-performance deep-blue emissions with Commission Internationale de L’Eclairage (CIE) coordinates of (<i>X</i> = 0.15, <i>Y</i> = 0.09) and (<i>X</i> = 0.16, <i>Y</i> = 0.08), respectively. Thus, the synthesized boron-containing materials are ideal candidates for fabricating high-performance deep-blue organic light-emitting diodes

    2‑(2-Hydroxyphenyl)benzimidazole-Based Four-Coordinate Boron-Containing Materials with Highly Efficient Deep-Blue Photoluminescence and Electroluminescence

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    Two novel four-coordinate boron-containing emitters <b>1</b> and <b>2</b> with deep-blue emissions were synthesized by refluxing a 2-(2-hydroxyphenyl)­benzimidazole ligand with triphenylborane or bromodibenzoborole. The boron chelation produced a new π-conjugated skeleton, which rendered the synthesized boron materials with intense fluorescence, good thermal stability, and high carrier mobility. Both compounds displayed deep-blue emissions in solutions with very high fluorescence quantum yields (over 0.70). More importantly, the samples showed identical fluorescence in the solution and solid states, and the efficiency was maintained at a high level (approximately 0.50) because of the bulky substituents between the boron atom and the benzimidazole unit, which can effectively separate the flat luminescent units. In addition, neat thin films composed of <b>1</b> or <b>2</b> exhibited high electron and hole mobility in the same order of magnitude 10<sup>–4</sup>, as determined by time-of-flight. The fabricated electroluminescent devices that employed <b>1</b> or <b>2</b> as emitting materials showed high-performance deep-blue emissions with Commission Internationale de L’Eclairage (CIE) coordinates of (<i>X</i> = 0.15, <i>Y</i> = 0.09) and (<i>X</i> = 0.16, <i>Y</i> = 0.08), respectively. Thus, the synthesized boron-containing materials are ideal candidates for fabricating high-performance deep-blue organic light-emitting diodes

    Dicyanomethylenated Acridone Based Crystals: Torsional Vibration Confinement Induced Emission with Supramolecular Structure Dependent and Stimuli Responsive Characteristics

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    A series of dicyanomethylenated acridone derivatives, DCNAC-C<i>n</i> (<i>n</i> = 1, 4, 6) and DPA-DCNAC-C4, are designed and synthesized. They are highly luminescent in the crystalline state but nonemissive in the amorphous state. The interesting crystallization-induced-emission (CIE) behavior is attributed to the restricted torsional vibrations of the molecular skeletons in crystal lattices. DCNAC-C<i>n</i>-based crystals display obvious molecular-packing-dependent emission properties. The molecular packing of DCNAC-C<i>n</i> in crystals is easily regulated by modifying the length of alkyl chains, resulting in the tunable emission colors from green to red. A DPA-DCNAC-C4 molecule consisting of a DCNAC acceptor and two diphenylamino donors shows intramolecular charge-transfer (ICT) characteristic and strong near-infrared emission (λ<sub>em</sub> = 707 nm, Φ<sub>F</sub> = 0.16) in the crystalline state. Mechanical, thermal, and organic-vapor stimuli can reversibly alter the aggregation phases between crystalline and amorphous states. Therefore, this study presents a stimuli-responsive emission on/off switching system with various emission colors (560 to 700 nm)

    Highly Efficient Long-Wavelength Thermally Activated Delayed Fluorescence OLEDs Based on Dicyanopyrazino Phenanthrene Derivatives

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    Highly efficient long-wavelength thermally activated delayed fluorescence (TADF) materials are developed using 2,3-dicyanopyrazino phenanthrene (DCPP) as the electron acceptor (A), and carbazole (Cz), diphenylamine (DPA), or 9,9-dimethyl-9,10-dihydroacridine (DMAC) as the electron donor (D). Because of the large, rigid π-conjugated structure and strong electron-withdrawing capability of DCPP, TADF molecules with emitting colors ranging from yellow to deep-red are realized with different electron-donating groups and π-conjugation length. The connecting modes between donor and acceptor, that is, with or without the phenyl ring as π-bridge, are also investigated to study the π-bridge effect on the thermal, photophysical, electrochemical, and electroluminescent properties. Yellow, orange, red, and deep-red organic light-emitting diodes (OLEDs) based on DCPP derivatives exhibit high efficiencies of 47.6 cd A<sup>–1</sup> (14.8%), 34.5 cd A<sup>–1</sup> (16.9%), 12.8 cd A<sup>–1</sup> (10.1%), and 13.2 cd A<sup>–1</sup> (15.1%), with Commission Internationale de L’Eclairage (CIE) coordinates of (0.44, 0.54), (0.53, 0.46), (0.60, 0.40), and (0.64, 0.36), respectively, which are among the best values for long-wavelength TADF OLEDs
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