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
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
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>(ÎĽ<sub>4</sub>-O)Â(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
Two
new deep-red iridiumÂ(III) complexes, (fpiq)<sub>2</sub>IrÂ(dipba) (<b>fIr1</b>) and (f<sub>2</sub>piq)<sub>2</sub>IrÂ(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 IrÂ(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
The successful preparation
of two-dimensional (2D) single crystals
can promote the development of organic optoelectronic devices with
excellent performance. A Schiff base compound salicylideneÂ(4-dimethylamino)Âaniline
with aggregation induced emission (AIE) property was employed as the
building block to fabricate 2D thin single crystal plates with scales
from around 50 ÎĽm 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
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
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
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)Âbenzimidazole 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
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)Âbenzimidazole 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
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
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