Realization of Long Operational Lifetimes in Vacuum-Deposited Organic Light-Emitting Devices Based on para-Substituted Pyridine Carbazolylgold(III) C

A new series of robust C^C^N carbazolylgold(III) complexes is designed and synthesized through the introduction of inert and sterically bulky oligophenyl substituents on the pyridyl moiety of the cyclometalating ligand. High photoluminescence quantum yields of up to 96% are recorded with these complexes doped in solid-state thin films, and short excited-state lifetimes of 0.3 µs or less in the solid state at room temperature are found. Promising electroluminescence (EL) performances are shown by the vacuum-deposited organic light-emitting devices (OLEDs) based on this series of gold(III) complexes. High external quantum efficiencies of up to 19.5% with efficiency roll-offs of down to 10% at a practical luminance brightness level of 1000 cd m-2 are achieved. More importantly, record-long operational lifetimes (LT50) of up to 470,700 h at 100 cd m-2 are realized, which is currently the highest value among all classes of gold(III) complexes with tridentate pincer ligands. Particularly, by introducing a sterically bulky terphenyl moiety on the reactive site of the pyridine ring, the LT50 value is shown to attain ∼7 times longer half-lifetime than that based on the unsubstituted complex. These unprecedented EL performances and the simple synthetic route in a mercury-free fashion make them promising emitting materials for practical OLEDs toward commercialization.

Tetradentate C∧C∧N∧N Ligand-Containing Gold(III) Complexes with Orange to Deep-Red Thermally Activated Delayed Fluorescence (TADF) and Their Application in Organic Light-Emitting Devices.

A new class of thermally activated delayed fluorescence (TADF) tetradentate C∧C∧N∧N ligand-containing gold(III) complexes containing acridinyl moieties has been designed and synthesized. These complexes exhibit orange-red to deep-red emission with photoluminescence quantum yields (PLQYs) of up to 0.76 in solid-state thin films. Short excited-state lifetimes of ≤2.0 µs and large radiative decay rate constants (kr) in the order of 105 s-1 have also been found in the complexes. High-performance solution-processed and vacuum-deposited organic light-emitting devices (OLEDs) based on these complexes have been fabricated, demonstrating high maximum external quantum efficiencies (EQEs) of 12.2 and 12.7%, respectively, which are among the best values ever reported for red-emitting gold(III)-based OLEDs. In addition, satisfactory operational half-lifetime (LT50) values of up to 34,058 h have been attained in these red-emitting devices. It is found that the operational stability is strongly dependent on the choice of functional groups on the acridinyl moieties, of which the incorporation of -O- and -S- linkers can effectively prolong the LT50 value by an order of magnitude. The TADF properties of the complexes are substantiated by the hypsochromic shift in emission energies and the remarkable enhancement in the emission intensity upon increasing temperature. The TADF properties have also been supported by temperature-dependent ultrafast transient absorption studies, with the direct observation of reverse intersystem crossing (RISC) and the determination of the activation parameters for the very first time, together with their excited-state dynamics.

Si/Organic Integrated Narrowband Near-Infrared Photodetector.

Spectrally selective narrowband photodetection is critical for near-infrared (NIR) imaging applications, such as for communicationand night-vision utilities. It is a long-standing challenge for detectors based on silicon, to achieve narrowband photodetection without integrating any optical filters. Here, this work demonstrates a NIR nanograting Si/organic (PBDBT-DTBT:BTP-4F) heterojunction photodetector (PD), which for the first time obtains the full-width-at-half-maximum (FWHM) of only 26 nm and fast response of 74 µs at 895 nm. The response peak can be successfully tailored from 895 to 977 nm. The sharp and narrow response NIR peak is inherently attributed to the coherent overlapping between the NIR transmission spectrum of organic layer and diffraction enhanced absorption peak of patterned nanograting Si substrates. The finite difference time domain (FDTD) physics calculation confirms the resonant enhancement peaks, which is well consistent with the experiment results. Meanwhile, the relative characterization indicates that the introduction of the organic film can promote carrier transfer and charge collection, facilitating efficient photocurrent generation. This new device design strategy opens up a new window in developing low-cost sensitive NIR narrowband detection.

Molecular Design of Luminescent Gold(III) Emitters as Thermally Evaporable and Solution-Processable Organic Light-Emitting Device (OLED) Materials.

The advancement of high-efficiency luminescent and thermally stable organometallic complexes has offered opportunities for the commercialization of metal phosphors for fabricating organic light-emitting devices (OLEDs). Since the first report on the potential use of iridium(III) and platinum(II) complexes for applications in OLEDs in the late 1990s, extensive efforts have been made by researchers on the development of various heavy metal-containing compounds with rich photophysical and luminescence properties and the engineering of device architectures to improve device efficiencies. Apart from the more well-studied iridium(III) and platinum(II) complexes, complexes of gold(III) recently have demonstrated their capabilities to serve as phosphorescent or thermally stimulated delayed phosphorescent or thermally activated delayed fluorescent emitters, and their promising performances in OLEDs have attracted growing interest in the past decade. Nowadays, complexes of gold(III) with emission energies ranging from sky-blue to near-infrared with high electroluminescence performances have been obtained. In addition, high-efficiency vacuum-deposited and solution-processed OLEDs with benchmark efficiencies comparable to those of the iridium(III) and platinum(II) complexes have been realized. This Focus Review summarizes the development of various series of luminescent gold(III) complexes to date and highlights important milestones in the development and advancement of gold(III)-based OLEDs. Focus will be made on the molecular design strategies for gold(III) emitters for application as dopants in OLEDs, including those fabricated by vacuum-deposition and solution-processing techniques.

Multicomponent Copper-Zinc Alloy Layer Enabling Ultra-Stable Zinc Metal Anode of Aqueous Zn-ion Battery.

Constructing stable surface modification layer is an effective strategy to suppress dendrite growth and side reactions of Zinc (Zn) metal anode in aqueous Zn-ion battery. Herein, a multicomponent Cu-Zn alloy interlayer with superior Zn affinity, high toughness and effective inhibition effect on lattice distortion is constructed on Zn foil (Cu-Zn@Zn) to fabricate ultra-stable Zn metal anode. Owning to the advantages of high binding energy of Cu-Zn alloy layer with Zn atoms and less contact area between metallic Zn and electrolyte, the as-prepared Cu-Zn@Zn electrode not only restricts the aggregation of Zn atoms, but also suppresses the pernicious hydrogen evolution and corrosion, leading to homogeneous Zn deposition and outstanding electrochemical performances. Accordingly, the symmetric battery with Cu-Zn@Zn electrode exhibits an ultra-long cycle life of 5496 h at 1 mA cm-2 for 1 mAh cm-2 , and the Cu-Zn@Zn//V2 O5 pouch cell demonstrates excellent cycling stability with a capacity retention of 88 % after 600 cycles.

One-Pot Synthesis of Boron-Doped Polycyclic Aromatic Hydrocarbons via 1,4-Boron Migration.

Herein, we demonstrate a novel one-pot synthetic method towards a series of boron-doped polycyclic aromatic hydrocarbons (B-PAHs, 1 a-1 o), including hitherto unknown B-doped zethrene derivatives, from ortho-aryl substituted diarylalkynes with high atom efficiency and broad substrate scopes. A reaction mechanism is proposed based on the experimental investigation together with the theoretical calculations, which involves a unique 1,4-boron migration process. The resultant benchtop-stable B-PAHs are thoroughly investigated by X-ray crystallography, cyclic voltammetry, UV/Vis absorption, and fluorescence spectroscopies. The blue and green organic light-emitting diode (OLED) devices based on 1 f and 1 k are further fabricated, demonstrating the promising application potential of B-PAHs in organic optoelectronics.

Toward the Design of Phosphorescent Emitters of Cyclometalated Earth-Abundant Nickel(II) and Their Supramolecular Study.

A series of cyclometalating tridentate N^C^N and tetradentate N^C^N^O ligand-containing complexes of earth-abundant nickel(II) has been designed and synthesized. Among them, the carbazolylnickel(II) complex demonstrates, for the first time, an orange color room-temperature luminescence. Such a complex is also found to exhibit intense luminescence with excited state lifetimes in the submicrosecond regime at 77 K, suggesting the triplet nature of the emissive state. Meanwhile, the self-assembly property of the tetradentate ligand-containing nickel(II) complex in solution has been investigated. Owing to its nearly perfect square planar geometry, as evidenced by X-ray crystal structure determination, it is found to exhibit self-assembly properties with the aid of π-π interactions and possibly weak Ni···Ni interactions, which have been supported by DFT calculations and NCI plot. Indeed, the ground-state aggregation behavior of this complex has been confirmed by concentration-dependent UV-vis absorption spectroscopy. Moreover, in the solution-induced aggregation studies, upon the addition of nonsolubilizing solvents, the emergence of low-energy absorption bands has been realized, and such a complex is found to demonstrate interesting self-assembly behaviors to offer well-defined and highly ordered supramolecular architectures.

Thermally Stimulated Delayed Phosphorescence (TSDP)-Based Gold(III) Complexes of Tridentate Pyrazine-Containing Pincer Ligand with Wide Emission Color Tunability and Their Application in Organic Light-Emitting Devices.

A new class of pyrazine-based carbazole-containing gold(III) complexes featuring thermally stimulated delayed phosphorescence (TSDP) properties has been designed and synthesized. The emission colors are found to be sensitive to the coordinating atom of the carbazolyl ligands at the gold(III) center, with emission energies spanning from green to red. The efficiency of TSDP can be enhanced by lowering the polarity of the solvent, as supported by the variable-temperature emission and computational studies. Interestingly, a significant spectral shift in electroluminescence with the change of Commission Internationale de L'Eclairage (CIE) coordinates from (0.35, 0.60) to (0.44, 0.54) has been achieved by simply changing the host material from CBP to TmPyPB. Solution-processable organic light-emitting devices (OLEDs) have also been fabricated, with maximum current efficiencies of up to 22.4 cd A-1 and maximum external quantum efficiencies (EQEs) approaching 7.0%. A higher current efficiency of 35.1 cd A-1 and EQE of 10.7% can be achieved for the vacuum-deposited device based on 1, representing the first demonstration of pyrazine-based tridentate ligand-containing gold(III) complexes as phosphorescent material for OLED application.

Isomeric Tetradentate Ligand-Containing Cyclometalated Gold(III) Complexes.

A simple one-pot two bond-forming reaction for the rapid construction of cyclometalated gold(III) complexes with fully π-conjugated tetradentate ligand is reported. The coupling of the bifunctional gold(III) precursor with the bifunctional aromatic compound has led to the formation of two regioisomers with either C- or N-coordination. Through monitoring by high-throughput high performance liquid chromatography, the regioselectivity of the reaction has been effectively tuned toward the formation of a single isomer, allowing easy separation of the metal complexes. The structures of the complexes have been determined by X-ray crystallography, and the photophysical, electrochemical, and electroluminescence (EL) studies have been carried out. Computational study has been performed to provide insights into the nature of the excited states. Isomeric effect has been shown to have a significant influence on the EL behavior of the organic light-emitting devices.

Design Strategy Towards Horizontally Oriented Luminescent Tetradentate-Ligand-Containing Gold(III) Systems.

Phosphorescent dopants are promising candidates for organic light-emitting diodes (OLEDs). Although it has been established that the out-coupling efficiency and overall performances of vacuum-deposited OLEDs can be significantly improved by a horizontal orientation of the dopants, no horizontally oriented gold(III) complexes have been reported to date. Herein, a novel class of tetradentate C^C^N^N ligand-containing gold(III) complexes with a preferential horizontal orientation successfully generated through a one-pot reaction is reported. These complexes demonstrate high photoluminescence quantum yields of 70 % and a high horizontal dipole ratio of 0.87 in solid-state thin films. Green-emitting OLEDs based on these complexes operate with a maximum external quantum efficiency of 20.6 % with an estimated out-coupling efficiency of around 30 %. A promising device stability has been achieved in the vacuum-deposited OLEDs, with operational half-lifetimes of around 37 500 h at 100 cd m-2 .

Judicious Choice of N-Heterocycles for the Realization of Sky-Blue- to Green-Emitting Carbazolylgold(III) C

A new class of sky-blue- to green-emitting carbazolylgold(III) C^C^N complexes containing pyrazole or benzimidazole moieties has been successfully designed and synthesized. Through the judicious choice of the N-heterocycles in the cyclometalating ligand and the tailor-made carbazole moieties, maximum photoluminescence quantum yields of 0.52 and 0.39 have been realized in the green- and sky-blue-emitting complexes, respectively. Solution-processed and vacuum-deposited organic light-emitting devices (OLEDs) based on the benzimidazole-containing complexes have been prepared. The sky-blue-emitting device shows an emission peaking at 484 nm with a narrow full-width at half-maximum of 57 nm (2244 cm-1 ), demonstrating the potential of this class of complexes in the application of OLEDs with high color purity. In addition, high maximum external quantum efficiencies of 12.3 % and a long operational half-lifetime of over 5300 h at 100 cd m-2 have been achieved in the vacuum-deposited green-emitting devices.

Realization of Thermally Stimulated Delayed Phosphorescence in Arylgold(III) Complexes and Efficient Gold(III) Based Blue-Emitting Organic Light-Emitting Devices.

To address and overcome the difficulties associated with the increased reactivity and susceptibility of blue emitters to deactivation pathways arising from the high-lying triplet excited states, we have successfully demonstrated an innovative strategy of harvesting triplet emission via the "thermally stimulated delayed phosphorescence" mechanism, where thermal up-conversion of excitons from the lower-energy triplet excited states (T1) to higher-energy triplet excited states (T1') are observed to generate blue emission. The lower-lying T1 excited state could serve as a mediator to populate the emissive T1' state by up-conversion via reverse internal conversion, which could enhance the photoluminescence quantum yield by over 20-folds. Organic light-emitting devices with respectable external quantum efficiencies of up to 7.7% and sky-blue emission with CIE coordinates of (0.17, 0.37) have been realized. The operational stability for the device based on complex 1 has also been explored, and the device is found to show fairly respectable lifetime. This work opens up a new avenue to the design and synthesis of blue phosphorescent emitters.

Highly Emissive Fused Heterocyclic Alkynylgold(III) Complexes for Multiple Color Emission Spanning from Green to Red for Solution-Processable Organic Light-Emitting Devices.

A new class of fused heterocyclic tridentate ligand-containing alkynylgold(III) complexes with tunable emission color has been successfully designed and synthesized. Structural modification of the σ-donating fused heterocyclic alkynyl ligands, including substituted fluorene, carbazole, and triphenylamine, enables a large spectral shift of about 110 nm (ca. 3310 cm-1 ) that covers the green to red region to be realized with the same tridentate ligand-containing alkynylgold(III) complexes in solid-state thin films. Interestingly, the energy of the excimeric emission can be controlled by the rational design of the fused heterocyclic alkynyl ligands. Superior solution-processable organic light-emitting devices (OLEDs) with high external quantum efficiencies (EQEs) of 12.2, 13.5, 9.3, and 5.2 % were obtained with green, yellow, orange, and red emission. These high EQE values are comparable to those of the vacuum-deposited OLEDs based on structurally related alkynylgold(III) complexes.

Sky-Blue-Emitting Dendritic Alkynylgold(III) Complexes for Solution-Processable Organic Light-Emitting Devices.

A new class of tridentate ligand-containing cyclometalated gold(III) complexes featuring dendritic alkynyl ligands with carbazole moieties as dendrons and peripheral groups has been synthesized up to the third generation. High-performance solution-processable organic light-emitting devices (OLEDs) with maximum current efficiency of up to 23.7 cd A-1 and external quantum efficiency of up to 6.9% have been realized by a simple spin-coating technique. With the incorporation of bulky carbazole moieties to form higher generation dendrimers, the undesirable excimeric emission could be effectively reduced, allowing the fine-tuning of the emission color toward the blue region. This represents the first successful demonstration of sky-blue-emitting alkynylgold(III) complexes and its application in solution-processable OLEDs.

Strategy for the Realization of Efficient Solution-Processable Phosphorescent Organic Light-Emitting Devices: Design and Synthesis of Bipolar Alkynylplatinum(II) Complexes.

A new class of highly luminescent bipolar alkynylplatinum(II) complexes has been synthesized, characterized, and applied as phosphorescent dopants in the fabrication of solution-processable organic light-emitting devices (OLEDs). Through the incorporation of a delicate balance of electron-donating carbazole moieties and electron-accepting phenylbenzimidazole or oxadiazole moieties into the platinum(II) core, the platinum(II) complexes have been demonstrated to exhibit bipolar charge transport character with high photoluminescence quantum yields of up to 0.75 in thin films. The introduction of meta-linkages into the complexes further helps weaken the donor-acceptor interactions, facilitating better carrier-transporting abilities. More importantly, high-performance solution-processable green-emitting OLEDs with maximum current efficiencies of up to 57.4 cd A-1 and external quantum efficiencies of up to 16.0% have been realized. This is among the best performances for solution-processable phosphorescent OLEDs reported based on platinum(II) complexes as well as bipolar metal complexes.

Versatile Design Strategy for Highly Luminescent Vacuum-Evaporable and Solution-Processable Tridentate Gold(III) Complexes with Monoaryl Auxiliary Ligands and Their Applications for Phosphorescent Organic Light Emitting Devices.

A new class of brightly blue-green-emitting arylgold(III) complexes has been synthesized, characterized, and applied as phosphorescent dopants in the fabrication of solution-processable and vacuum-deposited organic light-emitting devices (OLEDs). These arylgold(III) complexes can be readily synthesized by reacting the corresponding arylboronic acids with the gold(III) precursor complexes in a one-pot Suzuki-Miyaura coupling reaction. When compared to the structurally related alkynylgold(III) complex, arylgold(III) complexes 1 and 2 exhibit much higher photoluminescence quantum yields in solution state. High photoluminescence quantum yields are also observed in solid-state thin films. More importantly, the solid-state emission spectra show strong resemblance to those in solution, irrespective of the dopant concentration, leading to significant improvement in the color purity of the OLEDs by suppressing any excimer emission resulting from the π-stacking of the tridentate ligand. High performance solution-processable and vacuum-deposited blue-green-emitting OLEDs have also been realized, with maximum external quantum efficiencies of 7.3% and 14.7%, respectively, representing the first demonstration of efficient blue-green-emitting OLEDs based on cyclometalated arylgold(III) complexes.

Design Strategy for High-Performance Dendritic Carbazole-Containing Alkynylplatinum(II) Complexes and Their Application in Solution-Processable Organic Light-Emitting Devices.

A new class of luminescent dendritic carbazole-containing alkynylplatinum(II) complexes has been synthesized, characterized, and applied as phosphorescent dopants in the fabrication of solution-processable organic light-emitting devices (OLEDs). These complexes exhibit high photoluminescence quantum yields of up to 80% in spin-coated thin films. In addition, the incorporation of carbazole dendrons into the platinum(II) center can significantly suppress intermolecular interactions in solid-state thin films, giving rise to emission spectra that are similar to those found in solution irrespective of dopant concentrations. High-performance solution-processable OLEDs have also been fabricated, with a maximum external quantum efficiency of up to 10.4%, which is comparable to that of the vacuum-deposited devices based on the small-molecule counterpart. This is one of the highest ever reported values for solution-processable devices based on platinum(II) complexes with tridentate ligands.

Dual-Emissive Cyclometalated Iridium(III) Polypyridine Complexes as Ratiometric Biological Probes and Organelle-Selective Bioimaging Reagents.

In this Article, we present a series of cyclometalated iridium(III) polypyridine complexes of the formula [Ir(N^C)2(N^N)](PF6) that showed dual emission under ambient conditions. The structures of the cyclometalating and diimine ligands were changed systematically to investigate the effects of the substituents on the dual-emission properties of the complexes. On the basis of the photophysical data, the high-energy (HE) and low-energy (LE) emission features of the complexes were assigned to triplet intraligand ((3)IL) and triplet charge-transfer ((3)CT) excited states, respectively. Time-dependent density functional theory (TD-DFT) calculations supported these assignments and indicated that the dual emission resulted from the interruption of the communication between the higher-lying (3)IL and the lower-lying (3)CT states by a triplet amine-to-ligand charge-transfer ((3)NLCT) state. Also, the avidin-binding properties of the biotin complexes were studied by emission titrations, and the results showed that the dual-emissive complexes can be utilized as ratiometric probes for avidin. Additionally, all the complexes exhibited efficient cellular uptake by live HeLa cells. The MTT and Annexin V assays confirmed that no cell death and early apoptosis occurred during the cell imaging experiments. Interestingly, laser-scanning confocal microscopy revealed that the complexes were selectively localized on the cell membrane, mitochondria, or both, depending on the nature of the substituents of the ligands. The results of this work will contribute to the future development of dual-emissive transition metal complexes as ratiometric probes and organelle-selective bioimaging reagents.

Bipolar gold(III) complexes for solution-processable organic light-emitting devices with a small efficiency roll-off.

A new class of bipolar alkynylgold(III) complexes containing triphenylamine and benzimidazole moieties has been synthesized, characterized, and applied as phosphorescent dopants in the fabrication of solution-processable organic light-emitting devices (OLEDs). The incorporation of methyl groups in the central phenyl unit has been found to rigidify the molecule to reduce nonradiative decay, yielding a high photoluminescence quantum yield of up to 75% in spin-coated thin films. In addition, the realization of highly efficient solution-processable OLEDs with an extremely small external quantum efficiency (EQE) roll-off has been demonstrated. At practical brightness level of 1000 cd m(-2), the optimized devices exhibited a high EQE of up to 10.0% and an extremely small roll-off of less than 1%.

Saturated red-light-emitting gold(III) triphenylamine dendrimers for solution-processable organic light-emitting devices.

A novel isoquinoline-containing C^N^C ligand and its phosphorescent triphenylamine-based alkynylgold(III) dendrimers have been synthesized. These alkynylgold(III) dendrimers serve as phosphorescent dopants in the fabrication of efficient solution-processable organic light-emitting devices (OLEDs). The photophysical, electrochemical, and electroluminescence properties were studied. A saturated red emission with CIE coordinates of (0.64, 0.36) and a high EQE value of 3.62% were achieved. Unlike other red-light-emitting iridium(III) dendrimers, a low turn-on voltage of less than 3 V and a reduced efficiency roll-off at high current densities were observed; this can be accounted for by the enhanced carrier transporting ability and the relatively short lifetimes in the high-generation dendrimers. This class of alkynylgold(III) dendrimers are promising candidates as phosphorescent dopants in the fabrication of solution-processable OLEDs.