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Owing to the high technology maturity of thermally activated delayed fluorescence (TADF) emitter design with a specific molecular shape, extremely high-performance organic light-emitting diodes (OLEDs) have recently been achieved

Three pyridine-carbonitrile (PPC) fluorophores with amine-type donors, carbazole, tert-butylcarbazole, and spiroacridine have been designed and synthesized. A high-performance green OLED based on SAcmPPC dopant exhibited an external quantum efficiency of 37.2%.

A series of new functional pyridine-appended pyrene derivatives, viz., 2,6-diphenyl-4-(pyren-1-yl)pyridine (Py-03), 2,6-bis(4-methoxyphenyl)-4-(pyren-1-yl)pyridine (Py-MeO), 4-(pyren-1-yl)-2,6-di-p-tolylpyridine (Py-Me), and 2,6-bis(4-bromophenyl)-4-(pyren-1-yl)pyridine (Py-Br) were designed, developed, and studied as the hole-transporting materials (HTMs) for organic light-emitting diode (OLED) application. The crystal structures of two molecules revealed to have a large dihedral angle between the pyrene and pyridine units, indicating poor π-electronic communication between them due to ineffective orbital overlap across the pyrene–pyridine systems as the two p-orbitals of pivotal atoms are twisted at 66.80° and 68.75° angles to each other in Py-03 and Py-Me, respectively. The influence of variedly functionalized pyridine units on the electro-optical properties and device performance of the present integrated system for OLED application was investigated. All of the materials have suitable HOMO values (5.6 eV) for hole injection by closely matching the HOMOs of indium tin oxide (ITO) and the light-emitting layer. All of the synthesized molecules have suitable triplet energies, glass transition temperatures, and melting temperatures, which are highly desirable for good HTMs. The pyrene–pyridine-based devices demonstrated stable performance with low-efficiency roll-off. The device with Py-Br as HTM showed a maximum luminance of 17300 cd/m2 with a maximum current efficiency of 22.4 cd/A and an EQE of 9% at 3500 cd/m2 with 7% roll-off from 1000 to 10 000 cd/m2. Also, the devices with Py-Me and Py-03 showed performance roll-up while moving from 1000 to 10 000 cd/m2.

Transforming triplet excitons into singlet excitons is a topic of great interest to material scientists in order to surpass the exciton utilization efficiency (EUE) limit of 25% in electro-fluorescent devices. Towards this goal, the donor–acceptor strategy of molecular design has been proven to be an effective approach to obtain high electroluminescence (EL) efficiency. In this context, herein, we report two benzothiadiazole (BTD)-based donor–acceptor π-conjugated fluorescent molecules, 1 and 2, which exhibited an external quantum efficiency (EQE) as high as 7.0% and 8.1%, respectively, in solution-processed doped green OLED devices. The observed high photoluminescence (PL) quantum yield of 81% for 1 and 85% for 2 corroborate the high EUE values of 43% and 48%, respectively, exceeding the traditional limit (25%), hence suggest the utilization of triplet excitons. The reported emitters combine two parameters, i.e. high PL efficiency and high EUE, which are of key importance to harvest maximum EL in OLED devices. Based on the photophysical (solvatochromic experiment) and quantum chemical calculations, the impacts of the D–π–A–π–D molecular design on the regulation of the locally excited and charge transfer components were revealed, which explained the observed high EQE (>5%) and EUE (>25%) values for the BTD-based emitters. The development of emitters with a hybrid local and charge transfer state in combination with the ‘hot exciton’ mechanism is an important strategy to produce highly efficient fluorescent-emitter materials. Besides the impressive EL properties of the emitters, the studied compound 1 as a chemosensor showed the selective sensing of metal cation (Fe2+) and anion (I−) together with the staining agent of Hibiscus rosa-sinensis pollen grains.

We report three yellow-green to yellow TADF dopants 26DAcBPy, 25DAcBPy and 26DPXZBPy containing dibenzoyl pyridine as the acceptor and dimethylacridine (Ac) and phenoxazine (PXZ) as the donors with short delayed fluorescence lifetimes of 2.3 μs, 1.9 μs, and 1.0 μs, respectively. The crystal structures show that 26DAcBPy and 26DPXZBPy have a U shape conformation and 25DAcBPy a linear chain structure. All three molecules show intramolecular hydrogen bonding between the pyridine nitrogen and the o-hydrogen of a phenyl ring. These conformations appear to be the result of hydrogen bonding, which leads to rigid structures and provides higher photoluminescence quantum yield. Lastly, these molecules show large dihedral angles between the donor group and the spacer phenyl unit leading to a well-separated HOMO and LUMO and small ΔEST values. Combined with the small ΔEST values, and good photoluminescence (PL) quantum yields, the 26DAcBPy-based devices show a maximum efficiency of 23.1% with a mild efficiency roll-off.

A cobalt-catalyzed synthesis of 1-aminoindenes via enantioselective [3 + 2] annulation is described. In this reaction, the desired products can be selectively prepared in either (R)- or (S)-form by the ligand-controlled synthesis, which is initiated by the cleavage of C–B, C–Br, or C–O bonds under very mild reaction conditions. In addition, this enantioselective cobalt catalysis provides high regioselectivity for both internal and terminal alkynes, and affords products generally in high yields and ee values.

Hydroarylation of bicyclic alkenes has been developed using a low-valent ReI -catalyzed, directing group-assisted C-H bond activation strategy. The addition of sodium acetate significantly improves the reaction efficiency; moreover, bicyclic alkenes such as 7-oxa and aza benzonorbornadienes worked efficiently under this reaction condition. Preliminary mechanistic studies suggest that, after the alkene insertion, the rhenacycle preferentially undergoes protonolysis rather than reductive elimination.

A cobalt-catalyzed C–H/N–H annulation of anilides with allenes to synthesize 1,2-dihydroquinolines is described. The reaction proceeds via a C–H activation, allene insertion, followed by β-hydride elimination and an intramolecular 1,4-addition to a butadiene-group-containing intermediate. Allenes act as a three-carbon source in the present C–H activation strategy.

An Fe(III)-promoted oxidative annulation reaction was developed for the synthesis of 1,2-naphthoquinones. A variety of substituted arylglyoxals and internal alkynes undergo the transformation in the presence of FeCl3 at room temperature to afford the 1,2-naphthoquinone products in good yields in a short reaction time. Interestingly, the products show unusual pseudomigration of the substituent on the arene ring of arylglyoxals. A possible mechanism involving Fe(III)-promoted formation of a vinyl cation from arylglyoxal and alkyne, electrophilic addition of the vinyl cation to the ipso carbon of the aryl group to give a spiral intermediate, and then migration of the keto carbon to the ortho carbon was proposed as key steps and verified using quantum mechanics.

Simultaneous enhancement of out-coupling efficiency, internal quantum efficiency, and color purity in thermally activated delayed fluorescence (TADF) emitters is highly desired for the practical application of these materials. We designed and synthesized two isomeric TADF emitters, 2DPyM-mDTC and 3DPyM-pDTC, based on di(pyridinyl)methanone (DPyM) cores as the new electron-accepting units and di(tert-butyl)carbazole (DTC) as the electron-donating units. 3DPyM-pDTC, which is structurally nearly planar with a very small ΔEST, shows higher color purity, horizontal ratio, and quantum yield than 2DPyM-mDTC, which has a more flexible structure. An electroluminescence device based on 3DPyM-pDTC as the dopant emitter can reach an extremely high external quantum efficiency of 31.9% with a pure blue emission. This work also demonstrates a way to design materials with a high portion of horizontal molecular orientation to realize a highly efficient pure-blue device based on TADF emitters.

Highly substituted cationic heterocyclic nitrogen salts are versatile building blocks for a number of naturally occurring products and functional materials. In this paper, we review the very recently reported Co(III)-, Rh(III)- and Ir(III)-catalyzed inter- and intra-molecular sp2 CH activation/annulations with alkynes or alkenes for the synthesis of various quaternary ammonium salts containing isoquinolinium, cinnolinium, quinolizinium, mesoionic isoquinolone, 12-azapyrene, protoberberine, indolizinium, and isoindolium salts. In addition, the reaction scope, proposed catalytic mechanisms, and applications are also included. This review will help readers to easily understand the recent advances in this field.

Recently, thermally activated delayed fluorescence (TADF) materials have become the most promising hosts for realizing high-performance phosphorescent and fluorescent organic light-emitting diodes (OLEDs) because of their ability to upconvert triplet excitons to singlet excitons. However, despite a few TADF hosts having been introduced for low energy phosphorescent and fluorescent dopants, developing host materials with TADF properties for blue phosphorescent and TADF OLEDs is still a great challenge to date. In this study, bipolar hosts exhibiting TADF behavior and high triplet energy, consisting of the carbazole group as the donor, diphenylsulphone moiety as the acceptor, and m-bitolyl as the π-conjugated bridge, are synthesized and applied for the first time to blue devices. The ΔEST value of the TADF host is tuned via the introduction of a cyano group in the carbazole moiety due to the increase of the LE contribution in the CT excited state. Detailed photophysical studies confirm the efficient TADF pr...

Various substituted indolizidinium, quinolizinium and pyrido[1,2-a]azepinium salts synthesized from benzaldehydes (or α,β-unsaturated aldehydes) and alkyne-amines catalyzed by rhodium complexes via C-H activation are demonstrated. The reaction was carried out under mild reaction conditions using Cu(BF4)2·6H2O as oxidant and anion source and inexpensive oxygen as a co-oxidant. A reaction mechanism involving imine formation followed by an ortho C-H activation, alkyne insertion and reductive elimination via a 7-membered rhodacycle is proposed. The present method has been successfully applied to the synthesis of a natural product, ficuseptine.

Thermally activated delayed fluorescence (TADF) emitters are attractive for display and lighting applications. Here, a series of highly efficient blue TADF emitters including 3,5-bis((3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)(pyridin-4-yl)methanone (4BPy-mDTC), (3,5-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)(pyridin-3-yl)methanone (3BPy-mDTC), (3,5-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)(pyridin-2-yl)methanone (2BPy-mDTC) and (3,5-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)(phenyl)methanone (BP-mDTC) were designed and synthesized. The molecular structures feature two meta carbazole substituents attached to a benzoylpyridine (BPy) group or to a benzophenone (BP) group. These compounds show high thermal stability (Td = 371–439 °C), blue emissions (458–488 nm), high photoluminescence quantum yields (PLQY) (75–96%) in thin films and very small energy gaps between S1 and T1 (ΔEST) of 0.01–0.05 eV. In addition, they all reveal TADF properties including small ΔEST, two components in the transient PL decays, prompt emission and temperature-dependent delayed emission. The BPy series appears to give much higher photoluminescence quantum yields (PLQY > 92%) than BP-mDTC (75%) plausibly due to the more rigid structure caused by the interaction between pyridine nitrogen and the aromatic C–H bond. Furthermore, 4BPy-mDTC shows a more delayed component compared to 3BPy-mDTC and 2BPy-mDTC. The electroluminescent devices based on 4BPy-mDTC and 2BPy-mDTC as the dopant emitters exhibit sky blue emission with maximum external quantum efficiencies (EQEs) over 28%, and current and power efficiency and maximum luminance up to 67.0 cd A−1, 60.1 lm W−1 and 20 000 cd m−2, respectively. The presence of the pyridine ring and the position of the nitrogen atom in the molecules are critical for the high quantum yield and device efficiency. The PLQY EQE and luminance are dramatically improved by changing the phenyl into a pyridine group in the dopant in these devices.

Catalytic C-H functionalization has emerged as an efficient alternative to traditional coupling reactions. However, some of these reactions depend on environmentally harmful solvents, weakening the overall green nature of these methods. As organic processes consume large amount of solvents, the use of less harmful solvents enhance the sustainability of these reactions. Herein, we present an overview of transition metal-catalyzed C-H functionalization reactions for the synthesis of heterocycles in sustainable solvents based on CHEM21 solvent selection guide.

After the revelation of nonvisual lighting impact on human health, the lighting engineers are more concerned about the human benign light with low cost and high efficiency. The solution-processed fabrication technique with smart device engineering for high efficacy OLED devices is being anticipated to drastically reduce the fabrication cost leading to affordable desired end product. The co-host matrix could be a potential solution to improve device performance multi-folds with suitable band-gap engineering and most effective energy transfer from mixed host to guest. Here, rationally configured device architecture with two novel host materials possessing wide energy gap, high triplet energy, and excellent thermal and morphological stability resulted in highly-efficient solution-processed green, red and low color temperature (CT) OLEDs with sub-bandgap level driving voltage of 2.1 V i.e. record lowest within its own category. Perfect triplet energy match of our newly developed host materials with commercial p-type host m-MTDATA and the common phosphors enabled efficient energy transfer with very low energy loss led to high efficiency of resulting OLED. The resultant solution-processed triplet emitter based green and red OLED devices displayed a maximum efficacy of 75.0 and 30.2 lm W−1 without using light extraction out-coupling techniques, respectively. The designed blue-hazard free 2048 K low CT OLED exhibited a ηPE of 44.5 lmW−1, a ηCE of 47.6 cdA-1 and an EQE of 20.7% as the maximum value, the highest known so far within its own category. The melatonin suppression sensitivity (MSS) of the engineered low CT OLED is only 1.0% to that of the 480 nm blue light, which is much safer compared to other light sources. The impact of our design engineering was established by fabricating 1 cm × 1 cm device area prototype.

Palladium-catalyzed cycloaromatization of N-acyl-2-aminobiaryls, through a sequence of ortho C−H bond activation/alkyne insertion/meta C−H bond activation/alkyne insertion, was developed. An efficient synthesis of multiaryl-substituted naphthalenes, N-[2-(5,6,7,8-tetraarylnaphthalen-1-yl)aryl]acetamides, was demonstrated using molecular oxygen as the sole oxidant. Furthermore, through Buchwald's synthetic protocol, two compounds were converted into corresponding fluorescent carbazoles in 30–40% yield by intramolecular C−N bond formation.

A highly regioselective synthesis of pyrido[2,1-a]isoindolium salts from 2-arylpyridines and two equivalents of electron-deficient alkenes catalyzed by rhodium is demonstrated. The reaction was carried out in aqueous medium at 110 °C using inexpensive oxygen as oxidant. Reverse aza-Michael addition of the isoindolium salt occurs when the salt was treated with base to give a β-disubstituted alkene product. A reaction mechanism involving an ortho C–H olefination of 2-arylpyridine by alkene, intramolecular aza-Michael addition, deprotonation at the β-carbon of the alkene fragment followed by another Michael addition to give the final product is proposed.

A new cobalt-catalyzed phenolic OH-assisted C–H functionalization of 2-vinylphenols with allenes to give various 2H-chromenes is described. It is the first time that allenes are used as the coupling partners in the cobalt-catalyzed C–H activation reactions. In most cases, cobalt-catalyzed oxidative annulation of arenes with alkenes or alkynes via C–H activation gave [4 + 2] or [3 + 2] cyclization products, but the present catalytic reaction afforded an oxidative [5 + 1] cyclization products with the allenes acting as a one-carbon coupling partner. The catalytic reaction is proposed to proceed via the C–H activation of the vinyl group, allene insertion, and an unusual intramolecular regioselective phenoxide addition.

A highly diastereoselective method for the synthesis of dihydroepoxybenzofluorenone derivatives from aromatic/vinylic amides and bicyclic alkenes is described. This new transformation proceeds through cobalt-catalyzed C-H activation and intramolecular nucleophilic addition to the amide functional group. Transition-metal-catalyzed C-H activation reactions of secondary amides with alkenes usually lead to [4+2] or [4+1] annulation; to the best of our knowledge, this is the first time that a [3+2] cycloaddition is described in this context. The reaction proceeds under mild conditions and tolerates a wide range of functional groups. Mechanistic studies imply that the C-H bond cleavage may be the rate-limiting step.

Two benzoylpyridine-carbazole based fluorescence materials DCBPy and DTCBPy, bearing two carbazolyl and 4-(t-butyl)carbazolyl groups, respectively, at the meta and ortho carbons of the benzoyl ring, were synthesized. These molecules show very small ΔEST of 0.03 and 0.04 eV and transient PL characteristics indicating that they are thermally activated delayed fluorescence (TADF) materials. In addition, they show extremely different photoluminescent quantum yields in solution and in the solid state: in cyclohexane the value are 14 and 36%, but in the thin films, the value increase to 88.0 and 91.4%, respectively. The OLEDs using DCBPy and DTCBPy as dopants emit blue and green light with EQEs of 24.0 and 27.2%, respectively, and with low efficiency roll-off at practical brightness level. The crystal structure of DTCBPy reveals a substantial interaction between the ortho donor (carbazolyl) and acceptor (4-pyridylcarbonyl) unit. This interaction between donor and acceptor substituents likely play a key role to achieve very small ΔEST with high photoluminescence quantum yield.

A novel copper-promoted multiple aza-[4 + 2] cycloaddition reaction of N-methyleneanilines in situ generated from benzylic azide and alkenes afforded quinolinium salts, biquinolinium salts, biquinolines or substituted quinolines depending on the substitution on the phenyl ring of benzylic azide. The reaction of para substituted benzylic azides and 2 equivalents of alkenes afforded the corresponding substituted quinolinium salts, while benzylic azides without a para substituent provided biquinolinium salts. The copper-promoted cycloaddition reaction also allows biquinoline products to be obtained from ortho-substituted benzylic azides. These reactions work well with both terminal and internal alkenes. Unsymmetrical internal alkene reactions proceed with high regioselectivity. The reaction is likely started by Lewis acidic CuII-assisted rearrangement of benzylic azide to N-methyleneaniline, followed by a [4 + 2] cycloaddition with alkene. Detailed mechanistic studies suggest that the biquinoline and biquinolinium salts are likely formed via radical processes.

A novel p-type charge generation material, DPAF, composed of a ferrocene core and a bis(biphenyl)amino group is designed and synthesized for application to tandem OLED devices. This molecular design not only enhances the thermal properties of ferrocene and the hole mobility, but also maintains its electrochemical stability. The red, green, and blue tandem OLEDs all give excellent device performance with low efficiency roll-off by using n-type C60 and p-type DPAFs as charge generation layers.

Correction for ‘Superior upconversion fluorescence dopants for highly efficient deep-blue electroluminescent devices’ by Yi-Hsiang Chen et al., Chem. Sci., 2016, DOI: 10.1039/c6sc00100a.

A thermally activated delayed fluorescent (TADF) material containing two meta carbazolyl groups on the phenyl ring of the benzoyl-4-pyridine moiety was prepared and its luminescence showed a colour change from blue to green by external stimuli. The organic-blue-light-emitting device using this TADF dopant provided a high external quantum efficiency of 18.4%.

We describe a highly step and atom economical cobalt-catalyzed cyclization of 1,6-enynes with aldehydes to synthesize functionalized pyrrolidines and dihydrofurans with high chemo- and stereoselectivity. The catalytic reaction plausibly proceeds via the cobaltacycle intermediate generated from the reaction of enyne substrate with cobalt catalyst, followed by switchable C-H functionalization of weakly coordinating aldehydes depending on the electronic nature of the ligand.

A method for the synthesis of substituted quinolizinium salts from 2-ethylpyridines and alkynes is demonstrated. The transformation is conveniently achieved using 1 mol % of a Rh(III) catalyst along with an excess amount of copper(II) salt. The reaction gives high product yields with broad substrate scope and functional group tolerance. Detailed mechanistic studies suggest that 2-vinylpyridine is formed in situ from 2-ethylpyridine by a copper-promoted C(sp3)–H hydroxylation, followed by dehydration. Later, a Rh(III)-catalyzed pyridine-directed vinylic C(sp2)–H activation and annulation with alkynes provided the final product.

A highly regio- and stereoselective synthesis of 3,3-disubstituted phthalides from aryl carboxylic acids and allenes using a rhodium(III) catalyst has been demonstrated. The reaction features broad functional group tolerance and provides a simple and straightforward route to the synthesis of various 3-vinyl-substituted phthalides. Furthermore, the catalytic reaction can also be applied to the synthesis of biologically active 5-vinyl-substituted 2-furanones from α,β-unsaturated carboxylic acids and allenes. The reactions proceed through a carboxylate-assisted ortho-CH activation and [4+1] annulation. The preliminary mechanistic studies suggest that a CH cleavage is the rate-determining step.

Over the last three decades, transition-metal-catalyzed organic transformations have been shown to be extremely important in organic synthesis. However, most of the successful reactions are associated with noble metals, which are generally toxic, expensive, and less abundant. Therefore, we have focused on catalysis using the abundant first-row transition metals, specifically cobalt. In this Account, we demonstrate the potential of cobalt catalysis in organic synthesis as revealed by our research. We have developed many useful catalytic systems using cobalt complexes. Overall, they can be classified into several broad types of reactions, specifically [2 + 2 + 2] and [2 + 2] cycloadditions; enyne reductive coupling; reductive [3 + 2] cycloaddition of alkynes/allenes with enones; reductive coupling of alkyl iodides with alkenes; addition of organoboronic acids to alkynes, alkenes, or aldehydes; carbocyclization of o-iodoaryl ketones/aldehydes with alkynes/electron-deficient alkenes; coupling of thiols with aryl and alkyl halides; enyne coupling; and C-H bond activation. Reactions relying on π components, specifically cycloaddition, reductive coupling, and enyne coupling, mostly afford products with excellent stereo- and regioselectivity and superior atom economy. We believe that these cobalt-catalyzed π-component coupling reactions proceed through five-membered cobaltacyclic intermediates formed by the oxidative cyclometalation of two coordinated π bonds of the substrates to the low-valent cobalt species. The high regio- and stereoselectivity of these reactions are achieved as a result of the electronic and steric effects of the π components. Mostly, electron-withdrawing groups and bulkier groups attached to the π bonds prefer to be placed near the cobalt center of the cobaltacycle. Most of these transformations proceed through low-valent cobalt complexes, which are conveniently generated in situ from air-stable Co(II) salts by Zn- or Mn-mediated reduction. Overall, we have shown these reactions to be excellent substitutes for less desirable noble-metal systems. Recent successes in cobalt-catalyzed C-H activation have especially advanced the applicability of cobalt in this field. In addition to the more common low-valent-cobalt-catalyzed C-H activation reactions, an in situ-formed cobalt(III) five-membered complex with a 1,6-enyne effectively couples with aromatic ketones and esters through ortho C-H activation, opening a new window in this research area. Interestingly, this reaction proceeds under milder reaction conditions with broad substrate scope. Furthermore, many of the reactions we have developed are highly enantioselective, including enantioselective reductive coupling of enones and alkynes, addition of organoboronic acids to aldehydes, and the cyclization of 2-iodobenzoates with aldehydes. Overall, this Account demonstrates the versatility and utility of cobalt catalysis in organic synthesis.

An efficient o-arylation of pivalamides by aryl iodides via rhodium(III)-catalyzed C–H activation is demonstrated for the first time. Further, the biaryl products can be converted effectively into biologically active phenanthridine and phenanthridinone derivative.

Transition-metal-catalyzed C - H activation is considered to be an important tool in organic synthesis and has been accepted and widely used by chemists because it is straightforward, cost-effective, and environmentally friendly. A variety of functional groups have been used to direct metal complexes and achieve regioselective C - H activation. Most directing is achieved through the σ-bond coordination of functional groups to the metal catalyst, followed by ortho-selective C - H bond cleavage. However, recent work has demonstrated that π-coordinating functional groups can also assist in guiding metal complexes for site-selective C - H bond activation. This emerging approach significantly expands the scope of C - H activation reactions in organic synthesis. Herein, recent developments in this field are summarized.

Altering the luminescence properties of a material through external factors is an attractive feature that has the potential for various luminescence-related applications. Here, we report the synthesis and luminescence properties of two anthracene-based donor acceptor compounds, N,N-di-p-tolylanthracen-9-amine (TAA) and 10-bromo-N,N-di-p-tolylanthracen-9-amine (TAAB). In the solid state, the bromo-substituted compound TAAB shows reversible visible switching of the emission by external stimuli such as solvent, mechanical grinding and temperature. Single crystal X-ray studies, powder-XRD analysis and theoretical calculations reveal that switchable emission originated from the different stacking modes of TAAB. Furthermore, we have found that the bromo group interaction in the solid state plays a crucial role in this tunable emission. The other anthracene-based compound TAA does not show such switching of the emission by external stimuli. The observed changes in the luminescence of TAAB by external stimuli suggest potential applications in rewritable optical media, sensors, and optoelectronic devices.

A high glass transition temperature (Tg = 220 °C), high triplet energy gap (ET = 2.76 eV) and high electron mobility material bis(m-terphenyl)oxadiazole was readily synthesized. It can serve as a universal electron transporter for blue, green and red phosphorescent OLEDs with excellent efficiencies. The material shows high current density compared to other electron transport materials and exhibits reduced driving voltage for all color PhOLEDs irrespective of the energy level of the host materials, due to efficient electron injection from 2,5-di([1,1′:3′,1″-terphenyl]-5′-yl)-1,3,4-oxadiazole (TPOTP) to the host material. For the green PhOLED, maximum external quantum efficiency (EQE) over 25%, current efficiency of 97.6 cd A−1 and power efficiency of 100.6 lm W−1 were achieved. The red and blue devices using TPOTP as the electron transporter also show EQE higher than 23% with very low roll-off in efficiencies in practical brightness level.

In this study, we determined that the film morphologies, crystallinities, and optical properties of CH3NH3PbI3−xClx perovskite (PVSK) layers can be manipulated by incorporating a small amount of ethylammonium iodide (EAI) into the perovskite precursor solution. For our EAI-derived films, we observed higher absorbances at higher wavelengths and higher degrees of crystallinity, both of which were associated with the higher surface coverage of the PVSK films. The optimized power conversion efficiency (PCE) improved from 9.4 ± 0.76 to 10.2 ± 0.58% after the addition of 0.5 vol% of EAI. Devices based on EAI-containing PVSK exhibited extremely high stability, retaining approximately 80% of their PCEs (T80) under accelerated heating (65 °C) in a dark N2-filled glove box for over 360 h. In contrast, the corresponding normal device was relatively sensitive to this temperature, with a T80 value of only 45 h. The improved device performance (PCE, stability) arose as a result of the presence of EAI suppressing the crystallization of CH3NH3PbI3−xClx.

A novel copper promoted synthesis of substituted quinolines from various benzylic azides and internal alkynes has been demonstrated. The reaction features a broad substrate scope, high product yields and excellent regioselectivity. In contrast to the known two-step process of acid promoted [4 + 2] cycloaddition reaction and oxidation, the present methodology allows the synthesis of quinolines in a single step under neutral reaction conditions and can be applied to the synthesis of biologically active 6-chloro-2,3-dimethyl-4-phenylquinoline (antiparasitic agent) and 3,4-diphenylquinolin-2(1H)-one (p38αMAP kinase inhibitor). A plausible reaction mechanism involves rearrangement of benzylic azide to N-arylimine (Schmidt reaction) followed by intermolecular [4 + 2] cycloaddition with internal alkynes.

An efficient Co-catalyzed 1,4-addition reaction of alkyl/aryl triflates and tosylates with activated alkenes is described. In this reaction, an air-stable cobalt(ii) complex, a mild reducing agent Zn and a simple proton source (H2O) are used. A radical mechanism for the addition of alkyl tosylates to activated alkenes is likely involved.

A versatile palladium-catalyzed synthesis of highly substituted α,β-unsaturated carbonyl compounds has been developed. In contrast to the known Heck-type coupling reaction of unsaturated carbonyl compounds with aryl halides, the present methodology allows the use of stable and readily available saturated carbonyl compounds as the alkene source. In addition, the reaction proceeds well with low catalyst loadings and does not require any expensive metal oxidants or ligands. A variety of saturated aldehydes, ketones, and esters are compatible for the reaction with aryl halides under the developed reaction conditions to afford α,β-unsaturated carbonyl compounds in good to excellent yields. A possible reaction mechanism involves a palladium-catalyzed dehydrogenation followed by Heck-type cross couplings.

A new method for the synthesis of highly substituted naphthyridine-based polyheteroaromatic compounds in high yields proceeds through rhodium(III)-catalyzed multiple C-H bond cleavage and C-C and C-N bond formation in a one-pot process. Such highly substituted polyheteroaromatic compounds have attracted much attention because of their unique π-conjugation, which make them suitable materials for organic semiconductors and luminescent materials. Furthermore, a possible mechanism, which involves multiple chelation-assisted ortho C-H activation, alkyne insertion, and reductive elimination, is proposed for this transformation.

Low color-temperature (CT) light sources are preferred for physiologically-friendly illumination at night due to their low suppression of melatonin secretion. We fabricated low-CT hybrid organic light-emitting diodes (OLEDs) by constructing a double emissive-layer (EML) structure, with a blue-red fluorescent-phosphorescent hybrid EML and a green phosphorescent EML, separated by a bipolar inter-layer. By doping a red phosphor in a blue fluorescent mixed-host with a decent concentration, blue and red emissions from the host and dopant, respectively, were obtained. The CT of the optimized device was tuned to less than 2500 K, with the brightness ranging from 100 to 10,000 cd m(-2). In addition, the low-CT OLED exhibited much higher efficacy than other low-CT light sources, such as incandescent bulbs and candles. The maximum power efficiency and external quantum efficiency of the hybrid OLED reached 54.6 lm W-1 and 24.3%, respectively, which only rolled off to 44.2 lm W-1 and 23.6% at 1000 cd m(-2), with a CT of 1910 K. Low-CT OLEDs with high efficacy provide a promising alternative for night lighting that will safeguard human health.

A regioselective synthesis of indoles from arylhydrazine hydrochlorides with alkynes and diethyl ketone catalyzed by a rhodium complex is described. A possible mechanism involving an in-situ generated oxidizing directing group NNCR1R2 assisted ortho-CH activation and reductive elimination are proposed. The catalytic reaction is highly compatible with a wide range of functional arylhydrazines and alkynes. The reaction proceeds under mild reaction conditions and is atom-step economical.

A nickel-catalyzed regio- and stereoselective reductive coupling of oxa- and azabicyclic alkenes with activated alkenes and electron-rich alkynes is described. Thus, 7-oxabenzonorbornadienes underwent reductive coupling with various vinyl ketones such as ethyl, methyl, propyl and alpha-methyl-substituted vinyl ketones, in the presence of a nickel(II) iodide (NiI2), zinc (Zn), and water catalyst system in acetonitrile at 50 degrees C for 14 h to afford 2-alkylnaphthalenes in good to excellent yields. Under similar reaction conditions, 7-azabenzonorbornadiene derivatives provided cis-2-alkyl-1,2-dihydro-naphthalene derivatives in high yields. On the other hand, the nickel(II) iodide, tris(4-fluorophenyl)phoshine [P(4-FC6H4)(3)] and zinc catalyst system successfully catalyzed the reductive coupling reaction of electron-rich alkynes, with 7-aza- and 7-oxabenzonorbornadienes to give cis-2-alkenyl-1,2-dihydronaphthalene derivatives in good to excellent yields. In the reaction, a mild reducing agent (zinc) and simple hydrogen source (water) were used.

Moreover, the intramolecular reductive coupling of ene-phthalimide (XI) proceeds highly diastereoselective.

An efficient method for the synthesis of functionalized vinyl arenes from the reaction of N-methoxybenzamides or N-phenoxyacetamides with vinylstannanes via rhodium(iii)-catalyzed C–H activation is described. The application of the methodology for the synthesis of a natural product thalactamine and a 7-membered ring oxepine are also demonstrated.

Metal-catalyzed annulation reactions to synthesize carbo- and heterocycles have been an attractive field of research for many years. The development of new cyclization reactions utilizing readily available less expensive metal catalyst is one of the important tasks. In this regard, this review summerizes and discusses about nickel- and cobalt-catalyzed [4+2] and [3+2] annulation reactions of ortho-halo substituted imines and alkynes. Nickel complexes under suitable reaction conditions underwent [4+2] annulation to form six-membered isoquinoline (salts) derivatives. However, cobalt complexes afforded aminoindenes via [3+2] annulation reactions. Both reactions proceed through a five membered metallacycle. The regioselective insertion of alkyne containing keto or ester groups into the metallacycle further demonstrates the difference in selectivity of these metal complexes.