Search

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.

A novel procedure for the transition-metal-free tandem cyclization/N-arylation reaction sequence of an aryne with a 1,2,3,4-benzothiatriazine-1,1-dioxide is reported. This reaction goes through the...

Three pyridine-carbonitrile-carbazole-based thermally activated delayed fluorescence (TADF) materials with highly sterically congested structures have been synthesized. The donor-acceptor-type TADF emitters (26-, 246-, and 35tCzPPC) consist of a 2,6-diphenylpyridine-3,5-dicarbonitrile core (PPC) as the acceptor and a di( t-butyl)carbazole-substituted phenyl group attached to C4 of the PC core as the donor. The molecules show a unique structure containing two consecutive large twisted angles along the donor and acceptor groups. The structure leads to a nearly complete space separation of the highest occupied molecular orbital and lowest unoccupied molecular orbital, a small Δ E

Exciplex emitters have emerged as an important class of thermally activated delayed fluorescence (TADF) materials for highly efficient OLEDs. A TADF exciplex emitter requires an intermolecular donor/acceptor pair. We have synthesized a bipolar donor-type material, DPSTPA, which was used to pair with known acceptor materials (2CzPN, 4CzIPN, or CzDBA). The OLEDs based on the exciplex emitters, DPSTPA/X, where X = 2CzPN and CzDBA, give green and orange-red colors with record-high external quantum efficiencies (EQEs) of 19.0 ± 0.6 and 14.6 ± 0.4%, respectively. In contrast, the exciplex pair DPSTPA/4CzIPN gave a very low photoluminescence quantum yield (PLQY) and a very low EQE value of the device. The DFT calculations indicate that the intermolecular distance between the donor and the acceptor plays a key factor for the PLQY and EQE. The observed low PLQY and the poor device performance for the DPSTPA/4CzIPN pair are probably because of the relatively long distance between the DPSTPA and 4CzIPN in the thin film caused by the four congested carbazole (Cz) groups of 4CzIPN, which effectively block the interaction of the nitrile acceptor with the triphenylamino donor of DPSTPA.

Five emitters CzAZB, tBuCzAZB, tmCzAZB, dmAcAZB, and PxzAZB based on dibenzo-1,4-azaborine as the electron acceptors and two identical amine groups as the donors were designed and synthesized. The dihedral angles between the planes of dibenzo-1,4-azaborine acceptors and amine-based donors greatly affect the thermally activated delayed fluorescence (TADF) property of these materials. A simple concept "steric switching" is introduced to predict whether the emitter possesses TADF property. CzAZB and tBuCzAZB, with very high photoluminescence quantum yields (PLQYs) but small dihedral angles, do not show TADF. In contrast, tmCzAZB reveals a PLQY of only 56% but with a large dihedral angle due to the presence of two methyl groups at C1 and C8 of the carbazole groups, the steric switching operates, and the compound shows TADF property with a deep-blue color having CIE coordinates of (0.14, 0.15). In a similar manner, in dmAcAZB and PxzAZB with high PLQYs and large dihedral angles between the donor and acceptor planes, the "TADF steric switch" readily operates to achieve device external quantum efficiencies as high as 20.8 ± 1.2 and 27.5 ± 1.9% with blue and green emissions, respectively.

We have developed an effective ortho C–H functionalization of arylpyridines and detachable N-pyrimidyl indoles by terminal and internal alkynes using a Re(I) catalyst providing an efficient access to various E-selective alkenylation products. The catalytic reaction is compatible with various aliphatic alkynes, aromatic terminal alkynes and internal alkynes, and structurally different nitrogen heterocycles. Deuterium-labeling experiments indicate that significant deuterium scrambling occurs with the directing groups and acetylenic sp C–H bonds before the migratory insertion.

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 unique strategy for the attainment of a discotic nematic (ND) mesophase is reported consisting of a central benzene core to which are attached two 4-alkylphenyl and two 4-pentylbiphenyl moieties diagonally via alkynyl linkers. The rotational nature and incompatibility of unequal phenylethynyl units led to the disruption of π-π interactions within cores that aids to the realization of ND phase and favors high solid-state emission. When used in OLEDs, compounds act as an efficient solid-state pure deep-blue emitter with Commission Internationale de L'Eclairage (CIEx,y) coordinates of (0.16, 0.07).

Highly efficient deep-blue emission is crucial to realize energy-efficient and high-quality display and solid-state lighting applications. A solution-processable deep-blue emitter is essential for producing cost-effective large-area devices via roll-to-roll fabrication. Here, we demonstrate a highly efficient solution-processable deep-blue organic light-emitting diode by utilizing a carbazole-based fluorescent emitter 6-((9,9-dibutyl-7-((7-cyano-9-(2-ethylhexyl)-9H-carbazol-2-yl)ethynyl)-9H-fluoren-2-yl)ethynyl)-9-(2-ethylhexyl)-9H-carbazole-2-carbonitrile (JV55). The resultant device showed a maximum external quantum efficiency (EQE) of 6.5% and an EQE of 5.5% at 100 cd/m2 with CIE coordinates of (0.16, 0.06). The optimized device showed a maximum EQE of 6.5%. Additionally, the deep-blue emission also realized a 101% color saturation according to the NTSC standard. The high efficiency may be attributed to engineering appropriate device architecture and enabling balanced carrier injection, effective host-...

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.

As an earth-abundant first-row transition metal, cobalt catalysts offer a broad range of economical methods for organic transformations via C–H activation. One of the transformations is the addition of C–H to C–X multiple bonds to afford alkylation, alkenation, amidation, and cyclization products using low- or high-valent cobalt catalysts. This hydroarylation is an efficient approach to build new C–C bonds in a 100% atom-economical manner. In this review, the recent developments of Co-catalyzed hydroarylation reactions and their mechanistic studies are summarized.

Reaction mechanisms for the synthesis of indenamines, indenols, and isoquinolinium salts through cobalt- and rhodium-catalysis were investigated using density functional theory calculations. We found that the valence charge of transition metals dramatically influences the reaction pathways. Catalytic reactions involving lower-oxidation-state transition metals (MI/MIII, M = Co and Rh) generally favor a [3 + 2] cyclization pathway, whereas those involving higher oxidation states (MIII/MV) proceed through a [4 + 2] cyclization pathway. A catalytic cycle with novel MIII/MV as a crucial species was successfully revealed for isoquinolinium salts synthesis, in which highly valent MV was encountered not only in the [RhCp*]-catalysis but also in the [CoCp*]-catalysis.

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.

Considerable research attention has been directed towards the use of first-row transition metals in organic synthesis. The more abundant, and less expensive cobalt is considered to be an effective alternative for expensive second and third-row noble metals, especially in C-H bond functionalization reactions. In this mini-review, we will summarize the features, and recent achievements of the Co-catalyzed directing group assisted C-H activation/cyclization reactions and their mechanistic insights.

Highly efficient thermally activated delayed fluorescence (TADF) molecules are in urgent demand for solid-state lighting and full-color displays. Here, the design and synthesis of three triarylamine-pyridine-carbonitrile-based TADF compounds, TPAPPC, TPAmPPC, and tTPAmPPC, are shown. They exhibit excellent photoluminescence quantum yields of 79-100% with small ΔEST values, fast reverse intersystem crossing (RISC), and high horizontal dipole ratios (Θ// = 86-88%) in the thin films leading to the enhancement of device light outcoupling. Consequently, a green organic light-emitting diode (OLED) based on TPAmPPC shows a high average external quantum efficiency of 38.8 ± 0.6%, a current efficiency of 130.1 ± 2.1 cd A-1 , and a power efficiency of 136.3 ± 2.2 lm W-1 . The highest device efficiency of 39.8% appears to be record-breaking among TADF-based OLEDs to date. In addition, the TPAmPPC-based device shows superior operation lifetime and high-temperature resistance. It is worth noting that the TPA-PPC-based materials have excellent optical properties and the potential for making them strong candidates for TADF practical application.

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.

Varying the structures of conjugated side chains can be an efficient approach toward tailoring the optoelectronic properties of conjugated polymers. In this study, we synthesized four indacenodithiophene (IDT)-based side chain conjugated donor–acceptor alternating polymers. We introduced four different acceptor units (difluorobenzothiadizole: PIDTHT-FBT ; difluoroquinoxaline: PIDTHT-QF ; dicyanoquinoxaline: PIDTHT-QCN ; diketopyrrolopyrrole: PIDTHT-DPP ) to study the effects of the conjugated side chains on the optoelectronic properties (absorption spectra, energy levels, hole mobility) of the polymers and their resulting organic photovoltaic (OPV) devices. The energy levels of the highest occupied molecular orbitals for the new polymers were deeper when they featured alkylthiophene side chains. Films of these materials blended with PC 71 BM exhibited sufficiently high space-charge-limited current (SCLC) hole mobilities (>1.2 × 10 −5 cm 2 V −1 s −1 ) for efficient charge carrier extraction. The greatest OPV performance was that of the device incorporating PIDTHT-QF , with a power conversion efficiency of 5.15% under illumination with AM 1.5G solar light (1000 W m −2 ). Thus, side chain conjugated (two-dimensional) IDT polymers incorporating optimized acceptor groups are prospective materials for OPV applications.

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...

Most of the metal-catalyzed C–H activation/annulation reactions were carried out in organic solvents using expensive oxidants such as Cu(II) and Ag(I) salts. Here, we reported a new approach for a highly regioselective synthesis of isoquinolones from N-alkyl benzamides and alkynes using an Rh(III) catalyst and inexpensive oxygen as the sole oxidant in an aqueous medium. In the reaction, water gave the highest product yield among the solvents used. In addition, at the end of the reaction, the isoquinolone product directly precipitated out from the aqueous solution. The methodology can be applied to a gram scale synthesis. This Rh(III)-catalyzed reaction shows interesting meta selectivity with the meta substituted benzamide and shows various regioselectivities with different substituted alkynes. Moreover, the methodology can be applied to the preparation of biologically active compounds having the isoquinolone core.

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.

A highly chemo- and stereoselective nickel-catalyzed borylative cyclization of 1,6-enynes with bis(pinacolato)diboron is described. Enynes containing an electron-deficient alkene such as a vinyl ketone provided alkenylboronates while enynes containing a terminal alkene gave homoallylic boronates. A plausible mechanism involving a nickelacyclopentene intermediate is proposed. In addition, the resulted alkenyl- or homoallylic boronates can be transformed to the corresponding ketones and alcohols via oxidation. Application to a palladium-catalyzed cross coupling reaction of alkenylboronates with aromatic halides has been demonstrated as well.

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.

Three new quinoline TADF emitters, 2QPM-mDC, 2QPM-mDTC, and 4QPM-mDTC, were designed and synthesized and the emitters show ΔEST as low as 0.07 eV and high PL quantum yield (PLQY) up to 98%. An electroluminescence device based on 2QPM-mDTC can reach high EQE over 24%. Compared with the reported TADF devices, the device shows narrow emission bandwidth and high color purity. The excellent device performance is likely ascribed to the molecular design of 2QPM-mDTC containing an intramolecular H-bonding in the molecule.

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.

A cobalt-catalyzed oxidative annulation of amides with allenes to provide isoquinolin-1(2 H)-ones and pyridones was explored. The new catalytic reaction proceeded through aminoquinoline-directed C−H activation followed by unusual regioselective insertion, annulation, and isomerization. A variety of functionalized amides and allenes were converted into the corresponding products under mild reaction conditions.

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.