Benzimidazole Units Research Articles

Preparation and Properties of Inherently Black Polyimide Films with Extremely Low Coefficients of Thermal Expansion and Potential Applications for Black Flexible Copper Clad Laminates

In the current work, a series of black polyimide (PI) films with excellent thermal and dimensional stability at elevated temperatures were successfully developed. For this purpose, two aromatic diamines including 4,4′-iminodianline (NDA) and 2-(4-aminophenyl)-5- aminobenzimidazole (APBI) were copolymerized with pyromellitic dianhydride (PMDA) to afford PIs containing imino groups (–NH–) in the molecular structures. The referenced PI film, PI-ref, was simultaneously prepared from PMDA and 4,4′-oxydianiline (ODA). The introduction of imino groups endowed the PI films with excellent blackness and opaqueness with the optical transmittance lower than 2% at the wavelength of 600 nm at a thickness of 25 μm and lightness (L*) below 10 for the CIE (Commission International Eclairage) Lab optical parameters. Meanwhile, the introduction of rigid benzimidazole units apparently improved the thermal and dimensional stability of the PI films. The PI-d film based on PMDA and mixed diamines (NDA:APBI = 70:30, molar ratio) showed a glass transition temperature (Tg) of 445.5 °C and a coefficient of thermal expansion (CTE) of 8.9 × 10−6/K in the temperature range of 50 to 250 °C, respectively. It is obviously superior to those of the PI-a (PMDA-NDA, Tg = 431.6 °C; CTE = 18.8 × 10−6/K) and PI-ref (PMDA-ODA, Tg = 418.8 °C; CTE: 29.5 × 10−6/K) films.

Green synthesis of quinolines via A3-coupling by using graphene oxide-supported Brønsted acidic ionic liquid

Graphene oxide-supported Bronsted acidic ionic liquid ([GrBenzImi]SO3H) has been prepared by covalent grafting of benzimidazole unit in the matrix of graphene oxide followed by reaction with 1,4-butane sultone and hydrochloric acid. [GrBenzImi]SO3H has been characterized by various techniques including Fourier transform infrared spectroscopy (FTIR), FT-Raman (FT-Raman spectroscopy), CP-MAS 13C NMR spectroscopy, thermogravimetric analysis, energy-dispersive X-ray analysis, Brunauer–Emmett–Teller surface area, X-ray diffraction, and transmission electron microscopy. [GrBenzImi]SO3H was successfully employed as heterogeneous catalyst in A3-coupling reaction of aryl aldehydes, anilines and phenylacetylene for the synthesis of 2,4-disubstituted quinolines using water/ethanol system (1:1) as green medium. [GrBenzImi]SO3H could be recycled six times without significant loss in the yield of product.

Neutral iridium(iii) complexes bearing BODIPY-substituted N-heterocyclic carbene (NHC) ligands: synthesis, photophysics, in vitro theranostic photodynamic therapy, and antimicrobial activity.

The synthesis, photophysics, and photobiological activities of a series of novel neutral heteroleptic cyclometalated iridium(iii) complexes incorporating boron dipyrromethene (BODIPY) substituted N-heterocyclic carbene (NHC) ligands (Ir1-Ir5) are reported. The effect of the substitution position of BODIPY on the NHC ligands, either on C4 of the phenyl ring (Ir1-Ir3) or C5 of the benzimidazole unit (Ir4 and Ir5), and its linker type (single or triple bond) on the photophysical properties was studied. Ir1-Ir5 exhibited BODIPY-localized intense 1IL (intraligand transition)/1MLCT (metal-to-ligand charge transfer) absorption at 530-543 nm and 1,3IL/1,3CT (charge transfer) emission at 582-610 nm. The nanosecond transient absorption results revealed that the lowest triplet excited states of these complexes were the BODIPY-localized 3π,π* states. Complexes Ir4 and Ir5 exhibited blue-shifted 1IL absorption and 1,3IL/1,3CT emission bands compared to the corresponding absorption and emission bands in complexes Ir1 and Ir3. However, replacing the methyl substituents on N3 of benzimidazole in complexes Ir1 and Ir4 with oligoether substituents in Ir3 and Ir5, respectively, did not impact the energies of the low-energy absorption and emission bands in the corresponding complexes. Water-soluble complexes Ir3 and Ir5 have been explored as photosensitizers for in vitro photodynamic therapy (PDT) effects toward human SKMEL28 melanoma cells. Ir3 showed no dark cytotoxicity (EC50 > 300 μM) but good photocytotoxic activity (9.66 ± 0.28 μM), whereas Ir5 exhibited a higher dark cytotoxicity (20.2 ± 1.26 μM) and excellent photocytotoxicity (0.15 ± 0.01 μM). The phototherapeutic indices with visible light (400-700 nm) activation were >31 for Ir3 and 135 for Ir5. Ir3 and Ir5 displayed 1O2 quantum yields of 38% and 22% in CH3CN, respectively, upon 450 nm excitation. Ir5 was more effective at generating reactive oxygen species (ROS) in vitro. Ir5 was also active against Staphylococcus aureus upon visible light activation, with a phototherapeutic index of >15 and EC50 value of 6.67 μM. These photobiological activities demonstrated that these neutral Ir(iii) complexes are promising in vitro PDT reagents, and substitution at C5 on the benzimidazole group of the NHC ligand was superior to C4 substitution on the phenyl ring.

Regulating Cu(II)-benzimidazole coordination structure in rigid-rod aramid fiber and its composites enhancement effects

Coordination crosslinking, as the kind of strongest supramolecular interaction, has been widely introduced into flexible polymer chains, including rubbers and aerogels, while that in rigid-rod polymer is much rare, due to the difficulty in rigid-rod macromolecules' configuration change. Moreover, the exact coordination structure inside those polymers is not clear. Herein, this coordination interaction was incorporated into a traditional rigid-rod polymer, aramid fiber, by Cu2+-benzimidazole coordination reaction, through the careful control of the dynamic reaction conditions, and the structural/performance relationships of fiber and its composites are detailed studied. It is seen that two different coordination structures, S-coordination style (Cu2+ coordination with single benzimidazole unit) and M-coordination style (Cu2+ coordination with multiple benzimidazole units from different macromolecular chains), could be both obtained inside fiber, using different solvents as the reaction medium. Moreover, using reaction kinetics equilibrium, we presented a mathematical method to investigate those two coordination structures in detail, including their average coordination numbers of Cu2+ and reaction equilibrium constant (K). Further, the experimental results show that the fiber with average coordination number of 2 exhibits a comprehensive improved performance in heat/solvent resistance, fluorescence emission as well as fiber's transverse properties, with the corresponding increase of 54.2% and 47.1% for its composites interfacial properties and compressive strength, compared with untreated fiber.

Imidazole-Linked Crystalline Two-Dimensional Polymer with Ultrahigh Proton-Conductivity.

Proton-exchange membrane fuel cells are promising energy devices for a sustainable future due to green features, high power density, and mild operating conditions. A facile proton-conducting membrane plays a pivotal role to boost the efficiency of fuel cells, and hence focused research in this area is highly desirable. Major issues associated with the successful example of Nafion resulted in the search for alternate proton conducting materials. Even though proton carrier loaded crystalline porous organic frameworks have been used for proton-conduction, the weak host-guest interactions limited their practical use. Herein, we developed a crystalline 2D-polymer composed of benzimidazole units as the integral part, prepared by the condensation of aryl acid and diamine in polyphosphoric acid medium. The imidazole linked-2D-polymer exhibits ultrahigh proton conductivity (3.2 × 10-2 S cm-1) (at 95% relative humidity and 95 °C) in the pristine state, which is highest among the undoped porous organic frameworks so far reported. The present strategy of a crystalline proton-conducting 2D-polymer will lead to the development of new high performing crystalline solid proton conductor.

C-N Coupling via Antiaromatic Endocyclic Nitrenium Ions.

Herein, we report a C-N coupling reaction via antiaromatic endocyclic nitrenium ions. The nitrenium ion intermediate was generated by a combination of iodine(III) reagent PhI(OCOCF3)2 and the N-H center of benzimidazole units at ambient laboratory conditions. Metal-free synthesis of benzimidazole-fused phenanthridine derivatives was achieved in good to excellent yields.

High-tenacity and high-modulus polyimide fibers containing benzimidazole and pyrimidine units

Polyimide fibers (PI) combine high thermal stability, good chemical and UV resistance. However, most commercial PI fibers including P84®, Kermel®, Yilun® and Suplon® do not exhibit sufficiently high mechanical properties. Finding an appropriate method that is commercially available to prepare PI fibers with a high tenacity and modulus is required urgently for making large scale manufacturing attractive. Herein, we describe an approach to preparing high-performance PI fibers by introducing the heterocyclic pyrimidine and benzimidazole units into PI backbones. PI fibers prepared by this way exhibited a higher tenacity and modulus compared to those previously reported PIs and even Kevlar 49® fibers due to the high molecular weight, strong hydrogen bonding interaction and highly oriented crystalline structure. In addition, the detailed structural analysis based on WAXD and SAXS has revealed that the stress-induced crystallization and more compact morphology formed in PI fibers by the post hot-drawing process. Accordingly, as the drawing ratio was set to 3.8, an optimum tenacity and modulus of the PI fiber reached to 2.3N/tex and 71.8N/tex, respectively, indicating that the resultant fibers have a great potential application as the reinforcing fiber in advanced composites.

Synthesis and Properties of Poly(imides) and Poly(imides)/Ionic Liquid Composites Bearing a Benzimidazole Moiety.

Three new aromatic poly(imides) containing benzimidazole units in the backbone were synthesized and characterized by several spectroscopic techniques. Flexible spacer groups were incorporated into the poly(imides) structure to improve their solubility in organic solvents and their oxidative stabilization. All poly(imides) were thermally stable (Td5% > 512 °C) and had the ability to form dense flexible films. Novel composite films were successfully prepared by loading poly(imide) with ionic liquid ([Bmim]Br) at different concentrations up to 25 wt.%. The resulting materials were characterized according to their morphology and elemental composition (SEM-EDX), water uptake capability, contact angle, and oxidative degradation resistance. Results suggested that poly(imide)/ionic liquid composites would be excellent candidates for future proton conductivity measurements.

Improving Compressive Strength of Aramid Fiber by Introducing Carbon Nanotube Derivates Grafted with Oligomers of Different Conformations and Controlling Its Alignment

AbstractLow compressive strength of aramid fiber is one of the most prominent obstacles for its application as a strengthening material. Herein, based on nucleophilic reaction of CF bonds, fluorinated carbon nanotube (FCNT) derivates grafted with oligomers of different conformations are prepared to modify (Poly‐p‐phenylene‐benzimidazole‐terephthalamide) (PBIA) fiber. CF bonds of FCNT can react with benzimidazole units and terminal amino groups of PBIA oligomers. Therefore, FCNT derivates grafted with oligomers of different conformations can be obtained. Then, the FCNT derivates are blended with PBIA solution to prepare PBIA/FCNT composite fibers. Compressive strength is improved by nearly 34.7% and 107% for the fiber modified by FCNT derivates grafted with oligomers of parallel and vertical conformations, respectively. It is found that FCNT derivates grafted with oligomers of vertical conformation may be forced to be aligned vertically to axis of the fiber, which is more beneficial to improve lateral interaction and compressive strength of the fiber.

Benzimidazole‐Substituted Indolo[3,2‐b]carbazoles: Acid‐Responsive Probes

AbstractBenzimidazole substituted indolo[3,2‐b]carbazole derivatives (5 and 6) were synthesized by formylation of N,N′‐dioctylindolo[3,2‐b]carbazole followed by reaction with o‐phenyelene diamine. The structures of these two compounds were characterized by high resolution mass‐spectrometry (HRMS) and NMR (1H and 13C) spectroscopy. Their photophysical and electrochemical properties were studied by absorption and emission spectroscopy and cyclic voltammetry. Compounds 5 and 6 showed sensitivity towards acid in solution as well as in the solid state. Density functional theory (DFT) studies showed that compound 5 is more planar compared to 6. Frontier molecular orbitals (FMO) analysis suggested that photoinduced electron transfer (PET) from indolo[3,2‐b]carbazole moiety (fluorophore) to the protonated benzimidazole unit results in quenching.

Fabrication of poly(bis-benzimidazole imide) fibers with enhanced mechanical properties and high limit oxygen indexes

A kind of diamine monomer 2,2′-p-phenylenebis (5-aminobenzimidazole) (PBABI) with bis-benzimidazole moiety was synthesized and a facile two-step wet-spinning method was employed to fabricate a series of polyimide fibers containing bis-benzimidazole units (PBIPI) with the 3,3′,4,4′-biphenyltetracarboxylic anhydride (BPDA), p-Phenylenediamine (p-PDA) and self-synthesized PBABI as the monomers. The structures and purity of self-synthesized PBABI was characterized in detail. Various temperatures for thermal-drawn process were studied and the 2D-WAXD showed that the higher the temperature for thermal-drawn process, the more orderly of the polymer chains. Attributed to the stronger intermolecular hydrogen bonding forces combined with the orientation and arrangement of molecular chains, the as-spun PBIPI fiber displayed improved mechanical properties with the tensile strength of 1.97 GPa and the initial modulus 59.5 GPa. Furthermore, the PBIPI fiber also showed improved thermal stability and flame resistance properties due to the existent of benzimidazole units. Correspondingly, the glass transition temperature (Tg) and the temperature at the maximum degradation rate (Td-max) of the PBIPI fiber in nitrogen increased by 76 °C and 17 °C respectively and the limit oxygen index (LOI) enhanced by 13%, making these novel polymeric fibers as good thermo-resistant and flame-retardant fiber in fire-fighting domain.

Improving Interfacial and Compressive Properties of Aramid by Synchronously Grafting and Crosslinking

AbstractImproving compressive strength of aramid and its adhesion to resin is of great significance for its application in reinforcing materials. In this study, a novel method for improving interfacial and compressive properties of aramid fiber is presented. α,α′‐Dichloro‐p‐xylene (DCX) is utilized as an external crosslinker to modify aramid fiber containing benzimidazole units during the post swelling process. Chloromethyl groups from DCX can react with benzimidazole moieties of the aramid fiber. The reaction can be regarded as crosslinking inside the fiber and grafting on the surface. By controlling the swelling effect of the solvent during modification, bulk crosslinking degree and surface grafting density can be adjusted. Therefore, intermolecular interaction and surface polarity of the aramid fiber can be improved simultaneously. After modification, the compressive strength of the fiber can be enhanced by nearly 100% and interfacial shear strength increases by 37%, while excellent mechanical properties are maintained. Therefore, comprehensive performance of aramid fiber can be improved significantly by synchronously crosslinking and grafting.

Highly alkaline stable anion exchange membranes from nonplanar polybenzimidazole with steric hindrance backbone

ABSTRACTThe anion exchange membranes (AEMs) with both high ionic conductivity and alkali stability are always the research focus of the AEM fuel cells. Here, a novel nonplanar polymer for AEMs manufacture, mPBI‐TP‐x‐R, with excellent hydroxide stability and satisfactory processability is reported for the first time. The serial mPBI‐TP‐x resins with steric hindrance were prepared by copolymerization among 3,3′,4,4′‐tetraaminobiphenyl, isophthalic acid and tetraphenyl‐terephthalic acid (TP) in different ratios under microwave condensation. The copolymers mPBI‐TP‐x were quaternized at N1/N3‐sites of benzimidazole unit in backbone with alkyl groups (RCH3, C2H5, n‐C3H7, or n‐C4H9) to prepare soluble ionomers, and the corresponding membranes in hydroxyl ion form were prepared by a solution casting method and subsequent ion‐exchange process. The chemical structure of all membranes was characterized using FTIR and 1H NMR spectroscopy. The properties of ion exchange capacity, water uptake, swelling ratio, tensile strength, ionic conductivity, and alkaline stability were measured. Among the prepared membranes, the mPBI‐TP‐15%‐(n‐Bu) exhibited the excellent alkaline stability (only degradation ca. 5% under 1M NaOH aqueous solution at 60 °C for 800 h) and satisfactory OH− conductivity (46.66 mS/cm at 80 °C). The current research provides a useful exploration to commercial application of alkaline fuel cell. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1087–1096

New type of metal-free and Zinc(II), In(III), Ga(III) phthalocyanines carrying biologically active substituents: Synthesis and photophysicochemical properties and photodynamic therapy activity

This study reports on novel phthalocyanines having benzimidazole units which are known to have biological properties. 4-(4-(5-chloro-1H-benzo[d]imidazol-2-yl) substituted metal-free, Zn(II), In(III) and Ga(III) phthalocyanines were synthesized, these newly synthesized molecules that were substituted by oxygen bridges were fully characterized. For the purpose of determining their potency for photodynamic therapy, the photophysicochemical properties were investigated in DMSO. The H2Pc (4) showed higher fluorescence quantum yield and fluorescence lifetime as compared to metallated phthalocyanines derivatives. However, the highest singlet oxygen (ΦΔ) and triplet state quantum yields (ΦT) values were obtained with the In(III)Pc (5).

Nondestructive modification of aramid fiber based on selective reaction of external cross-linker to improve interfacial shear strength and compressive strength

Poor adhesion to resin and low axial compressive strength are two prominent problems for application of aramid in fiber-reinforced composites. Simultaneously enhancing interfacial shear strength (IFSS) and compressive strength is still challenging. Herein, 4-(bromomethyl) benzoic acid (BBA) was utilized as external cross-linker to modify (Poly-p-phenylene-benzimidazole terephthalamide) (PBIA) fibers through post-swelling process. It was confirmed that bromomethyl groups of BBA could react with benzimidazole units of PBIA upon 80 °C and carboxyl of BBA could form cross-linking upon 300 °C by decarboxylation coupling reaction. Therefore, both surface grafting and bulk cross-linking can be obtained simultaneously by controlling temperature during modification process. After modification, IFSS and compressive strength of PBIA fibers are enhanced by nearly 27% and 100% respectively while maintaining excellent mechanical properties. Therefore, the method is nearly non-destructive and effective to simultaneously improve IFSS and compressive strength of PBIA fibers.

Trans-Bis{2-[bis(1H-pyrazol-1-yl)methyl]-1-methyl-1H-benzimidazole}iron(II) bis(perchlorate) acetonitrile disolvate

In the structure of the title complex, [Fe(C15H14N6)2](ClO4)2·2C2H3N, the asymmetric unit contains one complete ligand molecule, one perchlorate and one acetonitrile solvent molecule. The iron(II) atom, situated on an inversion centre, is surrounded by six nitrogen atoms from two ligands in an octahedral coordination sphere in which the two benzimidazole units adopt a trans-configuration. The crystal structure is stablized by extensive weak C—H...O and C—H...N interactions.

Synthesis, X-ray structure, photophysical properties, and theoretical studies of six-membered cyclometalated iridium(iii) complexes: revisiting Ir(pnbi)2(acac).

We have determined the X-ray structure of Ir(pnbi)2(acac) (pnbi = 2-phenanthren-9-yl-1-phenyl-1H-benzimidazole; acac = acetylacetonate), which exhibits a six-membered metallocycle around the Ir center. This result stands in sharp contrast to previously postulated structures of Ir(pnbi)2(acac), which assumed a five-membered metallocycle. In this paper, we focus on the relative stability of five- and six-membered Ir(C^N) ring structures. DFT calculations of the total energies of Ir-(C^N) complexes indicated that six-membered structures are more stable when bulky substituents are present in the benzimidazole unit. When the phenanthrene group of pnbi was replaced with a naphthalene moiety, DFT calculations predicted that five-membered cycles are more stable than six-membered rings, which was confirmed experimentally by a single-crystal X-ray diffraction analysis. The steric bulk of the phenanthrene-containing polyaromatic ring ligand thus induces greater interligand repulsion between the two ligands, which plays an important role in determining the cyclometalation route. The Ir complexes examined in this study exhibit red emission (λem ≈ 660 nm) with relatively low quantum yields.

Synthesis and Characterization of Poly(ether ether ketone-co-benzimidazole)s Based on 2-(2'-Hydroxyphenyl) benzimidazole

A series of novel poly(ether ether ketone)s containing benzimidazole groups with precise structures in high yields were synthesized from various stoichiometric ratio mixtures of m-dihydroxybenzene, 2-(2'- hydroxyphenyl)benzimidazole and 4,4′-difluorodiphenylmethanone via a C–N/C–O coupling reaction process using sulfolane as a solvent. The reaction was carried out at 210°C in the presence of anhydrous potassium carbonate. The structures of the resulted polymers were characterized by means of FTIR, 1H NMR spectroscopy, elemental analysis, and the results were largely consistent with the proposed structure. XRD studies indicated that the resulted polymers are non-crystalline. The polymers have good solubilities in common organic solvents. The polymers showed high glass transition temperatures (Tg = 125–237°C) and high thermal stability (Td5% = 497–539°C in nitrogen, 466–548°C in air). At the same time, as the benzimidazole unit content in the copolymer increased, the thermal properties of the prepared polymers improved. Moreover, the resulted polymers showed good fluorescence properties and the fluorescence emission peak was 465 nm.

Ternary Acceptor-Donor-Acceptor Asymmetrical Phenanthroimidazole Molecule for Highly Efficient Near-Ultraviolet Electroluminescence with External Quantum Efficiency (EQE) >4 .

A new ternary acceptor (A)-donor (D)-acceptor (A) asymmetrically twisted deep-blue emitting molecule, PPI-2BI, was synthesized by attaching two electrophilic benzimidazole (BI) units to the C2 and N1 positions of a phenanthroimidazole (PI) donor unit. Profiting from the enhanced D-A electronic coupling, the electron injecting and transporting abilities of the new triangle-shaped A-D-A molecule are considerably improved and the molecule shows high photoluminescence (PL) and electroluminescence (EL) efficiencies. By using PPI-2BI as a non-doped emitting layer (EML), the resulting organic light-emitting device exhibits emission with color coordinates of (0.158, 0.124) and a maximum external quantum efficiency (EQE), current efficiency (CE), and power efficiency (PE) of 4.63 %, 4.98 cd A-1 , and 4.82 lm W-1 , respectively. Additionally, a simple bilayer device using PPI-2BI as both the EML and the electron-transporting layer (ETL) also shows an EQE of 3.81 % with little changes to the color purity. Remarkably, a PPI-2BI-based doped device emits efficient near-ultraviolet EL with color coordinates of (0.154, 0.047) and an EQE of 4.12 %, which is comparable to that of the best reported near-UV emitting devices.

Fe3+ coordination induced selective fluorination of aramid fiber to suppress surface chain scission behavior and improve surface polarity

The selective fluorination of aramid fiber surface was reported by Fe3+ coordination on the benzimidazole unit. After the coordination, both of the two parts in benzimidazole unit, benzene ring and imidazole ring, take priority in the reaction with the fluorine gas, while the reaction with the amide bond is restrained. In this way, selective fluorination on benzimidazole unit is achieved, with the surface polarity increasing and chain scission behavior suppressed simultaneously. What’s more, the increased surface polarity enables the improvement of the interfacial shear strength by 24%, compared with that in a traditional fluorination way. In all, the study offers an easy and effective strategy for the regulation and controlling of direct fluorination reaction, and it provides a guideline for further adjustment of the reaction mechanism to meet the requirement in other applications.