Benzoxazole Groups Research Articles

Construction of polyimide films with highly linear structures using a structural reorganization approach

AbstractTo improve the thermodynamic and mechanical properties of asymmetric polyimide (PI), a method to enhance the linearity of PI by using a structural reorganization approach was designed. First, two novel diamines containing benzimidazole and benzoxazole groups, namely PADBZ and PDBOA, were constructed and synthesized. Thereafter, two new kinds of PI films (PADBZ‐PMDA and PDBOA‐PMDA) were prepared and polymerized with 1,2,4,5‐benzenetetracarboxylic anhydride (PMDA). Based on structural reorganization, PADBZ‐PMDA and PDBOA‐PMDA had repeating units of the same chemical composition and different linearity with PABZ‐BPDA and BOA‐BPDA, respectively. Comparing PADBZ‐PMDA and PABZ‐BPDA, due to the transfer in the position of benzene, PADBZ‐PMDA with high linearity showed the improved heat resistance (Tg up to 448°C), dimensional stability (CTE down to 2.3 ppm/K) and mechanical properties. PDBOA‐PMDA and BOA‐BPDA had the same situation. This study provided a unique solution to enhance the performances of PI by increasing the linearity using a structural reorganization approach.

Tailoring thermosetting benzoxazoles for optimal performance: Balancing thermal stability, dielectric properties, and processability

Polybenzoxazole (PBO) has excellent heat resistance and dielectric properties. However, it lacks a distinct melting point and is only soluble in sulfuric and methyl sulfonic acids. This limited solubility significantly hinders its practical application due to poor processability. In order to improve the processability of PBO while preserving its thermal stability and dielectric properties, this paper investigates the impact of introducing bridging structures between benzoxazole groups and employing cross-linking groups at the chain ends. The study primarily focuses on assessing the effects of these modifications on the thermosetting PBO properties, including heat resistance, dielectric properties, and processability. The results indicate that the cured polymer exhibits high thermal stability when a biphenyl group is used as bridging structure and a cyano group as the end group. Among these thermosetting monomers, p-LARBCN has the best overall performance. The 5 % thermal decomposition temperature (Td5) of cured p-LARBCN is 612 °C, which is very similar to PBO. The dielectric constant of the cured p-LARBCN is below 2.7, and the dielectric loss is below 0.02. The dielectric performance is close to that of PBO. In addition, p-LARBCN shows good solubility in solvents like DMSO, DMF, and DMAc, which greatly improves its processability compared to PBO. This study presents a modified thermosetting PBO resin that combines high thermal stability with improved processability. This resin holds promise for applications in the aviation and aerospace fields, particularly as a high-temperature-resistant material.

Soluble imide oligomers containing benzoxazole structures

A series of soluble thermosetting polyimide resins containing benzoxazole structure were synthesized by two-step polymerization using 4-phenylethynylphthalic anhydride (4-PEPA) as the end-capping reagent, 2-(4-aminophenyl)-5-aminobenzoxazole (BOA) and 3,4′-diaminodiphenyl ether (3,4′-ODA) as the aromatic diamines, and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) as the aromatic dianhydride. The imide oligomers were characterized by employing Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), solubility tests and rheological measurements. Thermosetting polyimides derived from the imide oligomers were then produced via a thermal cross-linking reaction of the phenylethynyl group. The thermal and mechanical properties of the thermosets were studied using thermogravimetric analysis (TGA), dynamic mechanical thermal analysis (DMA), and mechanical property measurements. The effects of chemical architectures and molecular weights of the imide oligomers on processability, thermostability and mechanical properties were systematically investigated. The results showed that all the copolymerized imide oligomers possessed good solubility in organic and low melt viscosity, and the corresponding thermosets exhibited high glass transition temperature (up to 401°C) and 5% weight-loss temperature (up to 533°C) in an air atmosphere while excellent mechanical properties (flexural strength up to 217 MPa and elongation at break up to 11.2%). With the increase of the concentration of the benzoxazole group, the imide oligomers of PI-X-2 (-O-, -BO-, -B-) exhibited less solubility and higher minimum melt viscosity but improved glass transition temperature after curing and mechanical properties of their thermosets.

Synthesis of 2‐Deoxy‐C‐Glycosides via Iridium‐Catalyzed sp2 and sp3 C—H Glycosylation with Unfunctionalized Glycals†

Comprehensive SummaryA new protocol for the synthesis of 2‐deoxy‐C‐aryl‐glycosides and 2‐deoxy‐C‐alkyl‐glycosides via iridium‐catalyzed directed C—H glycosylation with glycals is reported. The method is amenable for both the C2 C—H glycosylation of indoles and the methyl C—H glycosylation of secondary methyl amines under the control of an N‐linked benzoxazole directing group. The benzoxazole group can be cleanly removed by the treatment of KOH or LiAlH4.

Biphotochromic and ionochromic benzoxazolyl-substituted spirobipyrans

Novel photochromic spirobipyrans bearing benzoxazole group in the 3H-naphthopyran fragment have been synthesized. Spiro-conjugated benzopyran and naphthopyran fragments cause the observed dual photochromism of the molecules. In the presence of Cd2+, Mn2+, Co2+, Ni2+, Zn2+, Cu2+ metal ions thermal isomerization of the spirobipyrans is observed, followed by the formation of the intensely coloured complexes of the merocyanine form. The long-wavelength absorption band of the complexes is located at λ>600 nm.

Phenyl-pyta-tricarbonylrhenium(I) complexes: combining a simplified structure and steric hindrance to modulate the photoluminescence properties.

Strongly luminescent tricarbonylrhenium(I) complexes are promising candidates in the field of optical materials. In this study, three new complexes bearing a 3-(2-pyridyl)-1,2,4-triazole (pyta) bidentate ligand with an appended phenyl group were obtained in very good yields owing to an optimized synthetic procedure. The first member of this series, i.e. complex 1, was compared with the previously studied complex RePBO to understand the influence of the fluorescent benzoxazole unit grafted on the phenyl ring. Then, to gauge the effect of steric hindrance on the luminescence properties, the phenyl group of complex 1 was substituted in the para position by a bulky tert-butyl group or an adamantyl moiety, affording complexes 2 and 3, respectively. The results of theoretical calculations indicated that these complexes were quite similar from an electronic point of view, as evidenced by the electrochemical study. In dichloromethane solution, under excitation in the UV range, all the complexes emitted weak phosphorescence in the red region. In the solid state, they could be excited in the blue region of the visible spectrum and they emitted strong yellow light. The photoluminescence quantum yield was markedly increased with raising the size of the substituent, passing from 0.42 for 1 to 0.59 for 3. The latter complex also exhibited clear waveguiding properties, unprecedented for rhenium complexes. From this point of view, these easy-synthesized and spectroscopically attractive complexes constitute a new generation of emitters for use in imaging applications and functional materials. However, the comparison with RePBO showed that the presence of the benzoxazole group leads to unsurpassed mechanoresponsive luminescence (MRL) properties, due to the involvement of a unique photophysical mechanism that takes place only in this type of complex.

The effect of benzoxazole unit on the properties of cyclic thiourea functionalized triphenylamine dye sensitizers

Two D-π-A-A sensitizers (AZ6-B20 and AZ6-B21) were synthesized by inserting the benzoxazole group as an auxiliary acceptor between the π-linker and the acceptor. And a D-A-π-A sensitizer (AZ6-B19) was also synthesized in our previous works by the insertion of the benzoxazole between the donor and the π-linker. The effects of benzoxazole groups on the properties at different sites of dye sensitizers were distinguishing. Their light harvest abilities were investigated by UV–vis spectra both in the solution and on the films. The results show that the absorption bands of UV–vis spectra are quite different from D-A-π-A and D-π-A-A dyes. The much more intensive molar extinction coefficients (53807 M−1cm−1 and 52555 M−1cm−1) were observed at around 575 nm for D-π-A-A dyes. The photovoltaic properties of DSSCs were also evaluated by J-V curves and IPCE measurements. The results confirmed that D-π-A-A dyes delivered high photovoltaic efficiency (AZ6-B20: 7.48%, AZ6-B21: 8.67%) compared with that of D-A-π-A dye (AZ6-B19: 3.27%). The details on the relation of the structures/properties were discussed by the optical physical absorption, electrical chemical measurements and DFT calculations.

Mesomorphic properties improved via lateral fluorine substituent on benzoxazole-terminated mesogenic compounds

ABSTRACT Here, laterally monofluorinated heterocyclic mesogenic compounds, 2-[4-[2-[4-alkoxy-phenyl]-ethynyl]-3-fluorophenyl]-benzoxazole derivatives (nPEFPBx) with hydrogen, methyl and nitro terminal substituents (coded as nPEFPBH, nPEFPBM and nPEFPBN, respectively) at 5-position of benzoxazole unit, are synthesised and characterised. They display enantiotropic nematic mesophase with mesophase ranges of 22–30°C and 32–39°C on heating and cooling for nPEFPBH, 67–92°C and 87–115°C for nPEFPBM, 31–84°C and 42–51°C for nPEFPBN (n < 7), respectively, which is better than nonfluorinated and laterally difluorinated analogous . Improved mesophase property is ascribed to reduced dipole moment resulting from introduction of lateral fluorine atom in opposite direction of polar benzoxazole unit. This indicates that monofluorine substituent contributes to improve nematic mesophase for benzoxazole-terminated mesogenic compounds. In addition, the compounds nPEFPBx have high birefringence of 0.513–0.650 because of large π-conjugated mesogenic core composed of benzene, ethynyl and benzoxazole groups, which suggests a possible application in liquid crystal mixture to enhance birefringence. Meanwhile, except nPEFPBN, the compounds nPEFPBx show intense photoluminescence emission at 406–407 nm in methylene chloride solution with exciting them at absorption maxima.

Electrochemical sensing of acetaminophen using nanocomposites comprised of cobalt phthalocyanines and multiwalled carbon nanotubes

Herein, we report the fabrication of multiwalled carbon nanotube (MWCNT) conjugates of cobalt phthalocyanines (CoPcs) with peripherally substituted flavone (flav) or benzoxazole (bo) groups. The CoPc-X-f-MWCNT (X = flav or bo) conjugates were characterized by Transmission Electron Microscopy (TEM) and Infrared (IR) spectroscopy. The respective nanocomposite materials were drop-casted onto the surfaces of glassy carbon electrodes (GCEs) and the resultant chemically modified electrodes (CMEs) were used as electrocatalytic detectors for acetaminophen. Under optimized conditions, the peak currents for CoPc-flav-f-MWCNTs- and CoPc-bo-f-MWCNTs- GCEs were linear in wide acetaminophen concentration ranges of 1–1000 μM and 15–1000 μM, respectively. Electron transfer kinetics of the CMEs were superior than the bare electrode where diffusion- and convection-controlled electrocatalytic constants in the order of 102 and 104 M−1s−1 were obtained for both the CMEs. The CMEs showed good selectivity for APAP when tested in the presence of other emerging water pollutants. Electrochemical impedance spectroscopic experiments provided an insight into the mechanism of electrocatalysis occurring at the interfaces of the CMEs.

Влияние бензоксазола и его нитропроизводных на показатели роста и химический состав плодов томатов

The present work is devoted to the study of the biological activity of benzoxazole, 5-nitrobenzoxazole and 5,7-dinitrobenzoxazole in relation to tomato plants. The ability of these substances to stimulate growth processes in tomato seeds, to influence the synthesis of mono- and polysaccharides, to regulate the content of ascorbic acid and the total acidity in the fruits of tomatoes has been studied. The ability of plants to accumulate nitrogen in the nitrate form under the action of benzoxazole and its nitro derivatives has also been analyzed. Thus, the possibility of improving the sowing properties and chemical characteristics of tomato plants by treating them with compounds of the benzoxazole group was studied. In addition, an assessment of the toxicity of the studied drugs was carried out using the computer program GUSAR on-line. Predictions of bioaccumulation factor (BCF) and endotoxicity class for rats were obtained for four forms of drug administration in animals. Earlier, the authors of the article carried out studies of the fungistatism of the considered compounds in vitro on six pathogenic fungi of various taxonomic classes. The germination of tomato seeds treated with the tested drugs was determined in the laboratory on the 12th day of the experiment by counting the germinated seeds. The germination values are expressed as a percentage of the total number of seeds sown. Growing tomato plants and harvesting was carried out in open ground conditions. Plants were treated with benzoxazole and its nitro derivatives by watering with solutions with a concentration of 0.05 mol / l. Control plants were watered. Chemical analysis of tomato fruits was performed under laboratory conditions in accordance with GOST. The analysis of the obtained data showed that the introduction of nitro groups into the basic structure of benzoxazole is accompanied by a significant increase in the biological activity of the synthesized compounds, which has different patterns of manifestation depending on the stage of plant development. Thus, 5,7-dinitrobenzoxazole has the greatest stimulating effect on the growth processes in tomato seeds. While the most pronounced positive effect on the synthesis in the fruits of tomato sugars and ascorbic acid was 5-nitrobenzoxazole. For unsubstituted benzoxazole, no pronounced positive trends in the manifestation of biological activity have been identified. Evaluation forecast using the computer program GUSAR on-line allowed to establish a low level of toxicity of the studied substances. This work is part of the study of the biological activity of various classes of organic compounds. The effect of the test substance on the growth rate and development of agricultural plants, their chemical composition is analyzed. In addition, the fungicidal activity of these compounds is determined. Thus, the purpose of the research is the selection of substances capable of comprehensively solving the problem of obtaining and preserving the yield of crop production.

Preparation and Properties of High-performance Polyimide Copolymer Fibers Derived from 5-Amino-2-(2-hydroxy-5-aminobenzene)-benzoxazole

A series of polyamic acid copolymers (co-PAAs) with para-hydroxyl groups was synthesized using two diamine monomers, namely p-phenylenediamine (p-PDA) and 5-amino-2-(2-hydroxy-5-aminobenzene)-benzoxazole (m-pHBOA), of different molar ratios through copolymerization with 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) in N,N-dimethyacetamine (DMAc). The co-PAA solutions were used to fabricate fibers by dry-jet wet spinning, and thermal imidization was conducted to obtain polyimide copolymer (co-PI) fibers. The effects of the m-pHBOA moiety on molecular packing and physical properties of the prepared fibers were investigated. Fourier transform infrared (FTIR) spectroscopic results confirmed that intra/intermolecular hydrogen bonds originated from the hydroxyl group and the nitrogen atom of the benzoxazole group and/or the hydroxyl group and the oxygen atom of the carbonyl group of cyclic imide. As-prepared PI fibers displayed homogenous and smooth surface and uniform diameter. The glass transition temperatures (Tgs) of PI fibers were within 311−337 °C. The polyimide fibers showed 5% weight loss temperature (T5%) at above 510 °C in air. Two-dimensional wide-angle X-ray diffraction (WXRD) patterns indicated that the homo-PI and co-PI fibers presented regularly arranged polymer chains along the fiber axial direction. The ordered molecular packing along the transversal direction was destroyed by introducing the m-pHBOA moiety. Moreover, the crystallinity and orientation factors increased with increasing draw ratio. Small-angle X-ray scattering (SAXS) results showed that it is beneficial to reduce defects in the fibers by increasing the draw ratio. The resultant PI fibers exhibited excellent mechanical properties with fracture strength and initial modulus of 2.48 and 89.73 GPa, respectively, when the molar ratio of p-PDA/m-pHBOA was 5/5 and the draw ratio was 3.0.

High-performance polyimide copolymer fibers derived from 5-anino-2-(2-hydroxy-4-aminobenzene)-benzoxazole: Preparation, structure and properties

A series of high-performance polyimide copolymer (co-PI) fibers containing phenylenebenzoxazole moiety with one hydroxyl group are synthesized based on the copolymerization of 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (BPDA) with two diamine monomers, namely, p-phenylenediamine (p-PDA) and 5-anino-2-(2-hydroxy-4-aminobenzene)-benzoxazole (p-mHBOA), through a two-step method. The molar ratio of p-PDA/p-mHBOA varies from 10/0 to 0/10. Influences of the p-mHBOA moieties on the thermal stability, crystal structure, crystal orientation, microvoid morphology, and mechanical properties are systemically investigated. Fourier transform infrared results confirm that intra/inter molecular hydrogen bonds come from the OH group and nitrogen atom of the benzoxazole group and/or OH group and the oxygen atom of the carbonyl group of cyclic imide. The glass transition temperatures (Tgs) of co-PI fibers are in the range of 290 °C–325 °C. The prepared fibers show excellent thermal stabilities, and their T5% is within 528 °C–542 °C in air. Two-dimensional wide-angle X-ray diffraction spectra indicate that homo-PI and co-PI fibers present a regularly arranged polymer chains along the fiber axial direction. Moreover, the ordered molecular packing along the transversal direction of fibers is destroyed by the copolymerization. Small-angle X-ray scattering results show that co-PI fibers with optimal mechanical properties exhibit the shortest average length (L) and the smallest radius (R¯) of microvoids. When the p-mHBOA/p-PDA molar ratio is 5/5, the fracture strength and initial modulus can reach approximately 30.31 cN/dtex (4.40 GPa) and 894.88 cN/dtex (129.8 GPa), respectively. The relationship between structure and mechanical properties is also discussed.

Structural study of mono-, di- and tetranuclear complexes of the {Re(CO)3}+fragment with thiosemicarbazone/thiosemicarbazonate ligands containing benzothiazole or benzoxazole groups

Thiosemicarbazone form mononuclear and dinuclear complexes as bidentate ligands with {Re(CO)3}+and a tetranuclear complex with unusual bideprotonated thiosemicarbazonate.

Effects of the benzoxazole group on green fluorescent protein chromophore crystal structure and solid state photophysics

Most of the conjugates exhibited aggregation-induced emission enhancement, probably involving a unusual type of excimer.

Improved mesophase stability of benzoxazole derivatives via dipole moment modification

By modifying the molecular dipole moments with lateral monofluorine substituent, improved mesophase stabilities were obtained for novel benzoxazole derivatives, 2-(4ʹ-alkoxy-3-fluorobiphenyl-4-yl)-benzoxazole liquid crystals (coded as nPPF(3)Bx). The series of nPPF(3)Bx with lateral monofluorine substituent ortho to benzoxazole group have larger calculated dipole moments by about 2 D than the corresponding fluorine-substituted analogs (compounds I) with lateral monofluorine ortho to alkoxy group; it is interesting to note that they show lower melting and clearing points but better mesophase stability with wider mesophase ranges for the molecules with both polar (NO2, Cl) and nonpolar (CH3, H) terminal groups. Meanwhile, compounds nPPF(3)Bx show greater red-shifted photoluminescence emissions than compounds I, which suggest that π–π interaction between molecules is reinforced by the enhanced dipole–dipole interaction caused by increased dipole moments. These results suggest that modification of the molecular dipole moment is an effective method to improve the mesophase stability of the classical mesogenic compounds.

Preparation of Solution-Processable Reduced Graphene Oxide/Polybenzoxazole Nanocomposites with Improved Dielectric Properties

The abilities to enhance the degree of orientational freedom of dipole in polymer dielectrics and strengthen the homogeneous dispersion of conductive fillers in matrix are of crucial importance for fabricating composite materials with high dielectric constant, low dielectric loss, low density, and good processability. Compared with conventional main-chain polybenzoxazoles, whose processability and dielectric performance are strictly limited by the conjugated benzoxazole groups on the backbone, improved solubility in dimethylformamide and dielectric constant (4.92) were observed for poly(2-isopropenylbenzoxazole) (P(2-IBO)), due to the high mobility of the dipole (benzoxazole ring) on the side chains. In addition, improved dispersion of conductive graphene nanosheets was achieved by a surface-initiated atom transfer radical polymerization (ATRP) of the N-(2-hydroxyphenyl)methacrylamide (o-HPMAA), the precursor of 2-isopropenylbenzoxazole from reduced graphene oxide (RGO). The nanocomposites of functionalized graphene and P(2-IBO) possess a dielectric constant of 8.35 (approximately 70% higher than that of pure P(2-IBO) at 1 kHz) when the weight fraction of functionalized graphene reaches 0.015, the lowest so far among the reports on dielectric property of the graphene/polybenzoxazole system.

An efficient ratiometric fluorescent probe for tracking dynamic changes in lysosomal pH.

Lysosomes are acidic organelles (approximately pH 4.5-5.5) and tracking the changes in lysosomal pH is of great biological importance. To address this issue, quite a few of fluorescent probes have been developed. However, few of these probes can realize the tracking of dynamic changes in lysosomal pH. Herein, we report a new lysosome-targeted ratiometric fluorescent probe (FR-Lys) by hybridizing morpholine with a xanthane derivative and an o-hydroxy benzoxazole group. In this probe, the morpholine group serves as a targeting unit for lysosome, the xanthane derivative exhibits a pH-modulated open/close reaction of the spirocycle, while the o-hydroxy benzoxazole moiety shows a pH modulated excited-state intramolecular proton transfer (ESIPT) process. Such a design affords the probe a ratiometric fluorescence response towards pH with pH values ranging from 4.0 to 6.3. The response of the probe to pH was fast and reversible with high selectivity. Moreover, this probe possesses further advantages such as easy synthesis, high photostability and low cytotoxicity. These features are favorable for tracking dynamic pH changes in biosystems. It was then applied for dynamic imaging pH changes in lysosomes with satisfactory results.

Crystal structure and stereochemistry study of 2-substituted benzoxazole derivatives.

The structure of 2-[(4-chlorophenylazo) cyanomethyl] benzoxazole, C15H9ClN4O (I), has triclinic () symmetry. The structure displays N–H ⋯ N hydrogen bonding. The structure of 2-[(arylidene) cyanomethyl] benzoxazoles, C17H10N2O3 (II), has triclinic () symmetry. The structure displays C–H ⋯ N, C–H ⋯ C hydrogen bonding. In (I), the chlorophenyl and benzoxazole groups adopt a trans configuration with respect to the central cyanomethyle hydrazone moiety. Compound (II) crystallized with two molecules in the asymmetric unit shows cisoid conformation between cyano group and benzoxazole nitrogen, contrary to (I). In (II) the benzodioxole has an envelope conformation (the C17 atom is the flap atom). The molecular geometry obtained using molecular mechanics (MM) calculations has been discussed along with the results of single crystal analysis.

Crystal Structure and Molecular Mechanics Modelling of 2-(4-Amino-3-benzyl-2-thioxo-2,3-dihydrothiazol-5-yl)benzoxazole

The crystal structure of the title compound, 2-(4-amino-3-benzyl-2-thioxo-2,3-dihydrothiazol-5-yl)benzoxazole, was determined. The crystal has P1 space group and triclinic system with unit cell parameters a = 5.174(3) Å, b = 6.411(6) Å, c = 12.369(10) Å, α = 86.021(4)°, β = 84.384(5)°, and γ = 77.191(5)°. The structure consists of benzoxazole group connected with benzyl via thiazole (attached with amino and thione). Benzoxazole and thiazole rings are almost planar (maximum deviation at C1, −0.013(3) Å, and C10, 0.0041(3) Å, resp.). The phenyl ring is nearly perpendicular to both thiazole and benzoxazole rings. A network of intermolecular hydrogen bonds and intermolecular interactions stabilizes the structure, forming parallel layers. The molecular geometry obtained using single crystal analysis is discussed along with results of the molecular mechanics modeling (MM), and the results showed the same cis conformation between benzoxazole nitrogen atom and the amino group.

Intermolecular ionic cross-linked proton conducting electrolyte membranes derived from branched sulfonated poly(ether ether ketone)s with benzoxazole pendants

A series of novel branched sulfonated poly(ether ether ketone)s containing intermolecular ionic cross-linkable groups, benzoxazole groups, have been prepared for direct methanol fuel cells. The benzoxazole groups are grafted onto the polymer chain via a thiol-ene click chemistry reaction. The expected structures of the copolymers are confirmed by 1H NMR and Fourier transform infrared spectroscopy. Compared with the unmodified polymer membrane, the ionic cross-linked membranes show enhanced thermal and mechanical properties. We also investigate the changes in water uptake, proton conductivity and chemical stability. The dense membrane structures formed by branching and the interactions between sulfonic acid and benzoxazole groups make a great contribution to the improvements of dimensional stability and methanol resistance property. Although the proton conductivities of the ionic cross-linked membranes are lower than the pristine membrane, the selectivities are much higher. The results show that the novel copolymers in this study are possible potential candidate materials for proton electrolyte membrane.