Phenylethynyl Groups Research Articles

Tetraarylpyrrolo[3,2-b]pyrrole-BODIPY dyad: a molecular rotor for FRET-based viscosity sensing.

With the aim to develop a FRET-based viscosity sensor, two dyad molecules, 4 and 5, comprising tetraarylpyrrolo[3,2-b]pyrrole (TAPP) (donor) and naked boron-dipyrromethene (BODIPY) dyes (acceptor), were designed. Dyads were synthesized via acid-catalyzed multicomponent reactions followed by Sonogashira coupling. In both dyads, the BODIPY and TAPP moieties are linked through phenylethynyl groups, which allow free rotation of the BODIPY dyes; that is, they can act as molecular rotors. This was supported by X-ray crystallographic and DFT-optimized structures. Spectroscopic studies also confirmed the presence of both TAPP and BODIPY dyes in dyads with no electronic interactions that are suitable for fluorescence resonance energy transfer (FRET). Very high energy transfer efficiency (ETE >99%) from the donor TAPP moiety to the acceptor BODIPY moiety on excitation at the TAPP part was observed. However, due to the non-fluorescent nature of naked BODIPY dyes, no fluorescence emission was observed from the BODIPY moiety in both dyads. With increasing solvent viscosities, emission from the BODIPY moieties increases due to the restricted rotation of the BODIPY moieties. Plotting the logarithms of the fluorescent intensity of dyad 5 and the viscosity of the solution showed a good linear correlation obeying a Förster-Hoffmann equation. Non-fluorescent dyad 5 in methanol became greenish-yellow fluorescent in a methanol/glycerol (1:1) solvent. Furthermore, with an increase in the temperature of the methanol/glycerol (1:1) system, as the viscosity decreases, the fluorescence also starts decreasing. Thus, dyad 5 is capable of sensing the viscosity of the medium via a FRET-based "Off-On" mechanism. This type of viscosity sensor with a very large pseudo-Stokes shift and increased sensitivity will be useful for advancing chemo-bio sensing and imaging applications.

Improvement of bifunctional organocatalysts performance by water as an additive in the Michael addition of carbonyl compounds to maleimides

The diastereoselective Michael addition of ketones to maleimides using bifunctional organocatalysts presents a significat challenge. We developed a protocol in which the addition of 5 equivalents of water boosted the diastereoselectivity of six-membered ring ketones. However, the results were influenced by steric effects and varied outcomes were observed with different ring sizes of ketones and acyclic carbonyl compounds. The improvement in the asymmetric synthesis of succinimides due to water appears to be more related to hydrogen bonds at the interface rather than a water molecule embedded in the transition state. Additionally, we explored 3-substituted maleimides and found that only those with phenyl and phenylethynyl groups underwent the reaction. Finally, the desymmetrization of N-(2-tert-butylphenyl)maleimide generated the atropoisomer with good selectivity.

Enhancing mechanical and thermal properties of blends with novel phenylethynyl-terminated siloxane-containing ortho-hydroxy polyimide

A novel phenylethynyl-terminated siloxane-containing ortho-hydroxy polyimide (O-SPI) was synthesized and physically blended with thermoplastic polyimide (PI) to enhance both the thermal and mechanical properties of polyimide, addressing the growing demand for high-performance materials in harsh environments. The blend underwent conversion to semi-Interpenetrating Polymer Networks ( semi-IPNs) and benzoxazole structures through thermal curing of reactive phenylethynyl groups and thermal rearrangement of ortho-hydroxy imide units. The trends in thermal and mechanical properties were investigated in relation to the chemical structures and varying mass fraction of O-SPI. The covalent incorporation of semi-IPNs and rigid benzoxazole structures restrict segmental motion while the backbone linkage confers the toughness of the blends. These synergistic effects insure the cured blends with high glass transition temperatures (472.51°C) and tensile strength (117.81 MPa) simultaneously, demonstrating their potential for applications in challenging conditions.

Synthesis and Optical Properties of Binaphthyl Derivatives with Comprehensive Introduction of Phenylethynyl Groups.

In this study, compounds with phenylethynyl (PE) groups introduced at all of the possible positions of the methylene-bridged structure of the 1,1'-bi-2-naphthol backbone (3-PE to 8-PE) were synthesized. Compounds with four or six phenylethynyl groups (3,6-PE, 4,6-PE, 5,6-PE, 6,7-PE, and 3,4,6-PE) were also synthesized. The key reaction for the synthesis of these compounds was the Sonogashira reaction using halogen scaffolds. The new transformation methods include (1) selective bromination of the 5-position of the binaphthyl skeleton and (2) bromination of the 6-position and then iodination of the 4-position, followed by the Sonogashira reaction of iodine at the 4-position and lithiation and protonation of bromine at the 6-position. The optical properties of the compounds were evaluated. The extension of the π system greatly differed depending on the position of the phenylethynyl group. 4-PE, 4,6-PE, and 3,4,6-PE, in which the phenylethynyl groups were introduced in the extended direction of the naphthalene linkage axis, showed longer absorption and emission wavelengths and higher fluorescence quantum yields than the other compounds. In circularly polarized luminescence measurements, 7-PE showed a relatively large glum value, an interesting finding that reverses the sense.

Third-order nonlinear optical properties of highly electron deficient, nonplanar push-pull porphyrins: β-nitro-hexa-substituted porphyrins bearing bromo, phenyl, and phenylethynyl groups.

β-Heptasubstituted porphyrins [MTPP(NO2)X6; M = 2H, NiII, CuII, and ZnII; X = Br, Ph, and PE] were synthesized and their third-order nonlinear optical (NLO) properties explored using the single-beam Z-scan technique with femtosecond, MHz pulses in the visible range. The three-photon absorption (γ), third-order nonlinear optical susceptibility (χ3), three-photon absorption cross-section (σ3), and nonlinear refractive index (n2) have been determined from theoretical fits with experimental results. The sign and magnitude of the nonlinear refractive index (n2) have been obtained from the closed-aperture experiment while the three-photon absorption coefficient and three-photon absorption cross-section were determined from the open-aperture experiment. The magnitudes of the 3PA and σ3 extended in the range of (2.7-3.4) × 10-23 cm3 W-2 and (5.5-7.0) × 10-78 cm6 s2, respectively. The higher magnitude of the NLO coefficients ensures their utility in optical and photonic applications.

N-Heterocyclic carbene-stabilized gold-copper nanoclusters: synthesis, bonding and mechanochromism.

N-Heterocyclic carbene (NHC) ligands have emerged as highly effective surface ligands for the protection and functionalization of metal nanoclusters (NCs). However, research on NHC-stabilized metal NCs, including their synthesis, structure, properties, and applications, is still in its early stages. In this study, we present the first gold-copper alloy cluster protected by both NHC and alkyne ligands, denoted as Au3Cu(iPrNHCiPr)(PA)4 (abbreviated as Au3Cu, where iPrNHCiPr is a bidentate N-heterocyclic carbene ligand with isopropyl as the N-substituent, and PA is a phenylethynyl group). The precise composition of Au3Cu was confirmed through the utilization of electrospray ionization mass spectrometry (ESI-MS), and its structure was determined via X-ray single-crystal diffraction. It is worth noting that although the Au3Cu clusters do not display substantial light emission when exposed to UV lamps, they are capable of emitting green fluorescence subsequent to undergoing mechanical milling (λem = 500 nm). Powder X-ray diffraction (PXRD) analysis reveals that this transition is attributed to a crystalline-amorphous transformation of the cluster crystals. These atomically precise alloy clusters are expected to serve as a model for further investigation into the principles of mechanical milling of metal clusters for discolouration.

Dual-Function Sensing Platform for Hg2+ Based on a Redox-Active Thiosemicarbazone Receptor

Recently, our group developed a platform for adsorptive stripping voltammetric analysis of heavy metals based on electrodes modified with “clickable” thiosemicarbazone ligands, achieving detection limits for Hg2+ in the nM range1. Here, we present an extension of our previous results towards obtaining an innovative, dual-function sensing platform suitable for both rapid screening and accurate quantitation of mercury. For this purpose, we designed a novel ferrocene-based redox-active thiosemicarbazone receptor having an intramolecular signalling pathway between the binding site and redox-active center, a prerequisite for obtaining efficient redox-active receptors3. The metalloligand, which also contains an azido functional group, was synthesized by reacting 4-(6-azidohexyl)-3-thiosemicarbazide1 with ferrocenealdehyde. The binding properties of the ligand towards several heavy metal ions (Cd2+, Cu2+, Hg2+, Ni2+, Pb2+, Zn2+) were evaluated by UV-VIS spectroscopy, ESI-MS and cyclic voltammetry. Notably, the voltammograms recorded in the presence of sub-stoechiometric amounts of Hg2+ displayed a “two-wave” behavior4 for the Fc/Fc+ redox couple (ΔEp~100 mV), suggesting a high binding constant for this particular ion. Next, modified electrodes were prepared by grafting glassy carbon substrates with triisopropylsilyl-protected phenylethynyl groups through the electrochemical reduction of the corresponding diazonium salt5, followed by deprotection of the alkyne groups and „click” immobilization of the thiosemicarbazone receptor. The electrode surface functionalization was further assessed using electrochemical techniques and X-ray photoelectron spectroscopy, and the complexation behavior of the modified electrodes in the presence of heavy metal ions was investigated using Osteryoung square-wave voltammetry6. As expected, the Fc/Fc+ couple from the surface-immobilized ligand displayed the same voltammetric behavior as in solution, and the appearance of a new voltammetric wave shifted by ~100 mV allows the rapid qualitative screening of Hg2+. Furthermore, the modified electrodes were employed for the accurate quantitation of Hg2+ ions using the accumulation at open circuit-anodic stripping voltammetry technique, achieving a LOD of 5.0 nM. Finally, we demonstrate that electrodes modified with the thiosemicarbazone metalloligand have a very good reproducibility, reusability and stability. Acknowledgements This work was supported by a grant of the Ministry of Research, Innovation and Digitization, CNCS-UEFISCDI, project number PN-III-P1-1.1-TE-2021-1163, within PNCDI III.

Improving the high-temperature performance by constructing restricted amorphous regions in PEEK

Improving the high-temperature performance of polymers through crosslinking without compromising properties such as ductility and processability remains a significant challenge. In this study, we synthesize a cross-linkable poly (ether ether ketone) end-capped with phenylethynyl groups (PEEK-PEPs) and subsequently melt-blended it with semi-crystalline PEEK to create the PEEK alloy (PEEK/PEEK-PEPs). Under thermal treatment, the curing process of PEEK-PEPs is dominated by the formation of a cross-linked network, accompanied by chain growth reactions. The chain growth reaction will gradually become the dominant reaction as the treatment time increases. These results are validated by successive self-nucleation and annealing, as well as measurements of gel fraction and viscosity before and after thermal treatment. With this approach, the storage modulus (E') of PEEK/PEEK-PEPs is improved by 95 % at 290 °C, and the heat deflection temperature (HDT) is increased by 25 °C. Meanwhile, the tensile strength of PEEK/PEEK-PEPs at room temperature and 150 °C increases to 125 MPa and 72 MPa, respectively, which is 30 % and 31 % higher than that of pristine PEEK resins, while the strain at break remains at the same level as PEEK. These findings potentially provide an advanced polymer alloy preparation method for high-temperature applications, particularly in extreme environments.

MD analysis on structure and property of thermosetting polyimides end-capped by phenylethynyl groups

Four phenylethynyl-containing thermosetting polyimide monomers, based on aromatic diamines with various molecular structure and 4-phenylethynylphthalic anhydride, were designed and synthesized to investigate their structure-properties relationships from a molecular dynamics perspective. The trifluoromethyl linkage in the diamine moiety of a polyimide gives the highest flexibility whereas the amide linkage imparts the lowest flexibility to the polymer chain. A more flexible polyimide has a lower melting temperature, lower cohesive energy density, lower mechanical properties, and larger the fraction free volume. Besides, intermolecular hydrogen bonding plays a critical role in the maintenance of physical properties. These simulated values show good agreement with experimental data. This project provided an important opportunity to advance the understanding of structure-property relationships of polyimides.

Cyclization of an Achiral Flipping Panel to Homochiral Tubes Exhibiting Circularly Polarized Luminescence

AbstractMacrocyclization of the bendable 2,7‐dimethoxythianthrene with methylene linkages afforded a pair of homochiral macrocycles featuring a hex‐nut‐like geometry. Their structures were fully characterized by NMR spectroscopy, mass spectrometry, and single‐crystal X‐ray diffraction analysis. Their stable planar chirality facilitates efficient resolution of the pair of enantiomers which could be readily derivatized. Installing phenylethynyl groups on their rims leads to luminescent tubular macrocycles exhibiting circularly polarized luminescence with a large dissymmetry value |glum| of 5×10−3. Supramolecular binding of electron‐deficient guests by the tube results in fluorescence quenching, which proved its potential for the future development of switchable chiroptical systems.

Cyclization of an Achiral Flipping Panel to Homochiral Tubes Exhibiting Circularly Polarized Luminescence.

Macrocyclization of the bendable 2,7-dimethoxythianthrene with methylene linkages afforded a pair of homochiral macrocycles featuring a hex-nut-like geometry. Their structures were fully characterized by NMR spectroscopy, mass spectrometry, and single-crystal X-ray diffraction analysis. Their stable planar chirality facilitates efficient resolution of the pair of enantiomers which could be readily derivatized. Installing phenylethynyl groups on their rims leads to luminescent tubular macrocycles exhibiting circularly polarized luminescence with a large dissymmetry value |glum | of 5×10-3 . Supramolecular binding of electron-deficient guests by the tube results in fluorescence quenching, which proved its potential for the future development of switchable chiroptical systems.

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.

A coumarin-based fluorescent probe: single-wavelength excitation, discrimination of Cys/Hcy and GSH by naked eyes

Biothiols mainly include cysteine (Cys), homocysteine (Hcy) and glutathione (GSH), which play an important role in life activities and abnormal changes in their concentrations are closely related to certain diseases. Therefore, the quantitative tracking and analysis of biothiols in living organisms has become a hot research topic in recent years. In this work, a coumarin-based fluorescent probe COUN was designed and synthesized for the comparable color recognition of Cys/Hcy and GSH by introducing the phenylethynyl group as the recognition site of biothiols, which showed significant fluorescence enhancement and green fluorescence under the UV light at 365 nm. The probe specifically recognized Hcy, showing 40-fold fluorescence enhancement and strong green fluorescence at 492 nm. Moreover, there was a good linear relationship between the fluorescence intensity of the probe and certain concentrations of Cys/Hcy and GSH, with detection limits of 36.6 nM, 86.4 nM, and 174 nM, respectively. The recognition mechanism of COUN to distinguish Cys/Hcy and GSH was studied by TDDFT calculations. More importantly, COUN was successfully used for imaging biothiols in living cells. The results showed that this probe could provide an effective contribution to the understanding of the role of biothiols, especially Hcy.

Acceleration of the thermal back-reaction and the finding of a non-photochromic isomer for a negative photochromic binaphthyl-bridged imidazole dimer.

The development of visible or near-infrared (NIR) light-responsive fast photoswitchable molecules for the real-time, non-contact control of physical and chemical properties has received increased attention because of the non-invasive features to materials and biological tissues. We report a new molecular design to accelerate the thermal back-reaction of the negative photochromic binaphthyl-bridged imidazole dimer, BN-ImD. We also found that irradiation of the BN-ImD derivative with methyl groups on the bridging binaphthyl unit with visible light produced an unprecedented photoreaction product with a unique eight-membered ring structure. These observations provide fascinating clues for the future development of fast negative photochromic molecules.

Influence of crosslink density on thermal, mechanical and dielectric properties of cross-linked fluorinated poly(aryl ether)s

The rapid development of high-speed communication networks (for example, 5G) has imposed more stringent requirements on the comprehensive performance of low dielectric constant (low-k) polymeric materials, as an important member of which, fluoropolymer has gained much attention. In this study, a series of cross-linkable fluorinated poly(aryl ether)s with different phenylethynyl content have been synthesized through nucleophilic substitution reaction, then their polymeric films have been prepared and thermally cross-linked via phenylethynyl groups. Thermal, mechanical and dielectric properties of the films are systematically compared. Due to the presence of F atoms and cross-linked structure in polymer chains, these polymeric films exhibit remarkable dielectric properties with the lowest dielectric constant < 2.4 and dissipation factor < 0.003 at frequency from 100 Hz to 1 MHz. Moreover, the dielectric performance shows impressive temperature independence before 200 °C. Excellent mechanical properties of the films have been corroborated by the DMA data of Young’s modulus > 1.50 GPa and modulus retention rate > 70%. It is noteworthy that polymeric films possess very low dielectric constant and dielectric loss at high frequency of 10 GHz, of which the lowest values can reach 2.47 and 0.0018, respectively. The polymeric films constructed in this study have shown great application prospects in the field of high-speed communication.

A Ratiometric, Fast-Responsive, and Single-Wavelength Excited Fluorescent Probe for the Discrimination of Cys and Hcy

The ratiometric detection of cysteine (Cys) and homocysteine (Hcy) is very challenging because of their highly similar chemical structures and properties. By introducing the phenylethynyl group into a coumarin dye as the sensing group, the ratiometric fluorescent probe CP was developed to selectively and rapidly discriminate between Cys and Hcy. With a single-wavelength excitation, the presence of Cys or Hcy induced the probe to produce distinct ratiometric fluorescence changes: from red (λmaxem = 608 nm) to blue (λmaxem = 485 nm) toward Cys and from red to mixed red/blue toward Hcy. Moreover, the probe was capable of visualizing and discriminating between intracellular Cys and Hcy in HeLa cells and zebrafish by exhibiting different ratiometric fluorescence signals.

Resin Transfer Moldable Fluorinated Phenylethynyl-Terminated Imide Oligomers with High Tg: Structure-Melt Stability Relationship.

Phenylethynyl-terminated aromatic polyimides meet requirements of resin transfer molding (RTM) and exhibits high glass transition temperature (Tg) were prepared. Moreover, the relationship between the polyimide backbones structure and their melting stability was investigated. The phenylethynyl-terminated polyimides were based on 4,4′-(hexafluorosiopropylidene)-diphthalic anhydride (6FDA) and different diamines of 3,4′-oxydianiline (3,4′-ODA), m-phenylenediamine (m-PDA) and 2,2′-bis(trifluoromethyl)benzidine (TFDB) were prepared. These oligoimides exhibit excellent melting flowability with wide processing temperature window and low minimum melt viscosities (<1 Pa·s). Two of the oligoimides display good melting stability at 280–290 °C, which meet the requirements of resin transfer molding (RTM) process. After thermally cured, all resins show high glass transition temperatures (Tgs, 363–391 °C) and good tensile strength (51–66 MPa). The cure kinetics studied by the differential scanning calorimetry (DSC), 13C nuclear magnetic resonance (13C NMR) characterization and density functional theory (DFT) definitely confirmed that the electron-withdrawing ability of oligoimide backbone can tremendously affect the curing reactivity of terminated phenylethynyl groups. The replacement of 3,4′-ODA units by m-PDA or TFDB units increase the electron-withdrawing ability of the backbone, which increase the curing rate of terminated phenylethynyl groups at processing temperatures, hence results in the worse melting stability.

Development of High-Performance Composites with Molecular Weight Controlled Polyimide Oligomers End-Capped with Phenylethynyl Groups

A series of molecular weight controlled polyimide oligomer (Oligo-PI) resins were developed via the polymerization of 4,4′-(1,3-phenylenedioxy)dianiline (TPE-R), 2,3′,3,4′-biphenyltetracarboxylic dianhydride (BPDA) and 4-phenylethynyl phthalic anhydride (PEPA). PEPA was served as the molecular weight controlling and reactive end-capping agent. Oligo-PI resins have an asymmetric and amorphous structure, which could make better processability to fabricate composites. To investigate the effect of molecular weight (MW) and chain extension structures of phenylethynyl groups by thermal curing on thermal and mechanical properties, carbon fabric reinforced Oligo-PIs (Oligo-PI/CFs) were prepared via hot press technique. Morphology, mechanical and thermal properties of Oligo-PI/CFs were measured by SEM, TGA, IZOD impact tester, and UTM (three-point bending test). As MW got higher and the ordered network structures were formed, the composite exhibited excellent thermal stability. Flexural strengths also increased by building the crosslinked structures. On the other hand, impact strengths were less influenced. Among Oligo-PI/CFs, Oligo-PI/CF-3 showed comparatively good performance. The mechanical properties of Oligo-PI/CF-3 (5 ply) was evaluated at both 25 °C and 200 °C. The composite maintained high strengths even at high temperatures, demonstrating the durability of Oligo-PI/CFs in harsh conditions utilized for the aerospace and military applications.

Improving the Voltammetric Determination of Hg(II): A Comparison Between Ligand-Modified Glassy Carbon and Electrochemically Reduced Graphene Oxide Electrodes.

A new thiosemicarbazone ligand was immobilized through a Cu(I)-catalyzed click reaction on the surface of glassy carbon (GC) and electrochemically reduced graphene oxide (GC-ERGO) electrodes grafted with phenylethynyl groups. Using the accumulation at open circuit followed by anodic stripping voltammetry, the modified electrodes showed a significant selectivity and sensibility for Hg(II) ions. A detection limit of 7 nM was achieved with the GC modified electrodes. Remarkably, GC-ERGO modified electrodes showed a significantly improved detection limit (0.8 nM), sensitivity, and linear range, which we attribute to an increased number of surface binding sites and better electron transfer properties. Both GC and GC-ERGO modified electrodes proved their applicability for the analysis of real water samples.

Melt fluidity and thermal property of thermosetting siloxane-containing polyimide resins and their organic/inorganic hybrid characteristics

A series of thermosetting siloxane-containing polyimide resins were synthesized by incorporating of bis(p-aminophenoxy)dimethylsilane or bis(p-aminophenoxy)tetramethyldisiloxane with various concentrations into formulated oligoimides. These thermosetting polyimide resins exhibited good combination of processability and thermal resistance. It was found that siloxane-containing oligoimides provided significant advantages over unmodified oligoimides, relative to melt fluidity and processing window, due to the flexibility of D[(CH3)2SiO2/2] siloxy units. The siloxane-containing polyimide resins cured at 380 °C revealed relatively higher glass transition temperatures (Tg) than that of unmodified polyimides, despite the incorporation of flexible siloxane segment in oligoimides. Dynamic mechanical analysis and microstructure investigation suggested that some D[(CH3)2SiO2/2] siloxy units in the surface layer of polyimide transformed into T[CH3SiO3/2] and Q[SiO4/2] siloxy units in the curing procedure besides crosslinking of phenylethynyl groups, due to oxidation crosslinking of siloxane. That led to inorganic silica-like structures formed in situ, and inter-connected by organic polyimide segments. This organic/inorganic hybrid characteristics endowed polyimide resins with enhanced thermal property. After post-curing at 450 °C, D[(CH3)2SiO2/2] siloxy units completely transformed into T[CH3SiO3/2] and Q[SiO4/2] siloxy units, and the polyimide reins gave the Tg even exceeding 550 °C. Meanwhile, the corresponding T700 carbon fiber reinforced composite presented excellent mechanical property and durability at the temperature as high as 500 °C.