Imidazole Units Research Articles

Soft-Rigid Construction of Mechanically Robust, Thermally Stable, and Self-Healing Polyimine Networks with Strongly Recyclable Adhesion.

Reversible and recyclable thermosets have garnered increasing attention for their smart functionality and sustainability. However, they still face challenges in balancing comprehensive performance and dynamic features. Herein, silicon (Si)─oxygen (O) and imidazole units covalent bonds are coupled to generate a new class of bio-polyimines (Bio-Si-PABZs), to endow them with high performance and excellent reprocessing capability and acid-degradability. By tailoring the molar content of diamines, this Bio-Si-PABZs displayed both a markedly high glass transition temperature (162°C) and a high char yield at 800°C in an oxygen atmosphere (73.1%). These Bio-Si-PABZs with their favorable properties outperformed various previously reported polyimines and competed effectively with commercial fossil-based polycarbonate. Moreover, the scratch (≈10µm) on the surface of samples can be self-healing within only 2min, and an effective "Bird Nest"-to-"Torch" recycling can also be achieved through free amines solution. Most importantly, a bio-based siloxane adhesive derived from the intermediate Bio-Si-PABZ-1 by acidic degradation demonstrated broad and robust adhesion in various substrates, with values reaching up to ≈3.5MPa. For the first time, this study lays the scientific groundwork for designing robust and recyclable polyimine thermosets with Si─O and imidazole units, as well as converting plastic wastes into thermal-reversibility and renewable adhesives.

Catalytic Edges in One‐Dimensional Covalent Organic Frameworks for the Oxygen Reduction Reaction

Metal‐free covalent organic frameworks (COFs) are employed in oxygen reduction reactions (ORR) because of their diverse structural units and controllable catalytic sites, and the edge sites have high catalytic activity than the basal sites. However, it is still challenge to modulate the edge sites in COFs, because the extended frameworks in two‐ or three‐dimensional topologies resulted in limited edge parts. In this study, we have demonstrated the edge site modulation engineering based on one dimensional (1D) COFs to catalyze the ORR, which featured distinct edge groups‐carbonyl, diaminopyrazine, phenylimidazole, and benzaldehyde imidazole units. The synthesized COFs had same ordered frameworks, similar pore structure, but had different electronic states of the carbons along the edge sites, which results in tailored catalytic properties. Notably, the COF functionalized with a phenylimidazole edge group exhibited superior catalytic performance compared to the other synthesized COFs. And the theoretical calculation further revealed the different edge sites have tunable binding ability of the intermediates OOH*, which contributed modulated activity. Our findings introduce a novel way for designing COFs optimized for ORR applications through molecular level control of edge sites.

Catalytic Edges in One-Dimensional Covalent Organic Frameworks for the Oxygen Reduction Reaction.

Metal-free covalent organic frameworks (COFs) are employed in oxygen reduction reactions (ORR) because of their diverse structural units and controllable catalytic sites, and the edge sites have high catalytic activity than the basal sites. However, it is still challenge to modulate the edge sites in COFs, because the extended frameworks in two- or three-dimensional topologies resulted in limited edge parts. In this study, we have demonstrated the edge site modulation engineering based on one dimensional (1D) COFs to catalyze the ORR, which featured distinct edge groups-carbonyl, diaminopyrazine, phenylimidazole, and benzaldehyde imidazole units. The synthesized COFs have same ordered frameworks, similar pore structure, but had different electronic states of the carbons along the edge sites, which results in tailored catalytic properties. Notably, the COF functionalized with a phenylimidazole edge group exhibited superior catalytic performance compared to the other synthesized COFs. And the theoretical calculation further revealed the different edge sites had tunable binding ability of the intermediates OOH*, which contributed modulated activity. Our findings introduce a novel way for designing COFs optimized for ORR applications through molecular level control of edge sites.

Strong and pH dependent fluorescence in unprecedented anthra[2,3-d]imidazole derivatives

We here report the synthesis and characterization of three new molecules based on an unprecedented anthra [2,3-d]imidazole unit. The new heterocycle was unexpectedly formed while attempting to obtain 2,3-diacetamidoanthracene by reducing the corresponding anthraquinone molecules by sodium borohydride. The same reaction was successfully performed using two further different 2,3-diamidoanthraquinone derivatives, thus confirming its generality. The chemical identity of the novel molecules was also proved by realizing single crystals suitable for XRD diffraction and solving the crystalline structure of one of the prepared systems. All the molecules are strong blue emitters in ethanol, with fluorescence quantum yields around 0.40. Because of the acid-base properties of anthraimidazole ring, the optical response was investigated at different pH values. While slight differences were observed in acidic conditions, in the alkaline pH range we observed a dramatic change of the fluorescence spectra in a narrow pH range (from 11 to 13), with the color of the emission turning from blue to green. This feature makes the new class of derivatives here reported very promising as pH sensors working in strongly alkaline conditions.

Ionic Polymers with Phenolic Hydroxyl Groups as Hydrogen Bond Donors Toward Enhanced Catalytic Performance for CO2 Conversion

AbstractIn this study, imidazolium‐based multifunctional ionic polymer (IP 1–IP 3) series, co‐incorporated with phenolic hydroxyl groups as hydrogen bond donors (HBDs) and Cl− as nucleophiles, are synthesized by a facile quaternization method. The physicochemical characterizations of these IPs are systematically examined by using FTIR, XPS, BET, TGA, CO2‐TPD, SEM with elemental mapping and TEM methods. Their catalytic activities are evaluated toward the conversion of carbon dioxide (CO2) and epoxides into cyclic carbonates under solvent‐ and additive‐free environments. Apart from the synergy effect between HBDs and Cl−, it is found that the types of the spacer linking the two imidazole units in the diimidazole precursors (L1–L3) also play an important role in the catalytic activity. And IP 2, with a pyridine spacer as a Lewis base site, exhibits the best catalytic performance under solvent‐free mild conditions i. e., atmospheric pressure CO2, 80 °C, and 5 h. Notably, the catalyst demonstrates a good substrate applicability. Furthermore, IP 2 exhibited good reusability, stability, and it can be recycled for ten successive runs with stable and potential catalytic activity. This study provides an alternative route to construct IPs with efficient activity for CO2 catalytic conversion and fixation under mild‐conditions.

Imidazolium and Pyridinium-based Ionic Porous Organic Polymers: Advances in Transformative Solutions for Oxoanion Sequestration and Non-redox CO2 Fixation.

The rapid pace of industrialization has led to a multitude of detrimental environmental consequences, including water pollution and global warming. Consequently, there is an urgent need to devise appropriate materials to address these challenges. Ionic porous organic polymers (iPOPs) have emerged as promising materials for oxoanion sequestration and non-redox CO2 fixation. Notably, iPOPs offer hydrothermal stability, structural tunability, a charged framework, and readily available nucleophilic counteranions. This review explores the significance of pores and charged functionalities alongside design strategies outlined in existing literature, mainly focusing on the incorporation of pyridinium and imidazolium units into nitrogen-rich iPOPs for oxoanion sequestration and non-redox CO2 fixation. The present review also addresses the current challenges and future prospects, delineating the design and development of innovative iPOPs for water treatment and heterogeneous catalysis.

Stretchable interconnected modular electrochromic devices enabled by self-healing, self-adhesive, and ion-conducting polymer electrolyte

Here, we propose a versatile terpolymer electrolyte material, UPy-PEGMA-VBMI, comprised of three monomers: ureidopyrimidinone methacrylate (UPyMA), poly(ethylene glycol) methacrylate (PEGMA), and vinyl benzyl-methylimidazolium (VBMI). The UPy-PEGMA-VBMI, supported by a combination of soft ethylene glycol chains, an ion-conducting imidazole unit, and self-complementary quadruple hydrogen bonds of UPy, exhibits exceptional properties such as high stretchability, rapid self-repair, solution processability, self-adhesion, and ion conduction. The UPy-PEGMA-VBMI was then applied to make ion gel composite films, demonstrating a notable ionic conductivity of 3.84 × 10−3 S cm−1 while maintaining robust stretching and adhesive characteristics. The electrochromic devices (ECDs) fabricated by this ion gel demonstrate outstanding performance, with fast switching times, long-term kinetic stability, and extraordinarily high coloration efficiency of 443.83 cm2 C−1. The stretchable ECDs are fabricated by utilizing the stretchable nature of UPy-PEGMA-VBMI, exhibiting a transmittance contrast of 42.7 % at an extension of 53 % and operational stability during stretching cycles. Moreover, self-healing and self-adhesive features enable the fabrication of interconnected modular ECDs, implementing area-scalable devices. These modular ECDs, each powered independently, provide arbitrary positioning and shifting of individual device patches, overcoming the performance limitations of conventional large-area devices. The unprecedented material and resulting devices open new possibilities for electrochromic applications, particularly in stretchable ECDs, pattern-switching devices, and scalable flexible ECDs.

Adsorption and inhibition of rosin thiourea imidazole quaternary ammonium salt on steel surface in HCl solution

Rosin thiourea imidazole quaternary ammonium salt (RTIQAs) was synthesized by connecting rosin and imidazole units via thiourea linker, and its inhibitive action on the corrosion of CRS (cold rolled steel) in 1.0 M HCl solution was fully investigated. The results demonstrate that RTIQAs is an efficient mixed-type inhibitor with the maximum inhibition efficiency of 95%. The adsorption rule on the CRS surface fully complies with Langmuir isotherm. The efficient inhibition of RTIQAs can also be verified by AFM, SEM and CLSM (confocal laser scanning microscope). The direct adsorption proof of RTIQAs molecules on steel surface can be further presented in EDX and XPS.

Charging modulation of the pyridine nitrogen of covalent organic frameworks for promoting oxygen reduction reaction

Covalent organic frameworks (COFs) are ideal templates for constructing metal-free catalysts for the oxygen reduction reaction due to their highly tuneable skeletons and controllable porous channels. However, the development of highly active sites within COFs remains challenging due to their limited electron-transfer capabilities and weak binding affinities for reaction intermediates. Herein, we constructed highly active catalytic centres by modulating the electronic states of the pyridine nitrogen atoms incorporated into the frameworks of COFs. By incorporating different pyridine units (such as pyridine, ionic pyridine, and ionic imidazole units), we tuned various properties including dipole moments, reductive ability, hydrophilicity, and binding affinities towards reaction intermediates. Notably, the ionic imidazole COF (im-PY-BPY-COF) exhibited greater activity than the neutral COF (PY-BPY-COF) and ionic pyridine COF (ion-PY-BPY-COF). Specifically, im-PY-BPY-COF demonstrated a half-wave potential of 0.80 V in 0.1 M KOH, outperforming other metal-free COFs. Theoretical calculations and in situ synchrotron radiation Fourier transform infrared spectroscopy confirmed that the carbon atoms in the ionic imidazole rings improved the activity by facilitating binding of the intermediate OOH* and promoting the desorption of OH*. This study provides new insights into the design of highly active metal-like COF catalysts.

Creation of Cationic Polymeric Nanotrap Featuring High Anion Density and Exceptional Alkaline Stability for Highly Efficient Pertechnetate Removal from Nuclear Waste Streams.

There is an urgent need for highly efficient sorbents capable of selectively removing 99TcO4- from concentrated alkaline nuclear wastes, which has long been a significant challenge. In this study, we present the design and synthesis of a high-performance adsorbent, CPN-3 (CPN denotes cationic polymeric nanotrap), which achieves excellent 99TcO4- capture under strong alkaline conditions by incorporating branched alkyl chains on the N3 position of imidazolium units and optimizing the framework anion density within the pores of a cationic polymeric nanotrap. CPN-3 features exceptional stability in harsh alkaline and radioactive environments as well as exhibits fast kinetics, high adsorption capacity, and outstanding selectivity with full reusability and great potential for the cost-effective removal of 99TcO4-/ReO4- from contaminated water. Notably, CPN-3 marks a record-high adsorption capacity of 1052 mg/g for ReO4- after treatment with 1 M NaOH aqueous solutions for 24 h and demonstrates a rapid removal rate for 99TcO4- from simulated Hanford and Savannah River Site waste streams. The mechanisms for the superior alkaline stability and 99TcO4- capture performances of CPN-3 are investigated through combined experimental and computational studies. This work suggests an alternative perspective for designing functional materials to address nuclear waste management.

One-Step Cascade Synthesis of ortho-bay-Imidazolo-Extended Perylene Biscarboximides (OBISIM) and Their Application as Broad-Spectrum Fluorescent Dyes.

A one-step synthesis of perylene dyes with lateral extension by condensed imidazoles in a cascade reaction of sodium amide and benzonitrile is described in which multiple extensions can be controlled by the reaction conditions. The extensions lead to bathochromic shifts in absorption and fluorescence while maintaining high fluorescence quantum yields. The condensed imidazole units cause additional absorption bands in the hypsochromic visible region, resulting in broad-band absorbers. Multiple extensions of the aromatic system enable the NIR spectral approach of the spectra. Energy transfer (fluorescence resonance energy transfer, FRET) of dyads with perylene biscarboximides is very efficient and achieves quantum yields close to unity regardless of the lengths and orientation of the spacer. Applications as broad-band-absorbing fluorescent dyes, such as in solar collectors, are discussed.

Tuning sensing efficacy of anthraimidazoledione-based charge transfer dyes: nitro group positioning impact.

Anthraimidazoledione-based optical sensors have been designed by varying the position of the nitro functional group. All three positional isomers showed highly colored, photostable optical signals owing to intramolecular charge transfer interactions. Despite having the same anion-binding site (imidazole unit), the selectivity and sensitivity of the compounds depend on the positioning of the nitro group. The selectivity was fairly good for the meta isomer, followed by the ortho and para isomers, respectively. In contrast, the sensitivity towards anions followed a completely opposite trend, with the para isomer being the most sensitive one towards anions. Interestingly, the color changing response along the turn-on fluorescence signal was observed only with CN- ions in a semi-aqueous environment. Though the introduction of water as a co-solvent could improve the selectivity, the sensitivity was found to be slightly less than that observed in pure organic medium. Mechanistic studies indicated hydrogen bonding interactions between the imidazole -NH proton and cyanide, which further facilitated the extent of intramolecular charge transfer.

Optically transparent and mechanically tough glass with impact resistance and flame retardancy enabled by covalent/supramolecular interactions.

Exploring glass materials beyond inorganic components represents a new direction in the development of artificial transparent materials. Inspired by the successes of polymeric and supramolecular glasses, we shifted our attention to the preparation of a transparent glass through the polymerization of low-molecular-weight monomers that are naturally tailored with noncovalent recognition motifs. In this work, an imidazolium unit bearing a vinyl group and a tetrafluoroborate counter anion was selected to construct an artificial glass. Experimental and theoretical investigations revealed that the cross-linking behavior of anions effectively transformed linear polymeric chains into three-dimensional networks. The polymeric-supramolecular glass exhibits a tough tensile strength (61.31 MPa), high Young's modulus (1.17 GPa), and good optical transparency (>90%), which are comparable to those of polymethyl methacrylate. Moreover, the obtained glass maintains excellent mechanical toughness and optical transparency over a wide temperature range (from -150 to 150 °C). The material shows a superior impact resistance (18.34 kJ m-2) and flame retardancy (V0 rating), which are barely achieved by supramolecular materials.

Core charge of imidazolium annulated triphenylene derivatives induces discotic columnar mesomorphism.

Thermotropic ionic liquid crystals have remained a relatively little studied group of materials despite their many potential applications as anisotropic ionic liquids and charge (ion and electron/hole) transporting materials. Particularly rare are core charged discotic liquid crystals because their synthesis is usually more involved, and their molecular design is less established. Presented here is a straightforward and versatile synthetic approach to imidazolium annulated triphenylene derivatives. Their neutral imidazole precursors are not liquid crystalline while the imidazolium salts display hexagonal discotic columnar mesophases over a wide range of temperatures and as low as 47 °C. Computational studies at the DFT and PM6 levels of theory confirmed much higher stacking energies for the imidazolium salts compared to the neutral imidazole precursors. They also predicted the anions of columnar stacks of imidazolium salts to be positioned in the bay-positions next to the imidazolium unit and in-plane with the polyaromatic system. The anions were stabilized in the bay position by multiple interactions with partially positively charged H atoms and do not interfere with π-π stacking.

Bifunctional imidazolium linked tetraphenylethene based conjugated microporous polymers for dynamic antibacterial properties and supercapacitor electrodes

Using Sonogashira coupling reactions and a postmodification approach, we successfully synthesized TPET-Im CMP incorporating an imidazolium unit to enhance antibacterial properties and optimize its performance as a supercapacitor electrode.

Mixed matrix membranes incorporating amino-functionalized ZIF-8-NH2 in a carboxylic polyimide for molecularly selective gas separation

Mixed matrix membranes (MMMs) combine the advantages of polymers and inorganic materials and demonstrate higher gas permeability than polymeric membranes, which, however, face the challenge of incompatible interface ascribed to the intrinsically different nature of the polymer and inorganic phase. To overcome this hurdle, herein, co-polyimide (6FBDA) was designed with carboxylic side groups to enhance the interfacial compatibility with amino-functionalized MOF(ZIF-8-NH2) via intensive π-π stacking and hydrogen bonds. The imidazole units in 6FBDA resemble ZIF-8-NH2 ligands and promote π-π stacking of polymer and MOF while the carboxylic moieties establish hydrogen bonds with the amino ligands of ZIF-8-NH2, significantly improving the interfacial compatibility of polymer and MOF. The defect-free MMMs with 50 wt% MOF loading demonstrate a CO2 and H2 permeability of 80.8 Barrer and 127.5 Barrer, respectively, with a CO2/CH4 and H2/CH4 selectivity of 89.4 and 141.7, respectively, exceeding 2008 Robeson upper bounds. The experimental concept of this work opens a door for fabricating molecularly selective gas separation membranes with prospects for energy-efficient CO2 capture and hydrogen separations.

A hybrid ionic liquid crystal comprising imidazolium surfactant-graphene oxide

ABSTRACT To produce graphene oxide liquid crystal composites with better controllability, imidazolium surfactant with biphenyl mesogenic core (CBphCM) has been synthesised and used to modify the negatively charged surface of graphene oxide (GO) to obtain a hybrid ionic liquid crystal (CBphCM-GO). The process of GO and CBphCM recombination was monitored by various experimental techniques such as FT-IR, Uv-vis, Raman and XPS. The experimental results indicated that the C=O bonds on GO sheets are all reduced and C−O bonds are partially reduced due to the imidazolium units being electrically active and nitrogen-rich, and the presence of the N−O bonds indicates that a new hybrid is formed between CBphCM and GO. The recombination destroys the electrostatic repulsion balance among the GO lattices, and the CBphCM-GO is observed a fluffy appearance by TEM. The liquid crystal properties of CBphCM and CBphCM-GO were investigated by DSC, polarised optical microscopy (POM) and variable temperature X-ray diffraction, respectively. As an ionic liquid crystal, CBphCM has SmA as well as the rare SmC phases exhibits de Vries-like behaviour with a layer shrinkage. The liquid crystal properties of CBphCM-GO are derived from CBphCM, and the layer shrinkage behaviour from SmA to SmC phase has also been observed.

Fabrication of an imidazolium-based magnetic ionic porous organic polymer for efficient heterogeneous catalysis of Betti reaction

In this study, post modification of the imidazole units in the porous organic polymer (POP) via the formation of imidazolium salt is reported. Addition of FeCl3 to anionic moiety of POP leads to synthesis of magnetic ionic POP namely Im-MIPOP which is applied as a heterogeneous catalytic system. This polymer was characterized by different analytical techniques including Fourier transform infrared (FT-IR) spectroscopy, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), energy-dispersive X-ray spectroscopy (EDS), elemental mapping analysis, vibrating-sample magnetometer (VSM), thermo gravimetric analysis/derivative thermo gravimetric (TGA/DTG) and Brunauer-Emmett-Teller (BET) methods. Due to unique structure and active centers of Im-MIPOP, we delve its catalytic potential for the Betti reaction by using 2-naphtol, different amines and aldehydes. High yields (up to 93 %), short reaction times and also, the acceptable recyclability and reusing capability, are the main advantages of the reported heterogeneous method.

Synthesis of Imidazolium Cations Linked to Para-t-Butylcalix[4]arene Frameworks and Their Use as Synthons for Nickel-NHC Complexes Tethered to Calix[4]arenes.

A series of cationic p-tert-butylcalix[4]arenes, with side-arms that are functionalized with imidazolium groups, have been synthesized in good yields. The parent tetrahydroxy para-t-butyl-calix[4]arene was dialkylated at the phenolic hydrogen atoms using α,ω-dibromo-alkanes to yield bis(mono-brominated) alkoxy-chains of variable length. The brominated side-arms in these compounds were then further alkylated with substituted imidazoles (N-methylimidazole, N-(2,4,6-trimethyl-phenyl)imidazole, or N-(2,6-di-isopropylphenyl)imidazole) to yield a series of dicationic calixarenes with two imidazolium groups tethered, via different numbers of methylene spacers (n = 2-4), to the calixarene moiety. Related tetracationic compounds, which contain four imidazolium units linked to the calix[4]arene backbone, were also prepared. In all of these compounds, the NMR data show that the calixarenes adopted a cone configuration. All molecules were characterized by NMR spectroscopy and by MS studies. Single crystal X-ray diffraction studies were attempted on many mono-crystals of these cations, but significant disorder problems, partly caused by occluded solvent in the lattice, and lack of crystallinity resulting from partial solvent loss, precluded the good resolution of most X-ray structures. Eventually, good structural data were obtained from an unusually disordered single crystal of 5a, (1,3)-Cone-5,11,17,23-tetra-t-butyl-25,27-di-hydroxy-26,28-di-[2-(N-2,6-diisopropylphenyl-imidazolium)ethoxy]calix[4]arene dibromide and its presumed structure was confirmed. The structure revealed the presence of H-bonded interactions and some evidence of π-stacking. Some of these imidazolium salts were reacted with nickelocene to form the nickel N-heterocyclic carbene (NHC) complexes 7a-7d. A bis-carbene nickel complex 8 was also isolated and its structure was established by single crystal X-ray diffraction studies. The structure was disordered and not of high quality, but the structural data corroborated the spectroscopic data.

Dual-crosslinked polyimide dielectric films containing Cu elements for high-temperature film capacitors

Organic polymers are widely used in film capacitors as they contain excellent flexibility, outstanding electrical insulating performance, fast charge-discharge rate, higher power density, etc. However, most of the commercially used polymer films suffer from poor heat resistance and low energy density, thus limiting their applications. To solve this problem, an effective method was adopted to prepare high-temperature resistant polyimide (PI) dielectric films in this work. A dual-crosslinked PI composite films containing Cu elements were fabricated by amine crosslinking agent and coordination of Cu2+ with the N element in imidazole unit. The dielectric constant of the film increased from 4.00 to 4.88 at 1 kHz, and the breakdown strength of the films increased from 437 MV/m to 460 MV/m at room temperature. The discharge energy density (Ud) also reached the maximum of 3.12 J/cm3 at 150 °C, and the charge-discharge efficiency (η) was 69.4% when the feeding content of Cu2+ of 20% mol. It is worth mentioning that the form of coordination bond making Cu2+ occupies the position of the lone pair electron, which effectively improved the hydrophobicity of PI composite films.