Imidazole Units Research Articles

Nitroxide TEMPO-containing PILs: Kinetics study and electrochemical characterizations

The cobalt-mediated radical polymerization (CMRP) of new ionic liquid monomers (ILMs), vinyl imidazolium functionalized with redox-active free radical 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)VIm and its CMR copolymerization with vinyl imidazolium units functionalized with triethylene oxide (TEG)VIm produced a well-defined PILs (co)polymers. The controlled nature of (co)polymerization can be seen from the linear first-order kinetic plot, linear evolutions of the molar mass with total monomer conversion and the low polydispersity of the resulting (co)polymers. By combining the redox activity of (TEMPO)PVIm and remarkable ionic conductivity of (TEG)PVIm, outstanding rate capability performance was achieved with a remarkable capacity of 69 mAh g−1 at 60C. The obtained organic electrode can serve as sustainable electrodes in lithium ion batteries.

Synthesis and photophysical properties of benzoxazolyl-imidazole and benzothiazolyl-imidazole conjugates.

Materials that have higher fluorescence emission in the solid state than molecules in solution have recently been paid more attention by the scientific community due to their potential applications in various fields. In this work, we newly synthesized benzoxazolyl-imidazole and benzothiazolyl-imidazole conjugates, which show aggregation-induced emission (AIE) features in their solid and aggregate states. It was found that oxygen and sulfur substitutions can dramatically influence the molecular structures and polarities of the dyes, leading to different degrees of the AIE phenomenon. The benzothiazolyl-imidazole molecule has lower polarity compared to that of benzoxazolyl-imidazole; therefore, the dye bearing a benzothiazolyl group shows higher emission intensity and dual emission in aqueous solution. Theoretical calculation results suggest that the benzothiazolyl-imidazole molecules might have electrostatic interactions between sulfur and nitrogen atoms, explaining the experimental observations of lower critical aggregation concentration and photophysical properties both in solution and in the solid state. The theoretical calculations agree with the experimental data, thus demonstrating a potent strategy to gain a deep understanding of the structure–property relationships to design solid-state fluorescent materials.

Supramolecular chirality and photochromism in Langmuir-Blodgett films of fabricated silver-induced phenylazoimidazole derivatives

Three non-classical amphiphilic phenylazoimidazole derivatives, viz. 2-methyl-4-(p-tolylazo)-1H-imidazole (4-TAIM), 2-methyl-4-(phenylazo)-1H-imidazole (4-PAIM), and 2-methyl-4-(p-bromophenylazo)-1H-imidazole (4-BPAIM), were synthesized herein and their in-situ molecular assemblies upon coordination with AgNO3 in the monolayer at the air/water interface were investigated. The surface pressure-area (π-A) isotherms showed that all these compounds could be spread on the surface of the AgNO3 solution, although they have no alkyl chains. The transferred multilayers were arranged in an H-aggregate and showed good photochromic properties, with 40%, 50%, and 20% trans-to-cis photoisomerization in the photo-stationary state for 4-TAIM, 4-PAIM, and 4-BPAIM films respectively. Notably, the Ag(I)-coordinated 4-PAIM films show supramolecular chirality, although the azo-imidazole ligand 4-PAIM itself is achiral. This supramolecular chirality was suggested to be due to a cooperative, stereoregular, π-π stacking between the neighboring azophenyl imidazolium units, and the orderly interfacial organization with symmetry breaking in some systems.

Insights into the effect of the spacer on the properties of imidazolium based AIE luminogens

With the aim to obtain organic salts with potential applications in high performance molecular electronics, we combined properties of π-conjugated spacers, like 1,4-diethynylbenzene and 1,6-diethynylpyrene, with the ones of both imidazole and imidazolium units. Physico-chemical properties of obtained fluorescent organic salts were investigated performing thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC) and cyclic voltammetry measurements (CV). Photophysical behavior of the salts was analyzed in conventional solvents and ionic liquids, by UV–vis and fluorescence investigation. Solution phase aggregation study revealed that these salts self-assemble in conventional solvents and ionic liquids, leading to aggregation induced emission processes. Notably, emission was maintained also in the solid state, with higher or lower intensity compared with the solution, depending on which spacer is present. This latter, also impacts on the morphology of the aggregates, allowing fine tuning the properties of the supramolecular materials formed.

Fused Hybrid Linkers for Metal–Organic Frameworks-Derived Bifunctional Oxygen Electrocatalysts

Noble metal free M-N-C oxygen electrocatalysts are generaly synthesized using inorganic salts, organometallic precursors, nanostructured carbon nanotubes, several dopants and carbonization under modifying environments such as NH3 or H2. Reducing synthesis steps or bringing versatility in post product is quite rare. We have introduced a series of metal-organic frameworks using iron/benzimidazole as the only primary precursor to obtain a uniform material. By merging catechol and imidazole units together, we prepared efficient bifunctional oxygen electrocatalyst. The proposed material outperforms the Pt-based materials with respect to electrocatalytic properties in alkaline media (ORR: Eon = 1.01 V, E1/2 = 0.87 V vs. RHE in 0.1 M KOH; OER: 1.60 V @10 mA cm–2 in 0.1 M KOH; ΔE = 0.73 V). It was also established that fine-tuning of organic linker can help to modulate the electrochemical properties of the single precursor based electro-catalyst material.

Tunable AI-CPL behavior by regulation of microstructure of AIE-active isomers through chiral emissive liquid crystals

Circularly polarized luminescence (CPL) emission materials with high luminescence dissymmetry factor (glum) and high quantum yield (QY) are currently in urgent demand for real applications. Three D-A type enantiomers (R-/S-1, 2 and 3) were designed and synthesized that combine a phenanthro [9,10-d]imidazole (PIP) unit to a naphthalimide (NI) at the p-, m-, o-positions. These AIE-active enantiomers were chosen as CPL emitters doped into nematic liquid crystals (E7, N-LCs) to form three chiral nematic liquid crystals (N*-LCs-1, 2 and 3). Interestingly, N*-LCs-1 shows higher glum (+0.91/-0.98) and QY (18.5%) than N*-LCs-2 (glum = +0.86/-0.89, QY = 1.3%) and N*-LCs-3 (glum = +0.010/-0.013, QY = 4.7%) due to effective chirality transfer and intramolecular electronic coupling from microstructure change of AIE-active isomers. This paper revealed that AI-CD and AI-CPL enhancement behavior of N*-LCs could be regulated not only by the chirality transfer via supramolecular self-assembly but also by the electronic coupling strength through microstructure change of AIE-active isomers of donor units in the chiral emitters. This work can provide a new strategy for the development of CPL LCs materials.

Recent Advances on Imidazolium-Functionalized Organic Cationic Polymers for CO2 Adsorption and Simultaneous Conversion into Cyclic Carbonates.

The cycloaddition reaction of CO2 with various epoxides to generate cyclic carbonates is one of the most promising and efficient approaches for CO2 fixation. Typical imidazolium-based ionic liquids possessing electrophilic cations and nucleophilic halogen anions have been identified as excellent and environmentally friendly candidates for synergistically activating epoxides to convert CO2 . Therefore, the feasible construction of a series of imidazolium-functionalized organic cationic polymers can bridge the gap between homogeneous and heterogeneous catalysis, thereby obtaining highly selective CO2 adsorption and simultaneous conversion ability. This Review describes the recent advancements made with regard to the design and synthesis of this type of polymeric networks having imidazolium functionality. They are considered as an outstanding heterogeneous catalyst for the cycloaddition of CO2 to epoxides. Based on the perspective from the design of building blocks to the synthesis of cationic polymers, the focus mainly lies on how to introduce imidazole units into the material backbone via a covalent linking approach and how to incorporate other active sites capable of activating CO2 and/or epoxides into such polymeric materials.

Formation of Functional Cyclooctadiene Derivatives by Supramolecularly‐ Controlled Topochemical Reactions and Their Use as Highly Selective Fluorescent Biomolecule Probes†

Summary of main observation and conclusionControlling the regio‐ and stereochemistry of the photoproducts in solution is far more challenging for polyenes than for monoalkenes. Herein, a supramolecularly‐controlled topochemical reaction of conjugated dienes in homogeneous system is developed, ultimately providing two cyclooctadiene‐cored tetraimidazolium molecular receptors exclusively. These cyclooctadiene derivatives exhibited highly sensitive and selective fluorescence sensing for thymine relative to other biologically relevant species in aqueous solution at physiological pH. Both the cyclooctadiene moieties and imidazolium units play important roles in the selective recognition observed. The presented supramolecularly‐controlled method allows the simple yet rare selective photoconversion of flexible cyclooctadiene derivatives in solution. This study offers a new synthetic strategy for the preparation of functional molecules with potential for use in biological applications.

π-Conjugated twin molecules based on 9,9-diethyl-1-phenyl-1,9-dihydrofluoreno[2,3-d]imidazole module: synthesis, characterization, and electroluminescence properties

A series of well-defined, π-conjugated twin molecules by connecting two 9,9-diethyl-1-phenyl-1,9-dihydrofluoreno[2,3-d]imidazole units via an ortho-, meta-, or para-benzene with high quantum efficiency of fluorescence is synthesized and fully characterized. The detailed thermal, electrochemical, photophysical, and electro-luminescence properties have been investigated. The electro-luminescence properties of the obtained materials are studied by fabricated the device using the configuration ITO/HATCN (5 nm)/NPB (20 nm)/TCTA (10 nm)/CBP: 5% doping (20 nm)/TMPYPB (40 nm)/LiQ (1 nm)/Al (80 nm). The doped OLED based on the compound with para-benzene as the emitting layer shows the best performance with the maximum current efficiency of 2.30 cd/A, maximum power efficiency of 1.52 lm/W, located in the deep-blue region with CIE (x, y) value of (0.1572, 0.0587) with relatively lower onset voltage of 4.25 V.

X-ray Crystal Structure of a Cyclic-PIP-DNA Complex in the Reverse-Binding Orientation.

Elucidation of the details of the associating mode is one of the major concerns for the precise design of DNA-binding molecules that are used for gene regulation. Pyrrole-imidazole polyamide (PIP) is a well-established synthetic DNA-binding molecule that has sequence-specificity for duplex DNA. By the design of the sequence of pyrrole, imidazole, and other synthetic units, PIP is bound to the target DNA sequence selectively. Here, we report the X-ray crystal structure of newly synthesized chiral cyclic PIP (cPIP) complexed with DNA at 1.5 Å resolution and reveal that cPIP binds in the reverse orientation in the DNA minor groove. Analysis of the crystal structure revealed that the positions of the hydrogen bonds between the bases and the pyrrole-imidazole moieties of cPIP were similar for both forward- and reverse-binding orientations and that the distortion of the B-form DNA structure caused by cPIP binding was also similar for both orientations. We further found that new hydrogen bonds formed between the amino groups on the γ-turn units and DNA at both ends of the cPIP molecule. Additionally, by comparing the reverse PIP orientation with the forward orientation, we could clarify that the cause of the preference toward the reverse orientation in the S-form cPIP as used in this study is the overall conformation of the cPIP-DNA complex, particularly the configuration of hydrogen bonds. These results thus provide an explanation for the different stereoselectivity of cPIP binding in the minor groove.

Fused Hybrid Linkers for Metal–Organic Frameworks-Derived Bifunctional Oxygen Electrocatalysts

Noble metal free M-N-C oxygen electrocatalysts are generaly synthesized using inorganic salts, organometallic precursors, nanostructured carbon nanotubes, several dopants and carbonization under modifying environments such as NH3 or H2. Reducing synthesis steps or bringing versatility in post product is quite rare. We have introduced a series of metal-organic frameworks using iron/benzimidazole as the only primary precursor to obtain a uniform material. By merging catechol and imidazole units together, we prepared efficient bifunctional oxygen electrocatalyst. The proposed material outperforms the Pt-based materials with respect to electrocatalytic properties in alkaline media (ORR: Eon = 1.01 V, E1/2 = 0.87 V vs. RHE in 0.1 M KOH; OER: 1.60 V @10 mA cm–2 in 0.1 M KOH; ΔE = 0.73 V). It was also established that fine-tuning of organic linker can help to modulate the electrochemical properties of the single precursor based electro-catalyst material.

Emission Enhancement of Perylene‐Bisimide‐Based Organogel Triggered by Ultrasound

AbstractDesign of mechanostress controlled luminescence in supramolecular gel is still a challenge. Herein, the molecular gelators PBI1 and PBI2 based on perylene bisimide (PBI) chromophores are prepared and characterized. With additional non‐covalent hydrogen bonding interactions between acid and imidazole units, stable gelator PBI2 self‐assembles into entangled supramolecular fibers that forms fluorescent‐enhancement gels triggered by ultrasound in DMSO. Moreover, the structure variation and gelation approaches on the gel properties are also contrasted and studied with several experiments.

Effects of solution-phase ordering on the spectroscopic properties and electrooxidative reactivity of isomeric mixtures and isolated isomers of synthesized amidine derivatives

We present the synthesis of amidine derivatives and the separation of their isomers obtained after the reaction of different bis(phthalic anhydrides) with 1,8-diaminenaphtalene (1,8DAN). The isolated isomers of 4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride) (BPADA) significantly differed in their optical and electrochemical properties, showing distinct changes in reactivity due to electrooxidation. The calculated HOMO energy and visualization of this orbital indicated its localization on the perimidine unit. Thus, the condensation of BPADA with 2,3-diaminonaphthalene was also performed to obtain the naphtho[2,3-d]imidazole units as terminal groups to compare its oxidative reactivity versus the perimidine segment. It was confirmed that only the perimidine-containing compounds were reactive due to electrochemical oxidation; however, in a solution containing a mixture of isomers, we only obtained soluble products. In turn, the isolation of isomers and electrooxidation in a solution containing only one type of isomer resulted in the production of a solid and redox-active product.

ZnO nanoparticles catalyzed synthesis of bis- and poly(imidazoles) as potential anticancer agents

A synthesis of bis- and poly(imidazoles) by one-pot three-component reaction of 1,2-diketone with aldehydes and ammonium acetate in the presence of catalytic amount of ZnO nanocatalyst is reported. The reactions were performed under conventional heating as well as under microwave irradiation. The anticancer activities of the synthesized compounds were evaluated against human breast adenocarcinoma cell line (MCF-7), liver cancer cell line (HepG-2), and epithelial colorectal adenocarcinoma cells (CaCO-2). The results of the cytotoxic activity revealed that compound 16 b with bis(imidazole) analog that incorporated a 4,5-difuran rings was potent against HepG-2 cancer cells (IC50 = 8.14 µM) with high selectivity index (SI = 27.47). Compound 25 incorporating four imidazole units was active against MCF-7 cell line (IC50 = 12.62 µM) and showed a significant selectivity index (SI = 7.71). Moreover, compound 27 containing six imidazole units exhibited the highest activity against the CaCO-2 cell line (IC50 = 32.51 μM) with SI = 4.09.

Two Highly Water-Stable Imidazole-Based Ln-MOFs for Sensing Fe3+,Cr2O72–/CrO42– in a Water Environment

Developing highly stable materials for harmful ion detection in a water environment is of much importance and challenging. Here, two three-dimensional porous structures (termed as Eu-MOF and Tb-MOF) were successfully constructed by the strategy of anchoring Eu3+/Tb3+ and rigid 1,2,4,5-benzenetetracarboxylic acid (H4BTEC) imidazole units (H3ICA) onto its frameworks. The obtained Eu-MOF and Tb-MOF display high water stability and fluorescence stability up to 30 days. Furthermore, luminescent studies reveal that Eu-MOF and Tb-MOF show rapid, recursive, and simultaneous sensing Fe3+ and Cr2O72-/CrO42- ions in water. In addition, the sensing function possesses remarkable cyclicity and selectivity even with the existence of other analogous ions.

Rational Design of Efficient Organometallic Ir(III) Complexes for High-Performance, Flexible, Monochromatic, and White Light-Emitting Electrochemical Cells.

Highly efficient light-emitting electrochemical cells (LECs) have attracted tremendous interest because of their simple structures and low-cost fabrication processing, showing great potential for full-color displays and solid-state lighting. In this work, we rationally designed and synthesized two red-emitting cationic Ir(III) complexes, [Ir(tBuPBI)2(biq)]PF6 (R1) and [Ir(tBuPBI)2(qibi)]PF6 (R2), in which a tert-butyl-functionalized 1,2-diphenyl-1H-benzo[d]imidazole (PBI) unit and conjugated 2,2'-biquinoline (biq) and 2-(1-phenyl-1H-benzo[d]imidazol-2-yl)quinolone (qibi) were employed as cyclometalated and ancillary ligands, respectively. The introduced tert-butyl group led to homogeneous and highly emissive thin films by increasing the solubility and suppressing the strong intermolecular interactions due to steric hindrance. Based on the abovementioned high-quality emissive layer, high-efficiency LECs were achieved. An efficient red-emitting LEC fabricated on a glass substrate achieved a current efficiency (ηC) of 7.18 cd/A and an external quantum efficiency (ηext) of 9.32%. By doping both complexes into a blue-green-emitting cationic Ir(III) complex, high-performance white LECs were also successfully fabricated with Commission International de L'Eclairage (CIE) coordinates of (0.39,0.39), a ηC of 17.43 cd/A, and a ηext of 8.92%. In addition, we also fabricated flexible red and white LECs with outstanding efficiencies and mechanical flexibilities. The ηC and ηext values of a flexible white LEC could be as high as 13.50 cd/A and 6.86%, respectively. The efficiency of the flexible device remained at approximately 95% of the initial value after 500 bends with a radius of curvature of 5 mm, demonstrating the great potential of these complexes for full-color displays and flexible optoelectronics.

Theoretical calculation of selenium N-heterocyclic carbene compounds through DFT studies: Synthesis, characterization and biological potential

N-heterocyclic carbene (NHC) is one of the significant class of compounds in the organometallic chemistry. Strong sigma donating property and weak pi-accepting property of NHC makes it prominent, so that they can interact with metals to form the stable organometallic complex. These ligand compounds have capability to release the metal in the form of ion slowly and sustainable rate at any site in the biological system. Selenium is also very active element having highly demanding applications like antioxidant agent and is necessary trace element for human body. In the current research work two new imidazolium salts (as pre ligands) and respective selenium-NHC compounds have been designed and computed theoretically before the synthesis of active compounds among the designed compounds. Compounds, namely ML1, ML2, MC1 ans MC2, on the basis of imidazole unit were designed and computed for different properties, absorption spectra, dipole moment, theoretically estimated biological potentials, and frontier molecular orbitals, by calculating the HOMO/LUMO energy orbitals via Density functional theory method. Density functional method was applied using Gaussian 09 software and Gauss view 5.0 program. Analysis of compounds were done at B3LYP level by using 6-31G (d) level of DFT (Density Functional Theory). Theoretical calculation showed that compounds are highly biologically active, as their synthesis is exigency of the time so these compounds were synthesized. Synthesized compounds were characterized by UV–visible, FT-IR, carbon and proton NMR spectroscopies. Antioxidant and anticancer properties of compounds were calculated and their charactristics were compared with the charactristics of imidazole present in the literature and results were the almost same as calculated by theoretical method.

Crystalline hydrogen-bonded supramolecular frameworks (HSFs) as new class of proton conductive materials

In attempt to explore new-type crystalline proton conductive materials in the field of fuel cells, three hydrogen-bonded supramolecular frameworks (HSFs), [M2(o-CPhH2IDC)2(H2O)6]·4H2O (M = Co (1) and Zn (2)) (o-CPhH4IDC = 2-(2-carboxylphenyl)-1H-imidazole-4,5-dicarboxylic acid) and [Mn(o-CPhH2IDC)(2,2′-bipy)(H2O)2] (3) (2,2′-bipy = 2,2′-bipyridine) have been carefully designed and elaborated with success. HSFs 1–3 show high water and chemical stability thanks to the adoption of imidazole multi-carboxylate ligand. Meanwhile, the hydrogen bond networks inside the frameworks formed by imidazole unit, carboxylate groups, and crystallized water molecules contribute to the high proton transfer performance. All above HSFs have temperature- and humidity-dependent proton conducting properties. Interestingly, the optimized proton conductivities of 1–3 are 1.78 × 10−4, 1.68 × 10−4 and 0.54 × 10−4 S⋅cm−1 under 98% relative humidity and 100 °C, respectively. Those results are comparable to that of the previously reported crystalline metal-organic frameworks/coordination polymers, covalent organic frameworks, and hydrogen-bonded organic frameworks. This report demonstrates promising application potentials of such crystalline materials in electrochemistry field.

Synthesis and chiroptical properties of organometallic complexes of helicenic N-heterocyclic carbenes.

Novel [4, 6]helicenes (4a,b) bearing a fused imidazolium unit have been prepared from [4, 6]helicene-2,3-di-n-propyl-amines 3a,b. The in situ formation of N-heterocyclic carbene (NHC) derivatives followed by their complexation to iridium(I) or rhodium(I) gave access to complexes 1a, 1'a, and 1b, containing mono-coordinated helicene-NHC, chloro and COD (COD = 1,5-cyclooctadiene) ligands. Ir and Rh complexes 1a and 1'a were characterized by X-ray crystallography. HPLC and NMR analyses showed that Ir(I) complex 1b existed as a mixture of two diastereomeric complexes corresponding to enantiomeric pairs M-(-)/P-(+)-1b1 and M-(-)/P-(+)-1b2 which differ by the position of COD through space. The chiroptical properties (electronic circular dichroism and optical rotation) of the four stereoisomers were measured. These complexes were also tested as catalysts in a transfer hydrogenation reaction.

Copper ion luminescence on/off sensing by a quinoline-appended ruthenium(II)-polypyridyl complex in aqueous media

Abstract An efficient chemosensor RuL based on a quinoline tethered Ru (bpy)22+ derivative is developed for Cu2+ ion detection in pure aqueous medium. Receptor RuL has been characterized using standard spectral studies including UV–visible, fluorescence, ESI-MS and 1H NMR techniques. The crystal structure of RuL is determined by X-ray diffraction studies which revealed that Ru(II) is coordinated to nitrogen atoms of phenanthroline moiety. However N atoms of quinoline and imidazole units are uncoordinated and freely accessible for further functionalization. Changes in photochemical properties of RuL, high selectivity, reversibility by EDTA, excellent detection limit (50.67 nM) and high binding parameters displayed excellent sensing ability for Cu2+ ion. This work illustrates application of a water-soluble receptor in excellent sensing of cupric ion.