Schiff Base Units Research Articles

Organoplatinum Complex Exhibiting Aggregation-Enhanced Emission (AEE) and Dual-Channel Ion-Sensing Properties by Terminating the Molecular Configuration Transformation (MCT) and Excited-State Intramolecular Proton Transfer (ESIPT).

Emitters produce weak emissions when they undergo structural changes such as molecular configuration transformation (MCT) or excited-state intramolecular proton transfer (ESIPT) but give out strong emissions after terminating these distortions. Herein, an organoplatinum complex, Pt-ppy-ABP, carrying a salicylaldehyde-based Schiff base unit is synthesized. It exhibits weak emission in dilute solutions but shows bright emission at the aggregated state or after interacting with F- and Zn2+. This suggests that it has an aggregation-enhanced emission (AEE) property and holds potential in ion detection. Supported by theoretical calculations and femtosecond transient absorption results, this complex suffers excited-state structural changes including MCT from a square-planar configuration to a tetrahedral one, as well as intramolecular rotation of a monodentate ligand and ESIPT, showing weak emission in its solutions. At the aggregated state, it releases strong yellow emissions because of the restraints of MCT and ligand rotation. Upon interacting with F- or Zn2+, it emits bright-red or -green emissions, achieving detection limits of 10-7 M. The sensing mechanism is concluded as deprotonation- and coordination-induced ESIPT terminations, respectively. Given its AEE property and ion-responsive emissions, its application in information encryption is also explored. Finally, these findings should provide valuable clues for the developments of chemosensors with dual-channel recognition abilities.

Preparation of Magnetic Nano-Catalyst Containing Schiff Base Unit and Its Application in the Chemical Fixation of CO2 into Cyclic Carbonates

The development of a catalyst for the conversion of CO2 and epoxides to the corresponding cyclic carbonates is still a very attractive topic. Magnetic nano-catalysts are widely used in various organic reactions due to their magnetic separation and recycling properties. Here, a magnetic nano-catalyst containing a Schiff base unit was designed, synthesized and used as a heterogeneous catalyst to catalyze CO2 and epoxides to form cyclic carbonates without solvents and co-catalysts. The catalyst was characterized using Fourier transform infrared (FTIR), X-ray diffraction (XRD), thermogravimetric (TG), VSM, SEM, TEM and BET. The results show that the magnetic nano-catalyst containing the Schiff base unit has a high activity in the solvent-free cycloaddition reaction of CO2 with epoxide under mild conditions, and is easily separated from the reaction mixture driven by external magnetic force. The recovered catalyst maintains a high performance after five cycles.

Multifunctional Logic Operations Based Upon Congruent Ion Sensing Appended with a Strategic Molecular Device: Spectroscopic Approach

AbstractA multi‐responsive smart molecular system is constructed using a newly synthesized Salen molecule, 1,3‐bis((E)‐2,3,4‐trimethoxy benzylideneamino) propan‐2‐ol (TMBP), to selectively recognize the presence and absence of Cu2+ ions aided by another selective metal ion, Zn2+. The emission efficiency of the non‐emissive probe is selectively and significantly enhanced in presence of Zn2+, while the improved emission of probe‐Zn2+ complex is completely quenched upon interaction with Cu2+. Thus, the probe acts as a reporter molecule for the selective detection of Cu2+ in the co‐presence of Zn2+. Comprehensive spectroscopic studies indicate that Zn2+ ion‐coordination significantly reduces the flexibility of the Schiff base unit and the extent of photoinduced electron transfer which in turn enhance the fluorescence intensity. While Cu2+, a d9 system, induces paramagnetic quenching over the enhanced emission through stable ground‐state complexation and metal‐ligand charge transfer. The spectroscopic results are translated into the designing of a multifunctional smart‐molecular system that could function as YES, NOT, INHIBIT, PASS 0, TRANSFER and NOT TRANSFER logic gates. Finally, a blueprint of a smart molecular device is proposed to present the relay sensing of Zn2+ and Cu2+ through logical outputs that would work in‐sync with the spectroscopic results.

AIE gels based on Schiff base with stimuli-responsive fluorescence switching behaviors as chemosensors

Based on Schiff base unit with/without a perfluoroalkyl group, novel multi-functional compounds 1 and 2 were proven to be able to form gels with different solvents. The difference in the molecular structure of compounds 1 and 2 was the presence of a perfluoroalkyl chain. The self-assembly pattern was studied by the employment of rheological analysis, UV–vis absorption, fluorescence spectrum, field emission scanning electron microscopy (FESEM), fourier transforms infrared (FTIR) spectra, and X-ray powder diffraction (XRD). The gelation behaviors showed a sensitive and selective “turn-off” fluorescence response with Cu2+. Due to the protonation or deprotonation of compounds 1 and 2 with trifluoroacetic acid (TFA) or triethylamine (TEA), the xerogel films which were prepared from DMSO:H2O (9:1, v/v) at 5 wt% presented the emission quenching and recovery upon TFA and TEA vapors. In this sense, the work will open up a novel pathway to detect Cu2+, TFA, and TEA in the environment, using stimuli-responsive fluorescent materials with aggregation-induced emission (AIE) effect.

The interactive effect between the oxazole-containing optical switch nucleus and carbazole-containing salicylidene Schiff base: Enhancing photoreactivity and tuning the ion sensing property

A functionalized diarylethene derivative consisting of an oxazole-containing optical switch nucleus and an appending carbazole-containing Schiff base unit was synthesized. The interactive effect of optical switch nucleus and carbazole-containing Schiff base was studied. Introducing a suitable receptor into diarylethene nucleus not only provided a useful strategy for controlling the photoreactivity, but also constructed an effective approach to tuning the ion sensing property. Specifically, appending a carbazole-containing Schiff base moiety to the oxazole-containing optical switch nucleus, the molar absorption coefficient, and the cyclization quantum yield was obviously enhanced. Adding the oxazole-containing optical switch nucleus to the carbazole-containing Schiff base, discrimination of Fe3+ and Cu2+ without any auxiliary reagent was achieved. This study provides a novel design strategy not only for modulating the photoreactivity, but also for the development of optical sensor for discrimination of Fe3+ and Cu2+ ions.

Fire Retardancy and Dielectric Strength of Cyclotriphosphazene Compounds with Schiff Base and Ester Linking Units Attached to the Electron-Withdrawing Side Arm.

A series of compounds with Schiff base and ester linking units attached to the electron-withdrawing side arm (Cl, NO2, and OH) have been successfully synthesized through four schemes of the chemical route. These compounds were characterized using Fourier Transform Infrared spectroscopy (FTIR), Nuclear Magnetic Resonance spectroscopy (NMR), and Carbon, Hydrogen and Nitrogen (CHN) elemental analysis. The epoxy resin was used as a matrix of molding to observe the refinement of fire-retardant properties of the modified cyclotriphosphazene compounds. The fire-retardant testing was done using Limiting Oxygen Index (LOI). The LOI value of pure epoxy resin was increased from 22.75% to 24.71% when incorporated with 1 wt.% of hexasubstituted cyclotriphosphazene (HCCP). Interestingly, all the final compounds gave a positive increment in the LOI value and the highest LOI value was obtained from the compound containing a nitro side arm with LOI value of 26.90%. In order to understand the thermal stability of these compounds, Thermogravimetric Analysis (TGA) was carried out. The compound with the nitro group at the terminal end has the highest char residue which is 34.2% at 700 °C. This indicated that the presence of the nitro withdrawing group was able to enhance the fire retardancy of the materials. Based on SEM observation, the shape of the final compound’s char residue demonstrated the formation of a porous protective layer with a dense surface. The dielectric property was conducted according to ASTM D149 AC breakdown voltage to determine its dielectric strength. The results showed that the highest dielectric strength value belonged to the compound containing a nitro group side arm with 24.41 kV/mm−1 due to the π electron delocalization.

Utilizing Organic Aromatic Melamine Moiety to Modify Poly(Vinyl Chloride) Chemical Structure and Micro CuO That Plays an Important Role to Enhance Its Photophysical Features

Three arms Schiff base unit based on melamine moiety was synthesized and introduced to polyvinyl chloride (PVC) to produce a modified PVC polymer. The polymer composite of new modified PVC polymer was blended with micro copper oxide as a reflecting mirror of UV light to enhance the photostability of PVC. Three different concentrations of micro copper oxide (0.01–0.03 wt.%) were mixed with the modified PVC and cast as a thin film. The photostability test has shown high resistance to photodegradation upon exposure to UV light. In this work, different approaches were applied to examining doped modified PVC's thin film efficiency against photodegradation after exposure to UV light for 300 h in an ambient atmosphere. The exhibited studies, such as infrared spectroscopy and weight loss percentage, have demonstrated the improvement of photophysical properties for modified PVC and blended modified films in comparison to blank PVC polymeric films. These outcomes are so interesting as they could contribute to reducing the consumption of PVC around the world hence its waste causing huge environmental problems for the marine ecosystem.

Synthesis, characterization, crystal structure and mesomorphic behavior of thiophene based homologous series

ABSTRACT Through condensation of 4-n-alkoxybenzaldehyde (n = 2 to 8, 10, 12, 14, 16, 18) with (E)-1-(4-aminophenyl)-3-(thiophen-2-yl)prop-2-en-1-one, new homologous series of rod shaped calamite liquid crystals that merge Schiff base, chalcone and thiophene units have been prepared. All synthesized compounds were characterized by FT-IR, 1H-NMR and 13C-NMR spectroscopy. The liquid crystalline properties of the synthesized compounds were investigated using a polarizing optical microscope (POM) and differential scanning calorimetry (DSC). The results indicate that n-heptyloxy (A7) to n-tetradecyloxy (A14) derivatives exhibited monotropic nematic phase while the remaining derivatives of homologous series are non mesomorphic. The n-ethoxy derivative (A2) crystallizes under monoclinic, space group P21/c with unit cell dimension a = 19.343(4) Å, b = 5.8353(9) Å, c = 16.574(4) Å, β = 98.78(2) °, V = 1848.8(7) Å3. The dihedral angle between two phenyl rings of imine linkage in compound A2 is 51.64 (2) °.

Binding Properties of a Dinuclear Zinc(II) Salen-Type Molecular Tweezer with a Flexible Spacer in the Formation of Lewis Acid-Base Adducts with Diamines

In this paper we report the binding properties, by combined 1H NMR, optical absorption, and fluorescence studies, of a molecular tweezer composed of two Zn(salen)-type Schiff-base units connected by a flexible spacer, towards a series of ditopic diamines having a strong Lewis basicity, with different chain length and rigidity. Except for the 1,2-diaminoethane, in all other cases the formation of stable 1:1 Lewis acid-base adducts with large binding constants is demonstrated. For α,ω-aliphatic diamines, binding constants progressively increase with the increasing length of the alkyl chain, thanks to the flexible nature of the spacer and the parallel decreased conformational strain upon binding. Stable adducts are also found even for short diamines with rigid molecular structures. Given their preorganized structure, these latter species are not subjected to loss of degrees of freedom. The binding characteristics of the tweezer have been exploited for the colorimetric and fluorometric selective and sensitive detection of piperazine.

Synthesis, Characterisation and Mesophase Transition of Hexasubstituted Cyclotriphosphazene Molecules with Schiff Base and Azo Linking Units and Determination of Their Fire Retardant Properties

Hexakis(oxy-4-benzaldehyde)cyclotriphosphazene, 1 was successfully synthesised by nucleophilic substitution reaction between hexachlorocyclotriphosphazene, HCCP and 4-hydroxybenzaldehyde. Azotization reaction of p-nitroaniline with phenol formed 4-(4-nitrophenylazo)phenol, 2 which was alkykated with heptyl, nonyl, decyl, dodecyl and tetradecylbromide to give a series of nitro compounds, 3a-e. Reduction of 3a-e and 2 formed the subsequent amine compounds 4a-f, 4-(4-alkyloxyphenylazo)phenylamine. Another similar reaction of protected aniline with a series of substituted aniline formed a series of compounds 4g-i. A series of hexasubstituted cyclotriphosphazene molecules containing Schiff base and azo linking units, 5a-i were synthesised from the reaction between intermediates 1 and 4a-i. Further reduction of compound 5i afford compound 5j with amino terminal end. All the synthesised intermediates and compounds were characterised using Fourier Transform Infrared spectroscopy (FT-IR), 1H and 13C Nuclear Magnetic Resonance spectroscopy (NMR) and CHN elemental analysis. The liquid crystal properties of intermediates and final compounds were determined using Polarised Optical Microscope (POM) and their phase transitions confirmed using Differential Scanning Calorimetry (DSC). Only intermediates 3a-e showed mesophase of smectic A and compounds 5a-e with alkoxy chain were mesogenic with smectic A and nematic phases. In addition, compound 5h exhibited nematic phase only. However, all the other intermediates and compounds were found to be non-mesogenic. Furthermore, the fire retardant of final compounds were determined using Limiting Oxygen Index (LOI) testing. The LOI value of pure polyester resin was increased from 22.53 to 24.71% when incorporated with 1 wt% of HCCP. Moreover, all the final compounds showed a positive in LOI value the highest LOI value was belonged to compound 5i with 27.90%.

A highly selective sequential recognition probe for Zn2+ and HSO4-/H2PO4- based on a diarylethene chemosensor.

A novel diarylethene derivative chemosensor DTP-o connected to Schiff base unit for fluorescent detection of Zn2+ and relay-detection of HSO4-/H2PO4- was designed and synthesized successfully. DTP-o displayed excellent photochromism and fluorometric sensing toward Zn2+ to form DTP-o-Zn2+ complex in acetonitrile with the detection limit of 5.62×10-7M. And the form of DTP-o combined with Zn2+ could further be verified by Job's plot titrations and mass spectrometry analysis. Furthermore, the complex of DTP-o-Zn2+ showed an excellent characteristic of fluorescent relay-response toward HSO4- and H2PO4- with high sensitivity and selectivity. The detection limits for HSO4- and H2PO4- were as low as 3.04×10-8M and 3.41×10-8M, respectively. Moreover, the sensor DTP-o could also be applied to detect Zn2+ on practical samples and test strips with high accuracy.

Biobased epoxy vitrimer from epoxidized soybean oil for reprocessable and recyclable carbon fiber reinforced composite

Traditional carbon fiber reinforced epoxy thermosets composites are nonrenewable and cannot be reprocessed or recycled due to the permanent crosslinked structure of the thermosets, causing resource crisis, environmental pollution, and resource waste. Herein, a biobased epoxy vitrimer (ESO-VA) with dynamic Schiff base groups was synthesized from epoxidized soybean oil (ESO), vanillin, and 4-aminophenol. The biobased epoxy vitrimer showed excellent malleability, recyclability, and mechanical properties, making it suitable as matrix to fabricate carbon fiber (CF) reinforced composites. The CF fabric reinforced ESO-VA composites showed superior mechanical strength and modulus over ESO-VA. The composites can be recycled through different approaches, owning to the dynamic Schiff base unit. The valued CF fabric can be recycled without changing structure and properties by deconstruction network structure of ESO-VA as a result of dissociation of Schiff base bond under acidic condition. The composites after crushing could be recycled thermally into short carbon fiber filled composite products through traditional processing techniques such as compression molding. We believe that this study provides a strategy to design recyclable carbon fiber reinforced biobased epoxy composites.

Synthesis and Characterization of Linear Thermally Stable polyester contain Schiff Bases

A copolymers are important compounds today because of their wide applications in various industrial and medical fields and in other fields. Therefore, the study of preparing many of these polymers has been studied. This research involved preparing linear polyester contain Schiff-base unit by interfacial polycondensation three type diacid chloride (Succinoyl Chloride, Adipoyl Chloride and sebacoyl Chloride) in a chloroform /water system employing phase transfer catalyst with monomer containing two hydroxyl which is derived from a 4-hydroxy aniline reacted with a 4-hydroxy benzaldehyde monomer. The monomer (EM1) and polyester (EM2, EM3, and EM4) were characterized by FTIR, 1H NMR, 13C NMR and TGA analysis. The polyester–Schiff base so obtained show good thermal stability.

An efficient water-soluble fluorescent chemosensor based on furan Schiff base functionalized PEG for the sensitive detection of Al3+ in pure aqueous solution

An efficient reversible fluorescent chemosensor, PEGFB, based on polyethylene glycol bearing a furan Schiff base unit has been successfully developed to sensitively detect Al3+ in pure aqueous solution.

Carbinol mediated clusterization of Nickel(II) ions in a Schiff base backbone: Structural & solution properties, phosphoester cleavage activity including theoretical support

In this study, the significant role of carbinol in the construction of a tetranickel(II) cluster, [Ni4II(μ-OHCH3)2(L)2(CH3OH)2]·2CH3OH (1) with a compartmental Schiff base, [H3L = N,N′-bis(3-methoxysalicylidene)-1,3-diamino-2-propanol] is reported and emphasized. The tetranickel cluster crystallizes in a monoclinic system with P21/n space group. The tetranickel(II) core exists in a dicubane structure adopting octahedral geometry for each nickel(II) centres. In forming tetrametallic core, carbinol as solvent molecules exhibit its uniqueness through versatile coordination motifs (bridging-, terminal- and solvent of crystallization) in assembling four nickel(II) ion with two Schiff base units. Hirshfeld analysis for 1 defines pivotal role of MeOH in construction of long range crystalline architecture. Examination of its ability towards cleavage of phosphoesterase bonds using 4-nitrophenylphosphate (PNPP) in carbinol authenticates its excellent cleavage efficiency with rate constant 1.61 × 10−4 min−1. Presence of coordinated methanol molecules at Ni(II) centre as well as multiple reaction centres in tetra-nickel(II) core remain the driving force for the phosphatase activity. Outcomes from extensive density functional theory (DFT) justify well the experimental observations.

Self-healing conductive hydrogels based on alginate, gelatin and polypyrrole serve as a repairable circuit and a mechanical sensor.

Conductive materials including graphene, metal and conjugated polymers, combined with self-healing hydrogels are attracting increasing attention in biosensors and bioelectrodes. In this work, we propose one self-healing conductive hydrogel with good morphology and performance based on an alginate-gelatin network and polypyrrole (Ppy) via low-temperature fabrication. The alginate/gelatin network consists of extensive reversible Schiff base units that can act as dynamic crosslinking agents to self-heal the hydrogel. Ppy as one conductive polymer provides the hydrogel with conductivity and good mechanical properties. To demonstrate the applications, we insert the hydrogel into a disconnected circuit to repair or act as one component to light up bulbs. In addition, the conductive hydrogel possesses mechanical responses towards bending or compression, thus it can monitor hand movements and paves the way to a flexible, mechanical sensor. This work proposes a facile method to fabricate one novel self-healing conductive hydrogel and demonstrates its applications in repairable circuits and mechanical sensors that may have potential prospects in circuit repair materials, biocompatible/medical devices, and flexible sensors.

A highly selective fluorescent probe for Cu2+ based on a diarylethene with a benzo[1,2,5]oxadiazol-4-ylamine Schiff base unit

A new photochromic diarylethene derivative with a benzo[1,2,5]oxadiazol-4-ylamine Schiff base unit was synthesized and its photochromic and fluorescent properties were systematically investigated in detail by the stimulation of light, metal ions, acid, and base in acetonitrile. Especially, upon addition of Cu2+, its emission peak was blue-shifted by 56 nm and the emission intensity was obviously enhanced by 90 fold, accompanied by the fluorescent color changed from dark red to bright red. And when HCl (0.1 mol L−1) was added into, on the vision, the change of the solution color could be easily seen from yellow to purple. As a result, the diarylethene derivative can sever as a highly selective fluorescent sensor for recognition of Cu2+. Furthermore, the photochromic and fluorescence behavior of the diarylethene derivative to Cu2+ and acid could be applied to the design of molecular logic circuit. More importantly, the diarylethene derivative also can be applied to detect Cu2+ in natural water samples with high accuracy.

Cyan-Blue Luminescence and Antiferromagnetic Coupling of CN-Bridged Tetranuclear Complex Based on Manganese(III) Schiff Base and Hexacyanoferrate(III)

A new tetranuclear cyanide-bridged MnIII–FeIII complex based on manganese(III) Schiff base and hexacyanoferrate(III) units, [Mn(L)(MeOH)2][{Mn(L)}{Fe(CN)6}{Mn(L)(MeOH)}].2MeOH, [H2L = N,N′-bis(2-hydroxy-1-naphthalidenato)-1,2-diaminopropane] (1), has been synthesized and characterized by elemental analysis, UV–Vis, FT-IR, PXRD, single crystal X-ray analyses, magnetic and photoluminescence measurements. Complex 1 consist of one trinuclear cyanido-bridged anion, in which [Fe(CN)6]3− anion bridge [Mn(L)]+ and Mn(L)(MeOH)}]+ cations via two C≡N groups in the cis positions, and also one isolated manganese [Mn(L)(MeOH)2]+ cation. DC magnetic susceptibility and magnetization studies showed that complex 1 indicates an antiferromagnetic coupling between low-spin Fe(III) and high-spin Mn(III) through the cyanide bridges. In addition, the complex 1 displays a strong cyan-blue luminescence emission in the solid state condition at room temperature. This behavior might be seen easily from the chromaticity diagram. Thus, the complex may be a good promising cyan-blue OLED developing electroluminescent materials for flatted or curved panel display applications due to the fact that it has such features.

A new diarylethene-derived probe for colorimetric sensing of Cu(II) and fluorometric sensing of Cu(II) and Zn(II): Photochromism and High Selectivity

A novel photochromic diarylethene derivative containing a 2-(methylthio)benzenamine Schiff base (1O) unit was synthesized and its selective fluorometric/colorimetric sensing of multiple metal ions in methanol was demonstrated. The addition of Cu2+ enhanced the absorption of 1O up to 44 folds with the concomitant color change from colorless to yellow, which could be easily observed by the naked eye. In addition, 1O exhibited selective fluorescence responses to Cu2+ and Zn2+ with different fluorescence signals. Cu2+ quenched the fluorescence of 1O up to 98%, while Zn2+ enhanced the fluorescence of 1O by 53.8 folds, accompanied by the fluorescence color changes from light red to dark and bright yellow, respectively. Both coordination stoichiometries between 1O and Cu2+, and 1O and Zn2+ were determined to be 1:1. In all, diarylethene 1O can be potentially used as a chemosensor of both Cu2+ and Zn2+.

Design and synthesis of indole triazole pendant siloxy framework as a chemo sensor for sensing of Cu2+ and Ni2+: A comparison between traditional and microwave method

A triazole tethered chemo sensor molecules with the capability of sensing cations have been synthesized by coupling two sensor based alkynyl indole schiff base unit to azide. The hybrid networks were able to donate electron via azomethine linkage, traizole ring and indole motif to bind copper and nickel effectively. Such indole based hybrids would have potential applications in biological systems. Indole traizoles (In-Tz) were synthesized under microwave irradiation with auto generated pressure (at 60 °C) and characterized by 1H NMR, 13C NMR, Mass and FTIR spectroscopy, thin-layer chromatography (TLC) and elemental analyses. The fabricated sensor exhibited higher sensitivity, large-dynamic concentration ranges and long term stability towards In-Tz conjugated copper and nickel complex for selective Cu2+and Ni2+sensor. The calibration plot is linear (r2: 0.9895, r2: 0.9808) over the large Cu2+ ions and Ni2+concentration ranges (1.0 µM). This novel effort has initiated a well-organize way of efficient cationic sensor improvement with triazole for heavy metallic pollutants in environmental and health-care fields in large scales.