Aromatic Schiff Bases Research Articles

The keto→enol photoisomerization of N‐salicilydenemethylfurylamine: Nonadiabatic ab initio dynamics simulation

AbstractThe photoinduced isomerization of cis‐keto and trans‐keto isomers in N‐salicilydenemethylfurylamine has been studied using the surface‐hopping approach at the CASSCF level of theory. After the cis‐keto or trans‐keto isomer is excited to S1 state, the molecule initially moves to a excited‐state local minimum. The torsional motion around relative bonds in the chain drives the molecule to approach a keto‐form conical intersection and then nonadiabatic transition occurs. According to our full‐dimensional dynamics simulations, the trans‐keto and enol photoproducts are responsible for the photochromic effect of cis‐keto isomer excited to S1 state, while no enol isomer was obtained in the photoisomerization of trans keto on excitation. The cis keto to enol and cis keto to trans keto isomerizations are reversible photochemical reactions. It is confirmed that this aromatic Schiff base is a potential molecular switch. Furthermore, the torsion of CN bond occurs in the radiationless decay of trans‐keto isomer, while it is completely suppressed by an intramolecular hydrogen bonding interaction in the dynamics of cis‐keto form. Moreover, the excited‐state lifetime of cis keto is longer than that of trans‐keto form due to the O···HN hydrogen bond.

SYNTHESIS, SPECTROSCOPIC INVESTIGATION AND CATALYTIC STUDIES OF NICKEL(II) AROMATIC AZOMETHINE COMPLEXES

Coupling reaction between aryl halide and terminal alkyne in Sonogashira coupling reaction is important due to its extensive application in the resynthesis of natural products, production of drugs, dyes, and polymers. Efforts to increase rate of reaction has involved exploration of new catalysts. The current catalysts such as phosphine-based complexes are costly, air-sensitive and environmentally harmful. Nickel(II) Schiff base complexes were synthesized by reacting aromatic Schiff base ligands 2,2'-((1E,1'E)-(1,2-phenylenebis(azanylylidene))bis(metha-nylylidene))diphenol (L1H), 2,2'-((1E,1'E)-(1,2-phenylenebis(azanylylidene))bis(methanylylidene))bis(4-fluorophenol) (L1F), and 2,2'-((1E,1'E)-(1,2-phenylenebis(azanylylidene))bis-(methanylylidene))bis(4-methylphenol) (L1M) with nickel(II) acetate tetrahydrate to form NiL1H, NiL1F and NiL1M. The chemical structures were elucidated through physicochemical and spectral techniques namely elemental analysis, melting point, FTIR, 1H and 13C NMR, magnetic susceptibility and molar conductivity. All nickel(II) complexes were tested as catalysts in homogenous Sonogashira reaction between iodobenzene and phenylacetylene in DMSO for 12 hours at 140 oC. NiLF, a new nickel(II) complex, converted the highest percentage of iodobenzene (91%) while NiLH and NiLC converted 78% and 83% of iodobenzene, respectively.

Studies on Synthesis of Aromatic Schiff Bases. Part-VI. Synthesis, Characterization and Biological Activity of Ketimines from 5-Chloro-2-hydroxy-4-methyl-acetophenone with substituted anilines

Studies on Synthesis of Aromatic Schiff Bases. Part-VI. Synthesis, Characterization and Biological Activity of Ketimines from 5-Chloro-2-hydroxy-4-methyl-acetophenone with substituted anilines

Studies on Synthesis of Aromatic Schiff Bases. Part-V. Evaluation of Antifungal Potential of Ketimines from 5-Chloro-2-hydroxy-4-methyl-acetophenone†

Studies on Synthesis of Aromatic Schiff Bases. Part-V. Evaluation of Antifungal Potential of Ketimines from 5-Chloro-2-hydroxy-4-methyl-acetophenone†

New application for aromatic Schiff base: High efficient flame-retardant and anti-dripping action for polyesters

Bonding aryl groups with carbon-nitrogen double bond is a critical structural factor for the self-crosslinking of Schiff bases at high temperature. In this study, a novel aromatic Schiff base “5-(benzylidene-amino)-isophthalic acid dimethyl ester (BA)” has been designed as a self-crosslinking monomer for poly(ethylene terephthalate) (PET) based copolyesters (BAnPETs). The cross-linking behaviors, flame retardancy and non-dripping performance of BAnPETs have been investigated by simultaneous thermal analysis (TG-DSC), dynamic rheology, limiting oxygen index (LOI), UL-94 vertical burning and cone calorimetry tests. It is found that BA units can cross-link during combustion resulting in high melting viscosity and enhance char forming for BAnPETs, which endows the copolyesters with excellent flame retardancy and non-dripping behavior. Incorporating of BA with a low content (only 7.7 mol%), the LOI value of copolyester increases from 22.0% to 31.0%, and at the same time it achieves V-0 rating in the UL-94 vertical burning test. The mode action of Schiff bases on flame retardation and anti-dripping of copolyesters also has been investigated, and the results show that the aromatic Schiff base groups can lead copolyesters to form nitrogen-containing cross-linkable networks and further transform into compact char layer during combustion. The char layer which acts as an effective barrier, cuts off oxygen, hinders the volatilization of combustible gas and isolates unburned polymer from fire resource. This work suggests that using Schiff base as a self-crosslinkable monomer is a new and effective way for fire-safe polymeric materials.

Nonadiabatic dynamics simulation of photoisomerization mechanism of the second stablest isomer of N-salicilydenemethylfurylamine

The photoisomerization processes of the second stablest isomer in the aromatic Schiff base, N-salicilydenemethylfurylamine, in the gas phase have been studied by static electronic structure calculations and surface-hopping dynamics simulations based on the Zhu-Nakamura theory. Various stable structures are obtained in the optimization because of different orientations of methyl-furyl part with respect to the salicylaldimine part and different orientations of hydroxy group with respect to the benzene ring. Upon photoexcitation into the first excited state, bond isomerization in the salicylaldimine part is completely suppressed until the strong excited-state hydrogen bond is broken. The decay pathway involves two excited-state minima, one in cis-enol form and the other in cis-keto form. After the excited-state proton transfer, twists of bonds lead to a conical intersection between the ground and excited states. After internal conversion around a conical intersection, the molecule is stabilized in cis- or trans-keto form. If the reverse hydrogen transfer process occurs in the ground state, the molecule will finally end up in the cis-enol region. The cis-keto and trans-keto isomers are observed as photoproducts. According to our full-dimensional nonadiabatic dynamics simulations, we find the excited-state intramolecular proton transfer and torsions of three single bonds in the chain to be responsible for photoisomerization of the second stablest isomer of N-salicilydenemethylfurylamine.

Fusion of Ultraviolet-Visible and Infrared Transient Absorption Spectroscopy Data to Model Ultrafast Photoisomerization.

Ultrafast photoisomerization reactions generally start at a higher excited state with excess of internal vibrational energy and occur via conical intersections. This leads to ultrafast dynamics which are difficult to investigate with a single transient absorption spectroscopy technique, be it in the ultraviolet-visible (UV-vis) or infrared (IR) domain. On one hand, the information available in the UV-vis domain is limited as only slight spectral changes are observed for different isomers. On the other hand, the interpretation of vibrational spectra is strongly hindered by intramolecular relaxation and vibrational cooling. These limitations can be circumvented by fusing UV-vis and IR transient absorption spectroscopy data in a multiset multivariate curve resolution analysis. We apply this approach to describe the spectrodynamics of the ultrafast cis-trans photoisomerization around the C-N double bond observed for aromatic Schiff bases. Twisted intermediate states could be elucidated, and isomerization was shown to occur through a continuous complete rotation. More broadly, data fusion can be used to rationalize a vast range of ultrafast photoisomerization processes of interest in photochemistry.

Liquid crystal dimers having vary oxyethylene flexible spacers

ABSTRACTIn this article, we are prepared that the liquid crystal dimers have aromatic-ester type mesogenic units or aromatic-Schiff base type mesogonic units and confirmed by 1H-NMR spectrometry. The mesomorphic and optical properties of the resultant dimers were studied by differential scanning calorimetry and polarizing optical microscopy.

Novel columnar liquid crystalline oligomers: Triphenylene tetramers with rigid aromatic Schiff-bases and hydrogen-bonding spacers via click chemistry

Three novel triphenylene tetramers with triazole bridges, rigid aromatic Schiff-bases and hydrogen-bonding spacers were designed and synthesized in yield of 73–78%. Their structures were confirmed by IR, NMR and MS. Their mesomorphic properties were studied by polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction. These novel triphenylene tetramers possessed the hexagonal columnar mesophase and exhibited excellent mesomorphic properties with melting points at 30–60°C, which was first observed near room temperature for triphenylene tetramers. This study suggested that the mesomorphic properties of triphenylene oligomers could be tuned conveniently by the structures of spacers.

A DFT based analysis of adsorption of Hg2+ ion on chitosan monomer and its citralidene and salicylidene derivatives: Prior to the removal of Hg toxicity

A Density functional theory based study of adsorption of the toxic metal Hg (II) ion by chitosan monomer and two of its derivatives; citralidene and salicylidene chitosan, has been performed. The effect of structural features on the stability of studied complexes has been analyzed by using Gaussian03 software package. All the possible conformations of these adsorbents were studied using the global minimum geometries. All the adsorbing sites were studied by placing the metal ion on the centroid of the atoms and the stable conformer of the adsorbent-metal ion complex was identified. Interaction between Hg (II) and the adsorbents is found to be electrostatic. Metal ion binding with nitrogen atom is stronger than that with oxygen atoms in all the cases as the charge density of nitrogen is enhanced on Schiff base formation. The advantage of derivatives over chitosan monomer is their stability in acidic media. ΔE value of the complexes are in the order SC–Hg (II)>chitosan–Hg (II)>CC–Hg (II) which indicates that the stability of complexes increases with increase in energy gap. The study reveals that aromatic Schiff base derivatives of chitosan is better for Hg(II) intake than aliphatic derivatives.

Synthesis, characterization and antimicrobial evaluation of two aromatic chitosan Schiff base derivatives

Recently, there have been significant scientific interests to scientists for the chemical modifications of chitosan to increase its applications. The main objective of this study was to prepare two aromatic chitosan Schiff bases (I and II) via coupling with 4-chloro benzaldehyde and benzophenone respectively for improvement the antimicrobial property of chitosan. The chemical structures of the prepared Schiff bases verified through FT-IR, TGA and DSC. However, degrees of substitution were estimated using potentiometric analysis, and they were 7.9% and 4.17% for Schiff bases (I and II) respectively. Antimicrobial activities evaluation were conducted against three Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa and Salmonella sp.), two Gram-positive bacteria (Staphylococcus aureus and Bacillus cereus) and Candida albicans strain. The antimicrobial activities of the new derivatives increased significantly more than chitosan in most microorganisms. The minimum inhibitory concentration (MIC) of Schiff base (I) with concentration (50μg/ml) exhibited the highest activity against C. Albicans with growth inhibition up to 27.42%. While, 50μg/ml of Schiff base (II) showed high activity against E. coli, Salmonella sp., S. aeureus and B. cereus more than chitosan. The results clearly suggested that the new Schiff bases could be applied as antimicrobial wound dressing agents to ameliorate wound healing.

The preparation of a new type of ferrocene-based compounds with large conjugated system containing symmetrical aromatic vinyl with Schiff base moieties and the study of their third-order nonlinear optical properties

Herein we reported the preparation of a new type of ferrocene-based compounds with large conjugated system containing symmetrical aromatic vinyl and Schiff base moieties and the study of their third-order nonlinear optical (NLO) properties. Their third-order NLO properties were measured using femtosecond laser and degenerate four-wave mixing (DFWM) technique. The obtained χ(3), n2 and γ values of these molecules were found in the range of 0.998–1.429×10−12esu,1.847–2.646×10−11esu and 1.026–1.449×10−30esu, respectively. The response time ranged from 43.65fs to 61.71fs. The results indicate that these compounds have potential nonlinear optical applications.

Aromatic Schiff Bases Multiply Substituted with Terminal Ethynyl Groups: Potential Building Blocks for Conjugated Polymers and Oligomers

Nine mostly novel aromatic Schiff bases containing from two-to-four terminal ethynyl groups and one or two methanimine groups per one molecule are reported. The spectral and density functional theory characteristics and the extent of conjugation are discussed in connection with the structure and architecture of the prepared compounds. The applicability of compounds as building blocks for conjugated polymers is shown in TaCl5-catalyzed polycyclotrimerization (proceeding in ethynyl groups) yielding either soluble luminescent or insoluble microporous polymers.

Catalyst-free dynamic exchange of aromatic Schiff base bonds and its application to self-healing and remolding of crosslinked polymers

Crosslinked polyacrylate is self-healed and reprocessed through rearrangement of networks based on catalyst-free dynamic exchange of aromatic Schiff base bonds.

Oligomeric-Schiff bases as negative electrodes for sodium ion batteries: unveiling the nature of their active redox centers

Novel hybrids between carboxylate and aromatic Schiff base show reversible sodium insertion below 1.2 V vs. Na+. Identifying the redox active units leads to sustainable and low cost anode materials beyond 250 mA h g−1.

Design, synthesis, and biological activities of aromatic gossypol Schiff base derivatives.

A series of aromatic gossypol Schiff bases have been successfully synthesized via a feasible chemical modification. The antiviral activity against tobacco mosaic virus (TMV) of these gossypol Schiff bases has been tested for the first time. The bioassay studies indicated most of these derivatives exhibited excellent anti-TMV activity, in which o-trifluoromethylaniline Schiff base (19) displayed the best antiviral activities. Furthermore, compound 19 exhibited an eminent anti-TMV effect in the field and low toxicity to mice. These results suggest it is a promising candidate for the inhibitor of plant virus.

Photoswitching of salicylidene methylamine: a theoretical photodynamics study.

Photoswitching of simple photochromic molecules attracts substantial attention because of its possible role in future photon-driven molecular electronics. Here we model the full photoswitching cycle of a minimal photochromic Schiff base–salicylidene methylamine (SMA). We perform semiempirical nonadiabatic on-the-fly photodynamics simulations at the OM2/MRCI level and thoroughly analyze the structural time evolution and switching efficiency of the system. We also identify and examine in detail the crucial steps in the SMA photochemistry ruled by excited-state intramolecular proton transfer. The results place the investigated model aromatic Schiff base among the promising candidates for novel photoswitching molecular materials. Our study also shows the potential of the semiempirical multireference photodynamics simulations as a tool for early stage molecular photodevice design.

4-Fluoro-N-(4-hy-droxy-benzyl-idene)aniline.

In the title compound, C13H10FNO, the benzene ring planes are inclined at an angle of 50.52 (8)°. A characteristic of aromatic Schiff bases with N-aryl substituents is that the terminal phenyl rings are twisted relative to the plane of the HC=N link between them. In this case, the HC=N unit makes dihedral angles of 10.6 (2) and 40.5 (2)° with the hy­droxy­benzene and fluro­benzene rings, respectively. In the crystal, O—H⋯N and C—H⋯F hydrogen bonds lead to the formation of chains along the c- and b-axis directions, respectively. C—H⋯π contacts link mol­ecules along a and these contacts combine to generate a three-dimensional network with mol­ecules stacked along the b-axis direction.

(E)-4-Chloro-2-{[4-(di-methyl-amino)-benzyl-idene]amino}-phenol.

In the title aromatic Schiff base compound, C15H15ClN2O, the mol­ecule exists in a trans conformation with respect to the C=N bond. The dihedral angle between the benzene rings is 14.49 (6)°. In the crystal, weak C—H⋯π inter­actions link mol­ecules into supra­molecular chains propagated along the a-axis direction.

Reaction of 2-chloro-1,3,2-benzodioxaphosphinin-4-one with 2-(arylmethylideneamino)phenols. Stereoselective formation of 10-aryl-3,4 : 8,9-dibenzo-5,7-dioxa-1-aza-6-phosphabicyclo[4.3.1]decane-2,6-diones

Cyclic mixed anhydrides derived from hydroxy carboxylic and phosphorous acids (2-R-1,3,2-benzodioxaphosphinin-4-ones or “salicyl phosphites”) contain a highly reactive macroergic POC(O) moiety and are convenient intermediate products for regioand stereoselective syntheses of various phosphorus-containing heterocyclic (including bridged polycyclic) systems which are difficult to obtain by other methods [1–4]. We previously reported on stereoselective synthesis of a 1,4,2-benzoxazaphosphepine derivative via intramolecular expansion of the six-membered ring in salicyl phosphite possessing a 2-(benzylideneamino)ethoxy group [5]. In the present communication we describe intramolecular cyclization processes in the system 2-chloro-1,3,2-benzodioxaphosphinin-4-one (I)–2-(arylmethylideneamino)phenol II in the absence of a base. Taking into account lower nucleophilicity of the nitrogen atom in aromatic Schiff bases and conformational rigidity of the aromatic ring, which should not favor intramolecular cyclization, we believed that the imine fragment in initially formed phosphite III (THF, 20°C) may act as a base. However, we failed to