Aromatic Schiff Bases Research Articles

Photophysics of a Schiff base: theoretical exploration of the excited-state deactivation mechanisms of N-salicilydenemethylfurylamine (SMFA)

Excited state reaction coordinates and the consequent energy profiles of a new Schiff base, N-salicilydenemethylfurylamine (SMFA), have been investigated with the CC2 method, which is a simplified version of singles-and-doubles coupled cluster theory. The potential energy profiles of the ground and the lowest excited singlet state are calculated. In contrast to the ground state, the excited state potential energy profile shows a barrier-less dissociation pattern along the O-H stretching coordinate which verifies the proton transfer reaction at the S1 (ππ*) state. The calculations indicate two S1/S0 conical intersections (CIs) which provide non-adiabatic gates for radiation-less decay to the ground state. At the CIs, two barrier-free reaction coordinates direct the excited system to the ground state of enol-type minimum. According to calculation results, a trans-keto type structure obtained from photoexcitation of the enol, can be responsible for the photochromoic effect of SMFA. Furthermore, our results confirm the suggestion that aromatic Schiff bases are potential candidates for optically driven molecular switches.

Synthesis, Spectroscopic and Biological Activities of Aromatic Schiff Base

In this paper the preparation of 5-[(2-aminoph enyl)imino]-3,3-dimethylcyclohexanone and 5-[(4-aminophenyl)imino]-3,3-dimethyl cyclohexanone in the ethanolic medium. The structures of these compounds were characterized by elemental analysis, FT-IR, 1 H-NMR and 13 C-NMR. The antibacterial and antifungal activity of these compounds has been investigated by agar disc diffusion method using Gram-negative and Gram-positive bacterial strain and four kinds of fungi.

4,6-Diacetylresorcinol in Heterocyclic Synthesis, Part I: Synthesis and Biological Evaluation of Some New Linearly and Angularly Substituted Pyrano[3,2-g] Chromenes via Vilsmeier–Haack Formylation of 4,6-Diacetylresorcinol, Its Schiff Bases, and Hydrazones

Application of Vilsmeier–Haack reaction on 4,6-diacetylresorcinol (1) led to the formation of 4,6-dioxo-4H,6H-pyrano[3,2-g]chromene-3,7-dicarboxaldehyde (2) in good yield. The dicarboxaldehyde 2 was condensed with some carbon and nitrogen nucleophiles. Some aliphatic and aromatic Schiff bases of 4,6-diacetylresorcinol (1) were subjected to Vilsmeier–Haack formylation reaction to afford 4,6-bis(alkyl/arylimino)-4H,6H-pyrano[3,2-g]chromene-3,7-dicarbaldehydes 10, 14, and 15. Also, treatment of some bis-hydrazones of 4,6-diacetylresorcinol 16–19 with Vilsmeier–Haack reagent afforded the corresponding 4,6-bis(4-formylpyrazol-3-yl)resorcinols 20 and 21, which underwent oxidation with iodine to yield the pyrano[3,2-g]chromeno[4,3-c:7,6-c]dipyrazole-4,8-diones 22 and 23, respectively. Most of the synthesized compounds revealed weak antimicrobial activities. It was noticed that the dicarboxaldehydes 2, 10, 14, and 15 exhibited moderate antibacterial activity against Gram-positive bacteria, yeast, and fungus. [Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]

Organized Assembly and Morphologies of Aromatic Schiff Base Compounds in Organized Molecular Films

A novel aromatic Schiff base ligand has been designed and its interfacial phase behavior as well as the in situ coordination with Cu(II) ion was investigated. A series of measurement methods, such as surface pressure-area isotherms and atomic force microscopy measurement, have been used to characterize the deposited monolayer and multilayer films. It has been found that both the ligand and the corresponding complex formed stable monolayer or multilayer films at the air/water interface, which could be subsequently transferred onto solid substrates to construct Langmuir-Blodgett films. It was interesting to note that there existed a novel phase transition when the ligand was spread on pure water surface. During this phase transition, the two dimensional flat film changed into a three dimensional fiber-like nano-architectures. However, upon coordinating with Cu(II) ions, only flat films were obtained. Such distinct difference was suggested to be mainly due to the change of molecular conformation and/or the hydrophobicity in the process of supramolecular assembly at the air/water interface.

Crowded Bis-(M-salphen) [M = Pt(II), Zn(II)] Coordination Architectures: Luminescent Properties and Ion-Selective Responses

For binuclear luminescent host systems, cooperativity between metal-organic moieties becomes feasible with regards to photophysical properties and sensing behavior. A new class of conformationally rigid binuclear platinum(II) and zinc(II) complexes bearing tetradentate aromatic Schiff base (salphen) ligands with limited rotational freedom has been prepared and characterized, and the molecular structure of a (Pt-salphen)2 derivative has been determined by X-ray crystallography. Their UV-vis absorption and emission properties have been investigated and are tentatively ascribed to different excited states depending on the metal and the extent of intramolecular π-stacking interactions. Colorimetric and phosphorescent responses by the bis-Pt(II) complexes in the presence of selected metal ions have been observed. The nature of the host-guest interactions has been examined by quantitative binding studies, mass spectrometry and DFT calculations, and through comparisons with control complexes.

Photodynamics of Schiff Base Salicylideneaniline: Trajectory Surface-Hopping Simulations

We report a computational study on the photochemistry of the prototypical aromatic Schiff base salicylideneaniline in the gas phase using static electronic structure calculations (TDDFT, OM2/MRCI) and surface-hopping dynamics simulations (OM2/MRCI). Upon photoexcitation of the most stable cis-enol tautomer into the bright S1 state, we find an ultrafast excited-state proton transfer that is complete within tens of femtoseconds, without any C═N double bond isomerization. The internal conversion of the resulting S1 cis-keto species is initiated by an out-of-plane motion around the C-C single bond, which guides the molecule toward a conical intersection that provides an efficient deactivation channel to the ground state. We propose that the ease of this C-C single bond rotation regulates fluorescence quenching and photocoloration in condensed-phase environments. In line with previous work, we find the S1 cis-keto conformer to be responsible for fluorescence, especially in rigid surroundings. The S0 cis-keto species is a transient photoproduct, while the stable S0 trans-keto photoproduct is responsible for photochromism. The trajectory calculations yield roughly equal amounts of the S0 cis-enol and trans-keto photoproducts. Methodologically, full-dimensional nonadiabatic dynamics simulations are found necessary to capture the preferences among competitive channels and to gain detailed mechanistic insight into Schiff base photochemistry.

Shape‐Persistent (Pt‐salphen)2 Phosphorescent Coordination Frameworks: Structural Insights and Selective Perturbations

The development of molecular frameworks derived from binuclear platinum(II) aromatic Schiff base (salphen) complexes and their supramolecular chemistry have been undertaken. A series of axially rotating (Pt-salphen)2 luminophores, tethered in a cofacial manner by a rigid linker (xanthene, 1; dibenzofuran, 2; biphenylene, 3), was synthesized in which the O(salphen) groups are potentially amenable for guest-binding. The molecular structures of 1 and 3 have been determined by X-ray crystallography, revealing intra- and intermolecular π-stacking interactions, as well as contrasting syn (1) and anti (3) configurations, for the (Pt-salphen)2 moiety. All complexes are luminescent in solution at room temperature. Their photophysical and solvatochromic properties have been examined, and the emissions are assigned to mixed triplet O(p)/Pt(d)→π*(diimine) excited states. The red-shifted fluid emissions and lower quantum yields of 1 and 3, relative to 2, are ascribed to enhanced intramolecular π-stacking interactions. Photophysical changes and selective responses to metal ions (particularly Pb(2+)) have been investigated by using various spectroscopic methods and DFT calculations, and through comparative studies with control complexes. A plausible binding mechanism is proposed based on occupation of the O(salphen)-binding cavity, which induces perturbation of intramolecular π-π interactions, and hence the self-quenching and emission properties, of the (Pt-salphen)2 unit.

Photophysics of Schiff Bases: Theoretical Study of Salicylidene Methylamine

The proton-transfer reaction in a model aromatic Schiff base, salicylidene methylamine (SMA), in the ground and in the lowest electronically-excited singlet states, is theoretically analyzed with the aid of second-order approximate coupled-cluster model CC2, time-dependent density functional theory (TD-DFT) using the Becke, three-parameter Lee-Yang-Parr (B3LYP) functional, and complete active space perturbation theory CASPT2 electronic structure methods. Computed vertical-absorption spectra for the stable ground-state isomers of SMA fully confirm the photochromism of SMA. The potential-energy profiles of the ground and the lowest excited singlet state are calculated and four photophysically relevant isomeric forms of SMA; α, β, γ, and δ are discussed. The calculations indicate two S(1)/S(0) conical intersections which provide non-adiabatic gates for a radiationless decay to the ground state. The photophysical scheme which emerges from the theoretical study is related to recent experimental results obtained for SMA and its derivatives in the low-temperature argon matrices (J. Grzegorzek, A. Filarowski, Z. Mielke, Phys. Chem. Chem. Phys. 2011, 13, 16596-16605). Our results suggest that aromatic Schiff bases are potential candidates for optically driven molecular switches.

4-Bromo-N-(4-hydroxybenzylidene)aniline

In the title compound, C13H10BrNO, the benzene ring planes are inclined at an angle of 48.85 (17)°, resulting in a nonplanar mol­ecule. A characteristic of aromatic Schiff bases with N-aryl substituents is that the terminal phenyl rings are twisted relative to the HC=N plane. In this case, the HC=N unit makes dihedral angles of 11.1 (4) and 38.5 (3)° with the hy­droxy­benzene and bromo­benzene rings, respectively. In the crystal, the molecules are linked by O—H⋯N hydrogen bonds to form infinite (C8) chains along the b axis.

Phase Behaviors and 2D-3D Morphological Transition of Aromatic Schiff Base Derivatives in Organized Molecular Films

A novel aromatic Schiff base ligand has been designed and its interfacial phase behavior as well as its in situ coordination with Cu(II) ions on the surface of pure water was compared with those of the corresponding pre-synthesized Cu(II) complex.Surface pressure-area isotherms,ultraviolet-visible spectroscopy,Fourier transform infrared spectroscopy,and atomic force microscopy were used to characterize deposited monolayer and multilayer films of the complexes.Both the ligand and corresponding complex formed stable monolayer or multilayer films at the air/water interface,which could be subsequently transferred onto solid substrates to construct Langmuir-Blodgett films.A novel phase transition was observed when the ligand was spread on the surface of pure water.During this phase transition,the two-dimensional(2D) flat film changed into three-dimensional(3D) fiber-like nanoarchitectures.However,upon coordination with Cu(II) ions,only flat films were obtained.This phenomenon was thought to be caused by the change of molecular conformation and/or hydrophobicity during supramolecular assembly at the air/water interface.This work provides a simple clue for regulating the nanostructures in organized films.

Studies of Optical Properties of Protonated Polyazomethine Thin Films

The poly(p-phenyleneazomethine) (PPI) belongs to alternately conjugated polymers revealing semiconducting properties, thus belonging to the family of organic semiconductors. The architecture of the most conjugated polymers consists of chains of carbon atoms linked by alternate single and double bonds or alternate C=C and B units, where B stands for the benzene (phenyl ring). This is the case for many prototypical conjugated polymers, such as polyacetylene, poly(p-phenylene) and poly(p-phenylene-vinylene). Since the –N–B–N=C– B–C– group is isoelectronic with the –C–B–C=C–B– C– group, the incorporation of nitrogen atoms into the conjugated system leads to another class of conjugated polymers closely related to poly(p-phenylene vinylene)s, namely polyazomethines poly(aromatic-Schiff bases) and polyketanils (polyketimines) [1–5]. Conjugated polyketanils can be considered as simple derivatives of the corresponding polyazomethines in which the hydrogen atom of the azomethine group is replaced by an aryl or alkyl group. Doping of conjugated polymers is a well established way of influencing on important electronic, optoelectronic and mechanical properties of semiconducting polymers. Doping of polyazomethines is realized mainly by acid base chemistry [1], which makes the process complex and difficult to control. The purpose of this work is to study optical properties of protonated PPI thin films and begin on theoretical studies on protonation mechanism of this group of materials, emphasis being put on a role of the counter ion. Our

ChemInform Abstract: Chemistry and Applications of Organotin(iv) Complexes of Schiff Bases

AbstractReview: 159 refs.

Research on Some Aromatic Schiff Base Compounds and Metal Complexes with Different Substituted Groups

Two aromatic Schiff base derivatives and the corresponding metal complexes with different substituted groups were synthesized and characterized by many methods. The products were characterized by UV-Vis spectra, FT-IR spectra and thermal analysis, while the thermal stability was measured by TG-DTA instrument. FT-IR analysis indicated that the nitrogen atom in imino group and oxygen atom in phenolic hydroxyl group participated in coordinating with transition metal ion in different bridged mode. UV spectra also verified that different coordination modes can be performed between metal ions and ligands. In addition, the thermal stability of metal complexes had been obviously superior to that of the ligands. All results give a useful clue to obtain Schiff base derivatives with versatile property by regulating intramolecular substituted group and species of metal ion. The present results have showed potential application in fields of functional material and catalyst.

Chemistry and applications of organotin(iv) complexes of Schiff bases

Schiff bases are the most widely used versatile ligands, able to coordinate many elements and to stabilize them in various oxidation states. Recently, this class of compounds has been employed as models for biological systems, and in control of stereochemistry in six-coordinate transition metal complexes. Recently, the chemistry of organotin(IV) complexes of Schiff bases has also stemmed from their antitumour, antimicrobial, antinematicidal, anti-insecticidal and anti-inflammatory activities. Furthermore, organotin(IV) complexes of Schiff bases present a wide variety of interesting structural possibilities. Both aliphatic and aromatic Schiff bases in their neutral and deprotonated forms have been used to yield adducts and chelates with variable stoichiometry and different modes of coordination. This critical review (>155 references) focuses upon the chemistry and biological applications of organotin(IV) complexes of Schiff bases reported in the past 15 years. Thermal behavior of these complexes is also discussed.

1-(4-{[(E)-5-Chloro-2-hydroxybenzylidene]amino}phenyl)ethanone oxime

The title compound, C15H13ClN2O2, is an aromatic Schiff base having an aldoxime substituent; the two rings on the azomethine linkage are twisted by 44.4 (1)°. The phenolic H atom is intra­molecularly hydrogen bonded to the azomethine N atom, generating an S(6) ring. In the crystal, inversion dimers linked by pairs of O—H⋯N hydrogen bonds occur. The crystal studied was a non-merohedral twin with a 35% minor component.

ChemInform Abstract: A New Synthesis of 1,4-Diaryl-1,3-butadienes Utilizing the Anil Synthesis.

Title synthesis was made from 1-arylpropenes and N-arylideneanilines (aromatic Schiff bases) in dimethylformamide solution and a strong base as catalyst obtained in situ by reacting metallic sodium with this solvent.

Functionally substituted aromatic schiff bases containing pyrrole and carborane fragments

Functionally substituted aromatic Schiff bases containing pyrrole and carborane fragments were synthesized by condensation of substituted benzaldehydes of the vanillin series with 2-(2-methyl-1 H-pyrrol-1- yl)ethanamine and N-(3-aminophenyl)-o-carborane-1-carboxamide.

Prediction of Corrosion Inhibitor Efficiency of Some Aromatic Hydrazides and Schiff Bases Compounds by Using Artificial Neural Network

Artificial neural networks are used for evaluating the corrosion inhibitor efficiency of some aromatic hydrazides and Schiff bases compounds. The nodes of neural network input layer represent the quantum parameters, total negative charge (TNC) on molecule, energy of highest occupied molecular orbital (E Homo), energy of lowest unoccupied molecular orbital (E Lomo), dipole moment (μ), total energy (TE), molecular volume (V), dipolar-polarizability factor (Π) and inhibitor concentration (C). The neural network output is the corrosion inhibitor efficiency (E) for the mentioned compounds. The training and testing of the developed network are based on a database of 31 published experimental tests obtained by weight loss. The neural network predictions for corrosion inhibitor efficiency are more reliable than prediction using other conventional theoretical methods such as AM1, PM3, Mindo, and Mindo-3. Key words: Neural network; Corrosion inhibitor efficiency. © 2010 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reservedDOI: 10.3329/jsr.v2i1.2757 J. Sci. Res. 2 (1), 108-113 (2010)

Bifunctional influence of 3-chloro substitution on structural and energetic characteristics of N-methyl-salicylidene imines

Energetic and structural effects of formation of intramolecular hydrogen bonds in the group of eight differently chloro-substituted ortho-hydroxy aromatic Schiff bases ( N-methyl-salicylidene imines) containing the 3-chloro substituent in all compounds were studied. The aim was to explain the specific function of this substituent, giving rise to an especially large increase of the strength of intramolecular hydrogen bonds. DFT B3LYP/6–31 + G(d,p) calculations of the structures of particular conformers as well as the potential energy surfaces were carried out. The method of thermodynamic cycle-like scheme was adapted, where the three open conformers are used to estimate the steric corrections connected with formation of chelate rings in the fourth conformer. Problems arising for the estimation of the energy of intramolecular hydrogen bonds connected with the selection of reference states and various structural aspects are discussed in detail. 3-Chloro-substituted Schiff bases can be accounted as sterically enhanced intramolecular hydrogen bonds. Participation of steric and electronic functions in increasing of the energy of intramolecular hydrogen bonds was analyzed. Low energetic proton transfer reaction was found in these molecules, which can be potentially interesting from the point of view of possible thermochromic applications.

Long-chain functionally substituted aromatic Schiff bases derived from cetylamine

New long-chain functionally substituted aromatic Schiff bases containing alkoxy and acyloxy groups, as well as carborane fragments, were synthesized by condensation of the corresponding benzaldehydes of the vanillin series with cetylamine.