Theoretical analysis on geometries and electronic structures of antiaromatic pentalene and its N‐substituted derivatives: monomer,oligomers and polymer

The antiaromatic compounds have received a great deal of attention for several decades because of their unusual electronic structures. The electronic structures and properties of antiaromatic pentalene and its six nitrogen heterocyclic derivatives were systematically studied by the density functional theory at the Becke, three‐parameter, Lee–Yang–Parr level with 6‐31G* basis set. The results indicated that all the monomers have stable singlet states and remarkable bond‐length alternations. From the dimer to polymer in those molecules, pentalene(P), cyclopenta[b]pyrrole(CPP), cyclopenta[d]imidazole(CPI), pyrrolo[2,3‐b]pyrrole(PP1) and pyrrolo[3,2‐d]imidazole(PI) are stable diradical structures; pyrrolo[3,2‐b]pyrrole (PP2) and imidazo[4,5‐d]imidazole(II) are stable singlet ground states. The electronic properties including bond length, bond‐length alternation, electron density at bond critical points, Wiberg bond index and nucleus‐independent chemical shift were analyzed. It was found that in diradical molecules the bond‐length alternations are diminished, the charge tends to equilibrate, the π‐electron delocalization and conjugation are strengthened. The electronic properties of singlet ground state molecules have nearly no variations from monomers to polymers. The band structure analysis shows that diradical structure molecules have small band gaps (<1.0 eV), wide bandwidth and small effective masses of holes and electrons which suggest that diradical structure molecules are very good candidates for conductive materials. Copyright © 2011 John Wiley & Sons, Ltd.     

Spectroscopic and stability studies on unsymmetrical 1,3‐dialkyl‐1,3‐diphosphacyclobutane‐2,4‐diyls

Air‐tolerant 2,4‐bis(2,4,6‐tri‐t‐butylphenyl)‐1,3‐diphosphacyclobutane‐2,4‐diyl singlet biradicals can be prepared by utilizing the unique reactivity of a kinetically stabilized P≡C triple bond compound. In this procedure, we studied the spectroscopic properties of a fundamental unsymmetrical P‐heterocyclic biradical containing both PEt and PMe moieties, and the effects of the PCH₂OMe group in relation to the stability of the P‐heterocyclic biradical skeleton. The experimentally observed nuclear magnetic resonance and photo‐absorption parameters of 1‐ethyl‐3‐methyl‐2,4‐bis(2,4,6‐tri‐t‐butylphenyl)‐1,3‐diphosphacyclobutane‐2,4‐diyl were discussed based on our previous findings and density functional theory calculations, suggesting particular structural characteristics of the P‐heterocyclic biradical skeleton and aromatic substituent effects on the sp²‐C atoms in the 4‐membered ring. Introduction of the methoxymethyl group in the P₂C₂ biradical moiety gave more stabilized 1,3‐diphosphacyclobutane‐2,4‐diyl derivatives. In comparison with considerably unstable biradicals bearing propargyl substituents, relatively higher lowest unoccupied molecular orbital energies suggest reluctant oxidation of the P‐heterocyclic skeleton. Copyright © 2011 John Wiley & Sons, Ltd.     

Electrochemically induced oxidative cyclization of 2,3‐dihydroxypyridine. Synthesis of a novel highly oxygenated heterocyclic compound

Electrochemical oxidation of 2,3‐dihydroxypyridine in aqueous phosphate buffer solution at a glassy carbon electrode has been studied using cyclic voltammetry and controlled potential coulometry. The results indicate that oxidation of 2,3‐dihydroxypyridine on glassy carbon electrode shows an irreversible feature in aqueous solution. This data indicates that the electrochemically generated pyridindione is unstable and via an oxidative conversion pathway converts to a novel highly oxygenated heterocyclic compound. By means of the obtained electrochemical data, an efficient, one‐pot method for the synthesis of this heterocyclic compound based on the oxidative cyclization of 2,3‐dihydroxypyridine under green conditions, and in a good yield and purity is described. Copyright © 2011 John Wiley & Sons, Ltd.     

Electrooxidation of pyrrole-terminated self-assembled lipoic acid derivatives

New pyrrole derivatives, pyrrolyl lipoic acid (Py-LA 3) and dipyrrolyl lipoic acid (Py₂-LA 2) have been used for surface attachment and immobilisation on gold surfaces, by self-assembly. The electrooxidation of the surface-confined pyrroles was analysed by cyclic voltammetry and the modified electrodes morphological and thickness changes addressed by scanning probe microscopy and ellipsometry. The data support the formation of oligomers as a result of the pendant-pyrrolyl units ease oxidation but provide no evidence of an effective subsequent polymerisation.     

Mesomorphic and optical properties of undoped and doped azomethines

Three calamitic azomethines were prepared by the condensation of the benzene-1,4-dicarboxaldehyde with the three aliphatic amines (LCOA1–LCOA3). The structures of the azomethines were characterized by means of FTIR, ¹H, ¹³C NMR spectroscopies and elemental analysis; the results showed an agreement with the proposed structure. The azomethines emitted blue or green light. An influence of n-decyl sulfonic acid (DSA) on mesomorphic behaviors, absorption and emission wavelengths was investigated. The liquid crystalline properties of the azomethines were studied by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and wide and small angle X-ray diffraction (WAXS and SAXS). The mesomorphic properties of the compounds depend on both the length of the outer flexible spacers and the kind of connection between the alkyl groups and the imine group, i.e. directly via aliphatic chain or by phenyl ring. LCOA1–LCOA2 exhibited smectic and nematic phases, whereas the LCOA3 did not exhibit thermotropic liquid crystal properties. Basing on the comparison of thermal behaviors and optoelectronic properties of undoped (LCOAX) and doped (LCOAX/DSA) azomethines it was shown that ionic self-organized processes are powerful and are able to tune: i) the processability, ii) the LC behavior, and iii) the maximum of emission band of the synthesized azomethines.     

Spacer‐free SERRS spectra of unperturbed porphyrin detected at 100 fM concentration in Ag hydrosols prepared by modified Tollens method

Surface‐enhanced resonance Raman scattering (SERRS) spectroscopy is a powerful tool for the selective and sensitive detection of porphyrins. We report a repeatable detection of unperturbed free base 5,10,15,20‐tetrakis(1‐methyl‐4‐pyridyl)21H,23H‐porphine in concentrations as low as 1 × 10^–13 M in the final system when Ag nanoparticles prepared by modified Tollens method are employed as Raman scattering amplifiers, i.e. without any further post‐modifications of their surface. Most probably the residues of sugar oxidation present on Ag nanoparticle surface are responsible for the effective protection of 5,10,15,20‐tetrakis(1‐methyl‐4‐pyridyl)21H,23H‐porphine molecules against the metalation by silver. Copyright © 2011 John Wiley & Sons, Ltd.     

Preparation and electrochemistry of one-dimensional nanostructured MnO2/PPy composite for electrochemical capacitor

One-dimensional nanostructured manganese dioxide/polypyrrole (MnO₂/PPy) composite was prepared by in situ chemical oxidation polymerization of pyrrole in the host of inorganic matrix of MnO₂, using complex of methyl orange (MO)/FeCl₃ as a reactive self-degraded soft-template. The morphology and structure of the composite were characterized by infrared spectroscopy (IR) X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the MnO₂/PPy composite consists of α-MnO₂ and PPy with nanotube-like structure. Electrochemical properties of the composite demonstrated the material showed good electrochemical reversibility after 500 charge-discharge cycles in the potential range of −0.4 to 0.6 V, the tube-like nanocomposite has the potential application in electrochemical capacitor.     

The Influence of the Molecular Structure of Cyanine Dye on the Component Composition of Molecular Layers

The formation of the component composition of symmetric cationic cyanine dyes on glass is studied. The absorption spectra of layers of three homologous series of dyes with end heterocyclic groups of different spatial and chemical compositions are measured, and the absorption spectra of monomer components and aggregates are separated. The component compositions of layers of different thicknesses are compared. It is shown that the widening of the absorption spectra of molecular layers against the spectra of ethanol solutions of these compounds is caused mainly by the formation of various monomer stereoisomers and molecular aggregates and their interaction with the substrate surface and the neighborhood. The number of isomer forms and their relative concentrations depend on the layer thickness, the electron donor ability and spatial structure of end groups, and the cation conjugation chain length. The influence of the anion manifests itself only in the concentration ratio of the formed monomers and a small shift of the maxima of their absorption bands. The increase in the number of monomer forms produced in the layer corresponds to the increase in the conjugation chain length. Spatial obstacles created by heterocyclic groups inhibit the formation of definite stereoisomers, which reduces the number of components of the layer.     

Acetylene-Substituted Two-Photon Absorbing Molecules With Rigid Elongated Pi-Conjugation: Synthesis,Spectroscopic Properties and Two-Photon Fluorescence Cell Imaging Applications

Two asymmetrical molecules with substituted acetylene as central rigid elongated conjugation are reported as potential chromophores for two-photon microscopic imaging. These molecules consist of a typical D–π–A structure, have different donors (D), the same π-conjugated center (π) and the same acceptor (A). Structural characterization and spectroscopic properties, including single-photon (linear) absorption, quantum yields, single-photon fluorescence, and two-photon absorption spectra, were studied in solvents with different polarity. These acetylene-substituted molecules were found to have high two-photon absorption cross-sections (for example, 690 GM for molecule 1 in toluene), which were determined by a two-photon induced fluorescence method using a femtosecond Ti: sapphire laser as excitation source. Single- and two-photon cellular imaging experiments demonstrate that the substituted acetylene derivatives could be one kind of promising two-photon fluorescence probes for cellular imaging.     

Redox properties and radical anions of fluorinated 2,1,3‐benzothia(selena)diazoles and related compounds

In comparison with 2,1,3‐benzothia(selena)diazoles, electrochemical oxidation and reduction of their 4,5,6,7‐tetrafluoro derivatives and a number of related compounds were studied by cyclic voltammetry. For nine examples of this class, the first reduction peaks are reversible and corresponding radical anions (RAs) are long‐lived at 295 K in MeCN and especially in DMF. The oxidation peaks were irreversible and corresponding radical cations were not observed. Electrochemically generated RAs were characterized by EPR measurements and DFT calculations at the UB3LYP/6‐31+G(d) level. The spin density distribution in the RAs is analyzed in connection with effects of S substitution by Se and/or H by F. The prospects of the studied RAs in the design and synthesis of magnetically active materials are discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

pH-dependent fluorescence property of methyl red isomers in silver colloids

We report the use of silver (Ag) colloids in the spectroscopic differentiation of methyl red (MR) isomers (o-MR, m-MR, p-MR) by fluorescence techniques. Under different pH conditions, the formation of MR-Ag complex has an impact on the fluorescence band shapes and peak position shift, which are distinctive between MR isomers. The fluorescence quenching between 400 and 414 nm accompanied by simultaneous enhancement between 510 and 541 nm changes with pH are closely related to energy transfer efficiency and the interaction between the MR isomers and the Ag surface.     

Molecular properties of selenomaltols: new interesting ligands for bioactive metal complexes

Properties of numerous selenium derivatives of maltol (3‐hydroxy‐2‐methyl‐4H‐pyran‐4‐one), which is an important ligand in medicinal chemistry, were studied. Selenium derivatives were obtained using consecutive in silico replacements of maltol oxygen atoms, which produced three mono‐substituted, three di‐substituted and one tri‐substituted derivatives. The geometry optimisations for these compounds in neutral, anionic and cationic forms were performed at the B1LYP/6‐311++G** level of theory. The aromatic properties of the considered selenium compounds were studied in their heterocyclic rings using several indices of aromaticity: harmonic oscillator model of aromaticity, nucleus independent chemical shift(0), nucleus independent chemical shift(1), aromatic stabilisation energy, H index, para delocalisation index and multicentre index. The methods cover all of the main types of aromaticity indices: geometric, magnetic, energetic and electronic. The calculated data show the identical aromaticity order (cation > neutral molecule > anion) for maltol and its thio and seleno derivatives. The predicted aromaticity levels of selenomaltols were compared with the previously studied maltol and various thiomaltols. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis,characterization, and biological activity of Schiff bases metal complexes

The new Schiff base 1‐[(2‐{1‐[(dicyclohexylamino)‐methyl]‐1H‐indol‐3‐yl}‐ethylimino)‐methyl]naphthalen‐2‐ol (HL) was prepared from 1‐{[2‐(1H‐Indol‐3‐yl)‐ethylimino] methyl}‐naphthalen‐2‐ol and dicyclohexyl amine. From this Schiff base, monomeric complexes [M (L)_n (H₂O)₂ Cl₂] with M = Cr, Fe, Mn, Cd, and Hg were synthesized and characterized based on elemental analysis (EA), FT‐IR, mass(MS), UV‐visible, thermal analysis, magnetic moment, and molar conductance. The results showed that the geometrical structural were octahedral geometries for the Cr(III) and Fe(III) complexes, square planer for Pd(II) complex, and tetrahedral for Mn(II), Cd(II), and Hg(II) complexes. Kinetic parameters such as ΔE*,ΔH*, ΔG*, and K of the thermal decomposition stages were calculated from the TGA curves using Coats‐Redfern method. Additionally, density functional theory (DFT) was applied for calculations of both electronic structure and spectroscopic properties of synthesized Schiff base and its complexes. The analysis of electrostatic potential (EPS) maps correlates well with the computed energies providing on the dominant electrostatic nature of N‐H‐‐‐O interactions. The biological activities had been tested in vitro against Staphylococcus aureus, Pseudomonas aeruginosa, as well fungi like Penicillium expansum, Fusarium graminearum, Macrophomina phasealina, and Candida albicans bacteria in order to assess their antimicrobial potential.     

Vibrational spectroscopic study of Sr2ZnTeO6 double perovskites

Sr₂ZnTeO₆ ceramics were prepared by the solid‐state route and their vibrational phonon modes were investigated using optical spectroscopic techniques, for the first time. X‐ray diffraction (XRD) and Raman and infrared spectroscopies were employed to investigate the structures of these perovskite materials and the results analysed together with group‐theoretical predictions. The number and behaviour of the first‐order modes observed in both spectroscopic techniques are in agreement with the calculations for a tetragonal I4/m space group. The complete set of the optical phonon modes was determined, and the intrinsic dielectric properties of the materials were evaluated, allowing us to discuss their potential application in microwave (MW) circuitry. Copyright © 2009 John Wiley & Sons, Ltd.     

The 2D Rancieite-type manganic acid and its alkali-exchanged derivatives: Part I — Chemical characterization and thermal behavior

The 2D Rancieite type manganic acid was prepared by reduction of KMnO₄ in acidic medium. Its ion exchange behavior allows to prepare alkali derivatives. All compounds were characterized with use of a combination of X-ray diffraction, chemical analyses, TGA, magnetic measurements and spectroscopic techniques. The evolution of their chemical composition versus temperature was studied between 180 and 400 °C. It shows that the dehydration process is partly reversible in these compounds whereas the weak reduction is irreversible. The 2D Rancieite-type manganic acid is readily different from a Birnessite-type phyllomanganate, as shown by several features: the interlayer distance, the ion exchange capacity, the thermal behavior, the interlayer cation content, the manganese average oxidation state, the magnetic behavior and the IR spectrum.     

Folate Conjugated CdHgTe Quantum Dots with High Targeting Affinity and Sensitivity for In vivo Early Tumor Diagnosis

CdHgTe-folate conjugates, acting as novel active-targeting fluorescence probes, were prepared by covalent conjugation of CdHgTe QDs and folic acid. Their characteristics, such as optical spectra, stability and cancer cell targeting were investigated in detail. The fluorescence wavelength of CdHgTe-folate conjugates was 790 nm and a full width at half-maximum (FWHM) of them was 50–70 nm. Their fluorescence stability could satisfy the need of long and continuous fluorescence imaging. The in vivo dynamic bio-distribution of CdHgTe-folate conjugates in S180 tumor beard mouse model was monitored by a NIR imaging system. The resultes indicated that CdHgTe-folate conjugates targeted to tumor effectively. The high fluorescence intensity together with targeting effect makes CdHgTe-folate conjugates promising candidates for imaging, monitoring and early diagnosis of cancer at molecular and cell level.     

Theoretical studies on aromaticity of selected hydroxypyrones and their cations and anions. Part 2. Electron delocalisation in the OCCO group

Electron delocalisation in the OCCO part of hydroxypyrones with two exocyclic oxygens linked by two carbon atoms was studied using well‐known aromaticity indices like: HOMA, EN, GEO, NICS(0) and NICS(1). This part of hydroxypyrones is very important due to the fact that the two exocyclic oxygens of deprotonated hydroxypyrone units are responsible for metal ion binding. Values of the aromaticity indices were obtained for geometries calculated by several theoretical methods (HF, SVWN, B3LYP and B1LYP) with 6‐311 ++ G(d,p) basis set. Electron delocalisation in the corresponding cations and anions was also considered. The data obtained in this work revealed that the relative delocalisation order in the OCCO group is the same as the aromaticity order determined earlier for the heterocyclic rings of hydroxypyrones (anions < neutral molecule < cation). The problem of quasiaromaticity in neutral hydroxypyrones and their cations is also considered and discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

三种五元化合物的荧光光谱的量子化学研究

采用密度泛函理论(DFT)中的B3LYP方法,在6-31G^*水平上对三种五元杂环物质进行了构型优化,对优化后的构型做振动分析,均未出现虚频率。在此基础上通过轨道分析,探索了分子内部电子跃迁的机理。结果表明,这三种五元化合物HOMO到LUMO的跃迁是电子从C1、C2、C3和C4转移到杂原子(吡咯中的N原子,呋喃中的O原子和噻吩中的S原子)上,并在6-31G^*水平上用单激发组态相互作用(CIS)方法分别计算了三种物质的荧光光谱,所得计算结果与实验值基本符合。