1,2,3-Triazabutadiene. IV MO-Berechnungen an photochromen Triazenen

1,2,3-Triazabutadienes. IV. MO Calculations of Photochromic Triazenes The π-π* electronic transitions of different cis-trans isomers of substituted 1-aryl-3-(3-methyl-benzthiazolin-2-ylidene)-triazenes and of 1-(p-chlorophenyl)-3-(1,3-dimethylbenzimidazolin-2-ylidene)-triazene have been calculated by the PPP-method. The observed spectral characteristics can be described satisfactorily on the basis of a cis-trans isomerism around the NN double bond. The Differences of the excitation energies between the cis and the trans form thus calculated render the experimental values with a deviation of ⩽0.06 eV. The influence of the substituents on the energy of the S₀—S₁ transitions has also been calculated and agrees in its tendency with the experimental results.     

Untersuchungen zur Sensibilisierung von Azofarbstoff-Perhalogenid-Systemen

Investigations Concerning Sensitization of Silver Free Information Recording Materials with Azo Dyes and Polyhalogen Compounds Recording materials mentioned in the title are sensitive to the visible region of light. The reason therefore is an energy transfer from the azo dye to the polyhalogen compounds, preferentially CBr₄. It's possible to separate the absorption spectra of azo compounds used in this work into two gaussian functions, which relates to n,π*- and π,π*-transitions. Only the excitation of the n,π*-transition causes sensitization. A mechanisms of sensitization is proposed.     

Colour and Constitution of Anthraquinonoid Dyes. Part II–Modified PPP Calculations and Annelation Effects

The Pariser–Parr–Pople (PPP) method with the variable (3, yapproximation has been used to calculate the ^–electronic excitation energy of 1, 4–disubstituted benzo– and dibenzo–anthraquinone dyes. A good linear correlation between the observed and calculated values for the first –* excitation was found for a series of benzo AQ dyes. The effect of annelation on the colour of benzo AQ dyes was studied on the basis of the calculated results. It was concluded that 2, 3–annelation differs from 5, 6– and 6, 7–annelation because the 2, 3–benzo ring is also included in the donor moiety.     

Thione Photochemistry: On Thiobenzophenone Photoannelation

The photochemistry of the reaction of thiobenzophenone with acrylonitrile, following excitation into both the n, π* and π, π* absorption bands, has been examined. The products obtained are different, indicating dual mechanisms. It has been shown that the thietane is not a primary product, but is the result of thermal decomposition of a 1,3-dithiane which can be isolated at low temperatures. This is the main product at the shorter wavelengths, but at longer wavelengths a 1,4-dithiane and a thiatetrahydronaphthalene are obtained. A disulphide is also produced as a result of a secondary photochemical attack of thiobenzophenone on the thietane. The mechanistic implications of these results are discussed.     

The effect of changes in π-conjugated terthienyl systems using thienyl and ethylenedioxybenzene functionalized thieno[3,4-b]pyrazine precursors: Multicolored low band gap polymers

New classes of thieno[3,4-b]pyrazines containing thienyl and ethylenedioxy phenyl units on electron-withdrawing moieties of π-conjugated terthienyl were synthesized. The effect of structural differences on electrochemical and optoelectronic properties of the resulting polymers was investigated. Changes in the electronic nature of the functional groups enable to tune the electrochemical properties of the π-conjugated terthienyl monomers by lowering oxidation potential from 0.62 V (DTTP) to 0.56 V (DBTP). Spectroelectrochemical analyses revealed that the neutral polymer (PDBTP) is dark green in its neutral state revealing π-π* transitions in two well-separated bands at 410 and 751 nm. The electronic band gap of polymer, defined as the onset of the π-π* transition, is found to be 1.0 eV. Using the thienyl unit instead of ethylenedioxy phenyl, a red shift in the band gap (0.95 eV) is observed. The polymer, PDTTP, exhibits multicolor electrochromism and can be switched between a dark yellow neutral state, a green intermediate state, and a brown oxidized state. PDBTP also shows a multicolored electrochromic behavior with three distinct states: dark green at the neutral state, a brown intermediate state, and a brown-violet oxidized state.     

Untersuchungen zum UV/VIS-Spektralverhalten von Azofarbstoffen. XV. Eine Analyse der Absorptionsspektren von 4,4′-Diaminoazobenzenen

Studies on UV/VIS Absorption Spectra of Azo Dyes. XV. An Analysis of the Absorption Spectra of 4,4′-Diaminoazobenzenes In the visible absorption spectrum 4,4′-bis-diethylaminoazobenzene shows two absorption maxima (λ_max = 426 nm and λ_max = 477 nm) with high intensity. Quantum chemical calculations and examination by peak separation of six 4-substituted azobenzenes and six 4′-substituted 4-diethylaminoazobenzenes ( 1a–k ) indicate that the longest wavelength band is due to a n-π* transition and the other band is due to a π-π*-transition. This is verified using an increment system for n-π* absorption maxima. A linear relation is found between intensity ratios of the two bands and the HAMMETT -σ-constants of the substituents. With increasing electron releasing tendency of the substituents the absorption intensity of the n-π*-band increases.     

煤燃烧过程中碳、氧官能团演化行为

采用X射线光电子能谱（XPS）系统研究燃烧过程中准格尔褐煤及其煤焦颗粒表面中碳、氧的存在形态及演化过程.研究结果表明，准格尔褐煤颗粒表面含碳官能团中石墨化碳含量非常低，但同时具有一定含量的双键碳;含氧官能团中无机氧含量较低，有机氧含量相对较高.随着燃烧的进行，颗粒表面碳、氧官能团呈现不同的变化趋势.     

Polymers and oligomers derived from pyrrole and N-hydroxymethylpyrrole: A theoretical analysis of the structural and electronic properties

This work reports a theoretical investigation about the structural and electronic properties of polymers constituted by pyrrole and N-hydroxymethylpyrrole in both neutral and p-doped states. Ab initio quantum mechanical calculations were performed on neutral and positively charged oligomers to evaluate the bond length alternation pattern in the π-system, the molecular conformation, the π-π* transition energies and the ionization potential. Results, which have been extrapolated to infinite polymer chains, allow analyze the influence of N-hydroxyalkylation of polypyrrole on these properties.     

Monomethine cyanine dyes with an indole nucleus: Microwave-assisted solvent-free synthesis,spectral properties and theoretical studies

Four asymmetric monomethine indocyanine dyes were rapidly synthesized by the condensation of indole quaternary salts with 2-methylthio quinoline quaternary salt in the presence of triethylamine under solvent-free, microwave irradiation. The effects of microwave power and irradiation time on yield were examined. The products were identified using elemental analysis, IR, MS, UV–Vis spectra, ¹H and ¹³C NMR. The absorption of the dyes was investigated both experimentally and theoretically. Calculations performed using a combination of the time-dependent density functional theory (TD-DFT) and the polarizable continuum model (PCM) reproduced the π → π¹ type absorption bands of the dyes. Multiple linear regression, applied to the theoretical absorption maxima in different solvents, fitted well with experimental data. Resonance frequency calculations were undertaken to study the IR spectra of the dyes and the calculated results were in good accordance with experimental values.     

Die UV-Spektren α,β-ungesättigter Ester und ihre Beeinflussung durch Lösungsmittel und Komplexbildung

UV Spectra of α,β-Unsaturated Esters and the Influence of Solvents and Complex Formation Positions and intensities of partially overlapped π-π* and n-π* transitions in spectra of methyl and ethyl esters of acrylic, methacrylic and crotonic acid are discussed. Reproducible values were determined by graphical and mathematical band-separations. n-π* bands in gaseous methyl acrylate show vibrationally fine structures. These are compared with fine structures in the spectra of α-methylene-γ-butyrolactone and α, β-dehydrobutyrolactone. In solutions with C_ester lt; 0,1 m self-associations are negligible. The transition-displacements Δv _max due to solvent effects closely correlate with the solvent parameters of KOSOWER . These correlations allow to calculate λ_max-values at which solvents absorb strongly. Equilibrium constants K of EDA-complexes with TCNE and chloranile were determined. With a competition method K was found in the range of 0.9 to 10.3 l · mol⁻¹.     

Fluorescence and photophysical properties of D-π-A push-pull systems featuring a 4,5-dicyanoimidazole unit

Absorption and fluorescence spectra and fluorescence quantum yields of 18 D-;π-A push-pull compounds were measured. The investigated chromophores consist of 4,5-dicyanoimidazole — bearing donor — substituted and systematically extended π-conjugated spacers. The influence of temperature and solvent polarity on the spectral and photophysical properties was investigated. Employing INDO/S calculations, the structure–property relationships were discussed.     

Electronic and Steric Control of n→π* Interactions: Stabilization of the α-Helix Conformation without a Hydrogen Bond

The preferred conformations of peptides and proteins are dependent on local interactions that bias the conformational ensemble. The n→π* interaction between consecutive carbonyls promotes compact conformations, including the α-helix and polyproline II helix. In order to further understand the n→π* interaction and to develop methods to promote defined conformational preferences through acyl N-capping motifs, a series of peptides was synthesized in which the electronic and steric properties of the acyl group were modified. Using NMR spectroscopy, van't Hoff analysis of enthalpies, X-ray crystallography, and computational investigations, we observed that more electron-rich donor carbonyls (pivaloyl, iso-butyryl, propionyl) promote stronger n→π* interactions and more compact conformations than acetyl or less electron-rich donor carbonyls (methoxyacetyl, fluoroacetyl, formyl). X-ray crystallography indicates a strong, electronically tunable preference for the α-helix conformation, as observed directly on the φ and ψ torsion angles. Electron-donating acyl groups promote the α-helical conformation, even in the absence of the hydrogen bonding that stabilizes the α-helix. In contrast, electron-withdrawing acyl groups led to more extended conformations. More sterically demanding groups can promote trans amide bonds independent of the electronic effect on n→π* interactions. Chloroacetyl groups additionally promote n→π* interactions through the interaction of the chlorine lone pair with the proximal carbonyl π*. These data provide additional support for an important role of n→π* interactions in the conformational ensemble of disordered or unfolded proteins. Moreover, this work suggests that readily incorporated acyl N-capping motifs that modulate n→π* interactions may be employed rationally to promote conformational biases in peptides, with potential applications in molecular design and medicinal chemistry.     

Optical properties of donor-π-(acceptor)n merocyanine dyes with dicyanovinylindane as acceptor group and triphenylamine as donor unit

Donor-π–(Acceptor)_n (D-π-A) type dyes were synthesized and their absorption and emission spectra investigated in different solvents. Strong acceptor units imparted large red-shifts in absorption; the twisting of the dye's structure imposed by an acceptor unit quenched fluorescence. Electron delocalization before and after excitation was observed according to molecular orbital calculations. The results indicated potential use of the dyes as electro-optical materials.     

Electrochemical and spectroscopic properties of dendritic cobalto-salicylaldiimine DNA biosensor

A metallodendrimer-based electrochemical DNA biosensor was constructed by a layer-by-layer assembly of cobalt(II) salicylaldiimine metallodendrimer (SDD-Co(II)) and a 21 bases oligonucleotide NH₂-5′-GAGGAGTTGGGGGAGCACATT-3′ (pDNA) on a gold electrode. The complementary oligonucleotide was 5′-AATGTGCTCCCCCAACTCCTC-3′ (tDNA). UV-visible spectra of SDD-Co(II) in 1:1 (v/v) acetone-ethanol solution showed absorption bands at 325 nm and 365-420 nm related to π-π* intra-dendrimer transitions and d-π* metal-dendrimer charge transfer transitions, respectively. Square-wave voltammetry (SWV) characterisation of the Au|SDD-Co(II)|pDNA biosensor system in phosphate buffer saline solution of pH 7.4, indicated a reversible one-electron electrochemical process with a formal potential, E°′, value of +210 mV. Electrochemical impedance spectroscopy (EIS) data confirmed that the hybridisation of the biosensor's pDNA with the tDNA to form double-stranded DNA (dsDNA) resulted in an increase of the impedimetric charge transfer resistance, R_ct, value from 6.52 to 12.85 kΩ. The limit of detection (LOD), calculated as 3σ of the background noise, and sensitivity of the sensor were 1.29 kΩ/nmol L⁻¹ and 0.34 pmol L⁻¹, respectively.     

Effect of thermal annealing on surface morphology and physical properties of poly(3-octylthiophene) films

An unusual morphology observed in poly(3-octylthiophene) (P3OT) films, solution grown at room temperature, which is previously shown by highly regioregular-poly(3-alkylthiophenes) (rr-P3ATs), is reported. Upon thermal annealing a rare well-arranged corrugated-rod-type (CRT) morphology, comes up gradually. It is observed by soft-heat treatment of pristine P3OT films, which is not reported for any members of polythiophenes family. This novel CRT morphology, observed by scanning electron microscopy (SEM), is supported by photoluminescence (PL) quenching, red shift of λ_max (π-π* absorption) in UV-vis spectra, and increase in conductivity. These improvements in physical properties are perhaps due to the increase in the planarity and 3D-π-π stacking of polymer chains by gradual soft-thermal annealing. It is worthwhile to mention here that the P3OT synthesized for the present investigation, with changed polymerization parameters, is comparable with its rr-P3ATs counterparts. The improvement in the quality of P3OT may induce self-assembling nature in former which results due to increased π-π interactions.     

含有醛基的偶氮苯的合成及其三阶非线性的研究

以对氨基苯甲醛、N,N 二甲基苯胺和苯酚为原料,通过重氮偶合反应制备了4 二甲氨基 4′ 醛基偶氮苯(ADMAA)和4 羟基 4′ 醛基偶氮苯(AHA)。用红外光谱和高压液相色谱/质谱联用分析仪测定了ADMAA和AHA的结构和纯度。高压液相色谱表明,ADMAA峰和AHA峰的面积百分比分别为94 4%和96 2%;质谱显示的相对分子质量分别为253 9和226 8。用紫外-可见光谱研究了它们的吸收特性,发现π-π 跃迁吸收峰分别在450和370nm。用简并四波混频实验测量ADMAA和AHA的三阶非线性系数分别为5 4×10-10和1 8×10-10esu。     

Chemical Tools for Studying Phosphohistidine: Generation of Selective τ-Phosphohistidine and π-Phosphohistidine Antibodies**

Nonhydrolysable stable analogues of τ-phosphohistidine (τ-pHis) and π-pHis have been designed, aided by electrostatic surface potential calculations, and subsequently synthesized. The τ-pHis and π-pHis analogues (phosphopyrazole 8 and pyridyl amino amide 13 , respectively) were used as haptens to generate pHis polyclonal antibodies. Both τ-pHis and π-pHis conjugates in the form of BSA-glutaraldehyde-τ-pHis and BSA-glutaraldehyde-π-pHis were synthesized and characterized by ³¹P NMR spectroscopy. Commercially available τ-pHis (SC56-2) and π-pHis (SC1-1; SC50-3) monoclonal antibodies were used to show that the BSA−G-τ-pHis and BSA−G-π-pHis conjugates could be used to assess the selectivity of pHis antibodies in a competitive ELISA. Subsequently, the selectivity of the pHis antibodies generated by using phosphopyrazole 8 and pyridyl amino amide 13 as haptens was assessed by competitive ELISA against His, pSer, pThr, pTyr, τ-pHis and π-pHis. Antibodies generated by using phosphopyrazole 8 as a hapten were found to be selective for τ-pHis, and antibodies generated by using pyridyl amino amide 13 were found to be selective for π-pHis. Both τ- and π-pHis antibodies were shown to be effective in immunological experiments, including ELISA, western blot, and immunofluorescence. The τ-pHis antibody was also shown to be useful in the immunoprecipitation of proteins containing pHis.     

Thieno[3,2-b]thiophene as π-bridge at different acceptor systems for electrochromic applications

Benzoselenadiazole, quinoxaline and thieno[3,2-b]thiophene are the units preferred in conducting polymers due to their electrochemical properties. There are no reports in the literature on polymers containing both moieties. In this study, novel benzoselenadiazole, quinoxaline and thieno[3,2-b]thiophene based monomers; 4-(3a,6a-dihydrothieno[3,2-b]thiophen-2-yl)-7-(thieno[3,2-b]thiophenyl)benzo[c][1,2,5]selenadiazole (BSeTT) and 2,3-bis(3,4-bis(decyloxy)phenyl)-5,8-dibromo-2,3-dihydroquinoxaline (QTT) were synthesized via Stille Coupling and polymerized electrochemically. These polymers were characterized in terms of their spectroelectrochemical and electrochemical properties by cyclic voltammetry and UV–Vis–NIR spectroscopy. Spectroelectrochemistry analysis of PBSeTT revealed an electronic transition at 525 nm corresponding to π–π* transition with a band gap of 0.93 eV whereas PQTT revealed electronic transitions at 440 and 600 nm corresponding to π–π* transitions with a band gap of 1.30 eV. Electrochromic investigations showed that PBSeTT has gray color PQTT switching between green and gray. Switching time of the polymers was evaluated by a kinetic study upon measuring the percent transmittance (%T) at the maximum contrast point.     

Geometry relaxation in singlet excited states of oligomers containing cyclopentadiene and fulvene and their cyano derivatives

Using the singles configuration interaction (CIS) theoretical approach, we investigated the nature of the geometric conformations and electronic transitions in π-conjugated oligo(cyclopentadiene)s and oligo(fulvene)s, and their cyano derivatives. Geometry optimizations were first carried out with the restricted Hartree-Fock (RHF/3-21G*) method which was followed by calculations of excitation energies using CIS (CIS/3-21G*) method. The trends in excitation energies as a function of chain lengths show that the band gaps in the cyano substituted compounds are lowered by approximately 0.5 eV relative to their parent polymers. The results of CIS/3-21G* oligomer calculations also show that delocalized singlet excited states are accompanied by a geometry relaxation in comparison to their ground state (HF) geometries.     

Preparation and characterization of polyaniline/multi-walled carbon nanotube composites

This study describes the synthesis of doped polyaniline in its emeraldine salt form (PANI-ES) with carboxylic groups containing multi-walled carbon nanotubes (c-MWNTs) via in situ polymerization. Both Raman and FTIR spectra indicate that carboxylic acid groups formed at both ends and on the sidewalls of the MWNTs. Based on the π-π* electron interaction between aniline monomers and MWNT and hydrogen bonding interaction between the amino groups of aniline monomers and the carboxylic acid group of c-MWNT, aniline molecules were adsorbed and polymerized on the surface of MWNTs. Structural analysis using FESEM and HRTEM showed that PANI-ES/c-MWNT composites are core (c-MWNT)-shell (doped-PANI-ES) tubular structures with diameters of several tens to hundreds of nanometers, depending on the PANI content. The conductivities of these PANI-ES/c-MWNT composites are 50-70% higher than those of PANI without MWNT.