Oligo(aromatic ether sulfone)-F as a Nonlinear Polarized Polymeric Material: an Experiment and DFT Study

Polymeric membranes with diverse structures have attracted much attention as new materials for nonlinear optical devices. In this report, a novel oligomer of poly(aromatic ether sulfone)(OAES) has been synthesized and characterized. The electronic structure as well as linear and nonlinear optical properties has been studied by density function theory. The effect for general nonlinear optical polarizability of various condition has been further researched such as absence of side chains and introduction of phenyl substituent on side chains. The static and frequency-dependent hyperpolarizabilities of OAES and its derivatives have been calculated. This work interprets an efficient adjustment for the frequency response and the intensity of nonlinear optical polarizability can be achieved by regulating the structure of system, which provides a new potential for the application of oligomeric materials on nonlinear optical field.     

Use of a porphyrin platform and 3,4-HPO chelating units to synthesize ligands with N4 and O4 coordination sites

Piperazine and 1,2-diaminobenzene have been previously used as anchoring molecules to synthesize 3-hydroxy-4-pyridinone (3,4-HPO) tetradentate ligands affording ligands with different flexibility and coordination properties. In order to have a relatively rigid and hindered structure, a porphyrin platform was selected to anchor one or two 3,4-HPO chelating units. This platform provides an additional N₄ coordination sphere and also very interesting optical properties to the synthesized conjugates. Depending on the metal ion present in the porphyrin core, conjugates with different spectroscopic properties are obtained. EPR spectroscopy has been used to characterize the copper(II) metalloporphyrins and to monitor and identify the species formed upon addition of copper(II) to solutions of two porphyrin conjugates with one and two 3,4-HPO arms. The porphyrin conjugates having two 3,4-HPO units are ligands that provide two separate binding sites with N₄ and O₄ coordination spheres, which allow accommodation of two metal ion centers that may be distinguished by spectroscopic methods.     

Towards the Design of New Materials: Regio- and Stereoselective (Cyclo-) Polymerization of 1-Alkynes and 1,6-Heptadiynes

Summary. The metathesis polymerization, respectively cyclopolymerization, of 1-alkynes and 1,6-heptadiynes using well-defined group VIA transition metal initiators is summarized. For purposes of comparison, selected quaternary catalytic systems used as alternatives as well as the properties of the resulting materials will be presented. Special consideration is given to the mechanistic advancements that have been made during the last decade, which allow the tailor-made synthesis of conjugated materials with interesting optical and electronic properties. E-mail: michael.r.buchmeiser@uibk.ac.at Received November 20, 2002; accepted November 21, 2002     

λ-Shaped mesogens. Structure, phase formation and properties

This contribution is concerned with molecules composed of rigid linear segments which are connected in such a way that a λ-shape results. Such types of shape have been predicted to lead to an enhanced solubility in low molar mass solvents and in the melt state of flexible chain molecules. The theoretical treatment predicted additionally that such molecules should be able to form lyotropic and thermotropic liquid crystalline phases. Experimental data on the thermodynamic properties, the structure formation in the solid and fluid condensed state, the solubility in low molar mass solvents and selected optical and electro-optical properties are reported; these are in good agreement with the predictions.     

One‐pot synthesis of polymer/inorganic hybrids: toward readily accessible,low‐loss,and highly tunable refractive index materials and patterns

The realization that modulated light pulses can be transported in a confined fashion over long distances within a structure that comprises a controlled spatial distribution of the refractive index n—as in optical fibres and waveguides—has, without doubt, underpinned the telecommunications revolution witnessed during the 20th century. The refractive index n, quantifying how light propagates in a given medium, as a consequence, has become one of the most important materials properties in designing photonics products. The other key characteristic for most optical and photonic applications is the amount of light that is absorbed by a material, expressed as the extinction coefficient κ. Although a range of organic/inorganic hybrid materials have been advanced with tunable refractive index, only a few systems combine a high n, sufficiently low κ and straightforward sample preparation to allow simple fabrication of highly transparent, low‐loss structures. Here, we present a hybrid material that can be readily produced in water via a one‐pot synthesis directly from commercially available, low‐cost precursors. Moreover, our hybrid material can be solution‐processed, yielding systems of an extinction coefficient <0.01, and a refractive index, which can be controlled to adopt values between 1.5 to at least 2.1. Unprecedentedly, simple post‐deposition procedures such as thermal annealing or irradiation with high‐intensity UV‐light allow adjusting n also after film fabrication, offering an exceptional degree of freedom in designing and tailoring also more complex photonic architectures or planar wave‐guides, for example, through creation of in‐plane refractive index patterns. As a proof‐of‐concept, we demonstrate fabrication of waveguides based on local heating. The versatility of our materials is further illustrated by the production of lenses and dielectric filters of ～100% reflectivity in a given wavelength regime. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 000: 000–000, 2011     

Poly(neutral red): Electrosynthesis,Characterization, and Application as a Redox Mediator

The synthesis by electropolymerization, the characterization, and applications of poly(neutral red) (PNR), including as a redox mediator, are reviewed. PNR's high electrical conductivity and its redox characteristics have led to special applications of the polymer, and it has been used for the development of electrochemical and optical sensors. Moreover, the attractive properties of PNR allow it to be applied in the development of electrochemical biosensors. Future perspectives are indicated.     

Sequence identification,structure prediction and validation of tannase from Aspergillusniger N5-5

Tannases produced by filamentous fungi are in a family of important hydrolases of gallotannins and have broad industry applications. But until now, the 3-D structures of fungi tannases have not been reported. The protein sequence deduced from the cDNA sequence obtained using RT-PCR amplification was identified as tannase through sequence alignment and phylogenetic analysis. Structure models based on the tannase sequence were collected using I-TASSER, and the model with the best match to the surface charge density-pH titration profile was selected as the final structure for tannase from Aspergillusniger N5-5. This work provides an effective method for protein structure research. The structure constructed in this work should be very important to understand the enzyme bioactivities and further developments of fungi tannases.     

Electron microscopy, spectroscopy, and first-principles calculations of Cs2O

Oxides of cesium play a key role in ameliorating the photoelectron emission of various opto-electronic devices. However, due to their extreme reactivity, their electronic and optical properties have hardly been touched upon. With the objective of better understanding the electronic and optical properties of Cs₂O in relationship to its structure, an experimental and theoretical study of this compound was undertaken. First-principles density functional theory calculations were performed. The preferred structural motif for this compound was found to be anti-CdCl₂. Here three Cs-O-Cs molecular layers are stacked together through relatively weak van-der-Waals forces. The energy bands were also calculated. The lowest transition at 1.45 eV, was found to be between the K point in the valence band to the Γ point in the conduction band. A direct transition at 2 eV was found in the center (Γ) of the Brillouin zone. X-ray powder diffraction, transmission electron microscopy and selected area electron diffraction were used to analyze the synthesized material. These measurements showed good agreement with the calculated structure of this compound. Absorption measurements at 4.2 K indicated two optical transitions with somewhat higher energy (indirect one at 1.65 and a direct transition at 2.2 eV, respectively). Photoluminescence measurements also showed similar transitions, suggesting that the lower indirect transition is enhanced by three nearby minima at 1.5 eV in the Brillouin zone.     

Growth,optical, thermal,dielectric and mechanical studies of sodium hydrogen succinate single crystal

Sodium hydrogen succinate, an alkali metallo-organic third-order nonlinear optical crystal, had been grown successfully using aqueous solution by slow evaporation technique at room temperature. Transparent single crystals were selected and subjected to single-crystal X-ray diffraction analysis to identify lattice parameters, space group and morphology. The grown crystal was further subjected to powder X-ray diffraction to analyze the crystalline quality, UV–Vis–NIR spectral analysis to reveal optical transparency, FTIR spectroscopy for confirmation of the functional group analysis and TG–DTG/DSC analysis to determine the thermal stability. The dielectric constant and dielectric loss were studied as a function of frequency at different temperatures, and the results were discussed. The mechanical properties were calculated by Vickers microhardness test, and the third-order nonlinear optical parameters such as nonlinear refractive index, nonlinear absorption coefficient and real and imaginary parts of the third-order nonlinear optical susceptibility were determined by Z-scan technique.     

MXenes as Emerging Materials: Synthesis,Properties, and Applications

Due to their unique layered microstructure, the presence of various functional groups at the surface, earth abundance, and attractive electrical, optical, and thermal properties, MXenes are considered promising candidates for the solution of energy- and environmental-related problems. It is seen that the energy conversion and storage capacity of MXenes can be enhanced by changing the material dimensions, chemical composition, structure, and surface chemistry. Hence, it is also essential to understand how one can easily improve the structure–property relationship from an applied point of view. In the current review, we reviewed the fabrication, properties, and potential applications of MXenes. In addition, various properties of MXenes such as structural, optical, electrical, thermal, chemical, and mechanical have been discussed. Furthermore, the potential applications of MXenes in the areas of photocatalysis, electrocatalysis, nitrogen fixation, gas sensing, cancer therapy, and supercapacitors have also been outlooked. Based on the reported works, it could easily be observed that the properties and applications of MXenes can be further enhanced by applying various modification and functionalization approaches. This review also emphasizes the recent developments and future perspectives of MXenes-based composite materials, which will greatly help scientists working in the fields of academia and material science.     

Design of a large,rigid, modular optical bed for versatile optical and spectroscopic experimentation

Described is a mechanically-rigid and referenceable, vibrationally-isolated, modular optical support bed which has demonstrated significant utility in recent research on the physical—chemical nature of the atmospheric pressure spark discharge. By interconnecting an assembly of pre-aligned, truss-like sub-structures, a complete instrumental complex has been fabricated which exhibits high mechanical stability. This stability is sufficient to allow alignment of, for example, a 5 m focal length, high-dispersion optical spectrometer, to be maintained for months without detectable degradation. The approach is versatile and can be easily extended to include a wide variety of optical and other research applications. Supporting mechanical, vibration, and optical data are included as well as documentation of fabrication details.     

An electron diffraction analysis of banded structures in thermotropic polymers

A detailed analysis of selected area electron diffraction patterns of a thermotropic liquid crystalline polymer exhibiting the banded structure, shows that the molecular trajectory is not sinusoidal in form, as was indicated by preliminary observations of the structure in the optical microscope. The use of electron microdiffraction techniques (for regions ～150 nm in diameter) also supports the view that significantly more molecules are oriented parallel to the shear direction than predicted by a sinusoidal trajectory. Microdiffraction further shows that the “micro-orientation” of the molecules is significantly better than is apparent from X-ray or selected area electron diffraction patterns. The apparent contradiction with the optical microscopy measurements is discussed.     

Different Schiff Bases—Structure,Importance and Classification

Schiff bases are a vast group of compounds characterized by the presence of a double bond linking carbon and nitrogen atoms, the versatility of which is generated in the many ways to combine a variety of alkyl or aryl substituents. Compounds of this type are both found in nature and synthesized in the laboratory. For years, Schiff bases have been greatly inspiring to many chemists and biochemists. In this article, we attempt to present a new take on this group of compounds, underlining of the importance of various types of Schiff bases. Among the different types of compounds that can be classified as Schiff bases, we chose hydrazides, dihydrazides, hydrazones and mixed derivatives such as hydrazide–hydrazones. For these compounds, we presented the elements of their structure that allow them to be classified as Schiff bases. While hydrazones are typical examples of Schiff bases, including hydrazides among them may be surprising for some. In their case, this is possible due to the amide-iminol tautomerism. The carbon–nitrogen double bond present in the iminol tautomer is a typical element found in Schiff bases. In addition to the characteristics of the structure of these selected derivatives, and sometimes their classification, we presented selected literature items which, in our opinion, represent their importance in various fields well.     

Synthesis,Spectroscopy, Nonlinear Optics,and Theoretical Investigations of Thienylethynyl Octopoles with a Tunable Core

We have synthesized three new molecules that have three thienylethynyl arms substituting a central benzene core and different electron donor/acceptor groups in the three remaining phenyl positions. The absorption, fluorescence, phosphorescence, and transient triplet–triplet spectra are analyzed in the light of the electronic structure of the ground and excited states obtained from quantum‐chemical calculations. From the above, the relevant photophysical data (including quantum yields, lifetimes, and rate constants) could be derived. It was found that the major deactivation pathway is internal conversion, which competes with the fluorescence and intersystem crossing processes. For the three investigated compounds, we provide convincing theoretical support corroborating these findings and further conclusions based on the theoretical information obtained. These molecules are one of the very few cases in which the depolarization ratios, obtained from the NLO optical measurements, clearly reflect the octopolar configuration. Molecular hyperpolarizabilities have been measured and display a typical dependence on the donor–acceptor substitution pattern.     

Invited Lecture. Hexagonal cholesteric blue phases

Using Landau theory, the possibility that two and three dimensional hexagonal structures can exist in cholesteric liquid crystals with positive dielectric anisotropy in an applied electric or magnetic field is considered. Both are found to be thermodynamically stable in different regions of the chirality-temperature-field phase diagram, in agreement with reported experimental data. Further, the theoretical results indicate that two different three dimensional hexagonal phases, having the same space group (P6₂22) but different structure factors, may exist. Ways of verifying this prediction by optical and N.M.R. studies are considered. Also noted is the need to develop further the theoretical model to allow for the existence of the experimentally observed body-centred tetragonal structure.     

Connecting pi-chromophores by sigma-P-P bonds: new type of assemblies exhibiting sigma-pi-conjugation

To study the ability of sigma-P-P skeleton to mediate interaction between pi-chromophores, 1,1'-biphospholes bearing phenyl or thienyl substituents at the 2,2' and 5,5'-position have been prepared and studied. These air-stable derivatives are readily available via a "one-pot" synthesis starting from diynes. Theoretical studies and UV-vis data clearly establish that the two pi-systems interact via the sigma-P-P bridge. This through-bond interaction results in a lowering of the optical HOMO-LUMO gap of the assemblies. The nucleophilic sigma(3)-P centers of these 1,1'-biphospholes allow chemical modifications of the sigma-bridge. These modifications offer further tuning of the optical properties of the assembly. Electrooxidation of the thienyl-substituted 1,1'-biphosphole results in electroactive materials characterized by low optical band gap and reversible p-doping.     

Coumarin derivatives for dye sensitized solar cells: a TD-DFT study

Time dependent density functional theory (TD-DFT) calculations have been carried out to study the electronic structure and the optical properties of five coumarin based dyes: C343, NKX-2311, NKX-2586, NKX-2753 and NKX-2593. We have found out that the position and width of the first band in the electronic absorption spectra, the absorption threshold and the LUMO energy with respect to the conduction band edge are key parameters in order to establish some criteria that allow evaluating the efficiency of coumarin derivatives as sensitizers in Dye Sensitized Solar Cells (DSSC). Those criteria predict the efficiency ordering for the coumarin series in good agreement with the experimental evidence. Presumably, they might be used in the design of new efficient organic based DSSC.     

Invited Lecture. Hexagonal cholesteric blue phases

Using Landau theory, the possibility that two and three dimensional hexagonal structures can exist in cholesteric liquid crystals with positive dielectric anisotropy in an applied electric or magnetic field is considered. Both are found to be thermodynamically stable in different regions of the chirality-temperature-field phase diagram, in agreement with reported experimental data. Further, the theoretical results indicate that two different three dimensional hexagonal phases, having the same space group (P6₂22) but different structure factors, may exist. Ways of verifying this prediction by optical and N.M.R. studies are considered. Also noted is the need to develop further the theoretical model to allow for the existence of the experimentally observed body-centred tetragonal structure.     

Effect of Zr and C Co-doping on the Optical Properties and Electronic Structure of TiO_2

The systematic trends and effect introduced by Zr and C co-doping to TiO2 of electronic structure and optical properties of anatase TiO2 have been calculated by the plane-wave ultra-soft pseudopotential density functional theory (DFT) method within the generalized gradient approximation (GGA) for the exchange-correlation potential. Through the current calculations, the density of states (DOS), energy band structure and optical absorption coefficients have been obtained for TiO2 and compared with the doped TiO2, and the influence of electronic structure and optical properties caused by Zr and C co-doping has been presented qualitatively together. The results revealed that the energy band gap has been decreased owing to the doped Zr and C, whereas the optical absorption coefficients have been increased in the region of 400～800 nm and a red shift of absorption band can be found. Accordingly, photo catalytic activity of TiO2 has been enhanced. The current calculations are in good agreement with the experimental data.