Synthesis and characterization of a cross-linkable nonlinear optical polymer functionalized with a thiophene- and tricyanovinyl-containing chromophore

This paper reports a novel nonlinear optical polymer BP-AVT-TCV functionalized with a thiophene- and tricyanovinyl-substituted chromophore. BP-AVT-TCV was synthesized by the post-tricyanovinylation of an epoxy-based precursor polymer BP-AVT, and had a high molar functionalization degree of chromophore (70 mol.%). It had an enhanced glass transition temperature (T_g = 164 °C) compared with BP-AVT (T_g = 114 °C), and a high decomposition temperature (T_d,5% = 295 °C). BP-AVT-TCV was further cross-linked to achieve the three-dimensional (3D) network of thermosetting polyurethane (PU). The poled PU films revealed an electro-optic (EO) coefficient (γ₃₃) value of 21 pm/V at a wavelength of 1315 nm. The structures of the polymers were confirmed by FT-IR, UV–Vis, and ¹H NMR spectra.     

Synthesis and optical properties of a series of thermally stable diphenylanthrazolines

A series of diphenylanthrazolines were synthesized by Friedländer condensation of 2,5-dibenzoyl-1,4-phenylenediamine and acetyl-functionalized compounds in the presence of polyphosphoric acid as catalyst, in yields ranging from 61% to 88%. The diphenylanthrazolines are thermally robust with high decomposition temperatures (>380.0 °C) and high melt transitions (317–462 °C). All of them show the lowest energy absorption bands (λ_max^Abs: 394–433 nm) from the π–π¹ transitions by virtue of their large molar extinction coefficients (? ≈ 10⁴ M^?1 cm^?1), revealing low optical band gaps (2.59–2.80 eV). The compounds emit blue fluorescence with λ_max^Em ranging from 430 to 466 nm in dilute toluene solution.     

The design,synthesis and nonlinear optical properties of a novel,Y-type polyurethane containing tricyanovinylthiophene of high thermal stability

A novel, Y-type polyurethane containing 1-(2,4-dioxyethoxy)phenyl-2-{5-(2,2-dicyanovinyl)-2-thiophenyl}ethenes as nonlinear optical chromophores present within the polymer backbone, was prepared and characterized. The compound was soluble in common organic solvents and displayed thermal stability up to 260 °C and a glass transition temperature (T_g) of 163 °C. The second harmonic generation coefficient (d₃₃) of poled polymer films at the compound's fundamental wavelength of 1560 nm was ～3.72 × 10^?9 esu. Dipole alignment exhibited high thermal stability up to the T_g, and there was no decay in d₃₃ below 148 °C owing to the partial main-chain character of the polymer structure.     

Synthesis and identification of organosoluble polyamides bearing a triaryl imidazole pendent: Thermal,photophysical, chemiluminescent,and electrochemical characterization with a modified carbon nanotube electrode

A novel monomer containing a triaryl imidazole pendent group was successfully synthesized by nucleophilic substitution of bisphenol A with 2-(2-chloro-5-nitrophenyl)-4,5-diphenyl-1H-imidazole (I). A series of new polyamides (PAs) with inherent viscosities of 0.95–1.2 dL/g was prepared by direct polycondensation of the diamine with various dicarboxylic acids. These PAs were readily soluble in many organic solvents and gave tough and flexible films by solution casting. These PAs exhibited T_gs between 189 °C and 252 °C, and 10% weight loss temperatures in excess of 400 °C with up to 68% char yield at 600 °C in air. All of the PAs emitted a greenish-yellow light in dilute THF solution, with photoluminescence (PL) quantum yields in the range of 10–25%. The chemiluminescent activity and electrochemical oxidation of the PAs were also investigated.     

Nonlinear optical,poly(amide-imide)–clay nanocomposites comprising an azobenzene moiety synthesised via sequential self-repetitive reaction

Poly(N-acylurea)–clay nanocomposites consisting of a modified montmorillonite and poly(N-acylurea) were prepared from which poly(amide-imide)–clay nanocomposites were subsequently obtained via the sequential self-repetitive reaction of poly(N-acylurea). The moderate T_g of poly(N-acylurea) allows the nonlinear optically active polymer to exhibit high poling efficiency; in situ poling and curing increased the T_gs of poly(amide-imide)–clay nanocomposites. Electro-optical coefficients, r₃₃ of ～17–20 pm/V (830 nm), were achieved; high temporal stability (120 °C) and waveguide optical losses of 3.4–3.9 dB/cm at 1310 nm were also obtained for poly(amide-imide)–clay nanocomposites.     

Synthesis and photoresponsive behavior of the high-Tg azobenzene polymers via RAFT polymerization

Well-defined photo-responsive alternating copolymers, poly(4-(N-maleimido)azobenzene-alt-styrene)s (PMSts), were successfully synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization. A divinyl monomer was used in this polymerization to prepare high molecular weight azobenzene polymers. These polymers had good solubility in most organic solvents, formed films well, and had high glass transition temperatures (T_g = 174–250 °C) and were heat resistant (T_d > 320 °C). The photo-induced trans–cis isomerization of the copolymers was examined in chloroform solution. Surface-relief-gratings (SRGs) formed on the polymer films were also investigated using illumination from a linearly polarized Kr⁺ laser beam.     

Strong photoluminescence and good electrical properties in Eu-modified SrBi2Nb2O9 multifunctional ceramics

Bismuth layer-structured ferroelectric (BLSFs) ceramics of Sr_1−xEu_x Bi₂Nb₂O₉ (SBT-xEu, x=0.000, 0.002, 0.004, 0.006) were prepared by a conventional solid-state reaction method. All the samples have a bismuth oxide layered structure with a dense microstructure. The ferroelectric, piezoelectric, dielectric and optical properties of the ceramics were investigated. After Eu³⁺ doping, samples show a bright red photoluminescence upon blue light excitation of the 400–500 nm. Upon the excitation of 465 nm light, the materials have two intense emission bands peaking around 593 nm (yellow) and 616 nm (red). Meanwhile, good electrical properties with large piezoelectric constant d₃₃ of 14 pC/N and large remnant polarization 2P_r of 11.97 μC/cm² are obtained at x=0.006. Moreover, this material has a high Curie temperature (T_c=429 °C) and high resistivity, which makes the material resistant to thermal depolarization up to its Curie temperature. This feature indicates that the SBN-xEu ceramics have a latent use in high temperature applications.     

Structural,dielectric, and piezoelectric properties of fine-grained NBT–BT0.11 ceramic derived from gel precursor

(Na_1/2Bi_1/2)TiO₃ doped in situ with 11 mol% BaTiO₃ (NBT–BT_0.11) powders were synthesized by a sol–gel method, and the electrical properties of the resulting ceramics were investigated. The powders consisting of uniform and fine preliminary particles of about 50 nm were prepared by calcining the gel precursor at 700 °C. (Na_1/2Bi_1/2)_0.89Ba_0.11TiO₃ ceramics, sintered at temperatures up to 1150 °C have a rhombohedral symmetry, while the ceramic sintered at 1200 °C exhibits a tetragonal crystalline structure. The ceramics show high dielectric constant (?_r ～ 5456), dielectric loss of 0.02, depolarization temperature T_d ～ 110 °C and temperature corresponding to the maximum value of dielectric constant T_m ～ 262 °C. The dielectric constant (?₃₃) and the piezoelectric constant (d₃₃) attain the maximum values of 924 and 13 pC/N, respectively, while the electromechanical coupling factor (k_p) value is 0.035. The NBT–BT_0.11 ceramics derived from sol–gel present high mechanical quality factor (Q_m ～ 860). The dielectric and piezoelectric properties values of NBT–BT_0.11 ceramics derived from sol–gel are smaller than those of samples produced by the conventional solid state reaction method, due to the grains size and oxygen vacancies that generate dipolar defects.     

Layered mixed-anion compounds: Epitaxial growth,active function exploration,and device application

Optoelectronic properties and device applications of layered mixed-anion compounds such as oxychalcogenide LaCuOCh (Ch = chalcogen) and oxypnictide LaT_MOPn (T_M = 3d transition metal, Pn = pnicogen) are reviewed. Several distinctive functions have been found in these materials based on our original material exploration concept. Fabrication of high-quality epitaxial films of LaCuOCh leads to clarifying the excellent electrical and optical properties such as high hole mobility of 8 cm²/(V s) and heavy hole doping at >10²¹ cm^?3 in LaCuOSe, and sharp and tunable-wavelength photoluminescence in the solid–solution systems in LaCuOCh. In addition, a room temperature operation of a light-emitting diode is demonstrated using LaCuOSe as a light-emitting layer. These results suggest that the layered oxychalcogenides have potential for light-emitting layers as well as transparent hole-injection layers in organic/inorganic light-emitting diodes. Furthermore, by extending the material system from the copper-based oxychalcogenides to isostructural compounds, transition metal-based oxypnictides LaT_MOP (T_M = Fe, Ni), we have found novel superconductors, LaFeOP and LaNiOP.     

The synthesis,crystal structure and photophysical properties of three novel naphthalimide dyes

Three new naphthalimide derivatives containing an electron-donor moiety (carbazole), 4-carbazolyl-N-methyl-1,8-naphthalimide, 4-carbazolyl-N-cyclohexyl-1,8-naphthalimide and 4-carbazolyl-N-phenyl-1,8-naphthalimide were synthesized and crystal structures confirmed. Crystallographic data revealed that the interplanar angles (θ) of the carbazole and naphthalimide moieties were, respectively, 70.7° and 66.5°. The UV–vis absorption and photoluminescent spectra of the systems in n-hexane, CHCl₃, tetrahydrofuran and CH₂Cl₂ were investigated. The lowest absorption band of the naphthalimide molecular centered at 400–420 nm was assigned to charge-transfer transition with emission at ≈440 nm in n-hexane and at ≈560 nm in CH₂Cl₂.     

The synthesis,structure and spectroscopic properties of novel oxazolone-, pyrazolone- and pyrazoline-containing heterocycle chromophores

A series of novel heterocycle-based chromophores containing oxazolone, pyrazolone or pyrazoline moieties were synthesized under microwave irradiation and characterized using elemental analysis, IR, ¹H NMR spectroscopy and mass spectrometry. The crystal structures of two of the dyes were found, using single crystal X-ray crystallography, to be monoclinic, space group P2₁/c types; the two molecules adopted a Z configuration about the central olefinic bond. The heterocyclic chromophores were fluorescent, with some examples emitting blue light (410–460 nm) whilst others emitted green light (529 nm). The absorption maxima of the chromophores were found to vary from 349 to 463 nm depending on the extent of conjugation.     

Luminescent and structural properties of manganese-doped zinc aluminate spinel nanocrystals

Manganese-doped zinc aluminate spinel (ZnAl₂O₄:Mn; Mn=0–6.0 mol%) phosphor nanoparticles were prepared by the sol–gel process. The effects of thermal annealing and dopant concentration on the structure, microstructure and luminescence of the powder phosphors were investigated. The X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) results confirmed that a single-phase spinel started to crystallize at around 600 °C for the investigated powders. On heating at 600–1200 °C, the powders had the average crystallite sizes of around 12–33 nm. The crystallite size and lattice constant increased as the doping level of Mn increased. FT-IR spectra exhibited only absorption bands of the AlO₆ octahedral groups, which suggested that the powder phosphors mainly crystallized in a normal spinel structure. Scanning electron microscopy (SEM) investigations showed the primary particle sizes were around 20–25 nm for the powders annealed at 1000 °C, and less than ca. 50 nm for those annealed at 1200 °C. Photoluminescence (PL) spectra under UV or visible light excitation exhibited a strong green emission band centered at 510 nm, corresponding to the typical ⁴T₁(⁴G)—⁶A₁(⁶S) transition of tetrahedral Mn²⁺ ions. The most intense PL emission was obtained by exciting at 458 nm. The PL intensity was significantly enhanced by the improved crystallinity and diminished OH^? groups. Optimum brightness occurred at a doping of 3.0 mol% Mn.     

Two step sintering of a novel calcium magnesium silicate bioceramic: Sintering parameters and mechanical characterization

Two-step sintering (TSS) was applied to control the grain growth during sintering of a novel calcium magnesium silicate (Ca₃MgSi₂O₈ – Merwinite) bioceramic. Sol–gel derived nanopowders with the mean particle size of about 90 nm were sintered under different TSS regimes to investigate the effect of sintering parameters on densification behavior and grain growth suppression. Results showed that sintering of merwinite nanopowder under optimum TSS condition (T₁ = 1300 °C, T₂ = 1250 °C) yielded fully dense bodies with finest microstructure. Merwinite compacts held at T₂ = 1250 °C for 20 h had the average grain size of 633 nm while the relative density of about 98% was achieved. Mechanical testing was performed to investigate the effect of grain growth suppression on the hardness and fracture toughness. Comparison of mechanical data for samples sintered under two sintering regimes, including TSS and normal sintering (NS), showed TSS process resulted in significant enhancement of fracture toughness from 1.77 to 2.68 MPa m^1/2.     

Formation of anatase TiO2 nanoparticles by simple polymer gel technique and their properties

Pure anatase nano-TiO₂ powders were successfully prepared by a simple polymer gel technique using poly-(vinylpyrrolidone) (PVP) as the polymer. The products were systematically characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), UV–visible spectroscopy and photoluminescence studies. The XRD and XPS results indicate that the prepared powder had a pure anatase nano-TiO₂ structure with lattice parameters a and c of 0.378 and 0.951 nm, respectively. The particle size analysed by TEM ranged between 7 and 12 nm. The maximum UV absorption for the TiO₂ nanoparticles was below 400 nm with an estimated direct band gap (Eg) of 3.55 eV. The photoluminescence peaks of the nanopowder were observed at 391 and 468 nm. The nanosized materials were produced using a simple and cost effective polymer gel technique.     

Electro-optical and electrochemical properties of an ionic polyacetylene derivative with azobenzene anisole moieties

An ionic polyacetylene derivative with azoanisole moieties was prepared by the activated polymerization of 2-ethynylpyridine by using 4-[4-(9-bromononyloxy)phenylazo]anisole without any additional initiator or catalyst in high yield. The chemical structure of poly[2-ethynyl-N-(p-methoxyphenylazophenyl)oxynonylpyridinium bromide] (PEMPB) was characterized by instrumental methods such as NMR (¹H and ¹³C), IR, UV–vis spectroscopies to have a conjugated polymer backbone system with the designed azobenzene moieties as substituents. This polymer was completely soluble in organic solvents and well processible. The electrochemical and electro-optical properties of PEMPB were studied. The cyclovoltammograms of this polymer exhibited the irreversible electrochemical behaviors between the oxidation and reduction peaks. The oxidation current density of PEMPB versus the scan rate is approximately linear relationship in the range of 30 mV/s–120 mV/s. The exponent of scan rate, x value of PEMPB, is found to be 0.6. The absorption spectrum starts around 700 nm and shows a characteristic absorption band at visible region of 464 nm due to the π → π* interband transition of the polymer backbone, which is a peak of the conjugated polyene backbone. The photoluminescence spectrum showed that the PL peak is located at 539 nm corresponding to the photon energy of 2.30 eV.     

Visible rays cutoff and infrared transmission properties of TeO2–GeO2–V2O5–PbF2 glass systems

Visible rays cutoff infrared transmitting glasses in TeO₂–GeO₂–V₂O₅–PbF₂ glass systems were investigated. Glasses without OH⁻ absorption band transmitting wavelength regions from 2·0 to 5·0 nm were obtained. The addition of fluoride to these glasses and the treatment of dry-air-bubbling during melting decreased markedly absorption coefficient and reflectivity of OH⁻ bands. Reflectivity of OH⁻ bands increased with increasing absorption coefficient. Values of glass transition points from 520 to 540 °C and flow points from 560 to 580 °C were obtained.     

A nitrogen rich Ni(II)–dithiolate system exhibiting acid–base behavior: Synthesis,supramolecular structure and spectroscopy of [Bu4N]2[NiII(ppdt)2] (ppdt = pyrido[2,3-b]pyrazine-2,3-dithiolate)

The compound [Bu₄N]₂[Ni(ppdt)₂] (1) (ppdt = pyrido[2,3-b]pyrazine-2,3-dithiolate) has been synthesized, starting from pyrido[2,3-b]pyrazine-2,3-dithiol, nickel chloride and tetrabutylammonium bromide in methanol. Compound 1 crystallizes in P2₁/c space group (monoclinic system). Its crystal structure is characterized by interesting C–H?S and C–H?N supramolecular weak interactions. Its solution state has been described with acid–base (protonation–deprotonation) behavior, that has rarely been investigated for a metal–dithiolene system. Compound 1 is first instance of a metal–dithiolene compound that has three ring nitrogen on each dithiolate ligand. The pH dependent changes in the charge-transfer absorption band are attributed to the protonation on an imine nitrogen of the ppdt ligand. The complex is electrochemically quasi-reversible with an oxidation potential of E_1/2 = +0.46 V vs. Ag/AgCl in methanol.     

Systematic examination of thermal,mechanical and dielectrical properties of aromatic polybenzoxazines

A series of bis-benzoxazines, prepared in high yield and purity using two synthetic procedures, is reported. Differential scanning calorimetry reveals similar temperatures for the onset of polymerisation (162–180 °C); the higher values representing monomers containing polar bridges or rigid backbones. Dynamic viscoelasticity data reveal glass transition temperatures for the polybenzoxazines ranging from 187 °C to 235 °C; a fluorinated polybenzoxazine consistently yields the highest T_g of the polymers studied. The latter is interesting since it is superior to many commercial benzoxazines with a relatively high T_g (235 °C), flexural modulus (5.0 GPa) and flexural strength (146.7 MPa), but coupled with a breaking strain (3.06%) that is uncharacteristically high for polybenzoxazines. The incorporation of fluorine results in a low dielectric loss properties (D_k = 3.71–4.12 at 10 MHz, D_f = 0.0109 – 0.0980 at 10 MHz), which are comparable with commercial polybenzoxazines, FR4 and aerospace epoxy resins and superior to commercial bismaleimides.     

Solid-state synthesis and spark plasma sintering of submicron BaYxZr1 − xO3 − x/2 (x = 0, 0.08 and 0.16) ceramics

Fine powders (particle size of 100–200 nm) of BaY_xZr_1 − xO_3 − x/2 (x = 0, 0.08, 0.16) were produced by solid-state reaction at 1000–1050 °C using nanocrystalline ZrO₂ and BaCO₃ raw materials. The powders were densified by means of the spark plasma sintering process resulting in dense and homogeneous submicron microstructures. Near full density ceramics with grain size < 300 nm were obtained by sintering at 1600 °C for 1–5 min.     

Facile corrosion synthesis and sintering of disperse pure tetragonal zirconia nanoparticles

Disperse pure tetragonal zirconia (t-ZrO₂) nanoparticles smaller than 10 nm are essential for preparation of structural and functional zirconia materials, but syntheses of t-ZrO₂ nanoparticles using inorganic zirconium salts usually result in severe agglomeration. In this paper, we report a hydrothermal corrosion approach for improving the dispersity of t-ZrO₂ nanoparticles synthesized by precipitation using zirconium oxychloride without any surfactants. Disperse pure t-ZrO₂ nanoparticles with average sizes of 4.5 and 6 nm and size distributions of 2–11 and 3–12 nm were obtained by calcining precipitates at 400 °C for 2 h and 500 °C for 0.5 h followed by HCl corrosion at 120 °C for 75 h, respectively. Disperse t-ZrO₂ nanoparticles with an average size of 6 nm and a size distribution of 3–12 nm were pressed into green compacts at 500 MPa and sintered by two-step sintering (heating to 1150 °C without hold and decreasing to 1000 °C with a 10 h hold). The sintered bodies are dense pure monoclinic ZrO₂ nanocrystalline ceramic with a relative density of 99.9% and an average grain size of 110 nm.