Synthesis, optical properties and ultrafast dynamics of a 2,1,3-benzothiadiazole-based red emitter with intense fluorescence and large two-photon absorption cross-section

A new 2,1,3-benzothiadiazole-based red fluorescent compound with a D-A-D type structure was synthesized and characterized. The central 2,1,3-benzothiadiazole core was symmetrically connected via the 4,7-positions with two donor groups in which the 7-position of a fluorenyl ring was substituted with a carbazol-9-yl moiety and the 2-position was substituted by a 5-thienyl moiety. The carbazol moieties were further derivatized by two 2-naphthyl moieties at the 3,6-positions. Femtosecond laser spectroscopic techniques including excited state fluorescence and pump-probe technique investigations, together with steady state absorption and one-photon fluorescence spectra, were employed to systematically investigate the optical properties and ultrafast dynamics of the new compound in tetrahydrofuran solution. It shows a large two-photon absorption cross-section and high fluorescence quantum yield, indicating potential application in two-photon fluorescence imaging field. The ultrafast dynamics results reveal competition between a pure excited state relaxation process and stimulated radiation in the red wavelength region.     

Linear and tri-branched copolymers for two-photon absorption and two-photon fluorescent materials

The one- and two-photon properties of linear (M2) and tri-branched (M3) copolymers with triphenylamine and cyano groups in the main chain were experimentally investigated. Open-aperture z-scan experiments were performed with 1 kHz, 120 fs, and 800 nm Ti:sapphire laser pulses to measure the two-photon absorption cross sections. The two-photon cross sections of M2 and M3 were determined to be 0.304 and 1.441×10⁻²⁰ cm⁴/Gw per repeating unit, respectively. In a CHCl₃ solution, M2 and M3 emit strong frequency up-converted fluorescence under the excitation of 120 fs pulses at 800 nm with the peaks located at 561 and 542 nm.     

Mesostructured self-assembled silica films with reversible thermo-photochromic properties

A spiropyran molecule has been introduced via one-pot synthesis into mesostructured silica films, which have been obtained through a micelle templating self-assembling process. The mesostructure has been characterized by transmission electron microscopy and small-angle X-ray scattering performed with synchrotron light. The final material exhibited a p6mm 2d-hexagonal organization and the mesostructure has not been affected by the introduction of spiropyrans in the precursor solution. A comparative characterization of the optical properties of the spiropyrans dissolved in different solvents and after incorporation in the mesostructured films has been done by UV–Vis absorption spectroscopy, fluorescence spectroscopy and ellipsometric spectroscopy. The spiropyran-doped films appeared transparent before external stimuli had applied, a colour change to yellow (thermally induced) or to red (light induced) has been observed. Both the colour changes have been observed to be reversible under room temperature or visible light exposure; the colour transitions have been attributed to different equilibria among the various forms of merocyanine of spiropyrans.     

Enhanced optical absorption cross-section characteristics of multi-wall carbon nanotubes

The optical absorption anisotropy of multi-walled carbon nanotubes (MWCNTs) has been quantitatively characterized through the determination of the absorbance and the degree of linear polarization. A model considering the orientation of the MWCNTs and the sensitivity to both co-polarized and cross-polarized radiation, through electric field depolarization effects, was used to understand the experimental results. The MWCNT optical absorption cross-sections for both the co-polarized radiation (∼0.1 Å²/atom) and the cross-polarized radiation (∼0.05 Å²/atom) were found to be much larger than for single-walled carbon nanotubes. Our results indicate the promise of MWCNTs for applications involving radiation absorption.     

Third-order nonlinear optical properties and two-photon absorption in polymers doped with p-phenyl sydnone

We report the measurements of the third-order susceptibilities and two-photon absorption in three different polymers doped with p-phenyl sydnone moiety viz., 2-benzylhydrazono-5-(3-p-tolylsydnone-4-yl)1,3,4,-thiadiazine, which is recently synthesized and characterized, with the prospective of reaching a good compromise between processability and high nonlinear optical properties. The measurements were done using nano second Z-scan at 532nm. The Z-scan spectra reveal a large negative nonlinear refraction coefficient n₂ of the order 10⁻¹⁴ cm²/W and a two-photon absorption β, which is determined to be the order of cm/GW. The absorption cross section is 10⁻⁴⁶ cm⁴ s/photon. The molecular second-order hyperpolarizability in PMMA matrix was calculated to be 1.47 × 10⁻³¹ esu, comparable with stilbazolieum derivatives, a well-known class of optical materials for photonics and biophotonics applications. The chromophore shows its optical power limiting behavior in all the three polymer matrices. All these results suggest that this moiety has potential for the application of all-optical limiting and switching devices. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

大粒径纳米硅溶胶的制备

采用硅粉氧化水解法制备大粒径硅溶胶,可以应用于涂料、陶瓷、吸附剂、化学机械抛光等领域。采用种子生长法,先制备出种子硅溶胶,再利用种子硅溶胶制备大粒径硅溶胶。通过实验,考察温度、种子质量、催化剂用量,得出较佳实验条件:种子(A)生成温度为75℃,催化剂用量为2 g,所得种子平均粒径为25 nm;硅溶胶(B)生成温度为85℃,催化剂用量为4 g,种子质量为14 g,所得溶胶平均粒径为60 nm。     

Highly ordered orthorhombic mesoporous silica films

Mesoporous silica films are made by the spin-coating technique using an ethylene oxide––propylene oxide––ethylene oxide triblock copolymer (Pluronic PE6800) as template. After optimization of the polymer concentration in the silica sol, films are textured and organized over all the thickness. They exhibit an orthorhombic symmetry (a=16.0 nm, b=10.2 nm, c=23.0 nm) with the b-axis perpendicular to the substrate. This results from a body-centered cubic (bcc) micellar structure which is deformed along the [0 1 1]_bcc cubic axis, i.e. perpendicular to the film plane.     

Gas absorption with large heat effects in packed columns

The system of design equations recently proposed by Treybal for adiabatic packed absorbers has been tested experimentally for ammonia absorption. Examination of temperature profiles and solute recoveries measured in a 6 in. packed column indicated effective interfacial areas for non-isothermal absorption to be larger than those found by Shulman for isothermal absorption. A modification of Shulman's interfacial area relationship, giving good agreement between measured and predicted recoveries and temperature profiles, is proposed. A convenient algorithm for computer solution of the design equations is described.     

Optical birefringence induced by two-photon absorption in polythiophene bearing an azochromophore

We carried out experiments of induced birefringence via two-photon absorption in spin-coated films of the conjugated polymer poly[2-[ethyl-[4-(4-nitro-phenylazo)-phenyl]-amino]-ethane (3-thienyl)ethanoate], PAzT, at 680 and 775 nm. This process allows recording in the bulk because of the spatial confinement of the birefringence provided by the two-photon absorption. The induced birefringence is associated with molecular reorientation caused by the two-photon induced isomerization of the azochromophores attached to the polymer backbone. In addition, the two-photon absorption spectrum of PAzT was measured to help selecting the excitation wavelength for two-photon absorption induced birefringence.     

Microporous polypropylene films containing ultrafine silica particles

Sol–gel reaction of tetraethoxysilane was carried out in molten polypropylene with the aid of an extruder. The resultant composites were used to mold sheets containing finely dispersed SiO₂ particles. These sheets were biaxially stretched to prepare microporous films, of which some properties were estimated (pore size, porosity, specific surface area, and gas permeability). © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1489–1494, 1999     

Alkali-silica reactivity of large silica fume-derived particles

Pozzolanic materials, including silica fume, are commonly added to concrete to reduce expansion due to alkali-silica reaction (ASR). It has been noted, however, that commercial silica fume is not always adequately dispersed, and large agglomerates may be present. These large particles have been hypothesized to act as amorphous silica aggregates, thereby participating in an expansive reaction with the alkalis present in cement paste pore solution. If such were the case, some silica fume particles would actually aggravate expansion due to ASR rather than suppress it. The present investigation characterizes the microstructure and morphology of agglomerated and sintered silica fume particles and compares their effects on alkali-silica-related expansion. While a 5% replacement of moderately reactive sand with sintered silica fume aggregates caused significant expansion under accelerated testing conditions (modified ASTM C1260), the replacement with large agglomerates of densified silica fume decreased expansion compared with control mortar bars containing only sand. Both the sintered aggregates and the agglomerates reacted with the pore solution; one reaction was expansive, while the other was not.     

Vinyl-pyridinium triphenylamines: novel far-red emitters with high photostability and two-photon absorption properties for staining DNA

A series of mono-, bis- and trisvinyl-pyridinium triphenylamines (TP-py) has been synthesised and evaluated for its one- and two-photon absorption (2PA) induced-fluorescence properties under biological conditions. Interestingly, these compounds are only weakly fluorescent in water, whereas their fluorescence emissions are strongly restored (exaltation factors of 20-100) upon binding to double-stranded DNA. Additional measurements in glycerol indicate that the fluorescence increases are the result of immobilisation of the dyes in the DNA matrix, which inhibits rotational de-excitation modes. This particular feature is especially remarkable in the case of the bis and tris derivatives (TP-2 py, TP-3 py), which each display a high affinity (K(d) ~ microM) for dsDNA. TPIF measurements have shown that TP-2 py and TP-3 py each have a large 2PA cross section (delta up to 700 GM) both in glycerol and in the presence of DNA, which ranks them amongst the best 2PA biological fluorophores. Finally, one- and two-photon confocal imaging in cells revealed that these compounds perform red staining (lambda(em)=660-680 nm) of nuclear DNA with excellent contrast. The remarkable optical properties of the TP-py series, combined with their high photostability and their easy synthetic access, make these compounds extremely attractive for use in confocal and 2PA microscopy.     

大断面内胎胎身厚薄不均的原因分析及解决措施

针对大断面内胎本身的结构造成的胎身厚萍不均问题提出了相应的解决措施,主要包括：计算平叠宽度时将伸张率取值范围改为23％－27％;增大半成品冠部、减小里口厚度;严格控制胶料塑性;挤出后半成品停放时间不少于4h;定方式改为卧式定型并采取二次定型法。     

Cooperative enhancement of two-photon absorption based on electron coupling in triphenylamine-branching chromophore

Two novel, triphenylamine derivatives N-(4-(4-(diphenylamino)styryl)phenyl)acetamide and N-(4-(4-(bis-(4-(4-(diphenyl-amino)styryl)phenyl)amino)styryl)phenyl)acetamide were synthesized. The two-photon absorption of N-(4-(4-(bis-(4-(4-(diphenyl-amino)styryl)phenyl)amino)styryl)phenyl) was 17-fold greater relative to N-(4-(4-(diphenylamino)styryl)phenyl)acetamide. Linear absorption spectra, steady-fluorescence and time-resolved fluorescence spectra revealed that electron coupling originating from π-electron delocalization is responsible for the strong cooperative enhancement of TPA within the compounds. This is confirmed by the Lippert-Mataga equation.     

Abrasion resistance of waterborne polyurethane films incorporated with PU/silica hybrids

We describe polyurethane (PU)/silica hybrids (PSHs) prepared through hydrolysis and condensation reactions of tetraethoxysilane (TEOS) with or without methyltriethoxysilane (MTES) in the presence of polyurethane dispersion, which were subsequently incorporated into waterborne polyurethane (WPU) to prepare composites. The effects of the solid mass ratio of PSHs/WPU on the particle size of composite emulsions, the dispersion of silica nanoparticles in composite films, and the hardness and abrasion resistance of the corresponding films were examined. Composite emulsions possess a nanoscale particle size when incorporated with PSHs prepared using TEOS and MTES as precursors, and are superior to those with PSHs prepared using TEOS alone. Transmission electron microscopy revealed that silica nanoparticles had a uniform distribution in the polymer matrix and agglomerates could be almost completely avoided through in situ modification of silica with Si-CH₃ groups in the polyurethane dispersion. Composite films prepared with this method exhibited a superior hardness and abrasion resistance even at a lower silica content compared with that containing unmodified silica. In particular, optical microscopy and scanning probe microscopy observations demonstrated wear behavior differences among these composite films from the macro- and nanoscale viewpoints, respectively. It is proved that abrasive wear occurs, and surface morphology studies are in accordance with the results of abrasion resistance tests.     

Investigation of the surface of silica films doped with Fe and Co

The silica films prepared from tetraethoxysilane sols and doped with iron and/or cobalt nitrates are investigated using atomic-force microscopy and Auger electron spectroscopy. The influence of the metal nature on the surface morphology of the films and the specific features of the distribution of doping elements over the film thickness are demonstrated.     

The synthesis,photophysical properties and two-photon absorption of triphenylamine multipolar chromophores

Triphenylamine core multipolar derivatives were synthesized via the Wittig reaction and Heck reaction and were characterized by MS, NMR, IR; melting points and decomposition temperatures were determined using differential scanning calorimetry. The photophysical as well as the linear and nonlinear spectral properties of multipolar compounds with a triphenylamine core were compared to those of corresponding dipolar compounds. The multipolar chromophores displayed large two-photon absorption and strong optical power limiting properties. An extended π-conjugated system and increased intramolecular cooperative effect are responsible for the observed, large two-photon absorption character.     

Adiabatic gas absorption in packed columns with large thermal effects

The performance of packed bed adiabatic gas absorbers has been analyzed using the enthalpy and material balance equations incorporating a new parameter, f_r, defined as the fraction of the heat of absorption that is accounted for in the gas stream. An experimental programme to evaluate f_r was carried out and the data correlated. It was found that f_r was dependent on the thermo-physical properties and the hydrodynamic conditions. It is postulated that the mechanism by which this heat transfer occurs is by turbulence at the interface and by entrainment.     

Water absorption in acrylic latex films

Water absorption in acrylic latex films was investigated. Films from post-stabilized latices exhibited low water uptake during a long-time immersion in water; this was caused by easier extraction of water soluble materials into water. The extraction of secondary emulsifiers was estimated by liquid chromatography; the structure of film surfaces was investigated by electron microscopy.     

Computational study of the one- and two-photon absorption properties of macrocyclic thiophene derivatives

The geometrical structure, electronic structure, one-photon and two-photon absorption properties of a series of macrocyclic thiophene derivatives C[3T_DA]_n (n = 2-5) have been studied using density functional theory (DFT) and Zerner’s intermediate neglect of differential overlap (ZINDO) methods theoretically. The results showed that the range of λ⁽¹⁾_maxs is 390-470 nm and λ⁽²⁾_maxs is 640-670 nm, while, both λ⁽¹⁾_max and λ⁽²⁾_max gradually enlarge as increasing the number of the C[3T_DA] unit. And C[3T_DA]_n compounds exhibited large TPA cross-section (δ_max), and the factors influencing on the δ_max values were analyzed in detail. Transition dipole moments M_0k and M_kn play important roles on δ_max. Both π-electron number (N_e) and the product of oscillator strengths from ground state to mediate state (?_0k) and from mediate state to final state (?_kn) are in proportion to δ_max. Moreover, δ_max linearly depends on the static second-order nonlinear optical susceptibilities (β₀).