Triplet-state ESR spectra of aromatic molecules oriented in stretched polyethylene films

Triplet-state ESR spectra show that when the aromatic molecules anthracene, anthracene-d₁₀, terphenyl, and acridine are dissolved in stretched, low-density polyethylene films, a fraction of these solute molecules become oriented with their X axis along the stretch direction but with their XY planes oriented randomly to the stretch direction. The fraction of molecules involved in the orientation process is largest for terphenyl.     

Ultraviolet and infrared spectra of substituted indoles

An investigation of the electronic absorption spectra of 5-bromo- and N-methyl indoles in the vapour and liquid state in near u.v. region along with their i.r. spectra in the region 400–4000 cm⁻¹ is presented. The vapour absorption spectra of N-methylindole contains two discrete systems in the region 2906.9-2707.5 Å and 2522-2454 Å. Only one system (2976.2-2844.8 Å) has been photographed in case of 5-bromoindole. The observed bands are interpreted in terms of fundamentals, combinations and overtones. The solution phase spectra contain very limited number of bands in each case. The position of these bands together with the nature of solvents used, has been an indicative of the fact that there is sufficient delocalization of the electrons over both the rings.     

Phosphorescence polarisation of aromatic compounds oriented in stretched polyethylene films

Phosphorescence polarisation measurements are reported for a number of planar aromatic compounds in stretched polyethylene. The phosphorescence is to about 80% polarised perpendicular to the molecular plane. In the in-plane intensity second order Herzberg-Teller coupling terms may be at least competitive with three-center ππ spin-orbit integrals, in agreement with suggestions of Friedrich, Metz and Dörr.     

Fabrication and characterization of orientation in skew stretched polyethylene terephthalate films

Skew stretched films were prepared by first unaxial stretching and subsequently skew stretching at 30 and 60 angles to various stretch ratios. The films were characterized by refractive index (birefringence), infrared absorption (dichroism) and wide-angle x-ray diffraction measurements. The data are represented in terms of ellipsoids and symmetry axes were determined. The results from the different methods are compared. Biaxial orientation factors are computed based on the experimentally determined axes.     

Polarized absorption spectroscopy of trans-azobenzene and trans-stilbene in stretched polyethylene films

The linear dichroism spectra of trans-azobenzene and trans-stilbene aligned in stretched polyethylene films are reported for the u.v.-vis region. On the basis of the results the u.v. transition moment directions with respect to the long molecular axis are determined. Infrared data indicate that trans-azobenzene has a non-planar geometry while trans-stilbene is more planar in the polyethylene matrix. The polarization direction of the nπ* transition in azobenzene is different from that of the first ππ* absorption band, which indicates a vibrational borrowing mechanism corresponding to a nonplanar geometry.     

Polarized infrared spectra of 1,4-dihydroxy-9,10-anthraquinone aligned in stretched polyethylene

The i.r. absorption spectrum of 1,4-dihydroxy-9,10-anthraquinone (quinizarin) has been studied in a stretched polyethylene matrix using linearly polarized radiation. The resulting two linearly independent spectra show that only three different transition moment directions are present in the 30 observed transitions, and this leads to a classification of the 30 peaks according to the point group symmetry of the excited state involved. This classification makes a complete assignment possible, and settles several questions on the assignment which have been discussed in the literature for several years.     

Linear dichroism and fluorescence polarization of diphenyl polyenes in stretched polyethylene films

A study of the linear diehroism and fluorescence polarization of diphenylpolyenes (C₆H₅—(CH=CH)_n—C₆H₅) with n = 1,2,3,4,6,8 in stretched polyethylene films shows that the polyenes orient in the anisotropic matrix with their transition dipole (emission and absorption, π → π^*) aligned with the direction of stretch. The maximum dichroic ratio is observed for 1,6-diphenyl-1,3,5-hexatriene (DPH), with n = 3, whereas the values are substantially lower for n < 3 or n > 3. The high orientation of DPH and poor alignment of the higher polyenes may be accounted for in terms of the growing flexibility of the polyene chains with increasing chain length. The results justify the use of DPH as a convenient fluorescence probe for biological and synthetic membranes.     

Absorption spectra of amorphous organic films

Using a low-temperature evaporation technique, amorphous-state films of naphthacence, perylene, coronene and 1,12-benzoperylene were prepared, and their absorption and fluorescence spectra were measured. The obtained results are discussed and compared with the corresponding crystal-state spectra.     

Ferroelectric liquid crystal composites based on the porous stretched polyethylene films

Electro-optically active polymer–liquid crystal composites based on ferroelectric liquid crystals and stretched porous polyethylene films were developed. The alignment of ferroelectric liquid crystals incorporated into the porous polyethylene films with average porous diameter of around 200 nm was observed and studied. It was shown experimentally that these samples containing ferroelectric liquid crystals are flexible electro-optical films exhibiting a saturation electric field near 2·10⁷ Vm^?1 and a response time of about 30 μs under the action of the saturation field. A simple theoretical model of ferroelectric liquid crystal molecules' complete reorientation in electric fields inside pores of the films has been proposed and confirmed experimentally.     

Cascades to substituted indoles

This paper describes the synthesis of dithioindoles from the free-radical cyclizations of arylisonitriles having pendant alkynes. Also described is the synthesis of substituted indoles and spiro-fused indoles from the coupling of dithioindoles with active hydrogen-containing compounds.     

Emission spectra of naphthalene,anthracene and naphthacene oriented in stretched polyethylene and in shpolskii matrices

Emission spectra of naphthalene, anthracene and naphthacene, oriented in stretched polyethylene sheets, have been studied. Absolute polarization of the bands and symmetry assignments of the vibrational modes are deduced and progressions of bands are drawn up. A comparison with other polarization investigation is given.To support the interpretation of the film spectra the molecules have also been measured (20 K) in suitable crystalline solvents (Shpolskú matries). Discrepancies with the literature are discussed. The anomalous behavior of the environment multiplet structure of naphthacene in n-nonane is described.     

Disorientation of crystallites in highly stretched polyethylene

Crystallite orientation in polyethylene has been investigated in the high range of stretching. Crystallite disorientation can be observed in samples subjected to various stretching procedures: hot drawing and elongation of oriented fibers at room temperature at constant rate and at constant load. Crystallite disorientation does not take place during elongation but is induced upon removal of the applied stress. The higher the rate of removal of stress the greater is the disorientation. Two mechanisms are postulated for the disorientation: one relating to the irregular residual strain developed in fibrils by high stretching, and the other concerning rotational movement of crystallites caused by amorphous chains terminated on the interfaces. The fibrillation brought about by high stretching is thought to play an important role in the crystallite disorientation.     

Calorimetric studies of high molecular polyethylene oxide films isothermally uniaxially stretched at room temperature

The melting behaviour of oriented polyethylene oxide (PEO) films when the film samples were heated in the free state and in the isometric state were investigated by use of DSC. It was shown that in the first case the endotherms of melting have multiple peaks, while in the other case they have one peak. Non-linear dependences of the melting temperature and enthalpy of oriented films on the pressing temperature of the initial PEO isotropic film samples were determined.

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Zusammenfassung Das Schmelzverhalten orientierter PEO-Filme beim Erhitzen der filmproben im freien und isometrischen Zustand wurde mittels DSC untersucht. Es wurde festgestellt, daß im ersten Falle der Schmelzvorgang durch mehrere endotherme Peaks gekennzeichnet ist, während im anderen Falle nur ein endothermer Peak auftritt. Nicht-lineare Abhängigkeiten der Schmelztemperatur und — enthalpie orientierter Filme von der Temperatur, bei der die Bestimmung der ursprünglich isotropen PEO-Filme erfolgte, wurden untersucht.

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Orientation effects in biaxially stretched linear polyethylene

The literature on polymer morphology contains many studies of structural and orientation changes occurring upon uniaxial stretching of films and fibers, but it has only an occasional reference to such studies on biaxially stretched film. This paper presents data on a structural change due to simultaneous biaxial stretching up to 6 × 6 stretch ratio of quenched linear polyethylene slightly below the melting temperature. At low stretch ratios the b axis of the orthorhombic unit cell orients predominantly in the biaxial plane of stretching or film plane. At higher than 4 × 4 stretch ratio, a second crystal orientation appears which is a (110) orientation in the film plane. Differential scanning calorimetry scans show two melting peaks occurring concurrently with diffraction effects of two crystal orientations. The evidence for two populations of crystals differing in orientation are discussed in the light of current concepts of folded-chain lamellae and their fragmentation with elongation.     

Analysis of the visible-near-ultraviolet spectrum of 9-aminoacridine using dichroic spectra in stretched polymer films

We have achieved a deconvolution of the absorption spectrum of 9-aminoacridine dispersed in polyvinyl alcohol films into 11 separate harmonic vibronic progressions of which 5 are polarised along the long axis and 6 along the short axis of the dye. The correlation between the experimental electronic transitions in this range and the calculated (π^*, π) transitions is very satisfactory.     

Absorption spectra and photoemission of ammonium-TCNQ salt evaporated films

A vacuum deposition of ammonium tetracyanoquinodimethanide, NH₄(TCNQ), on a glass substrate was carried out successfully. In the film deposited onto the cooled substrate, the TCNQ anion, which shows an electronic spectrum similar to that of the monomer in solution, was observed for the first time in the solid state. A preliminary result of the photoemission is also presented.     

An expedient synthesis of substituted indoles

Condensation of carboxylic acid esters with organodilithium reagents derived from N-trimethylsilyl-o-toluidine or N-trimethylsilyl-o-ethyl aniline affords substituted indoles.     

Excitation and emission spectra of polyethylene terephthalate and polyethylene 2,6‐naphthalate films

With excitation by the light of the wavelengths longer than 320 nm, fluorescence spectra of polyethylene terephthalate (PET) films had somewhat different shapes from those excited below 300 nm through the intrinsic absorption of PET molecules. Also, in the measurements taken with a polarizer in front of the receiving monochoromator but none before the sample, the intensity ratio of parallel (to the draw axis of the film) and perpendicular components of the emission spectra was different if excited above 320 nm or below 300 nm. Discussion was made about the first step of pumping photon energy at the wavelengths above 320 nm. Fluorescence spectra of polyethylene 2,6‐naphthalate films showed a mirror image of their absorption spectra, consisting of one broad band having the same polarization as their absorption spectra. Their fluorescence occurred from the lowest excited level, conforming to the Kasha law. Copyright © 1999 John Wiley & Sons, Ltd.     

The Neber route to substituted indoles

Two complementary procedures have been developed for the conversion of the oximes of alpha-aryl ketones to azirines. On heating, the azirines rearrange smoothly to the corresponding indoles. The overall transformation offers a versatile route to indoles, complementary to the Fischer indole synthesis.     

1H NMR of probes oriented in stretched polyethylene

¹H NMR spectra of some small molecules oriented in stretched polyethylene rods have been recorded. The band splitting due to direct dipole-dipole couplings is obtained and the corresponding orientation parameters are shown as a function of the draw ratio of the polymer and the temperature. This method is compared to that of using liquid crystals as the orienting solvent.