Electric-field-induced molecular alignment of side-chain liquid-crystalline polyacetylenes containing biphenyl mesogens

Electric-field-induced molecular alignments of side-chain liquid-crystalline polyacetylenes [-{HC=C[(CH2)(m)OCO-biph-OC7H15]}-, where biph is 4,4'-biphenylyl and m is 3 (PA3EO7) or 9 (PA9EO7)] were studied with X-ray diffraction and polarized optical microscopy. An orientation as high as 0.84 was obtained for PA9EO7. Furthermore, the molecular orientation of]PA9EO7 was achieved within a temperature range between the isotropic-to-smectic A transition temperature and 115 degreesC, and this suggested that the orientational packing was affected by the thermal fluctuation of the isotropic liquid and the mobility of the mesogenic moieties. The maximum achievable orientation for PA9EO7 was much greater than that for PA3EO7. This was the first time that the electric-field-induced molecular orientation of a side-chain liquid-crystalline polymer with a stiff backbone was studied.

Synthesis and properties of polyquinolines and polyanthrazolines containing pyrrole units in the main chain

A series of eight new polyquinolines and polyanthrazolines with pyrrole isomeric units in main chain were synthesized and characterized. The new polymers showed high glass transition temperatures (T-g = 242-339 degreesC) and excellent thermal stability (T-5% = 398-536 degreesC in air, TGA). Compared to the series of polyanthrazolines, the series of polyquinolines exhibited higher thermal stability, better solubility in common organic solvents, and lower maximum absorption wavelengths (lambda(max)(a)). Polyanthrazolines with 2,5-pyrrole linkage showed an unusually high lambda(max)(a) (565 nm) and small band gap (2.02 eV). All polymers in solution had low photoluminescence quantum yields between 10(-2%) and 10(-5%) and excited-state lifetimes of 0.28-1.29 ns. The effects of molecular structure, especially pyrrole linkage structures, on the electronic structure, thermodynamics, and some of the optical properties of the polymers were explored. A model of hydrogen bonds in the main chain of the polymers was suggested to explain the difference in the properties of the isomer polymers. In addition, a polyquinoline (PBM) was chosen to examine the proton conductivity; the result indicated that the PBM/H3PO4 complex exhibited a high conductivity of 1.5 x 10(-3) S cm(-1) at 157 degreesC.

Soluble, saturated-red-light-emitting poly(p-phenylenevinylene) containing triphenylamine units and cyano groups

A conjugated poly(p-CN-phenylenevinylene) (PCNPV) containing both electron-donating triphenylamine units and electron-withdrawing cyano groups was prepared via Knoevenagel condensation in a good yield. Gel permeation chromatography suggested that the soluble polymer had a very high weight-average molecular weight of 309,000. A bright and saturated red emission was observed under UV excitation in solution and film. Cyclic voltammetry showed that the polymer presented quasi-reversible oxidation with a relatively low potential because of the triphenylamine unit. A single-layer indium tin oxide/PCNPV/Mg-Ag device emitted a bright red light (633 nm).

Conformational and orientational analyses of 2,2 '-bithiophene under interaction of external electric field constructed by point charges

The fully relaxed single-bond torsional potentials and orientation-related rotational potentials of 2,2'-bithiophene (BT) under the interaction of an external electric field (EF) constructed by point charges have been evaluated with semi-empirical AMI and PM3 calculations. The torsional potentials are sensitive to both EF strength and direction. While the EF is parallel to the molecular long axis, the torsional barrier around C-x-C-x' bond obviously rises with increasing the EF strength, whereas the relative energies of syn and anti minima show a slight change. The interaction between the EF and the induced dipole moment has been proposed to elucidate this observation. On the other hand, the relative energy difference between the syn and anti minima shows an obvious change, while the EF is perpendicular to the molecular long axis. This feature has been ascribed to the interaction between the EF and the permanent dipole moment of BT. Furthermore, conformational and orientational analyses in two dimensions have been carried out by changing the torsional and rotational angles in the different EF. The conformation and orientation of a gas-phase BT in the EF are governed by both the above factors.

Novel bipolar conjugated polymer containing both triphenylamine and oxadizole units

A novel bipolar conjugated polymer containing triphenylamine and 1, 3, 4-oxadiazole units was synthesized by Suzuki reaction. Its structure and properties were characterized by NMR, IR, UV-Vis, PL spectroscopy and electrochemical measurement. The photo luminescent spectroscopy and cyclic voltammograms measurement demonstrated that the resulting polymer shows blue emission (477 nm) and possesses both electron and hole-transporting property.

Novel blue light-emitting PPV-based copolymer containing triazole and carbazole units

A novel alternating conjugated copolymer containing triazole and carbazole units was synthesized by the Wittig reaction. The resulting bipolar conjugated polymer emits a pure light with good thermal stability, which is a promising candidate for polymer light emitting display.

Study on single crystals of butyl branched polyethylene in the presence of electric field

Single crystal of butyl branched polyethylene with various molecular weight formed from the melt in the presence of electric field was studied. It was found that electric field influenced morphology and structure of the butyl branched polyethylene single crystals formed. The lateral habits of the single crystals were circular shape, which was different from truncated lozenge or lenticular shape single crystals formed from the melt in the absence of electric field. The stems in the single crystals formed in the presence Of electric field were perpendicular to the basal plane of the single crystals, which was different from chain tilting in single crystals formed from the melt in the absence of electric field. The electron diffraction patterns showed that the structure of the circular single crystals was a quasi-hexagonal with looser chain packing. This looser chain packing was favorable to thickening growth of single crystals through chain sliding diffusion. The thickness of the single crystals was much larger and depended on molecular weight. It indicated that the single crystal in the presence of electric field should be an extended chain type Single crystal.

Conformational analysis of 2,2 '-bithiophene under interaction of external electric field defined by point charges

Conformational analysis of 2,2'-bithiophene (BT) under the influence of an electric field (EF) constructed by point charges has been performed by using semi-empirical Austin Model 1 (AM1) and Parametric model number 3 (PM3) calculations. When the EF perpendicular to the molecular conjugation chain is applied, both AM1 and PM3 calculations show an energy increase of the anti-conformation. AM1 predicts that the global minimum shifts to syn-conformation when the EF strength is larger than a critical value. and PM predicts that the local minimum in anti-conformation vanishes. This kind of EF effect has been ascribed to the EF and dipole moment interaction.

Novel macrocyclic precursors of poly{aryl ether ketone (sulfone)} containing hexafluoroisopropylidene units: Synthesis, characterization, and polymerization

Cyclic oligomers containing hexafluoroiso-propylidene(HFIP) units were prepared in excellent yields by a nucleophilic aromatic substitution reaction of 4,4(7)- (hexafluoroisopropylidene) diphenol with difluoro-monomers in the presence of anhydrous potassium carbonate under pseudo high dilution conditions. A combination of GPC, MALDI-TOF MS and NMR analysis confirmed the structure of the cyclic oligomers. All macrocyclic oligomers are crystalline and undergo facile melt polymerization to give high molecular weight fluorinated polyethers.

Melt crystallization of poly(ether ether ketone ketone) under strong electric field

In this paper, melt crystallization of poly(ether ether ketone ketone) (PEEKK) under strong electric field was investigated. In the crystal structure of PEEKK, the length of c axis was found to he 1.075 nm, increasing by 7% compared to that of PEEKK crystallized without strong electric field. The molecule chains might take a more extended conformation through the opening of the bridge bond angles by increasing from 124 degrees to 144 degrees under strong electric field in the crystal structure.

Electric field-induced conformational transition of bovine serum albumin from alpha-helix to beta-sheet

The irreversible conformational transition of bovine serum albumin (BSA) from alpha-helix to beta-sheet, induced by electric field near the electrode surface, was monitored by circular dichroism (CD) with a long optical path thin layer cell (LOPTLC).

Synthesis and characterization of novel bipolar PPV-based copolymer containing triazole and carbazole units

Two new blue light-emitting PPV-based conjugated copolymers containing both an electron-withdrawing unit (triazole-TAZ) and electron-rich moieties (carbazole-CAR and bicarbazole-BCAR) were prepared by Wittig condensation polymerization between the triazole diphosphonium salt and the corresponding dialdehyde monomers. Their structures and properties were characterized by FT-IR, TGA, DSC, UV-Vis, PL spectroscopy and electrochemical measurements. The resulting copolymers are soluble in common organic solvents and thermally stable with a T-g of 147degreesC for TAZ-CAR-PPV and of 157degreesC for TAZ-BCAR-PPV. The maximum photoluminescence wavelengths of TAZ-CAR-PPV and TAZ-BCAR-PPV film appear at 460 nm and 480 nm, respectively. Cyclic voltammetry measurement demonstrates that TAZ-BCAR-PPV has good electrochemical reversibility, while TAZ-CAR-PPV exhibits the irreversible redox process. The triazole unit was found to be an effective pi-conjugation interrupter and can play the rigid spacer role in determining the emission colour of the resulting copolymer.

Synthesis and characterization of alternating copolymers containing triphenylamine as hole-transporting units

A series of light-emitting poly(p-phenylene vinylene)s with triphenylamine units as hole-transporting moieties in the main chain were synthesized via Wittig condensation in good yields. The newly formed vinylene double bonds possessed a trans configuration, which was confirmed by Fourier transform infrared and NMR spectroscopy. The high glass-transition temperature (83-155 degreesC) and high decomposition temperature (> 300 degreesC) suggested that the resulting copolymers possessed high thermal stability. These copolymers, especially TAAPV1, possessed a high weight-average molecular weight (47,144) and a low polydispersity index (1.55). All the copolymers could be dissolved in common organic solvents, such as tetrahydrofuran (THF), CHCl3, CH2Cl2, and toluene, and exhibited intense photoluminesence in THF (the emission maxima were located from 478 to 535 nm) and in film (from 478 to 578 nm). The low onsets of the oxidation potential (0.6-0.75 V) suggested that the alternating copolymers possessed a good hole-transporting property due to the incorporation of triphenylamine moieties. (C) 2001 John Wiley & Sons, Inc.