Vinylene Units Research Articles

Synthesis of poly(p-phenylene-vinylene) derivative having amphiphilic substituents by palladium-catalyzed three-component coupling polymerization of p-bromophenylallene and nucleophile containing oligo-oxyethylene units

The palladium-catalyzed three-component coupling polymerization of p-bromophenylallene and a nucleophile possessing oligo-oxyethylene units was performed to give a poly(p-phenylene-vinylene) derivative having amphiphilic substituents on each vinylene unit in a high yield. The polymer was found to be soluble in organic solvents such as benzene, chloroform, N,N-dimethylformamide, and methanol, whose number-average molecular weight (Mn) and the molecular weight distribution (Mw/Mn) were estimated as 8,600 and 1.76, respectively.

The Importance of Nanoscopic Ordering on the Kinetics of Photoinduced Charge Transfer in Aggregated π-Conjugated Hydrogen-Bonded Donor−Acceptor Systems

Aggregated complexes of diaminotriazine oligo(p-phenylene vinylene) (OPV) units hydrogen bonded to different complementary perylene bisimide (PERY) compounds have been investigated by means of absorption, circular dichroism, photoluminescence, and photoinduced absorption spectroscopy. These studies reveal that in the aggregated state an ultrafast photoinduced charge separation occurs via an intermolecular pathway in the J-type stack of hydrogen-bonded OPV-PERY arrays. The subsequent charge recombination reaction strongly depends on small structural differences within the J-type geometry as revealed by comparison of stacked supramolecular dimers, trimers, and covalently OPV-PERY linked systems. A coupled oscillator model is used to analyze absorption and circular dichroism spectra and to identify intermolecular arrangements that are consistent with the experimental spectra and the charge-transfer kinetics.

Environmentally stable organic thin-films transistors: Terminal styryl vs central divinyl benzene building blocks for p-type oligothiophene semiconductors

Abstract A series of linear oligomers combining thiophene, phenyl and vinyl units were designed and synthesized to investigate the influence of the number and sequence of the π-conjugating groups on the stability and performance of organic thin-film transistors. The optical and electrochemical properties of oligomers in solution were investigated by UV–vis absorption and photoluminescence spectroscopies, and cyclic voltammetry. High vacuum evaporated thin films were investigated by optical absorption, X-ray diffraction and AFM, and implemented as p-type semiconducting layers into organic thin-film transistors (OTFTs). Furthermore, shelf-live tests (under ambient conditions) of the OTFTs based on the distyryl-substituted oligomer, DS-2T , show that the mobility was almost unchanged for 100 days, indicating a high environmental stability and the great importance of end-substitution to provide stability against air-oxidation.

High-Performance Hole-Transport Polyurethanes for Light-Emitting Diodes Applications

A novel family of hole-transport polyurethanes (PUs) has been developed. The PUs were prepared from the condensation polymerization of isophorone diisocyanate (IPDI) with (E,E)-1,4-bis(2-hydroxystyryl)benzene, an oligo p-phenylene-(E)-vinylene (OPV) unit, and various amounts of 2,5-bis(4-hydroxyphenyl)-1,3,4-oxadiazole (OXD), as well as with 4-tert-butyl phenol as the terminal group. The PUs demonstrates superior properties that were concluded on the basis of the improved current injection in the corresponding hole-only device. The OLED device with the OPV−PU interfacial layer inserted in ITO/PEDOT:PSS(20 nm)/PU(30 nm)/α-NPB(10 nm)/Bebq2(20 nm)/Ca(10 nm)/Ag(100 nm) has a dramatic voltage reduction of 2.5 V under the current density of 100 mA/cm2. When compared to the control device, the current efficiency was improved 2.37 times. The maximum brightness increased to 14900 cd/m2 in comparison to that of 5780 cd/m2 for the control device. The performance of the OLED devices was fine-tuned by adjusting the co...

Reaction of Pyridine with Phenylcyanoacetylene: A New Route to Functionalized Polyconjugated 1,4‐Dihydropyridine Systems

AbstractPyridine reacts with phenylcyanoacetylene under mild conditions (20–25 °C, no catalyst) to unexpectedly give the 2:3 adduct — a C,N‐functionalized polyconjugated 1,4‐dihydropyridine system — containing two 1,4‐dihydropyridine cycles and four vinylene units formed by three molecules of phenylcyanoacetylene (the yield is up to 46 %). Other products are higher oligomers of phenylcyanoacetylene terminated by 1,4‐dihydropyridine cycles (approx. 30 % yield). Assembly of the 2:3 adduct proceeds regio‐ and stereoselectively — only one of the possible isomers is formed. The oligomers show paramagnetic and electroconductive properties. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Effect of a low-pressure plasma treatment on water vapor diffusivity and permeability of poly(ethylene-co-vinyl alcohol) and polyethylene films

Poly(ethylene-co-vinyl alcohol) and polyethylene films have been modified by CF 4 microwave plasma. The influence of vinyl alcohol comonomer contents on the properties of these materials under CF 4 microwave plasma has been studied by means of surface energies, atomic force microscopy (AFM), SIMS and calorimetric measurements (DSC). The CF 4 plasma treatment improved the hydrophobicity and the roughness of the film surfaces while the bulk phase in the films were hardly changed. Pervaporation measurements were carried out to characterize the effects of these plasma treatments on water vapor transport through the films. Fluorination of the film surfaces, obtained by the CF 4 plasma treatment allows reducing water permeability of the films. The barrier effect to water in plasma treated layers of EVOH was improved significantly, especially with the sample containing 71 mol% of vinyl alcohol comonomer unit and for which an increase of crystallinity was observed. Such a surface modification with fluorinated groups leads to decrease in the water uptake at the film surface at the feed side so that the plasticization effect of the hydrophobic films by the sorbed water molecules was decreased during the water vapor permeation.

Catalytic and Optical Behavior of Polymer Embedded Metal Nanoparticles

AbstractVery small metal aggregates (nanoaggregates) embedded in an inert polymer matrix, which simply stabilizes the nanodispersion, show unique catalytic and optical behaviour.Indeed Ru‐nanoparticles in vinyl‐aromatic polymers or polyphosphazenes display an enhanced reactivity for hydrogenation of different groups, such as aromatic rings, keto and nitro groups, oximes and nitriles which are converted into the corresponding saturated derivatives under mild conditions.The optical properties of terthiophenethiol‐coated gold nanoparticles in UHMWPE (concentration lower than 4 wt.%) are characterized by poor dichroism due to their centrosymmetric structure. High dichroism (R = 30 at 400 nm, DR = 30) is on the contrary recorded for the terthiophene band showing the chromophores to be sensitive to mechanical orientation also when complexed with gold. On the other hand, nanocomposites based on polymers containing vinyl alcohol units and dispersed gold nanoparticles with average diameter ranging from 3 to 20 nm have been efficiently prepared by an UV photo‐reduction process. Uniaxial drawing of the irradiated Au/polymer nanocomposites favours the anisotropic distribution of packed assemblies of gold particles, providing oriented films with polarization‐dependent tunable optical properties.

Synthesis of isoelectronic polyazomethine and poly(arylene vinylene) by a palladium‐catalyzed Suzuki coupling method

AbstractTwo fully conjugated copolymers containing 2,7‐(9,9‐dioctyl) fluorene and 3,6‐(N‐hexyl‐9H‐carbazole) disubstituted rings and arylene vinylene or azomethine units in the main chain were synthesized through a palladium‐catalyzed Suzuki coupling method of 2,7‐bis(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)‐9,9‐dioctyl fluorene with 1,4‐bis(6‐bromo‐N‐hexyl‐9H‐carbazole‐3‐yl vinyl) benzene or N,N‐bis(6‐bromo‐N‐hexyl‐9H‐carbazole‐3‐yl methylidene) 1,4‐phenylenediamine. Bisbromine arylene vinylene and arylenazomethine monomers were synthesized by condensation of 3‐formyl‐N‐hexyl‐6‐bromo carbazole with tetraethyl‐p‐xylylene diphosphonate or 1,4‐phenylenediamine. Copolymers were characterized by FTIR, 1H‐NMR, DSC, UV‐visible and photoluminescence methods. Copyright © 2005 Society of Chemical Industry

Supramolecular Fluorophores for Biological Studies: Phenylene Vinylene-Amino Acid Amphiphiles

We report here on a family of self-assembling fluorescent organic amphiphiles with a biomolecular L-lysine hydrophile and a photonically active phenylene vinylene hydrophobe. Unlike conventional amphiphiles, these segmented dendrimers feature a rigid, branched hydrophobe, and have packing characteristics controlled by the ratio of cross-sectional areas of the hydrophobe and hydrophile. In dilute solution, the amphiphiles form supramolecular aggregates, which are easily taken in by cells through an endocytic pathway, and have no discernible effect on cell proliferation or morphology. An analogous pyrene-based amphiphile was cytotoxic, suggesting that cell survival may be linked either to the self-assembling nature of the amphiphiles, or to the specific properties of the phenylene vinylene segment. The combination of photonic and biological components in these amphiphiles provides great potential for applications in sensing or delivery of molecules to intracellular targets.

Y-Aromaticity: Why Is the Trimethylenemethane Dication More Stable than the Butadienyl Dication?

[reactions: see text] Resonance energies of the trimethylenemethane dication (1) and the butadienyl dication (4) were evaluated using two independent computational methodologies to provide insight into the validity of Y-aromaticity. One methodology employed density functional theory calculations and examined the resonance contribution of the C=C double bond toward the double hydride abstraction enthalpies of methylpropene (6) and 2-butene (8), yielding 1 and 4, respectively. These resonance contributions by the double bond were determined by calculating the double hydride abstraction enthalpies of both the parallel and perpendicular conformations of vinylogues of 6 and 8, in which n = 1-4 vinyl units were inserted between the central carbon-carbon double bond and each of the reaction centers. Extrapolation of the resonance contribution in each vinylogue to n = 0 yielded the resonance contribution in the respective parent molecules. The second methodology employed an orbital deletion procedure (ODP), which effectively allowed us to examine the energies of individual resonance structures. The resonance energy of each dication is computed as the difference between the most stable resonance structure and that of the delocalized species. The two methodologies are in agreement, suggesting that the resonance energy of the trimethylenemethane dication is substantially greater than that of the butadienyl dication. The origin of this difference in resonance stabilization is discussed.

Electroluminescent and Photovoltaic Properties of the Crosslinkable Poly(phenylene vinylene) Derivative with Side Chains Containing Vinyl Groups

AbstractSummary: The photoluminescence (PL), electroluminescence (EL), and photovoltaic properties of a poly(phenylene vinylene) derivative with its side chains containing vinyl groups, poly[(2,5‐bis‐allyloxyphenylene vinylene)‐co‐(2‐methoxy‐5‐(2′‐ethylhexyloxy)phenylene vinylene)] (A‐PPV) are reported. A‐PPV with the active vinyl units in the end of its side chains can be crosslinked either by UV light irradiation or heating. The crosslinking does not change the color of light emitted from the A‐PPV polymer light‐emitting diode (PLED). FTIR confirms that the photo/heating‐induced crosslinking does not damage the conjugation of polymer at all. However, the PL and EL efficiency of A‐PPV decreased upon photoirradiation due to the existence of residual radicals in the solid‐state film. The relatively stable radicals function as a trap that quenches the luminescence. The blend of A‐PPV and noncrosslinkable polymer, poly(2‐methyloxy‐5‐ethylhexyloxyl‐1,4‐phenylene vinylene) (MEH‐PPV) was employed in the fabrication of PLEDs, and the PLED shows improved performance with a luminous efficiency of >1 cd · A−1. The blend keeps the advantage of crosslinkability of the polymers and lessens the effects of the photo‐produced radicals. The photovoltaic cells comprised of A‐PPV and C60 were fabricated and the energy conversion efficiency of the devices with and without UV treatment was similar, both around 0.3%. The UV irradiation on the blend film with C60 seems resistant to the residual radicals.The I‐V, L‐V plot of PLEDs with A‐PPV treated by UV light.magnified imageThe I‐V, L‐V plot of PLEDs with A‐PPV treated by UV light.

Probing pi-coupling in molecular junctions.

Charge transport characteristics for metal-molecule-metal junctions containing two structurally related pi-conjugated systems were studied to probe pi-pi interactions in molecular junctions. The first molecule contains a typical pi-conjugated framework derived from phenylene vinylene units, whereas the second has the phenylene vinylene structure interrupted by a [2.2]paracyclophane (pCp) core. Electrochemical investigations were used to characterize the defects and packing density of self-assembled monolayers of the two molecules on gold surfaces and to enable quantitative comparison of their transport characteristics. Current-voltage measurements across molecular junctions containing the two species demonstrate that the pCp moiety yields a highly conductive break in through-bond pi-conjugation. The observed high conductivity is consistent with density functional theory calculations, which demonstrate strong through-space pi-pi coupling across the pCp moiety.

Photocurrent Generation of Diarylethene Polymers

ABSTRACT The combination of photochromism and electrical properties in diarylethene (DA) polymers were investigated. Photoswitching function could be introduced into a polymer by incorporating 2,3-bis(2-methylbenzo[b]thiophene-3-yl)hexafluorocyclopentene (BTF) unit plus p-phenylene vinylene (PPV) unit alternatively. The photochromic film of BTF-PPV polymer become dark colored upon exposure to a UV light because π-conjugation delocalizes between the π-conjugative groups and the new absorption band centered at 570 nm was observed from the colored film. In dark the photochromic electrode coated with BTF-PPV copolymer did not show current generation. Upon exposure to UV, large incident photon-to-current generation was observed with the quinone/hydroquinone carrier couple under a bias potential of 165 mV (vs. Ag/AgCl). By optical modulation, a reversible photocurrent generation was observed from the photochromic electrode. On the otherhands, DA polymers derived from 2,3-bis(2-methyl-3-thienyl)hexafluorocyclopentene (TF) and PPV showed no photocurrent generation, indicating photodecomposition of the closed isomer.

The pure red light-emitting fluorene-based copolymers by introducing low energy band-gap dyes

Abstract Four novel fluorene-based light-emitting polymers (PFR1, PFR2, PFR3, and PFR4) containing different comonomers have been designed, synthesized, and characterized. These polymers were thermally stable and readily soluble in organic solvents. The single layer LED devices fabricated from these polymers emitted light from bluish green to pure red. The results show that the color of the light emitted by the homopolymer, poly(9,9-bis(2′-ethylhexyl)fluorene), could be tuned by incorporating comonomers (R1, R2, R3, and R4) with narrower band-gaps. The energy band-gap of the copolymers with those comonomers varied according to the position of the cyano group in the vinylene unit and the type of aromatic group (thiophene or phenylene) incorporated. Notably, PFR4 showed pure red emission (chromaticity values x = 0.67, y = 0.34) that is almost identical to the standard red (0.66, 0.34) demanded by the national television system committee (NTSC) and also exhibited a low turn-on voltage.

Polymer Light-Emitting Diodes Based on PPDFV Copolymers with Fluoro Groups in Vinylene Units

Organic light emitting diodes (OLEDs) have attracted much interest because of their particular low driving voltage, convenient design of the device structures, possible control of emission band, and low fabrication cost compared with any other devices. Since the discovery of electroluminescence (EL) from a conjugated polymer, main-chain conducting polymers such as poly(plenylene vinylene) (PPV), poly(p-phenylene) (PPP), their copolymers and soluble derivatives, has been studied intensively for the possible application as large-area light emitting diodes (LEDs). However, PPV has the disadvantage that electron injection is much more difficult than hole injection. Using additional organic charge-transporting layers, and adjusting the energy band of the polymer by introduction of electronwithdrawing groups attached to the polymer backbone were reported to overcome the imbalance of charge carrier injection or mobility. The introduction of electron-withdrawing groups onto the arylene rings or the vinyl groups of PPV lowers the HOMO and LUMO energy levels of the polymer, thereby permitting the use of a higher work function metal in the LED device. Numerous derivatives of PPV have been reported with electron-withdrawing substituents such as halide, cyano, trifluoromethyl, or methylsulfonylphenyl on the arylene rings. In our previous work, we reported poly(p-phenylenedifluorovinylene) (PPDFV) and poly(2-dimethyloctylsilyl-p-phenylenedifluorovinylene) (DMOS-PPDFV) with fluoro groups as electron withdrawing substituents on vinylene units of conjugated polymers, which showed the high performance of OLEDs. In the present paper, we report the synthesis and electroluminescent properties of the copolymers with p-phenylenedifluorovinylene and 2-dimethyloctylsilyl-p-phenylenevinylene units. The resulting EL polymers were synthesized by the Gilch polymerization method.

Stereoselective Cyclopolymerization of Polar 1,6‐Heptadiynes by Novel, Tailor‐Made Ruthenium‐Based Metathesis Catalysts

AbstractSummary: The cyclopolymerization of 4,4‐bis(hydroxymethyl)‐1,6‐heptadiyne (M1), 4‐(carboxyethyl)‐1,6‐heptadiyne (M2), 4‐(hydroxymethyl)‐1,6‐heptadiyne (M3), and 4‐carboxy‐1,6‐heptadiyne (M4) using five different well‐defined metathesis initiators was investigated. Control of molar mass was achieved with catalysts bearing trifluoroacetate ligands. 13C NMR experiments showed that poly‐M2, prepared by the action of any catalyst consisted solely of five‐membered ring structures, i.e., 1,2‐(cyclopent‐1‐enylene)vinylene units. Effective conjugation lengths of all polymers were calculated from the corresponding UV‐Vis absorption maxima, which varied reversibly with temperature. magnified image

Periodic Mesoporous Organosilica Materials Incorporating Various Organic Functional Groups: Synthesis, Structural Characterization, and Morphology

We describe the syntheses and characterization of a series of periodic mesoporous organosilica (PMO) materials containing various organic functional groups prepared using the direct synthesis method under basic conditions. This synthetic method allows the production of mesoporous organosilicas that have large surface areas and contain several different functional groups, such as a bridged amino, vinyl, ethyl, glycidoxypropyl, and cyanopropyl units. Moreover, the type of organosilane used as a co-precursor has a great influence on the final particle shape and modulates the overall properties of the resulting materials. By changing the precursor type, along with its concentration, the particles can adopt various morphologies, including rod-shaped and wormlike particles that have different degrees of bending. We propose a plausible mechanism to explain the formation of these shapes. We have used X-ray diffraction (XRD) patterns, nitrogen sorption properties, scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and 13C and 29S magic angle spinning (MAS) NMR spectroscopy to characterize the structures and organic functionalities present in the resulting functionalized PMO materials.

Photophysical study of a conjugated–non-conjugated PPV-type electroluminescent copolymer

This paper reports the photo- and electroluminescence studies of emitting species of one of the first reported blue emitters, the conjugated–non-conjugated multi-block copolymer, poly[1,8-octanedioxy-2,6-dimethoxy-1,4-phenylene-1,2-ethenylene-1,4-phenylene-1,2-ethenylene-3,5-dimethoxy-1,4-phenylene]. Because the conjugation length of the emissive center is very well defined (two and half phenylene–vinylene units) the differences found between the fluorescence profile of the fluorophore in solution, at several concentrations and that in the solid state allowed us to conclude that in solid the emission comes from associated forms, such as ground-state dimers and/or excimers. Time-resolved fluorescence in a nanosecond time scale recorded at ϖ em=24,096 cm −1 showed a monoexponential decay of 1.5 ns, which is compatible with rigid forms of stilbene derivatives.

Electrosynthesis of a copolymer containing C 60 in the main chain

The electrochemical synthesis of a copolymer consisting of phenylene vinylene units and C 60 was studied. The starting materials were α,α,α′,α′-tetrabromo- p-xylene and C 60. The fullerene is introduced into the polymer synthesis as a film on the working electrode. The C 60 film is dissolved upon reduction and the reduced fullerene species interacts with the simultaneously reduced precursor at the electrode surface resulting in a film on the substrate. The coupling reaction between the reduced species leads to a material where the fullerene units are incorporated into the main polymer chain. The film formed is characterized by cyclic voltammetry and by FTIR, Raman and UV–vis spectroscopy. The charging discharging reaction of the copolymer film was studied by in situ ATR-FTIR. The spectroscopic results indicate short chains of copolymeric structure. Fluorescence spectra were recorded from films of the copolymer and from PPV. The fluorescence of PPV was quenched to one tenth of its origin in the copolymer film.

Tandem (quadrupole‐time‐of‐flight) electrospray mass spectrometry of oligo(vinyl acetates) with isopropylol or (1‐hydroxyethyl)‐2‐oxyisopropanyl end groups

Poly(vinyl acetates) with either isopropylol or (1-hydroxyethyl)-2-oxyisopropanyl end groups were analysed by tandem mass spectrometry using a quadrupole-time-of-flight (Q-TOF) instrument. Random scission along the polymer backbone was not observed. Instead the initial scissions were derived from the cleavage of end-group species. The resultant macrocations were subject to further elimination reactions that eventually produced polyene macrocations. A smaller fraction of the initial macrocations also reacted by loss of ketene and this reaction produced macrocations containing vinyl alcohol units.