Structure investigation of poly(p-phenylene vinylene)

Electron diffraction patterns of highly oriented poly(p-phenylene vinylene) films obtained by the soluble polymeric precursor route are interpreted on the basis of a monoclinic unit cell containing two monomer units: c (chain axis) = 0.658 nm, a = 0.790 nm, b = 0.605 nm, α ? 123°. The molecules are nearly perfectly oriented along the stretching direction but exhibit partial axial translational disorder.     

Interface formation of metals and poly(p-phenylene vinylene): surface species and band bending

We used X-ray photoemission spectroscopy (XPS) to investigate the surface species of poly(p-phenylene vinylene) (PPV) and its interface formation with Ca and Al. PPV surfaces compositions varied with sample preparation. For relatively "clean'' surfaces with 4–5% O, analysis of the O 1s peak revealed four types of oxygen species, namely carbonyl (C=O), hydroxyl (C–OH), ether (C–O–C) and the carboxylic groups (HO–C=O). The oxygen groups, excluding ether, reacted with Al or Ca to form the corresponding metal oxides. Chemical interactions between the metals and the phenylene and vinylene units to yield new species were not detected. For sulfur-free surfaces, a C 1s peak shift of +0.5 eV followed the deposition of 15–30 Å of Ca on PPV. For sulfur-containing surfaces, the C 1s peak shift was −0.5 eV. We attribute this difference to the interaction of metal atoms with the sulfur impurities. For Al/PPV, a C 1s peak shift occurred at <2 Å of Al deposition and reached a constant value of about +0.4 eV after ⪅8 Å of Al. Again, the direction of the peak shift depended on the presence of sulfur impurities. We attribute the C 1s peak shifts to surface band bending and to Schottky barrier formation. Since surface oxidation of PPV can inhibit band-bending, our overall results suggest that the barrier height at the metal/PPV interface is highly sensitive to the surface preparation and relatively insensitive to the work function of the metals. The shift seen by XPS in the C 1s core level spectra of PPV points clearly to charge transfer and Schottky barrier formation at the interface as a result of metal deposition. These results imply that the metal/polymer interface is not rigid and that triangular barrier tunneling fails to take into account the effect of barrier formation. We propose a band-bending modified tunneling (BBMT) model to explain charge transfer at the Ca/polymer interface. © 1997 John Wiley & Sons, Ltd.     

Crystalline phases of electrically conductive poly(p-phenylene vinylene)

Poly(p-phenylene vinylene) (PPV) undergoes a first-order crystal-crystal phase transition when chemically doped with AsF₅, SbF₅, or H₂SO₄ or electrochemically oxidized with ClO^-₄ as the counterion. These structures have been observed using wide-angle x-ray diffraction. Doping with these agents does not disrupt the original orientation of the PPV crystallites. The crystalline phases obtained with all dopants employed here are similar in character, indicating a closely related family of electrically conductive structures having orthorhombic symmetry. An electrically conductive phase consisting of layers of polymer chains separated by a layer of the chemical dopant is proposed.     

Theoretical study of the conversion of sulfonyl precursors into chains of poly(p-phenylene vinylene)

The elimination and side reactions involved in the thermal conversion of sulfonyl precursor chains into poly(p-phenylene vinylene) (PPV) have been studied in detail, using Density Functional theory, along with the MPW1K functional. The performance of the MPW1K functional for describing radical dissociation and internal conversion reactions of sulfonyl precursors has been assessed against the results of benchmark CCSD(T) calculations. Enthalpies as well as entropies are calculated at different temperatures at the level of the rigid rotor-harmonic oscillator approximation. Entropy effects on internal elimination reactions are very limited. In sharp contrast, at the temperatures under which the conversion is usually performed (550 K), entropy contributions to the activation energies are found to be very significant and to strongly favor direct radical dissociations of the precursors. Further radical side reactions following an E(i) conversion through an alkyl substituent may also significantly contribute to the formation of sp(3) defects and/or cross-linked structures in the polymer-an advantageous feature for the making of materials with improved photoluminescence efficiencies.     

Regio-regular and cross-conjugated poly(thienylene vinylene)s through acyclic diene metathesis

Poly(thienylene vinylene)s (PTV's) are early examples of conjugated polymers but have not been extensively studied when compared with closely analogous polythiophenes. PTV's synthesized through previously reported techniques are similar in structures that contain various alkyl or alkoxy side-chains that exert limited impact on the polymer electronic properties. Herein, we report the preparation of a series of regio-regular PTV's (rr-PTV's) bearing cross-conjugated side-chains through ADMET polymerization of a common brominated di(thienylene vinylene) (DTV) monomer followed by PPM reactions on the resulting brominated PTV. These new polymers contain a bulky silyloxy alkyl side-chain and a functionalized thiophene moiety on every main-chain thiophene unit, and their regio-regular placement is confirmed by NMR spectroscopy. The thienyl based side-groups broaden polymer absorption ranges and at the same time lead to uncommon emission properties that are results of light-induced charge transfer events between the polymer main-chains and side-chains. Removal of the silyl groups on one of these rr-PTV's led to insoluble materials and x-ray diffraction experiments on the collected solids displayed distinct scattering peaks that are absent from similarly functionalized regio-random PTV's reported previously, thus suggesting better crystallinity originated from regio-regularity.     

侧基横挂偶极单元的液晶聚苯撑乙炔的合成与表征

为了制备电致偏振光发光材料, 以对苯二乙炔和2,5-二溴苯衍生物为单体,通过Sonogashira偶联反应, 采用不同Pd催化剂, 合成了一种侧基横挂偶极基团的液晶聚苯撑乙炔. 单体的化学结构通过IR, NMR和元素分析等方法得到确证. 聚合物外观为黄色粉状固体, 室温下溶于CHCl3和THF等有机溶剂. 将聚合物加热到各自的玻璃化转变温度以上都能形成液晶态并显示双向液晶性. 考察了不同催化剂对合成的聚合物的分子量、聚合物链中单体单元的结构排列以及液晶性质的影响. 结果表明, 两种不同的Pd催化剂对合成的聚合物的分子量以及液晶态温度范围影响不大, 但对聚合物的立构规整性以及聚合物的液晶态织构有较大的影响. Pd(PPh3)4作催化剂合成的聚合物中单体单元的结构排列较单一, 可以观察到清晰的液晶态织构. 以PdCl2(PPh3)2为催化剂合成的聚合物链中单体单元的结构排列相对复杂, 液晶态织构不明显. 变温X 射线衍射研究证实聚合物均为向列相液晶.     

Energy-transfer efficiency in stacked oligo(p-phenylene vinylene)s: pronounced effects of order.

The supramolecular structure of two types of oligo(p-phenylene vinylene) (OPV) building blocks in dodecane solution is studied. Monofunctional chromophores (MOPV) form well-defined helical assemblies, whereas bifunctional molecules (BOPV) aggregate into so-called frustrated stacks, lacking any higher helical order. This difference in organization has a major influence on the transfer of excitation energy through the assemblies. Energy transfer to supramolecularly incorporated guests (MOPV with lower bandgap) is used to probe the intrinsic differences in exciton mobility in these two types of mixed aggregates. From the observed donor fluorescence quenching, it can be concluded that the helically ordered nature of the MOPV stacks facilitates the transfer of excitation energy, yielding evidence for higher exciton mobility in the well-ordered assemblies than in the frustrated stacks. Finally, the concept of energy transfer in supramolecular assemblies is extended to the solid state by the successful implementation in a light-emitting diode (LED).     

Fabrication of poly(p-phenylene vinylene) (PPV) nanoheterocomposite films via layer-by-layer adsorption

The fabrication of polyelectrolyte multilayer film architectures composed of a polycation precursor (Pre-PPV) of the electroluminescent poly(p-phenylene vinylene) (PPV) and two different counter-polyanions, cellulosesulfate and poly(vinylsulfate), are reported. All multilayers were characterized by UV/VIS-spectroscopy and X-ray reflectometry. Due to the differences in spatial arrangement of charged groups, rigidity, and conformation of the polyanions, the corresponding multilayer films differ in properties such as average thickness increments and surface roughness. The adsorbed amounts per layer can be adjusted by addition of inorganic salts. Thermal conversion of Pre-PPV to PPV is achieved already slightly above 100 °C, yielding identical absorption spectra for after either 3 h at 160 °C or 20 h at 120 °C. The heat treatment causes the film thickness to be reduced by 24–40% due to elimination of dimethylsulfide and HCl and also the loss of water, but the films stay optically transparent.     

Synthesis and characterization of eumelanin‐inspired poly(indoylenearylenevinylene)s and poly(indoylenearyleneethynylene)s

Four novel conjugated polymers containing the eumelanin‐inspired indole core have been successfully synthesized using common cross coupling reactions. These polymers differed by the arylene and the carbon–carbon bond linkage. Optoelectronic experiments of these polymers suggest that the ethynylene linkage contributed to the red‐shifted absorption spectra and blue‐shifted emission spectra when compared to the vinylene linkage polymers. Furthermore, the optical bandgaps of the poly(indoylenearyleneethynylene)s (PIAEs) were smaller compared to the poly(indoylenearylenevinylene)s (PIAVs). Surprisingly, the HOMOs of these polymers were less affected by the nature of the carbon–carbon linkage. However, the LUMOs of the PIAEs were lower in comparison to the PIAVs. These eumelanin‐inspired PIAEs and PIAVs are good fluorophores with fluorescence quantum yields ranging from 0.12 to 0.67 and have good thermal stability for applications such as in organic light‐emitting diodes. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 457–463     

Aggregation of sulfonated poly(p-phenylene terephthalamide) in dilute solutions

The viscosities of dilute solutions of poly(p-phenylene terephthalamide), PPTS, in dimethylacetamide, water, and their mixtures were determined. The reduced viscosity plot in dimethylacetamide shows a negative slope. When the water content in the mixed solvent in 90% or higher, there is an upswing in the reduced viscosity values at concentrations below 0.1 g/dL. The latter behavior suggests a “polyelectrolyte” effect. However, an association model was found to be able to explain the viscosity behaviors in both solvents. ©1995 John Wiley & Sons, Inc.     

A new green-to-transmissive polymer with electroactive poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) as an interface layer for achieving high-performance electrochromic device

A new neutral green electrochromic (EC) polymer, namely poly(5,8-bis(2,3-dihydro[3,4-B][1,4]dioxin-5-yl)-2,3-dual(4-(hexadecyloxy) phenyl) quinoxaline) (PBOPEQ) was designed and synthesized. PBOPEQ-poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) film was further prepared by electrochemical polymerization on the PEDOT:PSS modified indium tin oxide (ITO) electrode. Scanning electron microscopy images and ultrasonic experiment indicate that PBOPEQ-PEDOT:PSS film shows better film-forming ability and stronger interface adhesive with ITO electrode compared to that of PBOPEQ film. It is worth mentioning that PBOPEQ-PEDOT:PSS film presents more reversible redox characteristic, better optical contrast (~40%) and coloration efficiency (~230 cm² C⁻¹) at 678 nm, excellent EC stability and memory property (36 hr), which should be ascribed to that the electroactive PEDOT:PSS layer facilitates the charge transfer process and enhances the ion doping/dedoping properties. EC device based on PBOPEQ-PEDOT:PSS film exhibits superior integrated performance such as reversible color change from green to transmissive, optical contrast of 41.0% and switching time less than 1 s. Accordingly, PBOPEQ-PEDOT:PSS is an excellent EC material when combined with electroactive PEDOT:PSS interface layer for achieving high performance device, which shows potential applications in displays, electronic papers, and tags.     

Poly(alkylthio‐p‐phenylenevinylene): Synthesis and electroluminescent and photovoltaic properties

Two alkylthio‐substituted poly(p‐phenylenevinylene) (AT–PPV) derivatives, poly(2‐octylthio‐p‐phenylenevinylene) (OT–PPV) and poly[5‐methoxy‐2‐(2′‐ethyl‐hexylthio)‐p‐phenylenevinylene] (MEHT–PPV), were synthesized by a Heck coupling reaction for the investigation of the effect of alkylthio groups on the optoelectronic properties of poly(p‐phenylenevinylene) derivatives. The absorption peaks of OT–PPV and MEHT–PPV solutions were located at 431 and 438 nm, respectively. As for solid films, an OT–PPV film showed an absorption maximum wavelength at 444 nm, 13 nm redshifted in comparison with its solution value, whereas an MEHT–PPV film displayed the same absorption peak position as its dilute solution; this indicated that there was no interchain interaction in the MEHT–PPV film. Polymeric light‐emitting diodes (PLEDs) and polymer solar cells (PSCs) based on OT–PPV and MEHT–PPV were fabricated and characterized. Very narrow bandwidths of the electroluminescence (EL) spectra of the two AT–PPVs were found, with the full width at half‐maximum of the emission being 40 and 47 nm for OT–PPV and MEHT–PPV, respectively. The maximum EL efficiency of the single‐layer PLED based on MEHT–PPV with Al as a cathode reached 1.49 cd/A. The PSC based on a blend of OT–PPV and [6,6]‐phenyl‐C₆₁ butyric acid methyl ester (PCBM) showed the power conversion efficiency of 1.4% under the illumination of AM1.5 (80 mW/cm²). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1279–1290, 2006     

All-cis poly(p-phenylene vinylene)s with high molar masses and fast photoisomerization rates obtained through stereoretentive ring-opening metathesis polymerization of [2,2]paracyclophane dienes with various aryl substituents

Poly(p-phenylene vinylene)s (PPVs) are some of the most widely studied conjugated polymers in academia and industry, but most production methods lack precise control over molar masses and alkene stereochemistry. These critical parameters have a large influence on processability, polymer morphology, and optical properties. Herein, we report the stereoretentive ring-opening metathesis polymerization (ROMP) of [2.2]paracyclophane dienes bearing either a linear alkyl substituent or a branched alkoxy substituent to form all-cis PPVs with great solubility in organic solvents. The introduction of 2-ethylhexyloxy side-chains permits the preparation of PPV with uncharacteristically high molar masses (up to 108.8 kg/mol) for a polymerization with living characteristics. Exposure to UV light (365 nm) rapidly induces isomerization of all-cis alkenes leading to the formation of all-trans PPV. This study proposes an attractive strategy to synthesize soluble all-cis and all-trans PPVs with tunable, high molar masses through careful design of the ROMP monomer.     

Synthesis and characterization of new copolymers of thiophene and vinylene: Poly(thienylenevinylene)s and poly(terthienylenevinylene)s with thioether side chains

Poly[3,4-bis(3-methylbutylthio)thienylenevinylene], poly[3,4-bis-(S)-(2-methylbutylthio)thienylenevinylene], poly[3′,4′-bis(3-methylbutylthio)-2,2′:5′,2″-terthienylene-5,5″-vinylene], and poly{3′,4′-bis-(S)-[2-methylbutylthio]-2,2′:5′,2″-terthienylene-5,5″-vinylene} have been synthesized. The synthesis starts from the thiophene monomers and trimers, which are formylated to give the corresponding dialdehydes. The dialdehydes are reductively polymerized using a McMurry coupling. The polymers are characterized by GPC, optical spectroscopy (FT-IR, UV-vis, circular dichroism spectroscopy and photoluminescence) and by proton and carbon NMR spectroscopy. The polymers are soluble in common organic solvents, such as THF, chloroform, toluene, benzene and 1,2-dichlorobenzene. The solvatochromism and thermochromism of the polymers in solution are investigated, while the optical activity of the polymers is used to investigate the supramolecular aggregation. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4629–4639, 1999     

两种[对苯乙炔-2,5-二(十二烷氧基)对苯乙炔]共聚物的合成及性能研究

用含氯前聚物路线和Ｈｅｃｋ反应分别合成［对苯乙炔－２，５－二（十二烷氧基）对苯乙炔］无规共聚物及交替共聚物．由元素分析、凝胶渗透色谱、吸收光谱及ＤＳＣ对其进行表征，研究了共聚物的组成与导电率、溶解性及发光性能的关系．比较了无规共聚物与交替共聚物在性能上的差别．     

Palladium‐catalyzed three‐component coupling polycondensation of aromatic diiodide,aromatic bis(boronic acid propanediol ester), and norbornadiene: A new route for poly(p‐phenylene vinylene)

A novel synthetic method for soluble precursor polymers of poly(p‐phenylene vinylene) (PPV) derivatives by the palladium‐catalyzed three‐component coupling polycondensation of aromatic diiodides, aromatic bis(boronic acid) derivatives, and norbornadiene is described. For example, the polymerization of 1,4‐diiodo‐2,5‐dioctyloxybenzene, benzene‐1,4‐bis(boronic acid propanediol ester), and norbornadiene at 100 °C for 3 days provided a polymer consisting of the three monomer units in a 97% yield (number‐average molecular weight = 3100, weight‐average molecular weight/number‐average molecular weight = 1.37). A derivative of PPV was produced smoothly by the retro Diels–Alder reaction of the polymer both in a dodecyloxybenzene solution and in a film at 200 °C in vacuo. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3403–3410, 2005     

Self-assembly and luminescence of oligo(p-phenylene vinylene) amphiphiles

We have synthesized a series of amphiphilic molecules consisting of oligo(phenylene vinylene) (OPV) asymmetrically end-substituted with a hydrophilic poly(ethylene glycol) (PEG) segment and a hydrophobic alkyl chain. This amphiphilic structure induces self-assembly into both thermotropic and lyotropic lamellar liquid crystalline (LC) phases. The molecules form strongly fluorescent, self-supporting gels in both water and polar organic solvents, even at high concentrations on the order of 30 wt %. These self-assembled structures have been characterized by small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), and polarized optical microscopy (POM). Photoluminescence (PL) is influenced by the structure of the material, with enhanced emission in the LC state due to assembly of the chromophore in confined two-dimensional layers. Self-assembly controlling molecular aggregation at the nanoscale could significantly improve the performance of OPV-based materials in optoelectronic devices.     

Properties of poly(p-phenylene)s and the perdeuterated analog

ESR data for poly(p-phenylene) (PPP) prepared from benzene and catalyst-oxidant systems were compared with data for PPP obtained by a variety of other methods. The results were similar, except for the Yamamoto preparation, and comparable to the spin densities for heterocyclic polymers of thiophene, pyrrole, and selenophene. Deuterated PPP from C₆D₆ showed significant differences in properties, in comparison to ordinary PPP, in relation to molecular weight, color, solubility, and spins/g in electron spin resonance (ESR). The implications are discussed with regard to the mechanism of benzene polymerization by AlCl₃-CuCl₂.