New luminescent polymers for leds and LECS

Statistical copolymers 5 containing poly(2-dimethyloctylsilyl-1,4-phenylenevinylene) (DMOS-PPV) and poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) have been synthesized using the dehydrohalogenation condensation route. The copolymers show a shift of photoluminescence maxima to longer wavelengths as the proportion of the MEH-PV unit increases. This trend is accompanied by reduced efficiencies and lower turn-on voltages in single layer electroluminescent devices. Light-emitting electrochemical cells (LECs) have been prepared using a blend of DMOS-PPV 1 with poly(ethylene oxide)/lithium triflate and the homopolymer poly[2-methoxy-5-(triethoxymethoxy)-1,4-phenylene vinylene] (MTEM-PPV) 9 with lithium triflate. In comparison with single-layer devices which were fabricated using the homopolymers 1 and poly[2,5-bis(triethoxymethoxy)-1,4-phenylene vinylene] (BTEM-PPV) 10 , the LEC devices showed lower turn-on voltages.     

Phase behavior of PCBM blends with different conjugated polymers

In this work the phase behavior of [6,6]-phenyl C(61)-butyric acid methyl ester (PCBM) blends with different poly(phenylene vinylene) (PPV) samples is investigated by means of standard and modulated temperature differential scanning calorimetry (DSC and MTDSC) and rapid heat-cool calorimetry (RHC). The PPV conjugated polymers include poly(2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylene vinylene) (MDMO-PPV), High T(g)-PPV which is a copolymer, and poly((2-methoxy-5-phenethoxy)-1,4-phenylene vinylene) (MPE-PPV). Comparisons of these PPV:PCBM blends with regioregular poly(3-hexyl thiophene) (P3HT):PCBM blends are made to see the different component miscibilities among different blends. The occurrence of liquid-liquid phase separation in the molten state of MDMO-PPV:PCBM and High T(g)-PPV:PCBM blends is indicated by the coexistence of double glass transitions for blends with a PCBM weight fraction of around 80 wt%. This is in contrast to the P3HT:PCBM blends where no phase separation is observed. Due to its high cooling rate (about 2000 K min(-1)), RHC proves to be a useful tool to investigate the phase separation in PPV:PCBM blends through the glass transition of these crystallizable blends. P3HT is found to have much higher thermal stability than the PPV samples.     

1064-nanometer-excited Fourier transform Raman spectroscopy of conducting polymers

Application of 1064-nm-excited Fourier transform (FT)-Raman spectroscopy to the characterization of conducting polymers is described. 1064-nm-excited FT-Raman spectra with high signal-to-noise ratios are obtained from polyacetylene (PA), poly(1,4-phenylene) (PPP), poly(1,4-phenylene vinylene) (PPV) and poly(2,5-thienylene vinylene) (PTV) in their neutral (insulating) state. The resonant Raman spectra of acceptor- or donor-doped (conducting) PA and PPV are also obtained wih 1064-nm excitation. The resonant Raman spectra of Na-doped PA change in two stages with increasing dopant concentration, the first change corresponding to the increase in electrical conductivity and the second to the appearance of a Pauli susceptibility. The 1064-nm-excited FT-Raman spectrum of Na-doped PPV indicates existence of negative bipolarons which are equivalent to divalent anions extending over a few repeating units in the polymer chains.     

Polymeric mesoions, 3. Synthesis of polymeric mesoionic 1,3-diazinium-olates via polymer analogous modification of a polythiourea from m-phenylenediamine and p-phenylene diisothiocyanate

Mesoionic poly(1,1′-(1,3-phenylene)-3,3′-(1,4-phenylene)-bis(5-decyl-2-decylthio-4,6-dioxo-1,3-diazine)) ( 6 ) was prepared by cyclisation of the isothiourea component of poly(1,1′-(1,3-phenylene)-3,3′-(1,4-phenylene)-bis(2-decylisothiourea)) ( 4 ) with decylmalonic acid (5) by use of dicyclohexylcarbodiimide (DCC). Polymer 4 was obtained by polymer analogous alkylation of poly(1,1′-(1,3-phenylene)-3,3′-(1,4-phenylene)-bisthiourea) ( 3 ). For comparison of spectroscopic data, 5-butyl-2-propylthio-4,6-dioxo-1,3-diphenyl-1,3-diazine ( 9 ) was synthesized as low molecular weight model compound.     

Space charge distribution in luminescent conjugated polymers

We have used for the first time the laser intensity modulation method (LIMM) to resolve the depth profile of space charges in films of poly[(2-(2-ethylhexyl)-5-methoxy-1,4-phenylene)vinylene] (MEH-PPV), poly(pyridine-2,5-diyl) (PPY) and poly(fluorene) (PFO). The results demonstrate that in conjugated polymers space charges can not only be created but also stored permanently.     

Synthesis and electroconductivities of poly(2-methoxy-5-methythio-1,4-phenylene vinylene) and copolymers

Poly(2-methoxy-5-methylthio-1,4-phenylene vinylene), PMTPV, and copolymers containing both unsubstituted or 2,5-dimethoxy-substituted and 2-methoxy-5-methylthio-1,4-phenylene vinylene units were prepared in thin films from their water-soluble, sulfonium salt precursor polymers. Doping of drawn and undrawn films of PMTPV with I₂ vapor led to conductivities of 10^?4–10^?3 S cm^?1, which is significantly lower than those reported for poly(2,5-dimethoxy-1,4-phenylene vinylene). Conductivity of I₂-doped copolymer films ranges from 10^?3–10⁰ S cm^?1 depending on composition.     

Rheological behavior of precursor PPV monolayers

The rheological behavior of different precursor poly(p-phenylene vinylene) (prec-PPV) monolayers at the air-water interface was investigated using an interfacial stress rheometer (ISR). This device nicely reveals a transition of the precursor poly(2,5-dimethoxy-1,4 phenylene vinylene) (prec-DMePPV) monolayer from Newtonian to elastic behavior with increasing surface pressure. The transition is accompanied by an increase in the modulus. This behavior coincides with the coagulation of different 2D condensed domains as revealed by Brewster angle microscopy (BAM). However, partly converted prec-DMePPV monolayers show elastic behavior even at low surface pressures, although a sudden increase of the moduli does occur. This phenomenon is attributed to enhanced hydrophobic interactions between the conjugated moieties in the partly converted polymers. The latter also explains the stretching behavior of the partly converted prec-DMePPV upon transfer in Langmuir-Blodgett-type vertical dipping. The increase of the moduli which is observed is much more gradual in the precursor poly(2,5-dibutoxy-1,4-phenylene vinylene), prec-DBuPPV, a monolayer which is in agreement with the expected expanded state of the latter monolayer.     

Photocurrent generation in multilayer self-assembly films fabricated from water-soluble poly(phenylene vinylene)

A novel, water-soluble, cationic PPV derivative poly[(2,5-bis(3-bromotrimethylammoniopropoxy)-phenylene-1,4-divinylene)-alt-1,4-(2,5-bis(2-(2-hydroxyethoxy)ethoxy))phenylene vinylene] (BH-PPV) has been synthesized by a Heck coupling reaction. Multilayered assemblies of the BH-PPV and the sodium salt of hexa(sulfobutyl)fullerenes (C(60)-HS) were fabricated successfully by an alternate deposition technique. The multilayer structures were studied by UV/Vis spectroscopy, small angle X-ray diffraction, and atomic force microscopy. The photoinduced charge transfer property of the self-assembled multilayer film was also measured by a three-electrode cell technique. A steady and rapid cathodic 5.5 microA cm(-2) photocurrent response was measured as the irradiation of the multilayer film was switched on and off. Importantly, the response of on/off cycling is prompt and reproducible. A possible mechanism for the electron-transfer process is proposed.     

Syntheses and properties of polymers from perchloro-p-xylene,perclorobi-p-tolyl,and perchloro-m-xylene with Fe(CO)5 as dechlorinating agent

We describe a new method for the polymerization of perchloroaromatic compounds using Fe(CO)₅ as a dechlorinating agent which allows the syntheses of perchloropoly-1,4-phenylene vinylene ( 8 ), perchloropoly-4,4'-biphenylene vinylene ( 9 ), and perchloropoly-1,3-phenylene vinylene ( 10 ) from perchloro-p-xylene ( 5 ), perchlorobi-p-tolyl ( 6 ), and perchloro-m-xylene ( 7 ), respectively. Polymer 10 , a new macromolecular chlorocarbon, was characterized by elemental analysis and infrared and ultraviolet spectra. The molecular weights (MW's) of the polymers were estimated by osmometry. The XPS spectra of these polymers are discussed. Their thermal properties were studied by thermogravimetry. Electron spin resonance (ESR) studies and some preliminary conductivity measurements, made after doping the polymers with SbF₅, are reported. © 1992 John Wiley & Sons, Inc.     

Syntheses of new poly (arylene vinylene) analogues: Poly (4,7-benzofuran vinylene) and poly (4,7-benzothiophene vinylene)

The reaction of bis(4,7-tetrahydrothiopheniomethyl) benzofuran dibromide with aqueous tetramethylammonium hydroxide leads to a water-soluble polyelectrolyte which can be film cast and thermolytically eliminated to give poly(4,7-benzofuran vinylene) (PBFV). Subjection of bis(4,7-tetrahydrothiopheniomethyl) benzothiophene dibromide to the same reaction sequence gives poly(4,7-benzothiophene vinylene) (PBTV). UV-VIS studies show that PBFV has a band gap of 2.76 eV, while PBTV has a band gap of 2.92 eV. These polymers are members of a new class of conjugated poly (arylene vinylene)s, in which heterocyclic pseudoaromatic rings are fused onto a poly(1,4-phenylene vinylene) backbone. © 1994 John Wiley & Sons, Inc.     

Chemical and electrochemical doping in poly(paraphenylene vinylene) blends

Blends of poly(p-phenylene vinylene) (PPV), with other polymers were made by film-casting from an aqueous mixture of the water-soluble sulfonium salt precursor to PPV and the second polymer. The rates of chemical doping, using As F₅, and of electrochemical doping, using perchlorate counter ion, of the PPV component are strongly influenced by the nature of the added macromolecule. In all cases studied the blends appear to be phase separated under all conditions. The most versatile blend was with poly(ethylene oxide) (PEO), which could be heated to 225°C without degradation and which yielded the highest electrical conductivity when doped. The utility of blends was demonstrated using free-standing PPV/PEO blend samples as rechargeable battery electrodes.     

Polarized optical spectroscopy applied to investigate two poly(phenylene-vinylene) polymers with different side chain structures

Two related poly(phenylene-vinylene) (PPV) light-emitting polymers have been investigated by means of polarized optical spectroscopy. The purpose of the investigation was to investigate the nature of the interactions in thin films and to examine what impact the difference in side chain structure and molecular weight in poly(2'-methoxy-5-2-ethyl-hexoxy)-1,4-phenylene vinylene (MEH-PPV) and poly(2-(3',7'-dimethyloctyloxy)-5-methoxy-1,4-phenylene-vinylene) (OC1C10-PPV) has on the electronic and optical properties of the two polymers. Aligning the polymers by dispersing them in anisotropic solvents and stretched films shows that the side chains have an impact on the relative orientations of the transition dipole moments. In anisotropic solvents the linear dichroism is larger for MEH-PPV than for the related polymer OC1C10-PPV, while in stretched films the opposite situation prevails. A lower polarization of the luminescence from OC1C10-PPV, relative to MEH-PPV, was also obtained independent of alignment medium used. The data therefore suggest that while mechanical stretching may align the OC1C10-PPV to a greater degree, the emitting species is distinct from the absorbing species. The circular dichroism (CD) spectra of both polymers undergo dramatic changes when the liquid phase and the solid state (film) are compared. The solution CD spectra shows no evidence of interchain interactions; instead the spectra of both systems indicate a helical conformation of the polymers. The CD spectra of films are dramatically different with the strong Cotton effect being observed. This points to the formation of an aggregate in the film, with an associated ground state interaction, an interchain species such as a physical dimer, or a more complex higher aggregate.     

Thermally‐Activated Pentanol Delivery from Precursor Poly(p‐phenylenevinylene)s for MEMS Lubrication

The synthesis of two new polyphenylene vinylene (PPV) precursor polymers which can be thermally induced to eliminate pentanol is presented. Pentanol has recently been discovered to be a very useful lubricant in MicroElectroMechanical Systems. The utilization of the elimination reaction of precursor polymers to PPV as a small molecule delivery platform has, to the best of our knowledge, not been previously reported. The elimination reactions were examined using thermal gravimetric analysis, gas chromatography, and UV–Vis spectroscopy. Using PPV precursors allows for (1) a high loading of lubricant (one molecule per monomeric unit), (2) a platform that requires relatively high temperatures (>145 °C) to eliminate the lubricant, and (3) a non‐volatile, mechanically and chemically stable by‐product of the elimination reaction (PPV).     

Femtosecond laser writing of PPV‐doped three‐dimensional polymeric microstructures

Poly(para‐phenylene vinylene) (PPV) is a key material for optoelectronics because it combines the potential of both polymers and semiconductors. PPV has been synthesized via solution‐processable precursor route, in which the precursor polymer poly(xylene tetrahydrothiophenium chloride) (PTHT) is thermally converted to PPV throughout the sample as a whole. Much effort has been devoted to fulfill spatial selectivity of PPV conversion. However, none of the methods proposed stand for PPV conversion three dimensionally, which would be appealing for the design of microdevices. Here, we demonstrate the potential of fs‐laser direct writing via two‐photon polymerization (2PP) to fabricate PPV‐doped 3D microstructures. PTHT is incorporated into the polymeric material and it is subsequently converted to PPV through a thermal treatment. Optical measurements, taken prior and after thermal conversion, confirm the PTHT to PPV conversion. Fs‐laser direct writing via 2PP can be exploited to fabricate a variety of 3D microdevices, thus opening new avenues in polymer‐based optoelectronics. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 479–483     

Syntheses and electroluminescence properties of conjugated poly(p‐phenylene vinylene) derivatives bearing dendritic pendants

A series of new poly(p‐phenylene vinylene) derivatives with different dendritic pendants—poly{2‐[3′,5′‐bis(2″‐ethylhexyloxy)benzyloxy]‐1,4‐phenylenevinylene} (BE–PPV), poly{2‐[3′,5′‐bis(3″,7″‐dimethyl)octyloxy]‐1,4‐phenylenevinylene} (BD–PPV), poly(2‐{3′,5′‐bis[3″,5″‐bis(2?‐ethylhexyloxy)benzyloxy]benzyloxy}‐1,4‐phenylenevinylene) (BBE–PPV), poly(2‐{3′,5′‐bis[3″,5″‐bis(3?,7?‐dimethyloctyloxy)benzyloxy]benzyloxy}‐1,4‐phenylenevinylene) (BBD–PPV), and poly[(2‐{3′,5′‐bis[3″,5″‐bis(2?‐ethylhexyloxy)benzyloxy]benzyloxy}‐1,4‐phenylenevinylene)‐co‐(2‐{3′,5′‐bis[3″,5″‐bis(3?,7?‐dimethyloctyloxy)benzyloxy]benzyloxy}‐1,4‐phenylenevinylene)] (BBE‐co‐BBD–PPV; 1:1)—were successfully synthesized according to the Gilch route. The structures and properties of the monomers and the resulting conjugated polymers were characterized with ¹H and ¹³C NMR, elemental analysis, gel permeation chromatography, thermogravimetric analysis, ultraviolet–visible absorption spectroscopy, photoluminescence, and electroluminescence spectroscopy. The obtained polymers possessed excellent solubility in common solvents and good thermal stability, with a 5% weight loss temperature of more than 328 °C. The weight‐average molecular weights and polydispersity indices of BE–PPV, BD–PPV, BBE–PPV, BBD–PPV, and BBE‐co‐BBD–PPV (1:1) were in the range of 1.33–2.28 × 10⁵ and 1.35–1.53, respectively. Double‐layer light‐emitting diodes (LEDs) with the configuration of indium tin oxide/polymer/tris(8‐hydroxyquinoline) aluminum/Mg:Ag/Ag devices were fabricated, and they emitted green‐yellow light. The turn‐on voltages of BE–PPV, BD–PPV, BBE–PPV, BBD–PPV, and BBE‐co‐BBD–PPV (1:1) were approximately 5.6, 5.9, 5.5, 5.2, and 4.8 V, respectively. The LED devices of BE–PPV and BD–PPV possessed the highest electroluminescent performance; they exhibited maximum luminance with about 860 cd/m² at 12.8 V and 651 cd/m² at 13 V, respectively. The maximum luminescence efficiency of BE–PPV and BD–PPV was in the range of 0.37–0.40 cd/A. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3126–3140, 2005     

Core-sheath functional polymer nanofibers prepared by co-electrospinning

Core-sheath polymer nanofibers with optoelectronic materials as the sheath and easily spinnable polymer as the core were prepared by co-electrospinning. Three prototypical systems of polystyrene/poly(p-phenylene vinylene) (PS/PPV), poly(vinyl alcohol)/poly(p-phenylene vinylene) (PVA/PPV) and polystyrene/tris(8-quinolinolato) aluminum (PS/Alq₃) were investigated. The fluorescence microscopy images showed that the resulting nanofibers with uniform morphologies exhibited outstanding emission properties. The core-sheath structures of these nanofibers were observed by TEM investigation. The photoluminescence spectra indicated that the fluorescent properties of these functional core-sheath nanofibers could be influenced by the interaction between core and sheath materials.     

An IR study of poly-1,4-phenylenevinylene (PPV), the 2,5-dimethoxy derivative [(MeO)2-PPV], and their corresponding xanthate precursor polymers and monomers

A detailed comparison of the infrared (IR) spectra of poly-1,4-phenylenevinylene (PPV), its xanthate precursor polymer, and its bis-xanthate precursor monomer along with the corresponding 2,5-dimethoxy derivatives has provided a clearer basis for characterizing these species with regard to both structure and purity. All the xanthate precursor monomers and polymers exhibit characteristic intense absorptions typical of the xanthate group near 1220, 1110, and 1050 cm(-1). Upon complete conversion of the precursor polymer to the vinylene linked final product, the intense IR peaks of the xanthate group have disappeared and new bands resulting from the vinylene linkages are found. The latter include a moderately strong band near 965 cm(-1) due to the out-of-plane -CHCH- deformation of the trans-vinylene conjugated with and linking the phenyl rings into an optoelectronic polymer. Unfortunately, the corresponding C-H stretching vibration of this same group of atoms expected to appear near 3020 cm(-1) falls in the same region of the spectrum as the aromatic C-H stretches of the phenyl rings. Similarly, for the 2,5-dimethoxy polymer derivative, [(MeO)(2)-PPV], the C-H stretching vibration near 3055 cm(-1) contains contributions from both aromatic and vinylene C-H. Density functional theory (DFT) calculations on the monomers were instrumental in assigning the infrared spectra of these materials. This study provides a systemic means for verifying that the precursor monomer has been polymerized into the precursor polymer and that thermal conversion to the conjugated polymer is complete.     

Effect of a dipolar self-assembly monolayer formation on indium-tin oxide on the performance of single-layer polymer-based light-emitting diodes

We report on the use of indium-tin oxide surface modification, by grafting of highly polar p-disubstituted benzenes, in the fabrication of light-emitting diodes. The polar compounds possess COCl or SO₂Cl grafting groups and CF₃ or NO₂ as highly electronegative groups, leading to the formation of a dipolar monolayer, which brings about an increase in ITO work function, thereby reducing the barrier for hole injection into luminescent polymers. We observe that the effect of this self-assembled monolayer, in terms of light-onset voltage, efficiency and luminance, is at least comparable to the use of a hole injection layer of doped poly[(3,4-ethylenedioxy)thiophene] for LEDs using poly({2-[(2-ethylhexyl)oxy]-5-methoxy-1,4-phenylene}vinylene) (MEH-PPV) and polyfluorene blends as active layers.     

Preparation and characterization of aromatic copolyesters containing the o,o′-biphenylene ring system

Poly[oxy-2,2′-diphenyleneoxyisophthaloyl-b-oxy(2-methyl-1,3-phenylene)oxyterephthaloyl] I, poly[oxy-2,2′-diphenyleneoxyterephthaloyl-b-oxy(2-methyl-1,3-phenylene)oxyterephthaloyl] II, poly(oxy-2,2′-diphenyleneoxyisophthaloyl-b-oxy-2,2′-diphenyleneoxyterephthaloyl) III, poly[oxy-2,2′-diphenyleneoxyterephthaloyl-b-oxy(2-methyl-1,4-phenylene)oxyterephthaloyl] IV, poly[oxy2,2′-diphenyleneoxyterephthaloyl-b-oxy(2-chloro-1,4-phenylene)oxyterephthaloyl] V, poly[oxy-2,2′-diphenyleneoxyterephthaloyl-co-oxy(2-chloro-1,4-phenylene)oxyterephthaloyl] VI, and poly[oxy-2,2′-diphenyleneoxyterephthaloyl-co-oxy(2-methyl-1,4-phenylene)oxyterephthaloyl] VII have been synthesized and characterized. Random copolyester VI appears to form a birefringent fluid phase above the melting temperature.     

Synthesis,characterization, and electroluminescence of new conjugated PPV derivatives bearing triphenylamine side‐chain through a vinylene bridge

Three new conjugated poly(p‐phenylene vinylene) (PPV) derivatives bearing triphenylamine side‐chain through a vinylene bridge, poly(2‐(4′‐(diphenylamino)phenylenevinyl)‐1,4‐phenylene‐vinylene) (DP‐PPV), poly(2‐(3′‐(3″,7″‐dimethyloctyloxy)phenyl)‐1,4‐phenylenevinylene‐alt‐2‐(4′‐ (diphenylamino)phenylenevinyl)‐1,4‐phenylenevinylene) (DODP‐PPV), and poly(2‐(4′‐(diphenylamino)phenylenevinyl)‐1,4‐phenylenevinylene‐co‐2‐(3′,5′‐bis(3″,7″‐dimethyloctyloxy)‐1,4‐phenylenevinylene) (DP‐co‐BD‐PPV), were synthesized according to the Gilch or Wittig method. Among the three polymers, the copolymer DP‐co‐BD‐PPV is soluble in common solvents with good thermal stability with 5% weight loss at temperatures higher than 386°C. The weight‐average molecular weight (M_w) and polydispersity index (PDI) of DP‐co‐BD‐PPV were 1.83 × 10⁵ and 2.33, respectively. The single‐layer polymer light‐emitting diodes (PLEDs) with the configuration of Indium tin oxide (ITO)/poly (3,4‐ethylenedioxythiophene): poly(4‐styrene sulfonate)(PEDOT:PSS)/DP‐co‐BD‐PPV/Ca/Al were fabricated. The PLED emitted yellow‐green light with the turn‐on voltage of ca. 4.9 V, the maximum luminance of ca. 990 cd/m² at 15.8 V, and the maximum electroluminescence (EL) efficiency of 0.22 cd/A. Copyright © 2007 John Wiley & Sons, Ltd.