Electrochemical and optical characterization of p- and n-doped poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene

We study electrochemical p- and n-type doping in the well-known light-emitting polymer poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV). Doping reactions are characterized using cyclic voltammetry. Optical measurements including photoluminescence and UV/Vis/NIR transmission were performed on doped samples. We find that oxidation in MEH-PPV is a highly reversible reaction resulting in stable freestanding doped films, while the reduced form is unstable and the reaction irreversible. We discuss the dependence of doping reactions on scan rate, film thickness, salt type and concentration, and working electrode type. We observe the development of two additional broad absorption bands in both lightly and heavily doped films accompanied by a slight blueshift in the primary optical transition, suggesting bipolaron band formation. Finally we find that both p and n dopings result in extremely sensitive photoluminescence quenching. We propose a physical model for understanding electrochemical doping in MEH-PPV and the implications this has on the development of such technologies as polymer light-emitting electrochemical cells, electrochromic devices, actuators, and sensors.     

Synthesis and characterization of novel poly(2-methoxy-(5-(6′-dimethylphosphonate)-hexyloxy)-1,4-phenylenevinylene-ran-2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene)s (MEH-PO-PPVs) and their tunable emission colors

Poly(2-methoxy-(5-(6′-dimethylphosphonate)-hexyloxy)-1,4-phenylenevinylene-ran-2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PO-PPV) was synthesized via Heck coupling reaction of MPOHOB-2Br (1) (1-methoxy-(4-(6-dimethylphosphonate)-hexyloxy)-2,5-dibromobenzene), MEHOB-2Br (2) (1-methoxy-4-(6-bromohexyloxy)-2,5-dibromobenzene), and MEHOB-DV (4) (1-methoxy-4-(2′-ethylhexyloxy)-2,5-divinylbenzene) by varying the molar ratios of monomers. The monomers and their intermediates were characterized by ¹H NMR, FT-IR, and melting point and elemental analyzer, and subsequent polymers by FT-IR, ¹H NMR, GPC, DSC, TGA, and solubility test. The optical (UV-vis, PL) and electrical properties (CV) of polymers were also evaluated. MEH-PO-PPV, containing phosphine oxide groups, exhibited better solubility, lower HOMO and LUMO levels, and larger band gaps. In addition, the PL emission gradually shifted to shorter wavelength, providing 570 (MEH-10PO-PPV), 519 (MEH-30PO-PPV), and of 465 nm (MEH-50PO-PPV) as the PO content increased, compared with 598 nm (MEH-PPV).     

Electrical conductivity and photoconductivity of films of composites based on poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] with additions of zinc octabutyl phthalocyanine and C60

Features of the photoconductivity of films of composites based on [2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] with additions of zinc 2,3,9,10,16,17,23,24-octabutylphthalocyanine and C₆₀ were studied. Luminescence quenching and an increase in the photoconductivity with the addition of C₆₀ to their composition were detected. The increase in the photoconductivity is connected with the capture of electrons and their transport along the C₆₀ molecules. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 5, pp. 271–275, September–October, 2006.     

Electrochemical behavior of poly(2-methoxy-5-dodecyloxy-1,4-phenylene vinylene) film electrode

The electrochemical behavior of poly(2-methoxy-5-dodecyloxy-1,4-phenylene vinylene) (MD-PPV) is investigated by cyclic voltammetry and in situ spectroelectrochemical measurement. The energy gap of MD-PPV is determined to be 2.05 eV based on the onset potentials of electrochemical p-doping and n-doping. That PEO affects the electrochemical behavior of MD-PPV/PEO blend positively is also observed.     

Novel green light-emitting diode with high efficiency; synthesis and electroluminescent property of poly(2-(2′-ethylhexylthio)-5-methoxy-1,4-phenylenevinylene) (PMEHTPV)

Poly(2-(2′-ethylhexylthio)-5-methoxy-1,4-phenylenevinylene) (PMEHTPV) was synthesized in thin films via a water-soluble precursor polymer and characterized with thermogravimetric analysis (TGA), FT–IR, and elemental analysis, etc. The PMEHTPV film could be stretched up to 10 times and showed conductivity of 0.13 Scm⁻¹ when doped with FeCl₃. The 2-ethylhexylthio group resulted in blue-shifted absorption and emission compared to those of poly(2-2′-ethylhexyloxy-5-methoxy-1,4-phenylenevinylene) (MEH-PPV). The relative quantum efficiency of the device made by PMEHTPV was 20 times higher than that of MEH-PPV. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2253–2258, 1997     

Application of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] for splitting of single-walled carbon nanotube bundles in polystyrene/SWCNT composite

Dispersions of single-walled carbon nanotubes (SWCNTs) in organic solutions containing poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) were studied by Raman spectroscopy, UV-vis-NIR spectroscopy, and electron microscopy. This polymer interacts with the nanotube resulting in the appearance of a new red-shifted absorption band in the electronic spectrum. This indicates the formation of a charge-transfer complex between MEH-PPV and SWCNTs. Additives of MEH-PPV make it possible to achieve stable suspensions of nanotubes in styrene. A polystyrene/SWCNT/MEH-PPV composite with a high degree of bundle splitting was obtained by polymerization. It was shown that the luminescence intensity of the nanotubes in the Raman spectrum can serve as a indicator for the estimation of the degree of splitting of SWCNT bundles in the composite.     

A solid-contact Pb(2+)-selective electrode using poly(2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene) as ion-to-electron transducer

In this work, a novel all-solid-state polymeric membrane Pb(2+)-selective electrode was developed by using for the first time poly(2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene) (MEH-PPV) as solid contact. To demonstrate the ion-to-electron transducing ability of MEH-PPV, chronopotentiometry and electrochemical impedance spectroscopy measurements were carried out. The proposed electrodes showed a Nernstian response of 29.1 mV decade(-1) and a lower detection limit of subnanomolar level. No water film was observed with the conventional plasticized PVC membrane. This work demonstrates a new strategy for the fabrication of robust potentiometric ion sensors.     

Synthesis and electrical conductivity of poly(1,4-phenylenevinylene-co-2-nitro-1,4-phenylenevinylene)

A series of PPV copolymers containing 2-nitro-1,4-phenylenevinylene (NO₂-PV) units were prepared via the water-soluble precursor route. They were obtained in film form and were doped with I₂ and FeCl₃. Doping increased the electrical conductivities to maximum values of about 3×10^?2 and 3×10^?1 s cm^?1, respectively, for the two dopants. Conductivity depended strongly on the composition of the copolymers; it reached a maximum value at ca. 1–2 mol % of NO₂-PV units in the copolymers and then dropped rapidly with further increase in NO₂-PV content. Electronic effects of the substituent and morphological changes induced by copolymerization appear to interplay intricately, resulting in the occurrence of a maximum conducting composition. © 1993 John Wiley & Sons, Inc.     

Surface modification of poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) by confined photo-catalytic oxidation

In this study, the surface of π-conjugated polymer, poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV), was successfully modified with the sulfate anion (SO(4-)) groups by the confined photo-catalytic oxidation (CPO). After the surface modification, the water contact angle of MEH-PPV is changed from 95.5° to 82.1° without influence on its optical properties (based on the UV and PL spectra), and the water droplet can be absorbed on the modified MEH-PPV surface without sliding even at substrate tilt angles of 90° and 180°. The CPO on the MEH-PPV surface is able to further expand the use of MEH-PPV for applications. In addition, the water transport test indicates that the modified MEH-PPV can be a candidate for transporting water droplet.     

Synthesis and characterization of poly(2,3,5,6-tetrafluoro-1,4-phenylenevinylene)

Poly(2,3,5,6-tetrafluoro-1,4-phenylenevinylene) (PTFPV) was prepared for the first time by the Stille cross-coupling reaction and the resulting material was characterized through MALDI-TOF mass spectrometry, employing a novel sample preparation protocol suitable for insoluble compounds; preliminary optical and electrooptical measurements were performed.     

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.     

Crystal structure of friction-transferred poly(2,5-dioctyloxy-1,4-phenylenevinylene)

Poly(2,5-dioctyloxy-1,4-phenylenevinylene) (DOPPV) was found to form a highly oriented film by a friction-transfer technique. Structural investigation of friction-transferred DOPPV was studied by means of polarized ultraviolet-visible (UV-vis) absorption spectroscopy, polarized photoluminescence (PL) spectroscopy, and synchrotron-sourced grazing incident X-ray diffraction (GIXD) analysis. The polarized UV-vis absorption and PL spectra indicate clear axial alignment. DOPPV backbones in friction-transferred film are highly aligned along the drawing direction of the friction-transfer. Further information of the molecular arrangement in friction-transferred DOPPV film was investigated by both the out-of-plane and the in-plane GIXD analyses with synchrotron source. The DOPPV molecules in friction-transferred films were perfectly arranged three-dimensionally: the backbones aligned along the drawing direction of friction-transfer, the alkyl side chains lay in the film plane, and the planar backbones were arranged parallel to the film surface. Additionally, two neighboring DOPPV molecules along the direction of inter-backbones separation by alkyl side chains were found to be shifted with respect to one another by the mean distance of half of a monomeric repeat.     

1,4-双氯甲基-2-甲氧基-5-壬氧基苯的均聚和共聚

以对甲氧基苯酚和溴壬烷为原料,经过醚化和双氯甲基化反应得到１,４－双（氯甲基）－２－甲氧基－５－壬氧基苯（ＢＣＭＮＯＮＯＢ）,ＢＣＭＭＯＮＯＢ在强碱作用下通过脱氯化氢得到可溶性的聚（２－甲氧基－５－壬氧基）对苯乙炔（ＰＭＯＮＯＰＶ）;首次采用脱氯化氢消除反应实现了ＢＣＭＭＯＮＯＢ与１,４－双（氯甲基）－２,５－二甲基（ＢＣＭＤＭＢ）共聚。讨论了两种单体结构和縻尔比率及溶剂因素对聚合反应和共聚物溶解     

Synthesis of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene-silica core-shell particles with a self-templating method and their fluorescent properties

Sub-micrometer particles with poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene (MEH-PPV) cores coated by silica-based shells were prepared with a self-templating method and their fluorescent properties were investigated in this paper. The characteristic of this method was that all reactions could be finished in one-pot, which exempted from removing the template and reduced reaction steps compared to the conventional process. Emission wavelength of the resultant core-shell particles can readily be tuned through chemical modification of MEH-PPV, which was carried out via regulating the conjugation length of the polymer. In addition, the size of MEH-PPV/SiO₂ core-shell particles could be controlled by altering reaction conditions. The obtained particles had clear core-shell structure and may be used as biolabeling materials. The morphologies, particle size distribution and fluorescent properties of MEH-PPV/SiO₂ particles were characterized by transmission electron microscopy (TEM), particle size analyzer and fluorescence emission spectra, respectively.     

聚(2-甲氧基-5-壬氧基)对苯乙炔的合成及其电致发光性质

以对甲氧基苯酚和溴代正壬烷为原料,通过醚化、氯甲基化和脱氯化氢反应得到可溶性的聚（２－甲氧基－５－壬氧基）对苯乙炔,以其为发光层装配了聚合物单层电致发光器件,研究了它的电致发光和光致发光性质;电致发光器件具有良好的稳定性,其起亮电压为７Ｖ。聚合物的结构由ＩＲ、＾１Ｈ－ＮＭＲ及ＵＶ／Ｖｉｓ光谱得到确认。     

Surface characterization and liquid crystal alignment behavior of comb-like poly(oxyethylene)/poly(3-hexylthiophene) blend films

The blend surfaces of poly[oxy(n-decylsulfonylmethyl)ethylene] (CH(3)-10SE) and poly (3-hexylthiophene) (P3HT) with different weight ratios were prepared by spin coating the polymer solution mixtures. In this study, their surface properties such as surface morphology, chemical composition, molecular structure, and wettability were systematically studied and correlated with liquid crystal (LC) alignment behaviors on the blend films. Therefore, we found that CH(3)-10SE part with a well-ordered side chain structure predominantly affects the both of wettability and LC alignment behavior of the blend films while there was no clear association between the wettability and the LC alignment behavior.     

Electrochemical behavior of high-molecular-weight poly(ferrocenylsilane) films in aqueous electrolyte solutions

The electrochemical behavior of high-molecular-weight poly(ferrocenyldimethylsilane) films and poly(ferrocenylmethylphenylsilane) films, which contained about 2.8 × 10⁻⁶ mol cm⁻² ferrocene sites in eight kinds of aqueous electrolyte solutions, was investigated with cyclic voltammetry (CV). In some aqueous electrolyte solutions, the CV peak currents diminished gradually with an increase in the scanning times, whereas in other aqueous electrolyte solutions, stable and repeated cyclic voltammograms were obtained. The polymer films were poor-solvent-swollen in aqueous electrolyte solutions, and this resulted in a high resistivity of mass transfer and a slow rate of electrode reaction; therefore; quasireversible or irreversible CV processes were obtained. The kinetic parameters of the film-electrode processes, such as the surface transfer coefficient, the apparent diffusion coefficient, and the standard rate constant for electron transfer, for the two films in aqueous LiClO₄ solutions were measured, and the electrode process mechanism of the films was examined. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2245–2253, 2004