Variable Temperature Single‐Molecule Dynamics of MEH‐PPV

Herein, we continue our investigation of the single‐molecule spectroscopy of the conjugated polymer poly[2‐methoxy,5‐(2′‐ethylhexyloxy)‐p‐phenylene‐vinylene] (MEH‐PPV) at cryogenic temperatures. First, the low temperature microsecond dynamics of single MEH‐PPV conjugated polymer molecules are compared to the dynamics at room temperature revealing no detectible temperature dependence. The lack of temperature dependence is consistent with the previous assignment of the dynamics to a mechanism that involves intersystem crossing and triplet–triplet annihilation. Second, the fluorescence spectra of single MEH‐PPV molecules at low temperature are studied as a function of excitation wavelength (i.e. 488, 543, and 568 nm). These results exhibit nearly identical fluorescence spectra for different excitation wavelengths. This strongly suggests that electronic energy transfer occurs efficiently to a small number of low‐energy sites in the multichromophoric MEH‐PPV chains.     

Conformational Relaxation of p‐Phenylenevinylene Trimers in Solution Studied by Picosecond Time‐Resolved Fluorescence

Two p‐phenylenevinylene (PV) trimers, containing 3′‐methylbutyloxyl (in MBOPV3) and 2′‐ethylhexyloxyl (in EHOPV3) side chains, are used as model compounds of PV‐based conjugated polymers (PPV) with the purpose of clarifying the origin of fast (picosecond time) components observed in the fluorescence decays of poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐p‐phenylenevinylene] (MEH‐PPV). The fluorescence decays of MBOPV3 and EHOPV3 reveal the presence of similar fast components, which are assigned to excited‐state conformational relaxation of the initial population of non‐planar trimer conformers to lower‐energy, more planar conformers. The rate constant of conformational relaxation k_CR is dependent on solvent viscosity and temperature, according to the empirical relationship k_CR=aη_o^?α?exp(?αE_η/RT), where aη_o^?α is the frequency factor, η_o is the pre‐exponential coefficient of viscosity, E_η is the activation energy of viscous flow. The empirical parameter α, relating the solvent microscopic friction involved in the conformational change to the macroscopic solvent friction (α=1), depends on the side chain. The fast component in the fluorescence decays of MEH‐PPV polymers (PPVs), is assigned to resonance energy transfer from short to longer polymer segments. The present results call for revising this assignment/interpretation to account for the occurrence of conformational relaxation, concurrently with energy transfer, in PPVs.     

Enhancing the electroluminescent efficiency of poly{5‐methoxy‐2‐[(2′‐ethyl‐hexyl)‐oxy]‐p‐phenylenevinylene}/poly(2,3‐diphenyl‐5‐octyl‐p‐phenylenevinylene) polyblends by the introduction of chemical bonding through a thermal treatment

A significant improvement in the electroluminescence (EL) properties was observed for a poly{5‐methoxy‐2‐[(2′‐ethyl‐hexyl)‐oxy]‐p‐phenylenevinylene} (MEH–PPV)/poly(2,3‐diphenyl‐5‐octyl‐p‐phenylenevinylene) (DPO–PPV) blend after a thermal treatment at 200 °C for 2 h in vacuo to furnish the chemical bonding between polymer chains. ¹H NMR spectroscopy and two‐photon excitation microscopy revealed that the chemical bonding turned the immiscible polyblend into a system more like a block copolymer with a vertically segregated morphology. Because both the lowest unoccupied molecular orbital and highest occupied molecular orbital levels of MEH–PPV in the wetting layer were higher than those of DPO–PPV in the upper layer, the heterojunction between the two layers of the polymers fit the category of so‐called type II heterojunctions. As a result, the turn‐on voltage of the polymer light‐emitting diode prepared with the thermally treated polyblend decreased to ～0.6 V, and the EL emission intensities and quantum efficiencies increased to about 4 times those of the untreated polyblend. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 62–69, 2006     

High‐quality poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐p‐phenylenevinylene] synthesized by a solid–liquid two‐phase reaction: Characterizations and electroluminescence properties

Poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐p‐phenylenevinylene] (MEH‐PPV) with a molar mass of 26–47 × 10⁴ g mol^?1 and a polydispersity of 2.5–3.2 was synthesized by a liquid–solid two‐phase reaction. The liquid phase was tetrahydrofuran (THF) containing 1,4‐bis(chloromethyl)‐2‐methoxy‐5‐(2′‐ethylhexyloxy)benzene as the monomer and a certain amount of tetrabutylammonium bromide as a phase‐transfer catalyst. The solid phase consisted of potassium hydroxide particles with diameters smaller than 0.5 mm. The reaction was carried out at a low temperature of 0 °C and under nitrogen protection. No gelation was observed during the polymerization process, and the polymer was soluble in the usual organic solvents, such as chloroform, toluene, THF, and xylene. A polymer light‐emitting diode was fabricated with MEH‐PPV as an active luminescent layer. The device had an indium tin oxide/poly(3,4‐ethylenedioxylthiophene) (PEDOT)/MEH‐PPV/Ba/Al configuration. It showed a turn‐on voltage of 3.3 V, a luminescence intensity at 6.1 V of 550 cd/m², a luminescence efficiency of 0.43 cd/A, and a quantum efficiency of 0.57%. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3049–3054, 2004     

Fluorescent PMMA/MEH‐PPV electrospun nanofibers: Investigation of morphology,solvent, and surfactant effect

Electrospinning is a powerful technique to produce nanofibers of tunable diameter and morphology for medicine and biotechnological applications. By doping electrospun nanofibers with inorganic and organic compounds, new functionalities can be provided for technological applications. Herein, we report a study on the morphology and optical properties of electrospun nanofibers based on the conjugated polymer poly[2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylenevinylene] (MEH‐PPV) and poly(methylmethacrylate) (PMMA). Initially, we investigate the influence of the solvent, surfactant, and the polymer concentration on electrospinning of PMMA. After determining the best conditions, 0.1% MEH‐PPV was added to obtain fluorescent nanofibers. The optical characterizations display the successful impregnation of MEH‐PPV into the PMMA fibers without phase separation and the preservation of fluorescent property after fiber electrospinning. The obtained results show the ability of the electrospinning approach to obtain fluorescent PMMA/MEH‐PPV nanofibers with potential for optical devices applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1388–1394     

NMR signal assignment of cis/trans‐conformational segments in MEH‐CN‐PPV

Poly[2‐(2′‐ethylhexyloxy)‐5‐methoxy‐1,4‐phenylene‐(1‐cyanovinylene)] MEH‐CN‐PPV and its all‐trans model compound 1,4‐bis(α‐cyanostyryl)‐2‐(2‐ethylhexyloxy)‐5‐methyloxybenzene were synthesized via Knoevenagel condensation. All‐cis isomer and cis–trans isomer of 1,4‐bis(α‐cyanostyryl)‐2‐(2‐ethylhexyloxy)‐5‐methyloxybenzene were prepared by the photoisomerization reaction. Comparison of the ¹H NMR spectra between MEH‐CN‐PPV and three model compounds proved the occurrence of cis‐vinylene in the backbone of MEH‐CN‐PPV. According to the ratio between the cis‐vinylene signal and trans‐vinylene signal, the content of the cis‐vinylene could be estimated to be 15% in MEH‐CN‐PPV. This large cis‐vinylene content came from the rapid photochemical isomerization of cyanovinylene and was likely relative to the poor electroluminescence property of MEH‐CN‐PPV. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1105–1113, 2008     

High red,green, and blue color purity electroluminescence from MEH‐PPV and polyalkyfluorenes‐based bright white polymer light emitting displays

A series of white polymer light emitting displays (PLEDs) based on a polymer blend of polyalkylfluorenes and poly(2‐methoxy‐5,2′‐ethyl‐hexyloxy‐1,4‐phenylene vinylene) (MEH‐PPV) was developed. MEH‐PPV or red light emitting alkyfluorene copolymer (PFR) was blended with blue light emitting alkyfluorene copolymer (PFB), and MEH‐PPV was blended with both green light emitting alkyfluorene copolymer (PFG) and PFB to generate white light emission PLEDs. Low turn on voltage (2.7 V), high brightness (12,149 nits), high efficiency (4.0 cd/A, 4.0 lm/W), and good color purity (Commission Internationale de L'Eclairage (CIE_x,y) co‐ordinates (0.32, 0.34)) were obtained for the white PLEDs based on the PFB and MEH‐PPV polymer blend. Exciplex formation in the interface between PFR and PFB induced a new green emission peak for these two components based white PLEDs. As a result, strong white emission (4078 nits) was obtained by mixing the red, green, and blue (RGB) three primary colors. High color purity of blue (CIE, x = 0.14, y = 0.08), green (CIE, x = 0.32, y = 0.64) and red (CIE, x = 0.67, y = 0.33) emissions was achieved for white PLEDs combining with dielectric interference color‐filters. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 330–341, 2007     

Comparative study of the optical,electrochemical, electrolumiscent,and photovoltaic properties of dendritic pendants modified poly(p‐phenylene vinylene)s

In this study, the optical, electrochemical, electrolumiscent, and photovoltaic properties of a series of poly(p‐phenylene vinylene) (PPV) derivatives bearing different dendritic pendants, poly{2‐[3′,5′‐bis(2″‐ethylhexyloxy)benzyloxy]‐1,4‐phenylenevinylene} (BE‐PPV), poly{2‐[2′,5′‐bis(3″,7″‐dimethyl)octyloxy]‐1,4‐phenylenevinylene} (BD‐PPV), poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylenevinylene] (MEH‐PPV), poly{2‐[3′,5′‐bis(2″‐ethylhexyloxy)benzyloxy]‐1,4‐phenylenevinylene}‐co‐poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylenevinylene] (BE‐co‐MEH‐PPV), and poly{2‐[2′,5′‐bis(3″,7″‐dimethyl)octyloxy]‐1,4‐phenylenevinylene}‐co‐poly[2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐1,4‐phenylenevinylene] (BD‐co‐MDMO‐PPV), were investigated. The steric pendants strongly affect the absorption spectra, photoluminescence (PL) sepctra, the onset oxidation/reduction potentials, and further affect the electrolumiscent and photovoltaic properties. Copolymerization can reduce the steric effect and improve the electrolumiscent and photovoltaic properties. The brightness of light‐emitting diodes base on copolymer BE‐co‐MEH‐PPV and BD‐co‐MDMO‐PPV reached 3988 and 3864 cd/m², respectively, much higher than that based on homopolymer BE‐PPV (523 cd/m²) and BD‐PPV (333 cd/m²), also higher than that based on MEH‐PPV (3788 cd/m²). The power conversion efficiency (PCE) of solar cells based on BE‐co‐MEH‐PPV and BD‐co‐MDMO‐PPV reached 1.41, 0.76%, respectively, much higher than that based on BE‐PPV (0.24%) and BD‐PPV (0.14%). Copyright © 2010 John Wiley & Sons, Ltd.     

Conformation and luminescence characteristics of nanopoly[2‐metoxy‐5‐(2′‐ethyl‐hexyloxy)‐p‐phenylene vinylene] in two‐dimensional arrays

With anodic alumina with an ordered nanopore array used as a template, poly[2‐metoxy‐5‐(2′‐ethyl‐hexyloxy)‐p‐phenylene vinylene] (MEH–PPV) was embedded into the nanopores, and then two‐dimensional arrays of light‐emitting nanopolymers were prepared. By the measurement and analysis of photoluminescence and photoluminescence excitation spectra of the samples, it was demonstrated that the optical properties of the nano‐MEH–PPV arrays were obviously different from those of MEH–PPV films. The conformations of the MEH–PPV chains in the nanopores, films, and solutions and their effects on the optical properties were examined. It was determined experimentally that the conformations of the MEH–PPV chains in the solutions were maintained in the nano‐MEH–PPV arrays. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3037–3041, 2006     

Effect of n‐type doping on the hole transport in poly(p‐phenylene vinylene)

N‐type doping of poly(2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐p‐phenylene vinylene) (MEH‐PPV) with decamethylcobaltocene (DMC) strongly improves the electron transport due to filling of the electron traps. Unexpectedly, the n‐type doping simultaneously suppresses the hole transport in MEH‐PPV. We demonstrate that this strong reduction of the hole transport originates from unionized DMC molecules that act as hole traps. This hole trapping effect explains why the current of a DMC‐doped MEH‐PPV polymer light‐emitting diode is orders of magnitude lower than that of the undoped device. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Fluorescence Quenching of Poly[2-methoxy-5-（2′-ethylhexoxy）-p-phenylene vinylene] （MEH-PPV） in Solutions

Fluorescence quenching processes of poly[2-methoxy-5-(2‘ethyl-hexoxy)-p-phenylene vinylene] (MEH-PPV) in solution by electron acceptors, O2 and acid, have been studied. Static quenching of the fluorescence from MEH-PPV by an electron acceptor (DDQ or TCNE) occurs due to electron transfer from MEH-PPV to the electron acceptor and this electron transfer quenching can be promoted by chloroform. Photooxidation takes place in the MEH-PPV solution and singlet oxygen is an intermediate in the photooxidation, according to the results of ESR spectroscopy. Acid also plays an important role in the fluorescence quenching process of MEH-PPV, by the protonation of the alkoxy groups in the molecular chain.     

Effect of trans‐ and cis‐isomeric defects on the localization of the charged excitations in π‐conjugated organic polymers

We use the long‐range‐corrected hybrid density functional theory models to study the effect of various conformational distortions of weak‐trans and strong‐cis nature on the spatial localization of charged states in poly(p‐phenylene vinylene) (PPV) and its derivative poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐p‐phenylene vinylene] (MEH‐PPV). The extent of self‐trapping of positive (P⁺) and negative (P^?) polarons is observed to be highly sensitive to molecular conformation that, in turn, controls the distribution of atomic charges within the polymers. It is shown that, to reach good agreement with recent experimental data on lattice distortion for P⁺ and P^? excitations, the polarization of the medium plays a critical role. The introduction of weak‐trans defects along the MEH‐PPV chain breaks the observed symmetry for P⁺ and P^? excitations. The P^? states exhibit more spatial localization owing to lattice relaxation than their vacuum counterparts in contrast to P⁺. These observations suggest higher mobilities of holes than that of electrons in MEH‐PPV, in agreement with the experimental observations. The predicted binding, reorganization, and solvation energies for PPV and MEH‐PPV are analyzed for this difference in the response behavior of holes and electrons for trans and cis distortions. This study allows for a better understanding of charge‐transport and photophysical properties in π‐conjugated organic materials by analyzing their underlying structure–property correlations. © 2013 Wiley Periodicals, Inc. 1 1 This article is a U.S. Government work, and as such, is in the public domain in the United States of America.
J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 935–942     

Synthesis of new polyfluorene copolymers with a comonomer containing triphenylamine units and their applications in white‐light‐emitting diodes

Novel conjugated polyfluorene copolymers, poly[9,9‐dihexylfluorene‐2,7‐diyl‐co‐(2,5‐bis(4′‐diphenylaminostyryl)‐phenylene‐1,4‐diyl)]s (PGs), have been synthesized by nickel(0)‐mediated polymerization from 2,7‐dibromo‐9,9‐dihexylfluorene and 1,4′‐dibromo‐2,5‐bis(4‐diphenylaminostyryl)benzene with various molar ratios of the monomers. Because of the incorporation of triphenylamine (TPA) moieties, PGs exhibit much higher HOMO levels than the corresponding polyfluorene homopolymers and are able to facilitate hole injection into the polymer layer from the anode electrode in light‐emitting diodes. Conventional polymeric light‐emitting devices with the configuration ITO/PEDOT:PSS/polymer/Ca/Al have been fabricated. A light‐emitting device produced with one of the PG copolymers (PG10) as the emitting layer exhibited a voltage‐independent and stable bluish‐green emission with color coordinates of (0.22, 0.42) at 5 V. The maximum brightness and current efficiency of the PG10 device were 3370 cd/m² (at 9.6 V) and 0.6 cd/A, respectively. To realize a white polymeric light‐emitting diode, PG10 as the host material was blended with 1.0 wt % of a red‐light‐emitting polymer, poly[9,9‐dioctylfluorene‐2,7‐diyl‐alt‐2,5‐bis(2‐thienyl‐2‐cyanovinyl)‐1‐(2′‐ethylhexyloxy)‐4‐methoxybenzene‐5′,5′‐diyl] (PFR4‐S), and poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylenevinylene] (MEH‐PPV). The device based on PG10:PFR4‐S showed an almost perfect pure white electroluminescence emission, with Commission Internationale de l'Eclairage (CIE) coordinates of (0.33, 0.36) at 8 V; for the PG10:MEH‐PPV device, the CIE coordinates at this voltage were (0.30, 0.40) with a maximum brightness of 1930 cd/m². Moreover, the white‐light emission from the PG10:PFR4‐S device was stable even at different driving voltages and had CIE coordinates of (0.34, 0.36) at 6 V and (0.31, 0.35) at 10 V. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1199–1209, 2007     

Segmented poly[2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylene vinylene] via xanthate and dithiocarbamate precursors: A comparative study of thermal eliminations

Segmented poly[2‐methoxy‐5‐(2‐ethylhexloxy)‐1,4‐phenylene vinylene] (MEH‐PPV)‐x's, which contain conjugated segments of varying lengths that are interspersed by nonconjugated units along the polymer backbone, were synthesized by selective thermal elimination of precursors containing controlled amounts (x) of a thermally labile group, namely, xanthate or dithiocarbamate (DTC). These precursors were in turn synthesized by competitive nucleophilic substitution of the Wessling polyelectrolyte with varying molar fractions of the respective nucleophiles—potassium ethyl xanthate or sodium diethyl dithiocarbamate. Methanol, used as the reaction medium, also served to introduce the second thermally less labile nucleophilic substituent. This approach for the preparation of segmented MEH‐PPV‐x is superior to the previous approach that used acetate as the thermally labile group, because it offers greater control over the composition despite a simpler synthetic procedure. Detailed studies of the thermal‐elimination kinetics of the three precursors, namely, acetate, xanthate, and DTC, both in solution and in thin films, were carried by in situ monitoring of their ultraviolet–visible spectra. These studies revealed that the rates of elimination followed the order, DTC > xanthate > acetate. The activation energies for the elimination were, however, not widely different (ca. 30 kcal/mol), suggesting that the rates primarily reflected differences in the pre‐exponential factor. After elimination, the segmented MEH‐PPV‐x samples exhibited the expected redshift in their absorption and fluorescence spectra with an increasing molar fraction (x) of eliminated segments, which was accompanied by a drastic reduction in the fluorescence quantum yields. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3929–3940, 2003     

Effect of the Solvent on the Conformation of Isolated MEH‐PPV Chains Intercalated Into SnS2

Photophysical processes in conjugated polymers are influenced by two competing effects: the extent of excited state delocalization along a chain, and the electronic interaction between chains. Experimentally, it is often difficult to separate the two because both are controlled by chain conformation. Here we demonstrate that it is possible to modify intra‐chain delocalization without inducing inter‐chain interactions by intercalating polymer monolayers between the sheets of an inorganic layered matrix. The red‐emitting conjugated polymer, MEH‐PPV, is confined to the interlayer space of layered SnS₂. The formation of isolated polymer monolayers between the SnS₂ sheets is confirmed by X‐ray diffraction measurements. Photoluminescence excitation (PLE) and photoluminescence (PL) spectra of the incorporated MEH‐PPV chains reveal that the morphology of the incorporated chains can be varied through the choice of solvent used for chain intercalation. Incorporation from chloroform results in more extended conformations compared to intercalation from xylene. Even highly twisted conformations can be achieved when the incorporation occurs from a methanol:chloroform mixture. The PL spectra of the MEH‐PPV incorporated SnS₂ nanocomposites using the different solvents are in good agreement with the PL spectra of the same solutions, indicating that the conformation of the polymer chains in the solutions is retained upon intercalation into the inorganic host. Therefore, intercalation of conjugated polymer chains into layered hosts enables the study of intra‐chain photophysical processes as a function of chain conformation.     

Hyperbranched framework of interrupted π‐conjugated polymers end‐capped with high carrier‐mobility moieties for stable light‐emitting materials with low driving voltage

A novel series of soluble hyperbranched interrupted π‐conjugated polymers (HICPs) based on complicated 9,9‐diarylfluorenes (CDAFs) branching core and end‐capped with high carrier‐mobility pyrene moieties were synthesized via the “A₂ + A′₂ + B₃” type Suzuki coupling condensation. The new polymer architecture improves the spectrum stability than the corresponding linear and hyperbranched polymers in PLEDs. Besides, it overcomes the drawback of high driving voltage of common interrupted π‐conjugated polymers. CDAF1 exhibits excellent thermal and morphological stability with a decomposition temperature (T_d) higher than 445 °C and a glass transition temperature (T_g) up to 128 °C. No obvious low‐energy green emission band at 520 nm was observed under extreme thermal annealing conditions in air at 200 °C for 12 h. The CDAF1 device shows stable blue emission with the peak at 422 and 447 nm. The Commission International d'Eclairage (CIE) 1931 coordinates is (0.18, 0.16) and the brightness reaches 1051 cd/m² at 15.7 V. White PLED based on CDAF1/MEH‐PPV blends exhibits a low turn‐on voltage of 4.8 V with voltage‐independent CIE of (0.32, 0.32). Molecular simulations were used to investigate the conformation and interchain interaction. HICPs based on CDAFs tethered with high‐mobility moieties are promising stable blue and host materials. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6451–6462, 2009     

Enhancing quantum efficiency of MEH‐PPV through the reduction of chain aggregations by thermal treatments

The quantum efficiencies of photoluminescence (PL) and electro‐luminescence (EL) of poly[2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐1,4‐phenylenevinylene] (MEH‐PPV) were significantly increased by heat treatments under vacuum with further removing the undissolved portion. The UV–vis absorption was found to decrease with heating time, while PL intensity increased. The maximum PL quantum yield was 6.5 times that of the untreated MEH‐PPV, which was attributed to the reduction of chain aggregations and the interruption of conjugation length. The maximum EL quantum yield of their prepared ITO/PANI/MEH‐PPV/Ca/AL light emitting diodes (PLED) was 46 (at 3 V) times that of the untreated sample. A typical turn‐on voltage of 2.5 V for MEH‐PPV PLED was able to decrease to 1 V after heat treatments, which was believed to result from the decrease of cis linkages in the polymer chains as revealed by the ¹H NMR spectroscopy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1705–1711, 2005     

Chain composition dependence of luminescence properties for copolymers of 2‐methoxy‐5‐2′‐ethyl‐hexyloxy‐1,4‐phenylenevinylene and 2,3‐diphenyl‐5‐octyl‐1,4‐phenylenevinylene

The copolymers of 2‐methoxy‐5‐2′‐ethyl‐hexyloxy‐1,4‐phenylenevinylene (MEH‐PV) and 2,3‐diphenyl‐5‐octyl‐1,4‐phenylenevinylene were prepared via the Gilch route with their chain compositions and the reactivity ratios of the monomers estimated by ¹H NMR spectroscopy. The results indicated that the copolymers tended to form an alternative copolymer as the feed ratio of the monomers closed to one‐half. When an individual copolymer solution in tetrahydrofuran was spun‐cast to form a film, the MEH‐PV units were able to attract the like units from the adjacent chains. As a result, the ultraviolet–visible absorption spectrum of the alternative copolymer in film form was broader than the spectra of those with different compositions. The photoluminescence spectra of the copolymers in film form exhibited the characteristic shoulder of poly(2‐methoxy‐5‐2′‐ethyl‐hexyloxy‐1,4‐phenylenevinylene), even though the content of MEH‐PV units was not great enough for the formation of repeat units in sequence. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2180–2186, 2003     

Preparation of MEH‐PPV/nanosized titania hybrids via in situ sol–gel reaction of titanium alkoxide: Optical property

Homogenously dispersed organic (MEH‐PPV)/inorganic (nanosized titania) hybrids were successfully synthesized. The method of preparation was based on a simple one‐step in situ sol–gel technique using titanium isopropoxide (TIP) as the precursor. The key benefit of this preparation was that TIP interacted with both 2‐chlorophenol and MEH‐PPV, so that the degree of aggregation and phase separation could be kept to a minimum with a suitable recipe. MEH‐PPV/TIP/H₂O/2‐chlorophenol of various weight ratios were synthesized to examine the morphology as well as optical properties of the MEH‐PPV/TIP(titania) hybrid. The observation of MEH‐PPV gelation and Fourier transform infrared results verified the interaction existing between MEH‐PPV and TIP. SEM photographs showed that TIP(titania) were homogenously dispersed in the MEH‐PPV film if the hybrid solution was clear from the use of a suitable recipe. UV–vis absorption measurements showed that the addition of TIP decreased the conjugation length of MEH‐PPV. A redshift in the photoluminescence (PL) emission was observed in almost all the hybrids in the solution state, because of the aggregation of MEH‐PPV. However, it was found that spinning destroyed the aggregation of MEH‐PPV, resulting in a blueshift in the PL emission of the hybrids. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 515–529, 2008     

Electrospinning of polystyrene/poly(2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylene vinylene) blends

Ultrafine polystyrene (PS)/poly(2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylene vinylene) (MEH‐PPV) fibers were successfully prepared by electrospinning of PS/MEH‐PPV solutions in chloroform, 1,2‐dichloroethane, and tetrahydrofuran (THF). Three concentrations of the solutions were prepared: 8.5, 16, and 23.5% (w/v), with the compositional weight ratios between PS and MEH‐PPV being 7.5:1, 15:1, and 22.5:1, respectively. Smooth fibers only observed from 23.5% (w/v) PS/MEH‐PPV solution in chloroform. Improvement in the electrospinnability of 8.5% (w/v) PS/MEH‐PPV solution in chloroform was achieved by addition of an organic salt, pyridinium formate (PF), or by addition of a minor solvent with a high dielectric constant value. The average diameters of the as‐spun PS/MEH‐PPV fibers were between 0.30 and 5.11 μm. Last, photoluminescence of 8.5% (w/v) solutions of PS/MEH‐PPV in a mixed solvent system of chloroform and 1,2‐dichloroethane of various volumetric compositions and the resulting as‐spun fibers was investigated and compared. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1881–1891, 2005