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     

Ruptured conjugated polymer thin films formed during spin coating

The formation of ruptured poly[2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐1,4‐phenyl vinylene] (MEH–PPV) thin films coated from undried tetrahydrofuran (THF) solutions was investigated. Because of the incompatibility of water and MEH–PPV, the polymer films coated from THF/water solutions showed a ruptured film structure. In the photoluminescence (PL) spectra of the polymer thin films, the ruptured polymer films showed a redshifted emission in comparison with continuous polymer thin films. According to a comparison of the PL spectra of polymer solutions and films, MEH–PPV in THF showed a coil–cylinder transition during precipitation from solution. Because of the incompatibility of water and MEH–PPV, an increase in the water content could increase the ratio of polymer chains in the cylinder conformation, resulting in a redshifted emission for the films. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 79–84, 2006     

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.     

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     

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     

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     

Hydrophobic and hydrophilic aggregation of tailor‐made urethane acrylate anionomers in various solvents and their network structures

Tailor‐made urethane acrylate anionomer (UAA) chains show higher viscosity and polyelectrolyte behavior in dimethyl sulfoxide (DMSO) than in water and toluene. Water is a nonsolvent for the hydrophobic soft segment but a good solvent for the hydrophilic hard segments, so hydrophobic segments are aggregated and form particles in the water phase, resulting in a smaller viscosity. Also, the fact that the viscosity of UAA chains is lowest in toluene can be interpreted as a result of ionic aggregation due to the nonpolarity of toluene. The structures of UAA networks dramatically change with the nature of the solvents used (i.e., the interaction between the UAA chains and the solvents used changes); this is confirmed by the results of tensile property, morphology, and wide‐angle X‐ray scattering data. Ionic aggregation formed in UAA/toluene (UATG networks) and hydrophobic aggregation formed in UAA/water (UAAG networks) are locked in by a chemical crosslinking reaction and result in a greater modulus and X‐ray scattering intensity. The greater elongation and swelling ratio in methylene chloride of UATG networks prepared in a UAA/toluene solution indicates that toluene is a better solvent than DMSO for the hydrophobic segments of UAA chains. Also, the greater swelling ratio in a pH 11 buffer solution and greater modulus of UAAG networks show that water is a better solvent than DMSO for hydrophilic ionic segments. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1903–1916, 2000     

Versatile route for tuning optical properties of poly(2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylenevinylene)

In this contribution, we report a versatile method for tuning optical properties of poly(2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylenevinylene) (MEH‐PPV) in its solution with 1,2‐dichloroethane, accomplished by reacting with pyridinium formate (PF), a volatile organic salt. We can systematically control the positions of absorption and photoluminescent (PL) spectra of MEH‐PPV by adjusting the concentration of PF in the solution. The addition of 10 vol % PF caused a blue‐shift in the absorption spectra by about 65 nm. When the concentration of PF decreased to 0.1 vol %, the blue‐shift occurred to a lesser extent, about 25 nm. The measurements of PL spectra showed similar behaviors. The λ_max shifted from 558 nm to 546 and 552 nm when 10 and 0.1 vol % of PF were added, respectively. The changes of PL colors from orange to yellow and green, respectively, were observed by naked eyes. Structural investigation by nuclear magnetic resonance and Fourier‐transformed infrared spectroscopy indicated that the changes of the optical properties were due to chemical modifications along the main chain and the side groups of MEH‐PPV. These results implied a simple route for engineering the HOMO–LUMO energy gap of MEH‐PPV, which could be utilized in advanced applications such as organic light‐emitting devices and solar cells. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 696–705, 2009     

Poly‐p‐phenylenevinylene‐g‐poly(2‐(methacryloyloxy)Ethyl)trimethylammonium chloride (PPV‐g‐PMETAC): A fluorescent,water‐soluble,selective anion sensor

The photophysical and ion‐sensing properties of densely grafted conjugated polymer poly‐p‐phenylenevinylene‐g‐poly(2‐(methacryloyloxy)ethyl)trimethylammonium chloride (PPV‐g‐PMETAC) are presented herein. The grafted polymer exhibits excellent iodide‐sensing which is easily observed using fluorescence spectroscopy. The iodide detection limit for PPV‐g‐PMETAC was found to be 10 nM and was independent of temperature and pH <12. The change in fluorescence of PPV‐g‐PMETAC, upon exposure to iodide, was attributed to polymer aggregation due to changes in the morphology of the grafted PMETAC side chains, which was observed using atomic force microscopic and dynamic light scattering studies. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1997–2003     

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     

Control of molecular aggregation in symmetrically substituted π‐conjugated bulky poly(p‐phenylenevinylene)s and their copolymers

A new series of symmetrically substituted bulky PPV‐copolymers based on poly(bis‐2,5‐(2‐ethylhexyloxy)‐1,4‐phenylenevinylene) ( BEH‐PPV ) bearing tricyclodecane (TCD) pendants were synthesized to study the effect of chain aggregation in the π‐conjugated polymer backbone. The composition of the copolymers was varied up to 100 mol % and the structures of the copolymer were confirmed by NMR and FTIR. The molecular weights of the copolymers were obtained as M_w = 11,500–1,78,800 depending on the TCD‐incorporation in BEH‐PPV. The origin of the π‐aggregation was investigated using mixture of solvents (polar or nonpolar) or temperature as external stimuli. Absorption, photoluminescence, and time‐resolved fluorescence decay techniques were employed as tools to trace molecular aggregation in solution and solid state. The TCD‐substituted bulky copolymers showed almost twice the enhancement in photoluminescence compared with that of BEH‐PPV . Solvent‐induced aggregation studies of copolymers revealed the existence of strong molecular aggregation in BEH‐PPV compared with that of bulky copolymers. Variable temperature studies further evidence for the reversibility of molecular aggregation on heating/cooling cycles and showed isosbetic points with respect to free and aggregated polymer chains. Time‐resolved fluorescent studies confirmed the existence of free and aggregated π‐conjugated species with a life time of 0.1 to 1.0 ns. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2631–2646, 2009     

Conformational change,intrachain aggregation and photophysical properties of regioregular poly(3‐octylthiophene) in alkanes

This study explores the role of segmental solubility of regioregular poly(3‐octylthiophene) (rr‐P3OT) on chain organization and its photophysical properties. In good solvent chlorobenzene (CRB), rr‐P3OT chain adopts an extended conformation, allowing long conjugation length of π‐electrons. Cyclohexane is a good solvent for octyl side chain but a poor solvent for the thiophene backbone. The selective segmental interactions of rr‐P3OT with this solvent induce conformational change of the polymer. Addition of cyclohexane into the CRB solution leads to chain coiling, which in turn causes significant decrease of the conjugation length. Absorption and photoluminescence spectra of the rr‐P3OT in cyclohexane exhibit a blueshift of about 16 nm compared to those of the CRB solution. The change of chain conformation is also detectable by monitoring the variation of quantum yield upon increasing cyclohexane ratio. The quantum yield drops from 0.17 ± 0.01 to 0.11 ± 0.01 when the extended rr‐P3OT chain transforms into coiled conformation. Hexane is a nonsolvent for rr‐P3OT due to its relatively low solubility parameter. The addition of hexane into rr‐P3OT solution in cyclohexane forces dense packing of thiophene rings within the coiled chain. An intrachain aggregation occurs in this system, leading to the appearance of three distinct redshift peaks in absorption spectra and the drastic drop of quantum yield. Correlation between the growth of redshift peaks and the decrease of quantum yield is clearly observed. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1288–1297     

Copolyfluorenes containing pendant bipolar carbazole and 1,2,4‐triazole groups: Synthesis,characterization, and optoelectronic applications

Three novel copolyfluorenes ( P1 ‐ P3 ) containing pendant bipolar groups (2.5–7.7 mol %), directly linked hole‐transporting carbazole and electron‐transporting aromatic 1,2,4‐triazole, were synthesized by the Suzuki coupling reaction and applied to enhance emission efficiency of polymer light‐emitting diodes based on conventional MEH‐PPV. The bipolar groups not only suppress undesirable green emission of polyfluorene under thermal annealing, but also promote electron‐ and hole‐affinity of the resulting copolyfluorenes. Blending the bipolar copolyfluorenes with MEH‐PPV results in significant enhancement of device performance [ITO/PEDOT:PSS/MEH‐PPV+ P1 , P2 or P3 /Ca(50 nm)/Al(100 nm)]. The maximum luminance and luminance efficiency were enhanced from 3230 cd/m² and 0.29 cd/A of MEH‐PPV‐only device to 15,690 cd/m² and 0.81 cd/A (blend device with MEH‐PPV/ P3 = 94/6 containing about 0.46 wt % of pendant bipolar residues), respectively. Our results demonstrate the efficacy of the bipolar copolyfluorenes in enhancing emission efficiency of MEH‐PPV. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Charge transport properties of MDMO PPV thin films cast in different solvents

Charge transport properties in thin films of Poly(2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐1,4‐phenylenevinylene) (MDMO PPV) cast using either chloroform (CF), toluene (TOL), or chlorobenzene (CB) as solvent were investigated. Hole mobility (μ) in these thin films measured using time‐of‐flight transient photoconductivity showed an increasing trend with respect to the solvent used in the same order, that is, μ_CF (2.4 × 10^?7 cm²/Vs) < μ_TOL (6.9 × 10^?7 cm²/Vs) < μ_CB (2.3 × 10^?6 cm²/Vs). Observed variations in mobilities were attributed to different morphologies of MDMO PPV chains in thin films cast using the aforesaid solvents. Nature of the interchain interactions and aggregate formation were obtained using photoluminescence (PL), Raman spectroscopy, and AFM studies. Ratio of PL peak intensities of 0–0 and 0–1 transitions, which is a direct measure of interchain interaction, was the highest in CB and lowest in CF. Variation in the relative intensities of out‐of‐plane wagging of vinylene group (～963 cm^?1 mode) in Raman spectra suggested different extent of coiling of polymer chains in these thin films. From these observations, it was elicited that aggregate size and interchain interactions are highest in CB and least in CF. AFM‐based topographic images of thin films further supported these variations in the size of aggregates. Variation in the aggregate sizes and interchain interactions explained the corresponding variation in the mobility. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1431–1439     

Diketopyrrolopyrrole‐based polymer nanowires: Control of chain conformation and nucleation

Understanding the nucleation process is very important in growing polymer nanowires as it plays a decisive role in determining the crystal structure and size distribution. Polymer chain conformation determines whether the polymer chains could assemble to nuclei or not. Here, chain conformation and the nucleation process were controlled to grow 3,6‐bis‐(thiophen‐2‐yl)‐N,N′‐bis(2‐decyl‐1‐tetradecyl)‐1,4‐dioxo‐pyrrolo[3,4‐c]pyrrole and thieno[3,2‐b]thiophene (DT‐PDBT‐TT) nanowires. We changed the conformation of DT‐PDBT‐TT in solution and controlled the nucleation process by using a main solvent:cosolvent system. The main solvent was a low boiling point good solvent, and the cosolvent was consisted of two high boiling point solvents with different solubility. In fact, the chain conformation in the pristine solution was changed by choosing different main solvents (with H‐bond, π–π or none interaction with the main chain) and temperatures. The absorption spectrum and TEM images showed that trichloro ethylene (TCE) was the best main solvent because it has H‐bond interaction with the polymer main chain and DT‐PDBT‐TT conformation in it approaching unimer coil conformation, which is beneficial to grow nanowires. Mixed o‐dichlorobenzene (ODCB) and anisole (AS) with different ratios were used to changing the solubility step by step to control nucleation process. Only when marginal cosolvent (ODCB:AS = 1:1) was added, could it decrease the nuclei number and avoided the aggregates simultaneously. As the main solvent evaporated slowly, the nucleation and growth happened, leading to the nanowires formation. The resulting nanowires were about 63 nm in width and one to two microns in length. The width of the DT‐PDBT‐TT structures suggests that the polymer chains are oriented along the fibril axis. Our results indicated that there are two requirements for the nanowire formation, (1) the polymer chain conformation should approach unimer coil; (2) the nucleation density should be optimized, not too much and no aggregation happened. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 833–841     

Controlled crystallization of poly(vinylidene fluoride) chains from mixed solvents composed of its good solvent and nonsolvent

Poly(vinylidene fluoride) (PVDF) chains with the same expanded state were obtained by dissolving PVDF resin in good solvent. Then, the crystallization of PVDF chains from mixed solvents composed of its good solvent and nonsolvent was investigated. N,N‐dimethylformamide (DMF) and ethanol were used as good solvent and nonsolvent of PVDF, respectively. The crystalline phases of PVDF were characterized by Fourier transform infrared (FTIR) spectroscopy and wide angle X‐ray diffraction (WAXD). For the crystallization of PVDF chains from mixed solvents, low ethanol content favored the formation of β phase, while high ethanol content resulted predominantly in the α phase. Different crystallization morphology was observed from the scanning electron microscopy (SEM) images. The obvious spherulite morphology disappeared with the increase in ethanol content in mixed solvent. According to thermal analyses, the crystallized PVDF from mixed solvents with high ethanol content had lower onset melting temperatures than that from low ethanol content. Smaller lamellar thickness calculated from WAXD data reasoned the low onset melting temperatures. The above results indicated that the crystallization of PVDF chains from mixed solvent was a “controlled” process by ethanol content. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 575–581, 2010     

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.