bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of Molecular Dipoles on the Photoluminescence and Electroluminescence of Dipolar Spirobifluorenes
Authors: Chiang C.‐L. , Tseng S.‐M. , Chen C.‐T. , Hsu C.‐P. , Shu C.‐F. 
Published: January 2008

AbstractThis Full Paper investigates a series of strongly fluorescent donor–acceptor‐substituted spirobifluorene compounds, red 2‐diphenylamino‐7‐(2,2‐dicyanovinyl)‐9,9′‐spirobifluorene (DCV), green 2‐diphenylamino‐9,9′‐spirobifluorene7‐carxoxaldehyde (CHO), and blue 2‐diphenylamino‐7‐(2,2‐diphenylvinyl)‐9,9′‐spirobifluorene (DPV), together with their spiro‐linked “dimeric” analogs, 2DCV, 2,2′‐bis(diphenylamino)‐9,9′‐spirobifluorene‐7,7′‐dicarboxaldehyde (2CHO), and 2,2′‐bis(diphenylamino)‐7,7′‐bis(2,2‐diphenylvinyl)‐9,9′‐spirobifluorene (2DPV), respectively. The emission optical density and, hence, the intensity of photoluminescence (PL) or electroluminescence (EL) of the “dimeric” analogs is presumed to increase, which is beneficial for organic light‐emitting diode (OLED) applications. The physical properties, including the dipole moments obtained from quantum chemistry calculations, emission solvatochromism, fluorescence quantum yield (Φf) as well as the EL of these six spirobifluorene compounds have been examined in detail. We found that Φf as well as OLED performance (EL efficiency and intensity) of the strongly dipolar DCV decrease significantly in the “dimeric” analog 2DCV, but less so in the moderately dipolar CHO and 2CHO, and only slightly in the weakly dipolar DPV and 2DPV. This is parallel to the intramolecular dipole moment, which is large for 2DCV, medium for 2CHO, and very small for 2DPV. Here, we show for the first time systematically that the luminescence intensity is closely correlated with the local electric field induced by the molecular dipole. A strong electric field may facilitate radiationless decay channels with a charge‐transfer nature, leading to a high quenching rate. Consistent with this conclusion, which is derived from the red DCV/2DCV and green CHO/2CHO, our new blue fluorophore DPV with an essentially zero dipole moment has successfully achieved one of the best electrofluorescent blue OLEDs. At the same time, by doping the highly dipolar DCV into an isolated environment with the low‐polarity Alq3 as the host matrix, we obtained a very high performance of saturated yellow OLEDs as well, This is possibly due to the reduction of emission‐quenching dipoles from the neighboring molecules. Our results have provided an important insight in designing luminescent materials, as follows: molecular dipole moments should be kept at a low magnitude to avoid quenching induced by a strong local electric field in the chromophore.
Photorefractive Performance of Hyperstructured Cyclotriphosphazene Molecular Glasses containing Carbazole Moieties
Authors: Zhang L. , Shi J. , Jiang Z. W. , Huang M. M. , Chen Z. J. , Gong Q. H. , Cao S. K. 
Published: January 2008

AbstractTwo hyperstructured photorefractive (PR) molecular glasses (M1 and M2) with a cyclotriphosphazene core are synthesized via nucleophilic substitution and an azo‐coupling reaction. These molecules exhibit excellent solubility in common organic solvents and maintain a complete amorphous state in spite of their high glass‐transition temperature. The nonlinear optical effects, two‐beam coupling and four‐wave mixing, respectively, are used to prove the PR performance in the optically transparent films of M1 and M2 doped with 30 % N‐ethyl‐carbazole. With no external electric field, a gain coefficient of 102 cm–1 and diffraction efficiency of 24 % are obtained in the composite made from M1, and an even higher gain coefficient of 214 cm–1 and diffraction efficiency of 31 % are obtained in the composite made from M2 owing to its higher chromophore loading.
A Smart Light‐Controlled Carrier Switch in an Organic Light Emitting Device
Authors: Zhang Z. , Liu X. , Li Z. , Chen Z. , Zhao F. , Zhang F. , Tung C.‐H. 
Published: January 2008

AbstractA real ON–OFF carrier switch based on a new ferrocenyl diarylethene compound (DTE‐FC) as the light‐sensitive and photoswitching layer in an organic light‐emitting device (OLED) with a multilayer sandwich structure has been prepared. This switch layer functions not only as a hole transporter but also as a good barrier block when needed, which arises from the light‐induced photochromic effect of the DTE‐FC. For the uncolored open‐ring form of DTE‐FC, no luminescence was observed despite the increase in applied voltage. On the contrary, for the colored photostationary state of DTE‐FC, which was obtained by irradiation with 365 nm light, the luminescence could be observed when the applied voltage reached 14.0 V and increased with applied voltage. Thus, the uncolored state corresponds to the OFF state of luminescence and the photostationary state corresponds to the ON state. The two states can be interconverted by control of the UV and visible light (>500 nm) irradiation.
Modeling Electron and Hole Transport in Fluoroarene‐Oligothiopene Semiconductors: Investigation of Geometric and Electronic Structure Properties
Authors: Koh S. E. , Risko C. , da Silva Filho D. A. , Kwon O. , Facchetti A. , Brédas J.‐L. , Marks T. J. , Ratner M. A. 
Published: January 2008

AbstractA theoretical study using density functional theory is undertaken to gain insight into how the structural, electronic, and electron‐transfer characteristics of three Fluoroarene‐oligothiophene semiconductors influence the preferred transport of electrons versus holes in field‐effect transistor applications. The intermolecular electronic coupling interactions are analyzed through both a simplified energy‐splitting in dimer (ESID) model and as a function of the entire dimer Hamiltonian in order to understand the impact of site energy differences; our results indicate that these differences are generally negligible for the series and, hence, use of the ESID model is valid. In addition, we also investigate the reduction and oxidation processes to understand the magnitudes of the intramolecular reorganization energy for the charge‐hopping process and expected barrier heights for electron and hole injection into these materials. From the electronic coupling and intramolecular reorganization energies, estimates of the nearest‐neighbor electron‐transfer hopping rate constant for electrons are obtained. The ionization energetics suggest favored electron injection for the system with perfluoroarene groups at the end of the thiophene core, in agreement with experiments. The combined analyses of the electron‐transfer properties and ionization processes suggest possible ambipolar behavior for these materials under favorable device conditions.
Giant Chromatic Lipid/Polydiacetylene Vesicles for Detection and Visualization of Membrane Interactions
Authors: Pevzner A. , Kolusheva S. , Orynbayeva Z. , Jelinek R. 
Published: January 2008

AbstractWe present the construction of microscopic vesicular particles comprising phospholipids and polydiacetylene (PDA), a polymer with unique color and fluorescence properties. We show that the vesicle‐embedded PDA domains function as chromatic reporters of membrane events, undergoing dramatic colorimetric and fluorescence transformations induced by interactions with membrane‐active species. In particular, the micrometer sizes of the giant vesicles facilitate their utilization for visual inspection of membrane events by conventional microscopy techniques. The morphology, size, and chromatic properties of the vesicular aggregates depend upon the type of phospholipids and the molecular ratio between the phospholipids and diacetylene, indicating that the lipids and polymer form interdependent domains within the vesicles. The giant chromatic aggregates have been employed for detection and microscopic visualization of varied membrane processes, including lipid interactions of lipophilic drugs, binding of antimicrobial peptides, and membrane attachment by virus particles.
Nanocomposite Films of a Polyfluorene Copolymer and Carbazole– Thiol‐Capped Gold Nanoparticles: Electrochemical Crosslinking and Energy‐Transfer Properties
Authors: Taranekar P. , Huang C. , Fulghum T. M. , Baba A. , Jiang G. , Park J.‐Y. , Advincula R. C. 
Published: January 2008

AbstractThe preparation and properties of an electrochemically crosslinked Au nanoparticle/polyvinylcarbazole (PVK)/polyfluorene (PFC) nanocomposite film is described. Blends of the blue‐light emitting PFC, PVK, and the 11‐(9H‐carbazol‐9‐yl)‐undecane‐1‐thiol‐capped Au nanoparticles (CBZ‐S‐Au) were prepared as thin films by spin‐coating and subsequent crosslinking by cyclic voltammetry (CV). The electrochemical properties are then evaluated on the basis of the redox behavior (reversibility) and electron‐transport properties of the films. They are further characterized by UV‐vis spectroscopy, photoluminescence spectroscopy, and atomic force microscopy (AFM). The large differences in photoluminescence properties of the CBZ‐S‐Au/PFCVK crosslinked copolymer composite film compared to the PFCVK polymer alone result in an efficient energy‐transfer system, in which the excimer peak is almost totally quenched. This indicates a compatible match between the absorbance of the Au plasmons and the emission of the excimer energy trap from PF polymers. Furthermore, electrochemical crosslinking enhances this match both by shifting the absorbance to greater overlap and decreasing the Förster distance between the Au nanoparticle and the PFCVK polymer chains.
Cover Picture: Self‐Organization of Ink‐jet‐Printed Triisopropylsilylethynyl Pentacene via Evaporation‐Induced Flows in a Drying Droplet (Adv. Funct. Mater. 2/2008)
Authors: Lim J. A. , Lee W. H. , Lee H. S. , Lee J. H. , Park Y. D. , Cho K. 
Published: January 2008

AbstractCharge carrier transport in organic electronic devices is influenced by the crystalline microstructure and morphology of the organic semiconductor film. Evaporation behavior during drying plays a vital role in controlling the film morphology and the distribution of solute in inkjet‐printed films. On p. 229, Kilwon Cho and co‐workers demonstrate the influence of the evaporation‐induced flow in a single droplet on the crystalline microstructure and film morphology of inkjet‐printed 6,13‐bis((triisopropylsilylethynyl) pentacene. The results provide an excellent method for direct‐write fabrication of high‐performance organic electronics.We have demonstrated the influence of evaporation‐induced flow in a single droplet on the crystalline microstructure and film morphology of an ink‐jet‐printed organic semiconductor, 6,13‐bis((triisopropylsilylethynyl) pentacene (TIPS_PEN), by varying the composition of the solvent mixture. The ringlike deposits induced by outward convective flow in the droplets have a randomly oriented crystalline structure. The addition of dichlorobenzene as an evaporation control agent results in a homogeneous film morphology due to slow evaporation, but the molecular orientation of the film is undesirable in that it is similar to that of the ring‐deposited films. However, self‐aligned TIPS_PEN crystals with highly ordered crystalline structures were successfully produced when dodecane was added. Dodecane has a high boiling point and a low surface tension, and its addition to the solvent results in a recirculation flow in the droplets that is induced by a Marangoni flow (surface‐tension‐driven flow), which arises during the drying processes in the direction opposite to the convective flow. The field‐effect transistors fabricated with these self‐aligned crystals via ink‐jet printing exhibit significantly improved performance with an average effective field‐effect mobility of 0.12 cm2 V–1 s–1. These results demonstrate that with the choice of appropriate solvent ink‐jet printing is an excellent method for the production of organic semiconductor films with uniform morphology and desired molecular orientation for the direct‐write fabrication of high‐performance organic electronics.
Bimaterial Microcantilevers as a Hybrid Sensing Platform
Authors: Singamaneni S. , LeMieux M. C. , Lang H. P. , Gerber C. , Lam Y. , Zauscher S. , Datskos P. G. , Lavrik N. V. , Jiang H. , Naik R. R. , Bunning T. J. , Tsukruk V. V. 
Published: January 2008

AbstractMicrocantilevers, one of the most common MEMS structures, have been introduced as a novel sensing paradigm nearly a decade ago. Ever since, the technology has emerged to find important applications in chemical, biological and physical sensing areas. Today the technology stands at the verge of providing the next generation of sophisticated sensors (such as artificial nose, artificial tongue) with extremely high sensitivity and miniature size. The article provides an overview of the modes of detection, theory behind the transduction mechanisms, materials employed as active layers, and some of the important applications. Emphasizing the material design aspects, the review underscores the most important findings, current trends, key challenges and future directions of the microcantilever based sensor technology.
The iodide iodate method to characterize microstructured mixing devices
Authors: Kölbl A. , Kraut M. , Schubert K. 
Published: January 2008

AbstractThe iodide iodate method (also known as Villermaux method) was used to characterize multilamination‐type mixers, manufactured at the Institute for Micro Process Engineering of the Forschungszentrum Karlsruhe. Mixing sensitive results were obtained using different reactant concentrations. It is shown that the experimentally obtained data cannot be treated as quantitative data in sense of a “mixing quality.” © 2008 American Institute of Chemical Engineers AIChE J, 2008
The effects of manifold flow on mass transport in electrochemical filter‐press reactors
Authors: Frías‐Ferrer Á. , González‐García J. , Sáez V. , de León C. Ponce , Walsh F. C. 
Published: January 2008

AbstractThe mass transport rates to planar electrodes, in a series of electrochemical laboratory filter‐press reactors were measured to quantify the effects of the inlet and outlet design manifolds on the fluid flow. In small reactors, entrance/exit effects are especially important due to the localized generation of fluid recirculation zones, which affect the overall rate of mass transport. Limiting current data, the cathodic reduction of Cu(II) ions on a copper surface (under convective‐diffusion control) were used to measure global mass transport coefficients. The data are compared with those from a well‐characterized laboratory cell, the FM01‐LC electrolyzer. The importance of manifold design in small‐scale electrochemical reactors is discussed, and several dimensionless parameters are used to characterize the manifold geometry. © 2008 American Institute of Chemical Engineers AIChE J, 2008
Polymerization of acrylonitrile initiated by cerium (IV)‐oxalic acid redox system: A kinetic study
Authors: Demappa T. , Mahadevaiah  
Published: January 2008

AbstractThe kinetics of aqueous polymerization of Acrylonitrile initiated by the Cerium (IV)‐Oxalic acid redox system in Sulfuric acid medium has studied under nitrogen atmosphere in the temperature range of 25–50°C. The rate of polymerization (Rp) and the disappearance of Cerium (IV) have been measured. The water‐miscible organic solvents and inorganic salts were depressed both the rate and the conversion. The effects of ionic strength, effects of surfactant have been investigated. The temperature dependence of the rate was studied and the activation parameters were computed using Arrhenius and Eyring plots. A mechanism consistent with the experimental data, involving Ce(IV)–Oxalic acid complexation that generates free radical was suggested. The chain termination step of the polymerization reaction was determined. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Sulfonated poly(ether imide) and poly(ether sulfone) blends for direct methanol fuel cells. II. Membrane preparation and performance
Authors: Shu Yao‐Chi , Chuang Fu‐Sheng , Tsen Wen‐Chin , Chow Jing‐Dong , Gong Chunli , Wen Sheng 
Published: January 2008

AbstractThis study describes the preparation and characterization of new ionomer blend membranes containing sulfonated poly(ether imide) (SPEI) and poly(ether sulfone) (PES). Thermogravimetric analysis indicated that the obtained blend membranes were more thermally stable than the parent SPEI. As the PES content increased, the extent of membrane swelling by water decreased, and the oxidative stability was significantly increased by the specific interactions between PES and the sulfonic acid groups. Under both dry and wet conditions, the tensile strength of all the blend membranes was larger than that of the pure SPEI membrane and Nafion 112 because of the reinforcing effect of PES. Scanning electron microscopy and atomic force microscopy indicated that the blend membranes became more compact as the PES content increased, and this reduced the methanol diffusion. The blend membranes with PES contents below 50% showed adequate proton conductivity. The lower permeability of the blend membranes compared with the Nafion 112 membrane resulted in higher methanol resistance. This considerable reduction in methanol crossover revealed the feasibility of the blend membranes as promising electrolytes for direct methanol fuel cells. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
The preparation and electrical conductivity of polyacrylamide/graphite conducting hydrogel
Authors: Tang Qunwei , Lin Jianming , Wu Jihuai 
Published: January 2008

AbstractPolyacrylamide/graphite superabsorbent composite was synthesized by free radical polymerization of acrylamide monomer using N,N′‐methylene‐bis‐acrylamide as crosslinker, potassium persulfate as initiator, and graphite as functional filler. On the basis of the superabsorbent composite, a hydrogel with a conductivity of 0.86 mS cm−1 was obtained. The preparation conditions were optimized. The influence of crosslinker, initiator, monomer, graphite, water absorbency, and temperature on the conductivity of the hydrogel was investigated, an adsorbed network structure model for polyacrylamide/graphite conducting hydrogel was purposed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008
Investigation on the crystallization behavior of poly(ether ether ketone)/poly(phenylene sulfide) blends
Authors: Zhang Ri‐Chao , Xu Yi , Lu Zhongyuan , Min Min , Gao Yong , Huang Yigang , Lu Ai 
Published: January 2008

AbstractThe morphology of nonisothermally crystallized poly(phenylene sulfide) (PPS) and its blend with poly (ether ether ketone) (PEEK) have been observed by polarized optical microscope (POM) equipped with a hot stage. The nonisothermal crystallization behavior of PPS and PEEK/PPS blend has also been investigated by differential scanning calorimetry (DSC). The maximum crystallization temperature for PEEK/PPS blend is about 15°C higher than that of neat PPS, and the crystallization rate, characterized by half crystallization time, of the PEEK/PPS blend is also higher than that of the neat PPS. These results indicate that the PEEK acts as an effective nucleation agent and greatly accelerates the crystallization rate of PPS. The Ozawa model was used to analyze the nonisothermal crystallization kinetics of PPS and its blends. The Avrami exponent values of neat PPS are higher than that of its blend, which shows that the presence of PEEK changed the nucleation type of PPS from homogeneous nucleation to heterogeneous nucleation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
New poly(phenylene oxide)/polystyrene blend nanocomposites with clay: Intercalation, thermal and mechanical properties
Authors: Tiwari Rajkiran R. , Khilar Kartic C. , Natarajan Upendra 
Published: January 2008

AbstractWe present the first study and results on the preparation and characterization of montmorillonite clay filler based polymer blend nanocomposites of the miscible poly(phenylene oxide)/polystyrene blend. Intercalated nanocomposites, prepared by a melt‐processing method with 2–6 wt % commercially available organically modified sodium montmorillonite, have been characterized with wide‐angle X‐ray diffraction, transmission electron microscopy analysis, thermal analysis (thermogravimetric analysis and differential scanning calorimetry), and mechanical tensile tests. We show that nanocomposites can be successfully prepared in a batch mixer at temperatures much below the conditions conventionally used for this blend without organic degradation. Thermal stability is enhanced by nanoscale hybrid formation. The level of intercalation (change in the d‐spacing) does not change with the clay loading. Better dispersion of clay in the blend matrix has been observed at a low level of clay content. The nanocomposites show improved tensile modulus (by 31%) in comparison to the blend, whereas the tensile strength (stress at break) and elongation decrease in the presence of the filler with an increase in the clay loading. The Halpin–Tsai model is able to predict the modulus of the nanocomposites in very good agreement with the experimental data. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Facile size‐controllable syntheses of highly monodisperse polystyrene nano‐ and microspheres by polyvinylpyrrolidone‐mediated emulsifier‐free emulsion polymerization
Authors: Du Xin , He Junhui 
Published: January 2008

AbstractA facile emulsifier‐free emulsion polymerization approach was developed to fabricate highly monodisperse polystyrene (PS) spheres using potassium persulfate as the initiator and polyvinylpyrrolidone (PVP) as a stabilizer, respectively. It was found that the size of monodisperse PS spheres tends to decrease with increase of the PVP concentration, and the size of monodisperse PS spheres could be easily controlled in a wide range from 200 to 1500 nm simply by adjusting the concentration of PVP. The increase of monomer concentration led to the increase in size of monodisperse PS spheres. In contrast, the increase of initiator concentration resulted in the decrease in size of monodisperse PS spheres. These concentration changes, however, did not significantly affect the size distributions of PS spheres. It was also found that the size of monodisperse PS spheres obtained by adding the initiator at room temperature was larger than that by adding the initiator at 70°C, and the existence of inhibitor resulted in smaller PS spheres. The mechanisms in which the above factors influence the size and size distribution were discussed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Evaluation of solubility parameters for nonvolatile branched hydrocarbons by inverse gas chromatography
Authors: Sreekanth T. V. M. , Reddy K. S. 
Published: January 2008

AbstractFlory‐Huggins interaction parameters determined by inverse gas chromatographic (IGC) technique have been used for the estimation of solubility parameters of nonvolatile branched hydrocarbon solvents. A family of isosteric branched hydrocarbons consists of one apolar stationary phase, 19,24‐dioctadecyldotetracontane (C78), and four polar stationary solvents formed by replacing one of the CH3 groups of C78 by OH (POH), CN (PCN), SH (PSH), CF3 (MTF), and two other polar solvents formed by replacing four CH3 groups of C78 with four CF3 (TTF) and OCH3 (TMO) are investigated. The three‐dimensional Hansen solubility parameters of the solvents have been estimated following the approaches of Voelkel and the method of Huang at five different temperatures. In the three components estimated by Voelkel method, the dispersion component is decreasing rapidly, whereas the polar, and hydrogen bonding components of the solubility parameters are increasing with temperature. In the components of solubility parameter estimated by Huang method, the dispersion and hydrogen bonding components are slowly decreasing with temperature, however, the polar components are almost constant with temperature. The components of solubility parameters for different solvents have been discussed in terms of solvent polarity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008