N-vinylcarbazole Research Articles

Characterization of thermal annealing of gravure printed PVK/Ir(ppy) 3 organic light emitting layers

We investigated gravure printing process as a promising large area and high throughput process for organic device fabrication. In this work, nanoscale organic light emitting PVK/Ir(ppy) 3 layers were formed using the gravure printing process to fabricate organic light emitting diodes (OLEDs), and roughness and morphology were controlled through thermal annealing processes. The fabricated OLED device had layer structure of glass/ITO/PEDOT:PSS/PVK + Ir(ppy) 3-active layer/LiF/Al. PVK(Poly ( N-vinyl carbazole)) and Ir(ppy) 3 were used as the host and green-emitting dopant materials, respectively. The effect of thermal annealing process was investigated on surface roughness, morphology and crystallinity of the gravure printed organic layers. The optimum conditions were determined to be around 80 °C for the gravure printed organic layers for the given materials and device structure.

Thermo-responsive fluorescent micelles from amphiphilic A3B miktoarm star copolymers prepared via a combination of SET-LRP and RAFT polymerization

A novel amphiphilic A3B miktoarm star copolymer poly(N-isopropylacrylamide)3-poly(N-vinylcarbazole) ((PNIPAAM)3(PVK)) was successfully synthesized by a combination of single-electron transfer living radical polymerization (SET-LRP) and reversible addition-fragmentation chain transfer (RAFT) polymerization. First, the well-defined three-armed poly(N-isopropylacrylamide) (PNIPAAM)3 was prepared via SET-LRP of N-isopropylacrylamide in acetone at 25 °C using a tetrafunctional bromoxanthate iniferter (Xanthate-Br3) as the initiator and Cu(0)/PMDETA as a catalyst system. Secondly, the target amphiphilic A3B miktoarm star copolymer ((PNIPAAM)3(PVK)) was prepared via RAFT polymerization of N-vinylcarbazole (NVC) employing (PNIPAAM)3 as the macro-RAFT agent. The architecture of the amphiphilic A3B miktoarm star copolymers were characterized by GPC, 1H-NMR spectra. Furthermore, the fluorescence intensity of micelle increased with the temperature and had a good temperature reversibility, which was investigated by dynamic light scattering (DLS), fluorescent and UV-vis spectra. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4268–4278, 2010

Phase controlled all-polymer bulk-heterojunction photovoltaic cells with high open-circuit voltage

All-polymer bulk-heterojunction photovoltaic cells based on poly(N-vinyl carbazole) and poly(9,9-dioctylfluorene-co-benzothiadiazole) co-casting films are investigated. One of the highest reported open-circuit voltage among the all-polymer solar cells is obtained due to the large energy offset between the highest occupied molecular orbital of the donor and the lowest unoccupied molecular orbital of the acceptor. Atomic force microscopy and photoluminescence study of the active layer with varied blending ratios and annealing temperatures reveals a phase controlled working mechanism, in which the charge generation efficiency is proved to be the main limiting factor of this material system. The incident photon-to-current conversion efficiency measurement shows a unique “double peak” phenomenon with increase in the annealing temperature, indicative of asynchronous chain movement between the two polymers due to their relatively large difference in glass transition temperature. Such a phase behavior might have potential value in further optimization of film morphology towards higher device performance.

Electromagnetic wave beam self - guidance in liquid crystal - semiconductor cell

A theoretical model and numerical results for a new kind of optical waveguide has been presented. The discussed waveguide is optically self-induced during light beam propagation along the boundary between a liquid crystal and a semiconducting polymer in an electrically driven lc cell. Experimental results obtained earlier are briefly reported here, and the theoretical model is discussed. The exploited liquid crystal was of birefringence close to 0.4. The photorefractive polymer was a poly (N-vinyl) carbazole doped with 2, 4, 7-trinitro-fluorenone. Full Text: PDF References H. Knobloch, H. Orendi, M. Buchel, T. Seki, S. Ito, W. Knoll,"Photochromic command surface induced switching of liquid crystal optical waveguide structures", J.Appl. Phys. 77, 481 (1995) [CrossRef] D.N. Christodoulides, R.I. Joseph,"Discrete self-focusing in nonlinear arrays of coupled waveguides", Opt.Lett. 13, 794 (1988) [CrossRef] A. Fratalocchi, G. Assanto, K.A. Brzdąkiewicz, M.A. Karpierz,"Discrete light propagation and self-trapping in liquid crystals", Opt. Expr. 13, 1808 (2005) [CrossRef] G. Assanto, A. Piccardi, A. Alberucci, S. Residori, U. Bortolozza,"Liquid Crystal Light Valves: a versatile platform for Nematicons", Phot. Lett. of Poland 1(4), 151 (2009) F. Sala, M. Karpierz,"Numerical simulation of beam propagation in a layer filled with chiral nematic liquid crystals", Phot. Lett. of Poland 1(4), 163 (2009) A. Spadlo, R. Dabrowski, J. Dziaduszek, S. Urban, E. Scibor, S. Gauza, S.T. Wu,"Liquid crystalline materials with high birefringence", J. Opt. Technol. 72, 659 (2005) [CrossRef] A. Walczak, E. Nowinowski-Kruszelnicki,"Polarization difference imaging system", ECLC Conference, Lisbona 2007 A. Walczak, E. Nowinowski-Kruszelnicki, Liquid Crystal Photonic Workshop, Cambridge 2008 Walczak, E. Nowinowski-Kruszelnicki,"Waveguide couplers induced optically over organic junction", Opt. Eng. 47(3) (2008) [CrossRef] N.V. Kukhtarev, S.F. Lyuksyutov, P. Buchhave, T. Kukhtareva, K. Sayano, P.P. Benerjee,"Self-enhancement of dynamic gratings in photogalvanic crystals", Phys. Rev. A 58, 4051 (1998) [CrossRef]

Effect of Fabrication Parameters on Three-Dimensional Nanostructures and Device Efficiency of Polymer Light-Emitting Diodes

By using 10 kV C(60)(+) and 200 V Ar(+) ion co-sputtering, a crater was created on the light-emitting layer of phosphorescent polymer light-emitting diodes, which consisted of a poly(9-vinyl carbazole) (PVK) host doped with a 24 wt % iridium(III)bis[(4,6-difluorophenyl)pyridinato-N,C(2)] (FIrpic) guest. A force modulation microscope (FMM) was used to analyze the nanostructure at the flat slope near the edge of the crater. The three-dimensional distribution of PVK and FIrpic was determined based on the difference in their mechanical properties from FMM. It was found that significant phase separation occurred when the luminance layer was spin coated at 30 degrees C, and the phase-separated nanostructure provides a route for electron transportation using the guest-enriched phase. This does not generate excitons on the host, which would produce photons less effectively. On the other hand, a more homogeneous distribution of molecules was observed when the layer was spin coated at 60 degrees C. As a result, a 30% enhancement in device performance was observed.

Use of a recyclable poly(N-vinyl carbazole) palladium(II) complex catalyst: Heck cross-coupling reaction under phosphine-free and aerobic conditions

A novel pathway for cross-coupling reaction of terminal alkenes with aryl halides (Heck cross-coupling) has been described using a new phosphine-free poly(N-vinyl carbazole) anchored palladium(II) complex as catalyst in aerobic conditions. The catalyst was found to be highly active for the couplings of a variety of substituted and non-substituted aryl halides with terminal alkenes and to smoothly afford the corresponding desired products in good to excellent yields. The catalyst can be reused at least six times without noticeable decrease in catalytic activity.

Effects of solution processing on the photovoltaic response of poly(n‐vinyl carbazole) films

AbstractThe effects of solution processing on the photovoltaic response of poly(n‐vinyl carbazole) (PVK) films were investigated. PVK films were formed by spincasting onto glass coated with indium tin oxide (ITO) and poly(3,4‐ethylenedioxythiophene) (PEDOT)–polystyrenesulfonate (PSS). Some of the PVK films were redissolved in chlorobenzene and redried in the absence or presence of an electric field. Illuminated current–voltage characteristics were measured for an ITO/PEDOT:PSS/PVK/Ca:Al device. Films spincast from a 50 mg/mL solution, redissolved, and dried in the absence of the electric field exhibited a 26% higher charge collection efficiency than films dried in the presence of the electric field. The increased charge collection efficiency was attributed to changes in the molecular configuration of the PVK films. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Synthesis, characterization and catalytic activities of a reusable polymer-anchored palladium(II) complex: effective catalytic hydrogenation of various organic substrates

A poly(3,6-dibenzaldimino N-vinyl carbazole) Pd(II) complex has been synthesized and characterized by physicochemical and spectroscopic techniques. The complex was found to be highly active toward hydrogenation reactions of various organic substrates under atmospheric pressure at ambient temperature. A tentative reaction mechanism is proposed on the basis of kinetic studies and isolation of reactive intermediates. The catalyst shows good conversion rates, thermal stability and recyclability.

Synthesis and Properties of Polymers Containing Charge Transport Pendant Group

Non-conjugated polymers containing charge transporting pendant groups were synthesized and characterized. Poly(N-(4-vinylphenyl)-carbazole) (PPCZ) with a hole transporting carbazole group and poly(2-methylphenyl-5-(4-vinylphenyl)-1,3,4-oxadiazole) (PPOXD) with an electron transporting 1,3,4-oxadiazole group were synthesized by free radical polymerization of corresponding monomers, respectively, N-(4-vinylphenyl)-carbazole (VPCZ) and 2-methylphenyl-5-(4-vinylphenyl)-1,3,4-oxadiazole (VPOXD). Poly(vinyl carbazole) (PVK), well-known hole transporting material, was also prepared for comparison. These polymers with moderate molecular weight and molecular weight distribution were found to be all solution-processable. Thermal, optical and electrochemical properties of these polymers were investigated for an attempt to apply for charge transporting layer and/or host matrix in emitting layer in OLEDs. It appeared that photophysical properties such as ionization potential and electron affinity were dependent on respective pendant groups in polymers. High band gap energy levels (3.19 eV ∼3.44 eV) could make polymers a promising candidate for host matrix in OLEDs.

One- and two-dimensional NMR studies of methyl acrylate/vinyl acetate/ N-vinyl carbazole terpolymers

Terpolymers of methyl acrylate/vinyl acetate/ N-vinyl carbazole (M/A/C) with different compositions were synthesized by solution polymerization using AIBN as an initiator. Composition of terpolymers was determined from quantitative 13C{ 1H} NMR spectrum. Two-dimensional heteronuclear single quantum correlation (HSQC) and total correlated spectroscopy (TOCSY) were used to assign the methylene and methine carbon resonances by analyzing two and three bond order couplings. Various resonance signals were assigned to different compositional and configurational sequences with the help of one- and two-dimensional NMR spectra. Three and four bond order coupling between carbonyl carbon and other neighboring protons have been investigated with the help of 2D heteronuclear multiple bond correlation (HMBC) spectra. The complex and overlapped 1H NMR spectrum of terpolymer was analyzed completely with the help of 2D HSQC and TOCSY spectra.

Microstructure and Electrical Properties of Poly-N-isopropylacrylamide- N-vinylcarbazole Copolymers

Conducting poly-N-isopropylacrylamide-N-vinyl carbazole (PNI-nvc) copolymers were synthesized via in situ deposition technique by dissolving different weight percentages of N-vinyl carbazole ( 10, 20, 30, and 40%). The structural morphology and FT-IR studies support the interaction between PNI and N-vinyl carbazole. The temperature-dependent DC conductivity of PNI-nvc was studied within the range of 300 ≤ T ≤ 500 K, presenting evidence for the transport properties of PNI-nvc. The DC conductivity of PNI-nvc copolymers signifies the future development of new nanocopolymers that acts as a multifunctional material.

Morphology and Properties of Core–Shell Nanocomposites of Poly(N-vinylcarbazole) with Multi-Walled Carbon Nanotubes

In this article, we present the morphology and properties of core-shell nanocomposites of poly(N-vinyl carbazole) (PNVC) with multi-walled carbon nanotubes (MWCNTs). Nanocomposites were synthesized by the in situ solid-state polymerization of N-vinylcarbazole (NVC) at an elevated temperature in the presence of MWCNTs. Fourier transform infrared (FTIR) studies confirmed the ability of MWCNTs to initiate the in situ polymerization of NVC monomers and the presence of PNVC polymer in the nanocomposites. X-ray photoelectron spectroscopy (XPS) studies supported the FTIR results. Field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) images showed the homogeneous covering of MWCNTs outer surfaces by PNVC matrix. The Raman spectroscopy studies also revealed the homogeneous wrapping of MWCNTs outer surfaces without disturbing the inherent electronic structure of MWCNTs. Thermogravimetric analyses revealed a significant improvement of thermal stability of the nanocomposites in the higher temperature region. The core-shell nanocomposites showed interesting fluorescence properties. The dc (direct current) electrical conductivity of pure PNVC dramatically improved after nanocomposites formation with MWCNTs and degree of improvement was dependent on the loading of MWCNTs in the nanocomposites. For example, dc electrical conductivity increased from 10(-16)-10(-12) S x cm(-1) for pure PNVC to approximately 12 S x cm(-1) for nanocomposite containing 50 wt% MWCNTs.

PH- and thermo-multi-responsive fluorescent micelles from block copolymers via reversible addition fragmentation chain transfer (RAFT) polymerization

Abstract Well-defined pH- and thermo- multi-responsive fluorescent micelles based on the self-assembly of diblock copolymers poly[( N -isopropyl-acrylamide- co - N -vinylcarbazole)- b -2-(dimethylamino)ethyl acrylate], (PNIPAAM- co -PNVC)- b -PDMAEA, are described. The diblock copolymers are prepared via the reversible addition fragmentation chain transfer (RAFT) copolymerization of N -isopropyl-acrylamide (NIPAAM) and N -vinylcarbazole (NVC) followed by chain extension in presence of 2-(dimethylamino)ethyl acrylate) (DMAEA). The micelles are formed in aqueous solutions in a wide range of temperature (25–60 °C), and their sizes increase from 40 to 65 nm when varying pH from basic to acidic. The cross-linking of the PDMAEA-containing shell with 1,2-bis(2-iodoethoxy)ethane (BIEE) results in spherical soft nanoparticles which size is increased by 20–25% when compared to the micelles. The presence of NVC in concentrations as low as 4% in the core of the micelles allow the nanoparticles to be tagged by fluorescence, making them well suited for therapeutic applications.

Device Performance and Polymer Layer Morphology in Polymer Bistable Device (PBD): The Control of Physicochemical Properties of Solvent

The surface morphology control of poly(N-vinyl carbazole) (PVK) layer for the improvement of polymer bistable devices (PBDs) performance was investigated based on the simultaneous consideration of the compatibility of polymer with solvent and the polymer ordering behavior during the solvent evaporation by introducing the bisolvent system of chloroform and 1,1,2,2-tetrachloro-ethane (TCE). It was confirmed by ultra violet (UV)-vis spectroscopy that PVK has significantly higher compatibility with chloroform than TCE. On the other hand, atomic force microscope (AFM) revealed that the chloroform/TCE = 9/1 bisolvent led to the improved film morphology (the surface roughness of 0.190 nm) than chloroform, because the presence of TCE representing slower evaporation rate contributed to the enhancement of PVK ordering and arrangement during the solvent evaporation for the film formation. The great correlation was made between the film morphology properties and I-V characteristics of PBDs. The PBDs with PVK layer cast from the chloroform/TCE = 9/1 bisolvent showed dramatically improved bistability characteristics (Vth approximately equal to 2 V and Ion/Ioff ratio > 10(3)).

Capacitive behavior of polycarbazole- and poly(N-vinylcarbazole)-coated carbon fiber microelectrodes in various solutions

The electrochemical behavior of polycarbazole (PCz) and poly(N-vinyl carbazole) P(NVCz) was investigated by means of electrochemical impedance spectroscopy (EIS). Supporting electrolytes made from various combinations of solvents (acetonitrile and propylene carbonate) and salts (sodium perchlorate, lithium perchlorate, and tetraethyl ammonium perchlorate) were employed in the investigation. Information on the double layer capacitance (Cdl) and specific capacitance (Csp) of P(NVCz) was achieved by cyclic voltammetry (CV), chronoamperometry and chronopotentiometry. Carbon fiber microelectrodes (CFME) were electrocoated by cyclic voltammetry in a monomer-free solution and displayed film thicknesses in the range ~200 nm to ~4.8 μm. The capacitive behavior of the PCz- and P(NVCz)-coated carbon fiber microelectrodes was also investigated by CV. The effects of the type of electrolyte and solvent on the electrochemical impedance spectroscopic data were subsequently fitted with an ((R(C(R(Q(RW))))(CR))-equivalent circuit model to calculate the numerical values of the proposed components. The obtained experimental Csp values for PCz/CFME and P(NVCz)/CFME, as measured in LiClO4/ACN, were 280.5 mF g−1 and 294.1 mF g−1, respectively.

Preparation of High Molecular Weight Poly(vinyl carbazole) Web by Electrospinning

High molecular weight poly(N-vinyl carbazole) (PVCz) webs were obtained by the electrospinning technique. PVCz solutions were prepared by dissolving PVCz in chloroform and were spun under various electrospinning conditions. Especially, to improve the spinnability of PVCz, a high molecular weight specimen was adopted. Effects of processing parameters such as solution concentration, applied voltage, and tip–to-collector distance (TCD) on the spinnability, shape, and diameter and uniformity of fibres in the web were investigated. The average diameter of fibres in the webs was about 5 μm. The higher the solution concentration, the voltage, and the TCD, the finer and more uniform were the fibres in the web. PVCz fibres in webs prepared at high initial solution concentration were not cylindrical but planar, similar to “ribbons” but with nano-sized pores.

Nanoscale Thickness and Roughness Control of Gravure Printed Organic Light Emitting Layer with Poly(N-vinyl carbazole) and Ir(ppy)3

A nanoscale organic light emitting layer of PVK/Ir(ppy)3 was formed by the gravure printing process for the fabrication of organic light emitting diodes (OLEDs) in this work. The control of the nanoscale thickness and roughness by gravure printing is known to be challenging. The thickness and roughness characteristics were investigated for various solvents and printing speeds in this work. The OLED device fabricated in this work has a layer structure of glass/ITO/PEDOT: PSS/PVK + Ir(ppy)3-active layer/LiF/Al. PVK (poly(N-vinyl carbazole)) was used as the host and Ir(ppy)3 as the green-emitting dopant. The thickness of the active layer was controlled by the multiple-printing technique. The effects of the solvent on the surface roughness and OLED brightness were investigated with three different widely used solvents, viz. chloroform (CF), chlorobenzene (CB), and 1,2-dichlorobenzene (DCB). DCB showed the smoothest surface and the best brightness. The low surface roughness obtained with DCB is attributed to its relatively low evaporation rate. We also investigated the effect of the printing speed. In the case of chloroform, the thickness was inversely proportional to the printing speed, because of its high evaporation rate. In the case of DCB, the thickness was proportional to the printing speed. When the evaporation rate is low, a higher rolling speed was preferred for the formation of a thicker layer. The evaporation rate is believed to affect the surface morphology of the active polymer material and the control of the evaporation rate is considered to be an important factor in the gravure printing of nanoscale organic layers.

A Conducting Nanocomposite of Polystyrene with Acetylene Black

During recent years increasing research attention is being paid to the preparation of conducting nanocomposites of vinyl addition polymers like polystyrene (PS), 1 polypyrrole (PPY), 2 polyaniline (PANI), 3 polymethylmethacrylate (PMMA), 4 etc. with carbon nanotube (CNT). Most of these materials are being exploited in regard to their electrical properties including electrorheology. 5 In view of the difficulty of availability of carbon nanotubes and their high cost any cheaper alternative for the CNT component is these composites would be indeed worth exploring. In this context we have successfully used one cheap and abundant allotrope of carbon namely acetylene black (AB) as the nanocomponent. The particle size of AB is in the nano order range and the material is highly conducting. We have reported that N-vinyl carbazole (NVC) monomer can be readily polymerized in bulk or in toluene in presence of AB without any extraneous catalyst; and a PNVC-AB nanocomposite can be isolated from the system. The composite possesses high dc conductivity and enhanced thermal stability compared to PNVC homopolymer. 6 While extending the above procedures for polymerization vis-a-vis composite formation between AB and vinyl polymers such as PMMA, polyacrylonitrile (PAN) 7,8 it was noted that unlike NVC, acrylonitrile (AN) or methyl methacrylate (MMA) monomers could not be bulk polymerized by AB alone. We, therefore, modified the procedure in which MMA or AN monomers were dissolved in aqueous medium in which acetylene black was kept dispersed by sonication and nanocomposites of PMMA-AB and PAN-AB could be isolated. To prepare polystyrene–acetylene black nanocomposite (PS-AB) we used the emulsion polymerization process since styrene monomer is insoluble in water. Sodium dodecyl sulphate (NaDS) was used as an emulsifier and K2CrO4 and NaAsO2 were used as the redox initiator. Details of these procedures and bulk property characterizations of the PS-AB nanocomposite are highlighted in this article. It may be of interest to point out here that Choi et al. 1 reported the preparation of carbon nanotube (CNT) adsorbed polystyrene and PMMA microspheres by using nanotubes sonicated in aqueous solutions of the surfactants to which PS or PMMA microspheres were dropped. The conductivity values of 2 10 4 –3 10 5 S/cm were observed for CNT adsorbed on PS microspherers using cetavelon or sodium dodecyl sulphate as surfactant respectively.

Copolymers of N-vinylcarbazole with Acrylic Acid, Itaconic Acid, and N-isopropylacrylamide: Synthesis, Determination of Monomer Reactivity Ratios, and Electrochemical Properties

Free radical copolymerizations of N-vinylcarbazole (NVCz) with acrylic acid (AA), itaconic acid (IA), and N-isopropylacrylamide (NIPAAm) at different feed ratios were conducted in 1,4-dioxane at 50°C. The copolymers were characterized by UV and FT-IR spectroscopic techniques, viscosity, and glass transition temperature measurements. The monomer reactivity ratios were determined by application of the extended Kelen-Tüdós method, which is one of the conventional linearization methods, and found to be rNVCz = 0.29 and rNIPAAm = 0.12, rNVCz = 0.84 and rIA = 0.12, rNVCz = 0.86 and rAA = 0.31 by UV, and rNVCz = 0.32 and rNIPAAm = 0.07 by FT-IR. Polymer-modified electrodes having electroactive, ionic, and hydrophobic properties were prepared by electro-oxidation using PNVCz, NVCz/NIPAAm, and NVCz/IA copolymers and tested as sensor electrodes to dopamine.

Functionalized ferrocenes and ferroceniums: synthesis, crystal structures and electrochemical properties based on carbazole/phenothiazine-ferrocene conjugated molecules

Four new D-pi-D (or D-pi-D-pi-D) complexes 9-ethyl-3-E-((1-ferrocenyl)vinyl)-carbazole (1), 9-ethyl-3,6-E,E-((1,1-diferrocenyl)vinyl)- carbazole(2), 10-ethyl-3-E-((1-ferrocenyl)vinyl)-phenothiazine (3), 10-ethyl- 3,7-E,E- ((1,1-diferrocenyl)vinyl)-phenothiazine (4), have been obtained by solid-phase Wittig reactions and fully characterized. The four complexes were treated with iodine leading to four corresponding [D-pi-A](+) I(3)(-) ferrocenium triiodides (+)I(3)(-) (5), (+)I(3)(-) (6), (+)I(3)(-) (7) and 4(+)I(3)(-) (8), respectively. The results of single crystal X-ray diffraction analysis show that and display better coplanarity between the Fc and carbazole subunits than that between the phenothiazine and ferrocene moieties, which leads to a better pi-electron delocalization. Both the poor pi-electron in [D-pi-A](+) ferroceniums and the heavy iodine atom have a negative effect on the electrochemical properties. The complexes 1-8 undergo multi-step redox processes and show lower oxidation potentials compared with those of ferrocene. Density functional theory (DFT) calculations are performed and the experimental redox properties of the complexes are studied. The eight complexes show MLCT and pi-pi transitions in the UV-visible range in solution, which have been verified by TD-DFT theoretical calculations. In all cases the highest-lying occupied molecular orbitals of the eight complexes are mainly localized on the Fe d orbitals and show a greater Fe proportion than that of alkyl in the complexes, whereas the LUMOs and LUMO+1 are mainly from the pi orbitals of the conjugated vinyl carbazole or phenothiazine unit.