Carbazole Polymers Research Articles

Preparation and properties of polymer/zinc oxide nanocomposites using functionalized zinc oxide quantum dots

Poly(methyl methacrylate) (PMMA)/zinc oxide (ZnO) or carbazole polymer (PCEM)/ZnO nanocomposites, which are composed of high molecular weight PMMA or PCEM with narrow molecular weight distributions and ZnO nanoparticles, were successfully prepared by atom transfer radical polymerization (ATRP) initiated by 2-bromo-2-methylpropionyl (BMP) group (ZnBM) introduced onto the ZnO nanoparticle surfaces. Introduction of the BMP group onto the ZnO surfaces was achieved by esterification of OH group of the ZnO surfaces. The chemically attached OH group-having ZnO nanoparticles (ZnHM) were fabricated by sol-gel reaction from zinc acetate dihydrate, followed by treatment of the ZnO nanoparticles with 2-hydroxypropionic acid (HPA). The ZnHM nanoparticles showed one UV absorption and two emission bands: UV emission peak and broad visible emission band, while the ZnBM exhibited broad UV absorption and no emission spectra. The PMMA/ZnO nanocomposites displayed UV absorption and photoluminescent (PL) band with blue emission on the basis of the ZnHM nanoparticles, where the ZnO nanoparticles dispersed homogeneously in the PMMA matrix. The PCEM/ZnO nanocomposites depicted UV emission peak due to the carbazole unit in the UV range, but no visible emission. Thermal properties of the PMMA/ZnO nanocomposites were improved by dispersion of the ZnO nanoparticles into the PMMA, but the PCEM/ZnO nanocomposites showed no improvement of the thermal properties.

Synthesis, characterization, and photophysics of a novel conjugated polymer with 1,3,4‐oxadiazole, carbazole, and naphthalene units

AbstractA polymer containing 1,3,4‐oxadiazole and carbazole units in the main chain and naphthalene moieties as side groups (P‐OCN) was synthesized by the Wittig reaction of [2,5‐bis(3‐tolylene)1′,3′,4‐oxadiazole]‐9‐(α‐naphthyl)‐carbazole polymer (P‐OCN). The optical properties were investigated with ultraviolet–visible absorption and fluorescence emission spectra. The results showed that the luminescence quantum yield of P‐OCN was 0.673 in chloroform, and it emitted blue and blue‐green light with a band gap of 3.49 eV estimated from the onset absorption. Thermogravimetric analysis and differential scanning calorimetry showed that the polymer exhibited good thermal stability up to 354°C with a glass‐transition temperature higher than 110°C. To investigate the donating and accepting capacities of P‐OCN, the fluorescent quenching technique was used to determinate the interactions between the polymer and the electron donor and electron acceptor. The results showed that the light emission could be quenched by both the electron donor (N,N‐dimethylaniline) and electron acceptor (dimethylterephthalate). Furthermore, the interaction between P‐OCN and fullerene was also studied with fluorescent quenching, and the processes followed the Stern–Volmer equation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Macromol. Rapid Commun. 2/2008

Cover: A new class of conjugated carbazole polymers, alkyne‐linked poly(1,8‐carbazole)s, was for the first time synthesized by Sonogashira cross‐coupling and acetylenic oxidative coupling reactions. Poly(1,8‐carbazole)s featured long effective conjugation length, strong fluorescence, and potent electrochemical activities, leading to a variety of optoelectronic applications. Further details can be found in the article by T. Michinobu,* H. Osako, and K. Shigehara* on page 111.

Alkyne‐Linked Poly(1,8‐carbazole)s: A Novel Class of Conjugated Carbazole Polymers

AbstractNovel conjugated carbazole polymers based on the alkyne‐linked 1,8‐carbazole structure are synthesized in high yield by the Sonogashira cross‐coupling reaction and acetylenic oxidative coupling reaction. The polymers are thermally stable and highly soluble in common organic solvents such as CHCl3, CH2Cl2, and THF. As compared to ethynylene‐linked polymer, the butadiynylene‐linked polymer display a bathochromic shift in the absorption maximum and end absorption position. In addition, the fluorescence behaviors in CH2Cl2 are almost identical for both polymers. Electrochemical measurements indicate that the ethynylene‐linked polymer possesses a lower first oxidation potential than the butadiynylene‐linked one.magnified image

A New Class of Blue‐Emitting Materials for LED Applications: Triarylamine N‐Functionalised 2,7‐Linked Carbazole Polymers

AbstractAttachment of triarylamino‐functional groups at the 9‐position of 2,7‐linked carbazole polymers results in blue‐emitting materials with two independent redox processes that were attributed to the triarylamino groups and the polymer backbone, respectively. This new class of blue‐emitting conjugated polymers was prepared via a Suzuki cross‐coupling reaction and showed low turn‐on voltages in electroluminescent devices as a result of their low ionisation potentials. The photophysical, electrochemical and electroluminescent properties of these materials are discussed.magnified image

Nitrogen-linked Aromatic Poly(2,7-carbazole)s: Partially Annulated Poly(m-aniline)s

Abstract Nitrogen-linked aromatic carbazole polymers were prepared by palladium-catalyzed amination reactions. They are classified as a partially annulated poly(m-aniline), and show a bathochromic shift of absorption maxima as well as reversible redox responses in solutions.

Preparation and Properties of 4-Dialkylamino-phenyl N-Functionalized 2,7-Linked Carbazole Polymers

The preparation of 2,7-linked carbazole polymers with 4-dialkylamino-phenyl substituents is presented. Poly(9-(4-dioctylamino-phenyl)-9H-carbazole-2,7-diyl) P1 and poly(3,6-dimethyl-9-(4-dioctylamino-phenyl)-9H-carbazole-alt-9-(4-dioctylamino-phenyl)-9H-carbazole-2,7-diyl) P2 were prepared through a Suzuki coupling polymerization route. The polymers were characterized by NMR spectroscopy, UV−vis absorption spectroscopy, and fluorescence spectroscopy and their molecular weights were estimated using gel permeation chromatography. Polymer P1 had one of the highest average molecular weights reported for 2,7-linked carbazole main chain conjugated polymers. Both polymers showed unusual photophysical properties with solvent-dependent emission spectra. The fluorescence quantum yields of the polymers were also determined both in solution as well as in the solid state. Cyclic voltammetric studies on these polymers reveal reversible oxidation waves up to 0.7 V (vs Ag/Ag+) for polymer P1 and up to 1.0 V for polymer P2. The polymers also displayed low ionization potentials as a result of their N-substitution with the 4-dialkylamino-phenyl substituents.

Postmodification of poly(9‐alkyl‐9H‐carbazole‐2,7‐diyl)s as a route to new main‐chain‐functionalized carbazole polymers

AbstractThe postmodification of poly[9‐(2‐hexyldecyl)‐9H‐carbazole‐2,7‐diyl] (P1) upon its reaction with N‐bromosuccinimide affords exclusive and full bromination of the 3,6‐positions of the carbazole repeat units to yield poly[3,6‐dibromo‐9‐(2‐hexyldecyl)‐9H‐carbazole‐2,7‐diyl] (P2). Brominated polymer P2 can be used as a precursor for further functionalization at the 3,6‐positions with the desired functional group to afford other useful polymers. Polymer P2 has hence been reacted with copper(I) cyanide to afford poly[3,6‐dicyano‐9‐(2‐hexyldecyl)‐9H‐carbazole‐2,7‐diyl] (P3). Full substitution of the bromide groups with nitrile‐functional groups has been achieved. The preparation and structural characterization of polymers P2 and P3 are presented together with studies on their electronic conjugation and photoluminescence properties. Cyclic voltammetry studies on polymer P3 indicate that the new polymer is easier to reduce (n‐dope) but more difficult to oxidize than its unsubstituted counterpart (P1) as a result of the introduction of the electron‐withdrawing nitrile‐functional groups at the 3,6‐positions on the carbazole repeat units on the polymer chains. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3336–3342, 2006

Properties of CuInS2 free surface and the effect of conductive polymer layers on these properties

The influence of thin conductive polymer layers on the surf ace photovoltage of CuInS2 (CIS) layers prepared using the so-called CISC uT method was studied. The deposition of poly(3,4- ethylenedioxythiophene) films on the free surf ace of CIS resulted in a small decrease in the height of the potential energetic barrier and in an increase in the efficiency of charge carriers transport through the CIS/polymer interface. The change of photovoltaic properties resulting from the polymer deposition on the free surface of CIS was also analysed for the carbazole polymers. Our results confirm the possibility of using the conductive polymer films as organic buffer layers in complete cell structures for photovoltaic cells based on the inorganic photoabsorber CIS.

Synthesis, Optical, and Electrochemical Properties of the High‐Molecular‐Weight Conjugated Polycarbazoles

AbstractSummary: A kind of novel dibromocarbazole monomer bearing three alkyl chains was prepared. Two strategies were developed to improve the solubility and molecular weight of carbazole polymers. One was the polymerization of N‐octyl‐2,7‐bis(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)carbazole with the alkylated dibromocarbazole. Another one was the polymerization of N‐octyl‐2,7‐bis(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)carbazole with N‐octyl‐3,6‐dibromocarbazole. All the polymerizations were carried out under palladium‐catalyzed Suzuki polycondensation (SPC) conditions. Through using carbazole monomer bearing three alkyl chains to polymerize, we have successfully boosted the number‐average molecular weight of 2,7‐linked carbazole polymers from not more than 5 to 67 kDa. The high‐molecular‐weight polymers were obtained in high yields and displayed good solubility in common organic solvents. Their optical, electrochemical, and thermal properties were also reported.Preparation of carbazole polymers by Suzuki polycondensation.magnified imagePreparation of carbazole polymers by Suzuki polycondensation.

Preparation of Carbazole Polymer Thin Films by Electron-Assisted Deposition of 3-(N-Carbazolyl)propyl Acrylate

Polymeric thin films having carbazole pendant groups were prepared by physical vapor deposition of 3-(N-carbazolyl)propyl acrylate (CPA). The conventional vacuum evaporation of CPA formed thin films that consist mainly of small molecules. The evaporated films had needlelike crystallites in the as-deposited state, and underwent severe coalescence upon annealing at 125°C. The deposition polymerization of CPA was achieved by initiating polymerization by electron irradiation onto the monomer vapor by ionization-assisted deposition (IAD). Infrared analysis showed that the polymerization reaction was enhanced by increasing the electron current used for irradiation. The deposition polymerization was effective in improving the uniformity and thermal stability of the film. Photoluminescence analysis suggested that excimer formation can be suppressed by the deposition-polymerization of CPA. The deposited film was found to function as the hole transport layer of the organic light-emitting diode.

Electrochemical copolymerization of Carbazole, Ethylcarbazole and N-Vinylcarbazole with methyl ethyl ketone-formaldehyde resin

Electrochemical polymerization of carbazole (Cz), N-Vinylcarbazole (NVCz), and Ethylcarbazole (ECz) in the presence of methyl ethyl ketone formaldehyde resin (MEKF-R) was accomplished by using acetonitrile-NaClO4 solution. The effects of monomer and resin concentration were investigated on the conductivity of the resulting products. Characterization of insoluble free standing films was carried out via FTIR spectrum, cyclic voltammogram, UV visible spectrum, four point probe conductivity measurements, and elemental analyses. The conductivities of the copolymers were in the range of 10−6 − 10−4 S/cm. All copolymers obtained electrochemically were insoluble in solvents.

Preparation of Carbazole Polymer Thin Films Chemically Bound to Substrate Surface by Physical Vapor Deposition Combined with Self-Assembled Monolayer

Vinyl polymer thin films having carbazole units were prepared by a new method combining physical vapor deposition and self-assembled monolayer (SAM) techniques. 3-(N-carbazolyl)propyl acrylate monomer was evaporated onto a gold substrate that had a VAZO 56 (DuPont) initiator attached as a SAM. The VAZO initiator was activated by irradiating ultraviolet light after depositing the monomer. Although the polymerization reaction can proceed even without the surface initiator, the SAM was effective in improving the surface smoothness, thermal stability, and film-substrate adhesion as a consequence of the formation of covalent chemical bonds between the film and the substrate. Thermal activation of the initiator was examined for the deposition polymerization of 9-H-carbazole-9-ethylmethacryrate. Substrate heating during the evaporation was not effective for accumulating thin films. On the other hand, performing postdeposition annealing on the film after deposition at room temperature resulted in the formation of a polymer thin film chemically bound to the substrate.

Novel 2,7-Linked Carbazole Trimers as Model Compounds for Conjugated Carbazole Polymers

In this paper we present a new synthesis for N-alkylated 2,7-dibromocarbazoles, from which 2,7-linked carbazole trimers have been synthesized by Suzuki cross coupling. The compounds were characterized regarding their thermal, optical, and electrochemical properties and compared to analogous fluorene trimers, which also have been prepared by Suzuki reactions. The carbazole and fluorene trimers exhibit thermal stabilities of more than 300 °C and are able to form molecular glasses. Only one of the carbazole trimers is crystalline. Both carbazole and fluorene trimers exhibit a bright blue fluorescence with a maximum at 393 nm and show similar absorption characteristics. Cyclovoltammetric experiments revealed the electrochemical stability of the fluorene trimers. Their HOMO and LUMO levels are at −5.6 and −2.5 eV, respectively. In contrast to the fluorenes, the 2,7-linked carbazole trimers showed nonreversible oxidations in the CV experiments.

Carbazole compounds as host materials for triplet emitters in organic light-emitting diodes: polymer hosts for high-efficiency light-emitting diodes.

A carbazole homopolymer and carbazole copolymers based on 9,9'-dialkyl-[3,3']-bicarbazolyl, 2,5-diphenyl-[1,3,4]-oxadiazole and 9,9-bis(4-[3,7-dimethyloctyloxy]phenyl)fluorene were synthesized and their electrical and photophysical properties were characterized with respect to their application as host in phosphorescent polymer light-emitting diodes. It is shown that the triplet energy of a polymer depends on the specific connections between its building blocks. Without changing the composition of the polymer, its triplet energy can be increased from 2.3 to 2.6 eV by changing the way in which the different building blocks are coupled together. For poly(9-vinylcarbazole) (PVK), a carbazole polymer often used as host for high-energy triplet emitters in polymer light-emitting diodes, a large hole-injection barrier of about 1 eV exists due to the low-lying HOMO level of PVK. For all carbazole polymers presented here, the HOMO levels are much closer to the Fermi level of a commonly used anode such as ITO and/or a commonly used hole-injection layer such as PEDOT:PSS. This makes high current densities and consequently high luminance levels possible at moderate applied voltages in polymer light-emitting diodes. A double-layer polymer light-emitting diode is constructed comprising a PEDOT:PSS layer as hole-injection layer and a carbazole-oxadiazole copolymer doped with a green triplet emitter as emissive layer that shows an efficacy of 23 cd/A independent of current density and light output.

Alkyne-Bridged Carbazole Polymers by Alkyne Metathesis

Alkyne-Bridged Carbazole Polymers by Alkyne Metathesis

Photorefractive properties of bifunctional N-arylated carbazole derivatives in a carbazole polymer host matrix

We report on the synthesis and the molecular properties of new N-arylated carbazole derivatives that are used as bifunctional chromophores in photorefractive (PR) polymer composites. The C–N bond of the N-aryl carbazole chromophore was formed directly by a nucleophilic aromatic substitution and Ullmann type coupling of carbazole with aryl halides. We performed calculations on the molecular conformation, the magnitude of the dipole moment and the linear polarizability tensor and their relative orientation. The PR performance of the chromophores, doped in an inert polymer host matrix and in a carbazole matrix, with C 60 as sensitizer, was evaluated using four-wave mixing experiments and photoconductivity measurements at 680 nm. The impact of the relative orientation of dipole moment and polarizability tensor on the Figure-Of-Merit (FOM) of photorefractive experiments was clearly demonstrated.

Synthesis and properties of σ–π conjugated alternating polymers consisting of carbazole and organosilicon units

AbstractWe have synthesized novel σ–π conjugated polymers with an alternating organosilanylene and π‐electron system, intending to utilize them for hole‐transporting materials of electroluminescent (EL) devices. 3,6‐Di(lithioethynyl)carbazoles were co‐polymerized with organodichlorosilanes to give the corresponding polymers with molecular weights of MW = 2000–5000. Another type of polymer with a thienylene unit was also synthesized by the nickel‐catalyzed reaction of the di‐Grignard reagent of 1,2‐bis[2‐(5‐bromothienyl)]tetraethyldisilane with 3,6‐dibromocarbazole, the molecular weight being Mn = 3100. The EL devices with a double‐layer system composed of tris(8‐quinolinolato)aluminum(III) and the present polymers as the emitting‐electron‐transporting and hole‐transporting layers, respectively, emit green EL with a maximum intensity of the order of 103 cd m−2. Of these, the device with the thienylene–carbazole polymers exhibited the highest luminance of 1480 cd m−2. Copyright © 2001 John Wiley & Sons, Ltd.

An unprecedented cation radical chain Diels–Alder polymerization leading to novel carbazole polymers

The polymerization of 3,6-bis( trans-1′-propenyl)- N-phenylcarbazole in the presence of tris(4-bromophenyl)aminium hexachloroantimonate ( 1 + ) leads to soluble, high molecular weight, thermally stable cycloaddition polymers containing carbazole units in the main polymer chain. The reaction appears to proceed via a highly efficient cation radical chain mechanism which circumvents the usual hole transfer step of the propagation cycle. This polymerization represents the first observation of direct cation radical Diels–Alder cycloaddition polymerization.

Polymer thin-film distributed feedback tunable lasers

We report on measurements of laser emission from poly-methylmethacrylate and poly-vinyl carbazole polymer films doped with rhodamine-6G, DCM and coumarin laser dyes in an optically pumped distributed feedback scheme. We obtain tunability on a broad spectral range for all samples. We show the impact of waveguiding in the polymer film on reducing the laser threshold. We also show that the number of laser modes increases with the polymer film thickness, following the guided mode dispersion.