Carbazole Polymers Research Articles

Synthesis and electrochemical, optical, and thermal properties of polycarbosilanes with silylene–vinylene–phenylene–vinylene backbones and triphenylamine or carbazole unit-containing side chains

Polycarbosilanes with silylene–vinylene–phenylene–vinylene backbones and triphenylamine or carbazole unit-containing side chains were conveniently prepared by Pd-catalyzed one-pot reactions of a trihydrosilane (phenylsilane) with aromatic diynes (p- and m-diethynylbenzene) and triphenylamine or carbazole-unit containing acetylenes. Cyclic voltammetry of these polycarbosilanes suggested that dimerization processes of the pendant units took place during the electrochemical oxidation steps. In UV/vis absorption and emission spectra, the p-phenylene or triphenylamine unit-containing polymers showed λmax peaks at longer wavelength regions than the corresponding m-phenylene or carbazole unit-containing polymers. An energy transfer process from the backbone to the side chain was suggested in the polycarbosilane possessing m-phenylene and triphenylamine units. Photoluminescence quantum yields of these polymers ranged from 0.16 to 0.34 with the m-phenylene and triphenylamine units-containing polymer exhibiting the highest value. DSC analyses revealed that the p-phenylene polymers showed higher glass transition points (148–180 °C) than the corresponding m-phenylene polymers (129–158 °C). In TGA, the 5% weight loss temperatures were in the range of 382–444 °C, suggesting considerably high thermal stability of these polycarbosilanes. Ionization potentials were estimated by atmospheric photoelectron spectroscopy at 5.6–5.9 eV with the values of carbazole polymers being higher than those of the triphenylamine polymers.

Copolymers of carbazoles and methyl ethyl ketone formaldehyde resin

PurposeThe purpose of this paper is to develop the soluble and processable conducting copolymers of carbazole (Cz), ethylcarbazole (ECz), N‐vinylcarbazole (NVCz) by oxidatively polymerising carbazoles by ceric ammonium nitrate (CAN) in the presence of methyl ethyl ketone formaldehyde resin (MEKF‐R); and to report the advantages of obtaining copolymer structure.Design/methodology/approachA new class of soluble and conductive P(Cz/MEKF‐R), P(NVCz/MEKF‐R) and P(ECz/MEKF‐R) copolymers were synthesised by the method of oxidative polymerisation with ceric ammonium nitrate. MEKF‐R, CAN and carbazole monomers (Cz, NVCz and ECz) were dissolved in acetonitrile separately. Then, the CAN solution was added dropwise into the mixture of MEKF‐R and Cz, NVCz or ECz solutions while stirring and a green powder was formed almost instantaneously. After one hour stirring at 25°C, the powder was filtered, washed with acetonitrile and dried at room temperature. A green coloured product was obtained. The colourless insulator copolymer present in this product was separated by selectively dissolving with toluene. The insoluble green copolymer was filtered off and dried at room temperature under vacuum. The products were characterised by FTIR, DSC thermograms, 1H‐NMR, four‐point probe conductivity and atomic absorption measurements.FindingsThe solubility and conductivity of the Cz/MEKF‐R copolymer P(Cz/MEKF‐R), the NVCz/MEKF‐R copolymer P(NVCz/MEKF‐R) and the ECz/MEKF‐R copolymer P(ECz/MEKF‐R) were regulated by the ratios of (Cz, NVCz, ECz)/CAN/MEKF‐R. By inclusion of the ketonic resin segments to the polycarbazole chains, thermally processable copolymers have been obtained with a melting point of about 80°C. FT‐IR results in different reaction time and the presence of metal in copolymers show together a complex between monomer‐metal and resin.Research limitations/implicationsThis study focuses on obtaining conductive, soluble and processable copolymers. Since the ketonic resin is an insulator, in order to obtain both conductive and totally soluble polymer, successively regulating the ratios of (Cz, NVCz, ECz)/CAN/MEKF‐R is necessary.Practical implicationsThis work provides technical information for the synthesis of conducting and totally soluble copolymer.Originality/valueThe conductive P(Cz/MEKF‐R), P(NVCz/MEKF‐R) and P(ECz/MEKF‐R) copolymers obtained by the method of oxidative polymerisation with ceric ammonium nitrate, which are totally soluble in DMF, could only be produced with this method and may increase the area of application of the carbazole polymers.

Multicolor emission and thin film transistor properties of 1,8-diethynylcarbazole-based conjugated copolymers

1,8-Carbazole-based conjugated copolymers are synthesized by the Sonogashira polycondensation between the 1,8-diethynylcarbazole derivative and dibromo comonomers. The resulting polymers are fully characterized by GPC, and 1H NMR and IR spectroscopies, and their high thermal stability with the 5% decomposition temperature exceeding 350 °C by thermogravimetric analyses. The optical properties of the carbazole polymers reveal that the comonomer structures significantly affect the absorption and emission spectra. For example, a bathochromic shift of the spectra is achieved when electron-accepting comonomers are selected, finally leading to the production of additive primaries. The mixtures of three carbazole polymers with red, green, and blue emission colors provide a white light emission both in solutions and in thin solid films. In addition, the thin film transistor properties of the carbazole polymers are investigated. The 1,8-carbazole-based polymers display an intermediate mobility between the 2,7-carbazole and 3,6-carbazole-based counter polymers. All these results suggest the potential application possibilities of the 1,8-carbazole-based conjugated polymers in optoelectronic devices.

Effects of surfactants on microwave-assisted solid-state intercalation of poly(carbazole) in Bentonite

The present preliminary investigation reports, for the first time, the effects of typical cationic and anionic surfactants on the microwave-assisted solid-state intercalation and polymerization of carbazole (Cz) in the basal spacings of Bentonite. The intercalation of cetyl pyridinium chloride (CPCl), a cationic surfactant, and naphthalene sulfonic acid (NSA), an anionic surfactant, in Bentonite was carried out at two loadings—25 and 50 wt%—using microwave irradiation. The in situ polymerization of Cz was successfully carried out into the surfactant-modified galleries of Bentonite. This was confirmed by Gel permeation chromatography (GPC). The intercalation of poly(carbazole) (PCz) was confirmed by FT-IR, UV–Visible, and XRD analyses. Although polymerization was carried out in the solid-state, the UV–Visible spectra revealed the doped state of PCz and the presence of a charge carrier tail. The XRD studies showed that the increase in the height of the galleries was higher in case of Bentonite/CPCl/PCz nanocomposites as compared to Bentonite/NSA/PCz nanocomposites. It also revealed different orientations of the two surfactants in the galleries of the clay. The average particle size of Bentonite/CPCl/PCz (1:0.25:0.25) and (1:0.5:0.5) nanocomposites was found to be in the range of 25–35 and 50–60 nm, respectively. The Bentonite/NSA/PCz (1:0.25:0.25) and (1:0.5:0.5) nanocomposites showed the average particle size in the range of 20–30 nm and 40–50 nm, respectively. The results revealed that both cationic and anionic surfactants strongly influenced the morphology of Bentonite/PCz nanocomposites. The difference in the mechanisms of solid-state intercalation of PCz in the presence of these surfactants has been proposed.

Novel Synthesis of Polycarbazole–Gold Nanocomposite

AbstractA polycarbazole–gold nanocomposite is synthesized based on two polymerization techniques, i.e., emulsion and interfacial using aqueous gold chloride and non‐aqueous carbazole monomer solutions. Use of gold chloride as an oxidant for carbazole not only provides a new chemical synthesis for polycarbazole conducting polymer but also allows the formation of conducting nanocomposite in one simple step. Polymerization of carbazole and further growth of the polymer along with gold nanoparticles are governed by the redox reaction between carbazole and Au cations. Two different morphologies of polymers and two different sizes (with narrow size distribution) of gold nanoparticles are obtained depending on the polymerization routes. Structural and thermal properties of the nanocomposites are studied using SEM/TEM, FT‐IR, XRD, and TGA. XRD of nanocomposites depicts the amorphous nature of the polymer and the highly phase selective crystalline nature of gold. Nanocomposites with improved properties show better dispersion in common organic solvents and potential for various technological applications. magnified image

Theoretical investigation of nitrogen-linked poly(2,7-carbazole)s as hole-transport materials for organic light emitting diodes

Nitrogen-linked poly(2,7-carbazole)s, a novel class of carbazole polymers, are new organic light-emitting materials (OLEDs), which are capable of transporting holes. In this paper, the electronic properties of the neutral molecules, HOMO–LUMO gaps (Δ H–L ), in addition to IPs and EAs, are studied using B3LYP functional. The lowest excitation energies ( E g ) and the maximal absorption wavelength λ abs are studied using the time dependent density functional theory (TDDFT). As a result of these calculations, the highest-occupied molecular orbital (HOMO) energies lift about 0.75–1.04 eV and thus the I P decrease about 0.52–0.74 eV compared to polycarbazole. This result suggested the significantly improved hole-accepting and transporting abilities of the nitrogen-linked poly(2,7-carbazole)s. Furthermore, the nitrogen-linked poly(2,7-carbazole)s also had longer maximal absorption wavelengths than polycarbazole.

Theoretical study on alkyne-linked carbazole polymers for blue-light multifunctional materials

This paper studied poly[(3,6-di-tert-butyl-N-hexadecyl-1,8-carbazolylene) butadiynylene] ( P1), butadiynylene-linked poly (3,6-carbazole) ( P2) and butadiynylene-linked poly (2,7-carbazole) ( P3) through the theoretical measurements with Gaussian 03 program package. To investigate the relationship between structures and properties of these multifunctional electroluminescent materials, their geometrical structures of ground and excited-states were optimized by B3LYP/6-31G (d) and CIS/6-31G (d) methods, respectively. The lowest excitation energies ( E g 's), and the maximum absorption and emission wavelengths of these polymers were calculated by time-dependent density functional theory methods (TD-DFT). The important parameters for luminescent materials were also predicated including the ionization potentials ( I p 's) and electron affinities ( E a 's). The calculated results show that the highest-occupied molecular orbital (HOMO) energies lift about 0.27–0.49 eV compared to N,N′-bis(naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB), suggesting the significant improved hole-accepting and transporting abilities. In addition, substitution of alkyne for carbazole resulted in a narrow band gap and a red shift of both the absorption and emission peaks. Through above calculations, it is evidenced that these polymers can be considered as candidates for excellent OLEDs with good hole-creating abilities and high blue-light emission.

Charge photogeneration and transport in side-chain carbazole polymers and co-polymers

The photoconductivity, hole mobility and charge photogeneration efficiency of a series of side-chain carbazole homopolymers and copolymers (with azo side-chains) have been investigated. Cyclic voltammetry measurement of frontier orbitals energies show that the HOMO energy is determined by the nature and the position of attachment of the linker between the main chain and the carbazole, the azo-moiety being not relevant in this respect. Hole mobility is not influenced by the HOMO energy but seems to depend on the degree of conformational mobility of the side-chains, reaching values of the order of 10 −3 cm 2 V −1 s −1 in the best cases. The HOMO energy is instead extremely important when considering photogeneration efficiency, that can change by 10 orders of magnitude depending on the density of the carbazole side-chains in co-polymers and on the linker nature and attachment position.

Antimicrobial graphene polymer (PVK-GO) nanocomposite films

The first report on the fabrication and application of a nanocomposite containing poly-N-vinyl carbazole (PVK) polymer and graphene oxide (GO) as an antimicrobial film was demonstrated. The antimicrobial film was 90% more effective in preventing bacterial colonization relative to the unmodified surface. More importantly, the nanocomposite thin film showed higher bacterial toxicity than pure GO-modified surface.

Postfunctionalization of Alkyne-Linked Conjugated Carbazole Polymer by Thermal Addition Reaction of Tetracyanoethylene.

The postfunctionalization of the main chain alkyne moieties of carbazole containing poly(arylenebutadiynylene)s was attempted by using a high yielding addition reaction between electron rich alkynes and a strong acceptor molecule, tetracyanoethylene (TCNE). After successful postfunctionalization, the polymer band gap decreased due to the intramolecular donor-acceptor interactions. The resulting donor-acceptor alternating polymer showed a very broad charge-transfer band in the visible region as well as redox activities in both anodic and cathodic directions. The optical band gap showed good agreement with the electrochemical band gap. Furthermore, the thermal stability was enhanced after postfunctionalization. These features of the donor-acceptor alternating polymer are expected to be useful for high performance activities in organic solar cell applications.

Synthesis and Properties of 1,8-Carbazole-Based Conjugated Copolymers

A new series of conjugated carbazole polymers based on the 1,8-carbazolylene unit was synthesized by the Pd-catalyzed polycondensation between the 1,8-diiodocarbazole derivative and various bifunctional counter comonomers. An alkyne spacer was found to be a key to increasing the molecular weight of the resulting polymers. All the obtained polymers showed good solubilities in the common organic solvents, and they were fully characterized by Gel permeation chromatography (GPC), and 1H NMR and infrared (IR) spectroscopies. The UV-vis absorption and fluorescence spectra revealed the relationship between the chemical structure and effective conjugation length. The efficiency order of the carbazole connectivity was 2,7-carbazolylene > 1,8-carbazolylene > 3,6-carbazolylene. The electrochemical properties of these polymers suggested the relatively facile oxidation at ca. +0.5–0.7 V vs. Fc/Fc+ or a high potential as p-type semiconductors. The combination of the electrochemical oxidation potentials and the optical band gaps allowed us to estimate the HOMO and LUMO levels of the polymers. It was shown that the energy levels of the 1,8-carbazole-based conjugated polymers can be tunable by selecting the appropriate comonomer structures.

Effect of Self-Assembled Monolayer Modification on Indium–Tin Oxide Surface for Surface-Initiated Vapor Deposition Polymerization of Carbazole Thin Films

With the aim of controlling the interface between an inorganic electrode and an organic layer, a surface-initiated vapor deposition polymerization method was employed to prepare carbazole polymer thin films that are chemically bound to an indium–tin oxide (ITO) surface. A self-assembled monolayer (SAM) that has an azo initiator as a terminal group was prepared on an ITO surface, on which carbazole acrylate monomers were evaporated under ultraviolet (UV) irradiation. The surface morphological characteristics of the films prepared with/without UV irradiation and with/without the SAM were compared. It was found that the UV irradiation leads to the polymerization of carbazole monomers irrespective of the type of substrate used. On the other hand, the surface morphological characteristics were largely dependent on the existence of the SAM. Uniform and smooth polymer thin films were obtained only when the monomers were evaporated on the SAM-modified surface under UV irradiation. A comparison of film growth characteristics on a UV–ozone-treated ITO surface suggested that the formation of uniform films was made possible not by the modification of surface energy but by the growth of the polymers chemically bound to the substrate surface.

Enzymatic polymerization of hydroxy-functionalized carbazole monomer

Up to date, enzymatic polymerization of phenolic compounds bearing different moieties such as ferrocene, sugar, furamide, and male-imide have been reported. In this study, horseradish peroxidase (HRP)-catalyzed polymerization of another hydroxy substituted aromatic compound, 2-hydroxycarbazole (HC), was firstly presented. The structure of the polymer (PHC) was verified by using nuclear magnetic resonance and infrared techniques. Further characterization was carried out by means of TG, DSC, CV (cyclic voltammetry), SEM (scanning electron microscopy), fluorescence analyses, and solid state conductivity measurements. Average molecular weight of the polymer was determined by gel permeation chromatography and was around two thousands. The optical and electrochemical band gaps of PHC were dramatically lower than those of HC. The photochemical behaviors of HC and PHC were investigated by recording the fluorescence spectra in two different solvents. Solid state conductivity measurement showed that the electrical conductivity value of hydroxyl-functionalized carbazole polymer is relatively higher than those of the previously reported phenol polymers in the literature. Moreover, the conductivity of PHC increased by doping with iodine vapour.

Aryl amine substituted low energy gap carbazole polymers: preparation and photovoltaic properties

The preparation of a series of donor/acceptor copolymers comprising alternating 2,7-linked 3,6-dimethyl-9-arylamino-carbazole units and 5,7-bis-(thiophen-2-yl)-2,3-diphenyl-thieno[3,4-b]pyrazine units is presented. The triarylamine substituents are attached to the carbazole repeat units either through the para- or meta-positions. The effect of the linkage position of triaryl amine substituents in this series of polymers as well as the effect of substitution of the phenyl groups at the 2,3-positions of 5,7-bis-(thiophen-2-yl)-2,3-diphenyl-thieno[3,4-b]pyrazine repeat units with alkoxy-substituents are investigated in this work. The polymers were characterized by NMR spectroscopy, UV-Vis absorption spectroscopy and fluorescence spectroscopy, and their molecular weights were estimated using gel permeation chromatography. Polymers P1–P4 absorb light up to 900 nm and have energy gaps ranging from 1.37 to 1.40 eV. Photovoltaic cells with ITO/PEDOT:PSS/P2:PC70BM(1/4, w/w)/Al showed an open circuit voltage of 0.60 V under white light illumination, power conversion efficiency of 0.67% and short circuit current of 3.6 mA cm−2.

Synthesis and Properties of Conjugated Poly(1,8-carbazole)s

During our search of novel conjugated carbazole polymers, we succeeded in the efficient synthesis of conjugated poly(1,8-carbazole) derivatives. The synthetic route to the 1,8-difunctionalized carbazole monomers and the polymerization methods under the Yamamoto, Sonogashira, and Hay conditions were established. The obtained poly(1,8-carbazole)s were comprehensively characterized by GPC, MALDI-TOF MS, 1H NMR, and IR spectroscopies, and it was found that the alkyne spacer is an important factor in obtaining the high molecular weight polymers. Thermal analysis revealed that the alkyne-linked poly(1,8-carbazole)s possess a higher thermal stability than the directly linked poly(1,8-carbazole). The energy diagrams of a series of polycarbazoles were carefully estimated from the electrochemical and optical measurements. The alkyne-linked carbazole polymers were potent blue-light-emitting polymers due to their narrow band gaps. Furthermore, the remarkable decreased aggregation behavior of the butadiynylene-linked ...

A new donor–acceptor double‐cable carbazole polymer with perylene bisimide pendant group: Synthesis, electrochemical, and photovoltaic properties

AbstractWe report here electrochemical synthesis of novel soluble donor–acceptor (D–A) polymer with suitably functionalized perylenetetracarboxylic diimide dye derivative covalently linked to carbazole moiety (Cbz‐PDI). The band gap, Eg was measured using UV–Vis spectroscopy and compared with that obtained by cyclic voltammetry (CV). Efficient intramolecular electron transfer from carbazole‐donor to perynediimide‐acceptor leads to remarkable fluorescence quenching of the perylene core. Furthermore, spectroelectrochemical property and surface morphology of the polymer film were investigated. Characteristic monoanion and dianion radical bands on the UV–Vis absorption spectra attributed to the electrochemical reduction of the neutral polymer were observed. During the reduction process, red color of the film turned into blue and violet, respectively. Finally, the photovoltaic performance of the D–A double‐cable polymer was checked and nearly 0.1% electrical conversion efficiency is obtained under simulated AM 1.5 solar light with 100 mW/cm2 radiation power. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6280–6291, 2009

Synthesis and properties of nitrogen‐linked poly(2,7‐carbazole)s as hole‐transport material for organic light emitting diodes

AbstractA novel class of carbazole polymers, nitrogen‐linked poly(2,7‐carbazole)s, was synthesized by polycondensation between two bifunctional monomers using the palladium‐catalyzed amination reaction. The polymers were characterized by 1H NMR, Infrared, Gel permeation chromatography, and MALDI‐TOF MS and it was revealed that the combination of the monomer structures is important for producing high molecular weight polymers. Thermal analysis indicated a good thermal stability with high glass transition temperatures, e.g., 138 °C for the higher molecular weight polymer P2. To pursue the application possibilities of these polymers, their optical properties and energy levels were investigated by UV‐Vis absorption and fluorescence spectra as well as their electrochemical characteristics. Although the blue light emission was indeed observed for all polymers in solution, the quantum yields were very low and the solid films were not fluorescent. On the other hand, the HOMO levels of the polymers estimated from the onset potentials for the first oxidation in the solid thin films were relatively high in the range of −5.12 to −5.20 eV. Therefore, light emitting diodes employing these polymers as a hole‐transport layer and iridium(III) complex as a triplet emitter were fabricated. The device of the nitrogen‐linked poly(2,7‐carbazole) P3 with p,p′‐biphenyl spacer, which has a higher HOMO level and a higher molecular weight, showed a much better performance than the device of P2 with m‐phenylene spacer. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3880–3891, 2009

White organic light-emitting diodes with improved performance using phosphorescent sensitizer and ultrathin fluorescent emitter

White organic light-emitting diodes (WOLEDs) have been fabricated by using a novel phosphor of bis(1,2-dipheny1-1 H-benzoimidazole) iridium (acetylacetonate) [(pbi) 2Ir(acac)] as a sensitizer doped into a carbazole polymer of poly(N-vinylcarbazole) (PVK), and a fluorescent dye of 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran(DCJTB) as an ultrathin red light-emitting layer. By characterizing the UV–Vis absorption spectra, photoluminescence (PL) spectra of (pbi) 2Ir(acac) and DCJTB, and the electroluminescence (EL) properties of the WOLEDs, the effect of ultrathin fluorescent light-emitting layer on the injection and transport characteristics of charge carrier and EL performance of WOLEDs was investigated. The results demonstrated that the device has stable EL spectra and Commissions Internationale de 1’Eclairage (CIE) coordinates in a wide bias range. Both energy transfer and charge trapping play the role on the performance of WOLEDs, and the device luminance was enhanced significantly with a maximum luminance of 9260 cd/m 2, which is about 70% higher than the codoped device.

N-Aryl 2,7-Linked Carbazole Polymers and Copolymers with Fluorine Protecting Groups: A New Class of Blue Emitting Polymers for LED Applications

N-functionalisation of 3,6-difluoro 2,7-linked carbazole polymers with aryl substituents affords blue emitting materials with good electrolytic stability and moderate quantum yields of fluorescence. Copolymers comprising N-aryl 2,7-linked carbazole repeat units with 3,6-fluoro protecting groups and triaryl amine repeat units afford blue emitting materials with enhanced electrolytic stability and high quantum yields of fluorescence. Both classes of materials were prepared using Suzuki cross-coupling polymerisation methods. The synthesis and characterisation of this new class of materials together with a study of their electrochemical and photophysical properties is presented.

Spectral Characteristics of White Organic Light-emitting Diodes Based on Novel Phosphorescent Sensitizer

White organic light-emitting diodes were fabricated by using a novel phosphorescence bis(1,2-dipheny1-1H-benzoimidazole)iridium(acetylacetonate)[(pbi)2Ir(acac)] as sensitizer and a fluorescent dye of 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) codoped into a car-bazole polymer of poly(N-vinylcarbazole) (PVK). Through characterizing the UV-Vis absorption spectra, the photoluminescence spectra of (pbi)2Ir(acac) and DCJTB, and the electroluminescence spectral properties of the WOLEDs, the energy transfer mechanisms of the codoped polymer system were deduced. The results demonstrate that the luminescent spectra with different intensity of (pbi)2Ir(acac) and DCJTB were co-existent in the EL spectra of the blended system, which is ascribed to an incomplete energy transfer process in the EL process. The efficient Forster and Dexter energy transfer between the host and the guests enabled a strong yellow emission from (pbi)2Ir(acac) and DCJTB, where (pbi)2Ir(acac) plays an important role as a phosphorescent sensitizer for DCJTB. With the blue emitting-layer of N,N-diphenyl-N,N-bis(1-naphthyl)(1,1-biphenyl)-4,4-diamine, the codoped system device achieved white emission. The codoped system showed that its Commissions Internationale de 1Eclairage coordinates were more independent of the variation of bias voltage than those of phosphorescent doped PVK systems.