Carbazole-containing Polymers Research Articles

Carbazole-Fluorene Copolymers with Various Substituents at the Carbazole Nitrogen: Structure-Properties Relationship.

Carbazole derivatives, carbazole-containing polymers and iridium complexes are of interest due to many possible applications in photonics, electronics and biology, particularly as active or hole-transporting layers in organic as well as perovskite devices due to their interesting properties. Here, a series of carbazole-fluorene conjugated copolymers with various substituents at the N-carbazole position (2-methoxycarbonylethyl, 2-carboxyethyl, 2-ethylhexyl, and nonan-2,4-dionatoiridium(III)bis(2-phenylpyridine-N,C2')-9-yl) was prepared by Suzuki coupling. Their photophysical, electrochemical and electroluminescence (EL) properties were studied. Effects of molecular weight and substituents attached to carbazole unit on their properties are reported. The carbazole-fluorene copolymers in dilute solutions exhibited intense photoluminescence (PL) emission in the blue spectral region with high PL quantum yields (78-87%) except for the copolymer with the iridium complex (23%). Similar PL spectra were observed in dilute solutions. More pronounced differences were found in thin film PL and EL properties due to excimer/aggregate formation. Light-emitting devices (LEDs) made of copolymers with 2-ethylhexyl as N-carbazole substituent exhibited efficient EL emission with the best performance and the lowest EL onset voltages (3-4 V), while the LEDs made of copolymers with other substituents were not as efficient, but showed anomalous behavior and memory effects in current-voltage characteristics promising also for bio-inspired electronics.

Peculiarities of the Energy Transfer of Electronic Excitation in Carbazolyle-Containing Polymers

Luminescence spectra of poly-N-vinylcarbazole (PVK), poly-N-epoxypropylcarbazole (PEPK), poly-N-vinyl-3-chlorocarbazole (Cl-PVK), and polystyrene (PS) films doped with bis[2-(2′-benzothienyl)-pyridinato-N,C3′](acetylacetonate) iridium [Btp2Ir(acac)] have been studied. The indicated carbazole-containing polymers are promising for the application in electroluminescence devices. The quantum yield of sensitized phosphorescence by Btp2Ir(acac) molecules in carbazole-containing polymer matrices is found to be lower than at their direct excitation in the PS matrix. The additional doping of the PVK-based composite with benzophenone, which transforms some of singlet excitons into triplet ones, diminishes the intensity of the sensitized phosphorescence of Btp2Ir(acac) molecules, which testifies that the efficiency of energy transfer via singlet excitons is higher than via triplet ones. The results obtained can be explained by a competition between the process of energy transfer onto the acceptor site, on the one hand, and the processes of exciton localization at the tail energy states and the trapping of triplet excitons by the products of polymer oxidation, on the other hand. The quantum yield of sensitized phosphorescence by Btp2Ir(acac) molecules in the PVK matrix is found to be almost 1.5 times lower than in the PEPK one. A conclusion is drawn that, in the PVKmatrix, the process of singlet exciton autolocalization at excimer-forming centers followed by the creation of sandwich-like excimers competes with the process of excitation energy transfer onto the acceptor.

Synthesis, characterization and visible-light-driven photoelectrochemical hydrogen evolution reaction of carbazole-containing conjugated polymers

Hydrogen (H2) is one of the most important fuel candidates and its low-cost production would necessitate the development of efficient electrocatalysts. In this study, we report the synthesis and evaluation of two new carbazole-containing polymers as organic photoelectrochemical (PEC) catalysts for hydrogen evolution reaction (HER). The synthesis of these new conjugated polymers, poly(N-(2-ethylhexyl)-3,6-carbazole-p-bisdodecyloxy-phenylene vinylene) (P1) and poly(N-(2-ethylhexyl)-3,6-carbazole-p-bis(2-ethylhexyloxy)-phenylene vinylene) (P2), was accomplished by the Horner–Emmons polymerization reaction and subsequently characterized by 1H NMR, FTIR, diffuse reflectance UV–vis spectroscopy (DR UV–vis), scanning electron microscope (SEM) and thermogravimetric analysis (TGA). The optical band gaps of P1 and P2, derived from the onset absorption edge, were found to be 2.10 and 2.14 eV, respectively. The chronoamperometric (CA) measurements revealed that the photo-current density generated at ∼0 V by P1 and P2, without the use of additional noble metal based cocatalysts or sacrificial electron donors, was −1.8 and −2.1 μA/cm2, respectively. The enhanced PEC performance of P2 was attributed due to its narrow band gap that enhanced light harvesting ability and the larger surface area which helped in minimizing charge recombination. The experimental observations were well supported by the drastic quenching of PL emission intensity of P2. The linear sweep voltammetry (LSV) measurements showed the onset potential at around −0.3 V for both polymers. The photocurrent density difference for P2 at −1.2 V reached to maximum value of 0.37 mA/cm2, amounting to ∼25% current enhancement under illumination. Long-term stability testing via CA measurements revealed that P2 was relatively more stable than P1, which warranted its potential as photocatalyst for solar water splitting. In addition, P1 and P2 are readily soluble in common organic solvents which make them potential candidates for photovoltaic devices application.

Characterization and Biological Potency of Mono- to Tetra-Halogenated Carbazoles.

This paper deals with the characterization and aryl hydrocarbon receptor (AhR) agonist activities of a series of chlorinated, brominated, and mixed bromo/chlorocarbazoles, some of which have been identified in various environmental samples. Attention is directed here to the possibility that halogenated carbazoles may currently be emitted into the environment as a result of the production of carbazole-containing polymers present in a wide variety of electronic devices. We have found that any carbazole that is not substituted in the 1,3,6,8 positions may be lost during cleanup of environmental extracts if a multilayer column is utilized, as is common practice for polychlorinated dibenzo-p-dioxin (dioxin) and related compounds. In the present study, (1)H NMR spectral shift data for 11 relevant halogenated carbazoles are reported, along with their gas chromatographic separation and analysis by mass spectrometry. These characterization data allow for confident structural assignments and the derivation of possible correlations between structure and toxicity based on the halogenation patterns of the isomers investigated. Some halogenated carbazoles exhibit characteristics of persistent organic pollutants and their potential dioxin-like activity was further investigated. The structure-dependent induction of CYP1A1 and CYP1B1 gene expression in Ah-responsive MDA-MB-468 breast cancer cells by these carbazoles was similar to that observed for other dioxin-like compounds, and the magnitude of the fold induction responses for the most active halogenated carbazoles was similar to that observed for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). 2,3,6,7-Tetrachlorocarbazole was one of the most active halogenated carbazoles and, like TCDD, contains 4 lateral substituents; however, the estimated relative effect potency for this compound (compared to TCDD) was 0.0001 and 0.0032, based on induction of CYP1A1 and CYP1B1 mRNA, respectively.

Clues to the electrical switching mechanism of carbazole-containing polyimide thin films.

The mechanism behind electrical memory behavior of carbazole-containing polyimides (PIs) in nanoscale thin films was investigated. For this investigation, a series of poly(3,3'-dihydroxy-4,4'-biphenylene-co-3,3'-bis(N-ethylenyloxycarbazole)-4,4'-biphenylene hexafluoro-isopropylidenedi-phthalimide)s (6F-HAB-HABCZn PIs) with various compositions was synthesized as a model carbazole-containing polymer system. The thermal properties, band gaps, and molecular orbital levels of the PIs were determined. Furthermore, the chemical compositions, as well as the nanoscale thin film morphologies and electron densities, were analyzed, providing detailed information on the population and positional distribution of carbazole moieties in thin films of the PIs. PI Devices were fabricated with aluminum electrodes and tested electrically. The PI thin film layers in the devices exhibited electrically permanent memory behavior, which was driven by trap-limited space-charge limited conduction and ohmic conduction. The permanent memory characteristics were found to be attributed to the incorporated carbazole moieties rather than from the other chemical components. Furthermore, the memory characteristics depended significantly on the population and positional distribution of carbazole moieties in the PI layer, as well as the film thickness. Considering that the backbone is not conjugated, the present results collectively indicate that the electrical switching behavior of the PI films is driven by the carbazole moieties acting as charge traps and a hopping process using the carbazole charge-trap sites as stepping-stones.

Preparation and properties of poly[9-hexadecyl-3-phenyl-6-(4-vinylphenyl)-9H-carbazole

Preparation of new carbazole-containing polymer, poly[9-hexadecyl-3-phenyl-6-(4-vinylphenyl)-9H-carbazole], is reported. The optical properties of the product have been studied in comparison with those of the starting compounds. Electrochemical properties of the polymer solution and its thin film have been investigated. The polymer film images were obtained by atomic force and scanning tunneling microscopy. Thermogravimetric analysis has shown high thermal stability of the obtained polymer.

Influence of macromolecule main chain structure on electron excitation energy transfer in carbazole-containing polymers

Efficiencies of energy transfer from singlet excitons to rubrene in poly-N-epoxypropylcarbazole (PEPC) and from triplet excitons to pyrene in poly-N-vinylcarbazole (PVC) were found to increase on heating from 5 to 295 K. At the same time, the transfer efficiency in PVC at rubrene concentration 2∙10–3 M decreased in the range T = 100–295 K, which correlated with a rise in the intensity of the fluorescence band of the matrix sandwich-like excimers. However, the transfer efficiency increased upon increasing the concentration, which caused the maximum donor–acceptor distance to approach the critical radius of the Forster model. The observed effects were explained by the fact that the free-path lengths of singlet excitons in PEPC and triplet excitons in PVC increased with increasing temperature and, correspondingly, the probability of them approaching the acceptor within distances where energy transfer was possible increased. Singlet-exciton self-trapping at excimer-forming sites and formation of sandwich-like excimers competed in PVC with energy transfer to rubrene.

Energy transfer by singlet and triplet excitons in carbazole-containing polymers

Quantum yields of pyrene fluorescence and bis[2-(2′-benzothienyl)-pyridinato-N,C3′](acetylacetonate)iridium [Btp2Ir(acac)] phosphorescence upon excitation via a matrix of poly-N-epoxypropylcarbazole (PEPC) or poly-N-epoxypropyl-3,6-dibromocarbazole (DBrPEPC), respectively, were found to be lower than those for the compounds directly excited in a polystyrene (PS) matrix. It was established that the energy in PEPC was transferred to an acceptor by both singlet excitons (by migration and long-range dipole–dipole interaction) and triplet excitons (through migration and short-range exchange electron interaction); however, only by triplet excitons in DBrPEPC, which did not show any fluorescence. The energy-transfer efficiency in PEPC by singlet excitons was higher than by triplet excitons. The observed effects were explained by the fact that energy transfer to the acceptor competed with such processes as localization of the excitons in the “tail” energy states, dissociation of singlet excitons into geminal electron–hole pairs (EHP), and capture of triplet excitons by polymer oxidation products.

Calix[4]arene–carbazole-containing polymers: Synthesis and properties

New highly fluorescent calix[4]arene-containing phenylene-alt-ethynylene-3,6- and 2,7-carbazolylene polymers (CALIX-PPE-CBZs) have been synthesized for the first time and their photophysical properties evaluated. Both polymers were obtained in good isolated yields (70–84%), having Mw ranging from 7660–26,700gmol−1. It was found that the diethynyl substitution (3,6- or 2,7-) pattern on the carbazole monomers markedly influences the degree of polymerization. The amorphous yellow polymers are freely soluble in several nonprotic organic solvents and have excellent film forming abilities. TG/DSC analysis evidences similar thermal behaviors for both polymers despite their quite different molecular weight distributions and main-chain connectivities (Tg in the range 83–95°C and decomposition onsets around 270°C).The different conjugation lengths attained by the two polymers dictates much of their photophysical properties. Thus, whereas the fully conjugated CALIX-PPE-2,7-CBZ has its emission maximum at 430nm (Eg=2.84eV; ΦF=0.62, CHCl3), the 3,6-linked counterpart (CALIX-PPE-3,6-CBZ) fluoresces at 403nm with a significant lower quantum yield (Eg=3.06eV; ΦF=0.31, CHCl3). The optical properties of both polymers are predominantly governed by the intrachain electronic properties of the conjugated backbones owing to the presence of calix[4]arenes along the polymer chain which disfavor significant interchain interactions, either in fluid- or solid-state.

Synthesis of main‐chain poly(carbazole)s via CuAAC

AbstractThe synthesis and characterization of a novel family of main‐chain carbazole‐containing polymers using copper‐catalyzed azide‐alkyne cycloaddition chemistry is reported. The reactions were performed under mild conditions using readily available copper catalysts and ligands, which afforded polymeric products with Mws up to 18 kDa. Using a range of techniques, the polymers were found to exhibit a glass transition temperature (Tg) of 85 °C, high thermal stability (Td = 274 °C), and high photoluminescent quantum efficiency (ϕf = 0.29; λem = 448 nm), which underscore their potential for use in organic light‐emitting diodes or other emissive devices, particularly where efficient blue emission is of value. The approach described offers practical advantages over other synthetic methods used to prepare main‐chain carbazole‐containing polymers, especially with regard to the lack of need for rigorously inert conditions and the absence of byproducts generated during the polymerization reaction. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Polycarbazoles for plastic electronics

This Review covers recent progress made in the synthesis of carbazole-based monomers and polymers and their applications in plastic electronics. That includes the first photoactive carbazole-containing polymer, namely PVK, conjugated poly(3,6-carbazole)s, and finally the latest developments in poly(2,7-carbazole) derivatives. We will mainly discuss photovoltaic cell applications because of the impressive performances that have been obtained in the past couple of years. Semi-ladder poly(indolo[3,2-b]carbazole)s that have recently shown interesting features will also be presented.

Synthesis and Characterization of CdTe Nanoparticle/Polymer Functional Composites

CdTe nanoparticle (NP)/poly(vinylcarbazole) (PVK) functional composite (composite 1) was synthesized via in-situ method. The composite was characterized by using Fourier transformed infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible (UV-vis), photoluminescence (PL), and transmission electron microscopy (TEM) instruments. The PL properties of composite 1 were compared with CdTe NP/carbazole containing polymer composites (composite 2 and composite 3) which were prepared through the electrostatic interaction between preformed NPs and carbazole-containing polymers. The efficient electron transfer (ET) made composite 1 possess the lowest PL quantum yield (QY), the part ET made composite 2 applicable in white-light illumination, and the Förster resonant energy transfer (FRET) made composite 3 possess the highest QY. The large difference in their PL properties was mainly resulted from the distance and the nature of interaction between NPs and polymers. These experimental results indicated that the composites with different function could be obtained just by varying the method of preparation.

Electrical and optical properties of composites based on carbazole derivatives and silicon particles

The electrical and optical properties of polymer-silicon composites with particles incorporated by different means have been studied. It is shown that both when silicon particles are embedded in a carbazole-containing polymer matrix and in the case of a pure polymer, the I–V characteristics are nonlinear and asymmetric (the I–V characteristics of the carbazole-containing polyorganosiloxane, which has silicon atoms in the monomer link, behave in a more symmetric pattern). In all cases, the I-V characteristics can be fitted with power laws, I(V) ∼ Vp, with three different slopes for different voltage intervals, which remainds one of the pattern typical of the mechanism of space-charge-limited currents. It is shown that, in its luminescent properties, the carbazole-containing polyorganosiloxane is similar to a carbazole-containing polymer matrix with embedded silicon particles. The results obtained argue for charge transfer between the polymer and silicon nanoparticles if they are embedded in the matrix and for an formation of an interchain charge-transfer complex in the case of chemically bound silicon.

Effect of Electrostatic Interactions on the Photophysical Properties of the Composites of CdTe Nanocrystals and Carbazole-Containing Polymers

We demonstrated in this study that the electrostatic interaction between nanocrystals (NCs) and polymers was dominant in the photophysical properties of their composites. This effect became more pronounced under illumination and in the presence of the carbazole moieties. The mechanism in which carbazole moieties influenced the PL properties was systematically investigated by means of steady-state fluorescence, fluorescence lifetimes, and ESR spectra. Our experimental results showed that the electrostatic interactions between CdTe NCs and polymers brought defects on the surface of NCs and hence led to the involvement of surface states in the carrier recombination process. Therefore, the composites were inclined to be oxidized when their net charges were slightly positive or negative. The optimal light emitting ratio of NCs to polymers was at the threshold point that NCs could be just completely transferred from the aqueous phase to the organic phase because the composite exhibited nearly electric neutrality at such a ratio. On the other hand, carbazole moieties had an important influence on the intrinsic recombination process of the CdTe NC's core states due to efficient electron transfer at the interface of the NCs and polymers.

Ellipsometric studies of carbazole-containing polymer layers

Ellipsometric studies of carbazole-containing polymer layers deposited onto ITO films on the Corning glass substrate are presented. The comparison of transmission coefficients data with those calculated from ellipsometric experiments allow us to conclude that both results are in good agreement. For all polymers studied, the spectral dependence of the refraction coefficient follows the Cauchy dispersion relation being, however, dependent on the film thickness. It appears that thinner films show a stronger dependence of refraction coefficient vs. wavelength suggesting an optical inhomogeneity of polymer layers.

Study of sensitometric and holographic properties of photoresist media based on carbazole-containing polymers sensitized with triiodomethane and pyran photochromic materials

Sensitometric and holographic properties of photoresist layers made from carbazolylalkyl methacrylate copolymers and polyepoxypropylcarbazole sensitized with triiodomethane and, additionally, spiropyran photochromic compounds were studied. It was found that the introduction of photochromic 6′-bromo-8′-nitro-1,3,3-trimethylindolylspirobenzopyran (8–12%) into photoresist layers increased their photographic sensitivity by a factor of 2.5–3 up to the values of 10−3–10−4 J cm−2 and shifted their spectral sensitivity to the blue-green region. The feasibility of recording quality holograms in the photoresist layers using coherent He-Cd laser light (λ = 420 nm), as well as argon laser light (λ = 490 nm), was shown. Diffraction gratings with an efficiency of 15–20% and a resolution of 2000 mm−1 were obtained.

Bi-stable State for WORM Application Based on Carbazole-containing Polymer

ABSTRACTRecently, several studies have been done by various groups to understand the memory effects behind organic materials, which include understanding in terms of conformation changes, conjugation modification and oxidation-reduction process. In this paper, a WORM (write-once read-many times) memory device using a new polymer material 2-(9H-carbazol-9-yl)ethyl methacrylate (PCz) containing carbazole donor group has been demonstrated. The device uses a MIM (metal-insulator-metal) structure with ITO coated glass as bottom electrode, the synthesized polymer material PCz as the active layer and Al as the top electrode. The toluene solution of PCz was spin-coated on the ITO, followed by solvent removal in a vacuum chamber. Finally, Al was thermally evaporated through shadow mask onto the PCz film.The memory effect of PCz was observed in the I-V characteristic of the MIM structure. The as-fabricated device is found to be in its OFF state, and can be programmed to ON state which is not reversible. The WORM device exhibits a high ON/OFF current ratio of up to 106, and shows a good retention time for both the ON and OFF states which can be sustained within a 24 h timeframe, and extrapolated to sustain for another 10 years. The effect of continuous read pulse on the ON and OFF states was evaluated and no resistance degradation is observed for read cycles up to 107 times. By comparing the electrical characteristics of PCz and PVK as well as their optimized geometry simulation corresponding to their minimized energy states, the memory effect or bi-stable states of PCz can be attributed to the long linker between the carbazole groups and backbone present in PCz which play a part in the conduction mechanism.

Soluble Variable Color Carbazole-Containing Electrochromic Polymers

Three new carbazole-containing polymers were synthesized through Suzuki cross-coupling between N-octylcarbazole-3,6-bis(ethyleneboronate) (NOctCz(BO2Et)2) and several arylene dibromides. 2,5-Dibromothiophene (DBT), 2,2‘-dibromo-5,5‘-bithiophene (DBBT), and 4,7-dibromo-2,1,3-benzothiadiazole (DBBTD) gave the three polymers PCzTh, PCzBi, and PCzBTD, respectively. Cyclic voltammetry showed two separate redox processes for each polymer, PCzTh (E1/2 = 0.33 V and E1/2 = 0.65 V vs Fc/Fc+), PCzBi (E1/2 = 0.32 V and E1/2 = 0.60 V vs Fc/Fc+), and PCzBTD (E1/2 = 0.56 V and E1/2 = 0.84 V vs Fc/Fc+). The two redox couples signify the presence of stable radical cation and dication oxidation states. In addition, the three materials were observed to display electrochromic properties. UV/vis/NIR absorbance spectroscopy revealed that each of the polymers displayed a unique absorbance maximum (345 nm for PCzTh, 375 nm for PCzBi, and 460 nm for PCzBTD) in their neutral states. Spectroelectrochemical analyses demonstrated tha...

Synthesis of Polyacetylenes Having Pendant Carbazole Groups and Their Photo- and Electroluminescence Properties

Novel carbazole-containing polymers, i.e., poly(3,6-di-tert-butyl-N-(p-ethynylphenyl)carbazole) [poly(t-Bu2CzPA)] and poly(N-(p-ethynylbenzoyl)carbazole) [poly(CzCOPA)] were synthesized by the polymerization of the corresponding carbazole-containing acetylene monomers using [(norbornadiene)RhCl]2−Et3N, WCl6−n-Bu4Sn, and WCl4 catalysts. The UV−vis absorption band edge wavelengths of the polymers obtained by the polymerization with W catalysts were longer than those of the Rh-based polymers. The photoluminescence quantum yield of the W-based poly(t-Bu2CzPA) was 55%, while that of the Rh-based one was as low as 3.6%. The photocurrent of poly(t-Bu2CzPA) was 40−50 times higher than the dark current. Poly(t-Bu2CzPA) in conjunction with iridium complexes exhibited electroluminescence (13−18 cd/m2).

Carbazole-containing light-emitting polymers: Properties of excited states

A series of light-emitting conjugated polymers alternatively involving carbazole and bivinylene arylene moieties in the main chain were synthesized via Wittig-Horner type copolymerization. The photoinduced charge transfer process relating to these polymers was investigated by using the technique of fluorescence spectroscopy. The interaction between excited copolymers and C60 in benzene solution was studied. The fluorescence quenching can be well described by the “sphere-of-action” mechanism. It is believed that two basic steps are involved in the quenching process, i.e. the diffusion of excitation within the conjugated polymers and the dissociation of the exctions trapped by fullerene. The radius of the sphere-of-action can be related to the excitation diffusion length, which depends on the lifetime of the exciton. The dynamic fluorescence quenching of the copolymers by another quencher, 1,4-dicyanobenzene (DCB) was also surveyed. Copolymers with different chain conformations show different temperature effects in the dynamic quenching. A planar conformation is beneficial for the quenching via bimolecular collision.