Carbazole-based Polymers Research Articles

Synthetic Strategies for 3,6-Substituted Carbazole-based Polymers and Their Opto-Electronic Applications-A Review.

The use of conducting polymers in devices makes them desirable due to their allowance for the fabrication of flexible, lightweight, and potentially inexpensive devices. This review explores the synthetic strategies and characterizations of 3,6-substituted carbazole-based polymers, emphasizing the influence of these modifications on their electronic structure and absorption properties. Polymers containing carbazole substituents are widely studied due to their unique optical and electronic properties, high electron-donating ability, and photoconductivity. The structural adaptability of the carbazole with the 3,6-substitution makes it as an outstanding candidate for their integration into polymers and also possesses improved stability and triplet energy. The role of intramolecular charge transfer (ICT) was highlighted by donor-acceptor architectures with tailoring energy levels to extract their advantageous physicochemical characteristics and optimized performances. Collectively, this comprehensive review delves into the burgeoning field of 3,6-substituted carbazole-based polymers and their crucial role in advancing optoelectronic applications. By amalgamating materials design, synthetic strategies, and application-driven insights, the review serves as a valuable resource for researchers to understand the structure-property relationships and foster innovative solutions for next-generation opto-electronic applications.

Photoinduced step-growth polymerizations of thiophene-carbazole based covalent organic polymer

A novel metal-free photochemical method for the synthesis of porous conjugated polymers was used to investigate the effects of introducing thiophene co-monomer to the carbazole-based polymer, 4,4′-bis(3,6-di(thiophen-2-yl)-9H-carbazol-9-yl)-1,1′-biphenyl (CBP–Th), in terms of its structural, optical, electrochemical and morphological properties. Irradiation of a CBP-Th monomer solution led to the formation of a dark-colored polymer, PCBP-Th, and the role of thiophene on polymerization was investigated, involving electron transfer between CBP-Th and the iodonium ion in the exciplex produced by proton release and radical coupling reactions. The UV–Vis spectra broadened and redshifted due to the elongation of conjugation and solid-state π-π interactions by extra thiophene additive after the polymerization process. The addition of thiophene co-monomer also resulted in decreasing the onset potentials and thus slightly raised HOMO positions determined by the DPV technique. In theoretical calculations, it has been observed that the charge distribution of PCBP-Th at HOMO is over the entire conjugated structure and it has localization in thiophene-thiophene bridges at LUMO. Since the thiophene co-monomer changes the intermolecular distance, the thermal stability of PCBP-Th polymers decreases and accordingly increases the amorphous characters. According to AFM, TEM and SEM images, introducing the thiophene co-monomer led to the formation of larger clusters, resulting in a more pronounced surface texture on both the powders and thin films.

Two hypercrosslinked microporous carbazole-based polymers for electrochemical recognition of penicillin

Two hypercrosslinked microporous carbazole-based polymers (namely C-POP-1 and C-POP-2) were prepared through an efficient Friedel − Crafts coupling approach. Both samples have different porous structures via regulating the length of two-node linear organic blocks. Meanwhile, they have lots of attractive advantages, such as large surface area, splendid stability and conjugate skeleton. As a research case, the aptasensor based on C-POP-2 with the large porous skeleton exhibits the excellent electrochemical detection behavior toward penicillin (PCL). More importantly, this aptasensor can quantitatively detect trace PCL in actual test samples.

PEG-functionalized carbazole-based polymers for UV-protected hydrophilic glass coatings

The UV-absorbing and non-fogging glass coatings containing carbazole-based conjugated backbone with different lengths of hydrophilic PEG subunit (KP-PEG) were produced. The characterizations of the polymers were carried out by using different techniques such as FT-IR, 1H NMR, GPC, TGA and DSC. Transmittance and thin-film morphology analyses, which are essential for UV protection and wettability, were investigated by UV–Vis absorption, AFM and TEM techniques, respectively. Transparent thin films prepared by the polymer solutions in chloroform were obtained by spin coating method at a scan rate of 2000 rpm. The wettability performance and antifogging properties of these surfaces were investigated depending on the PEG length in the polymer subunit. The water contact angle of the surfaces was improved to the range between 60° and 29° depending on the amount of PEG group. KP-PEG750 is the best polymer thin film in terms of having the highest roughness, optimum UV absorption and the low contact angle value.

Methoxy-substituted carbazole-based polymers obtained by RAFT polymerization for solution-processable organic light-emitting devices

New electroactive vinyl monomers, i.e., 3,6-dimethoxy-9-(4-vinylphenyl)-9H-carbazole and 3,6-dimethoxy-9-(3-vinylphenyl)-9H-carbazole were prepared by palladium catalyzed reactions of dimethoxy-9H-carbazole with 1-bromo-4-vinylbenzene or 1-bromo-3-vinylbenzene, respectively. Living radical polymerization of these monomers was carried out using 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid as a RAFT agent affording polymers with controlled molecular weight (up to Mn = 20,000) and low polydispersity (Đ<1.5). The obtained polymers exhibited delayed fluorescence caused by relaxation of excimer states. The lifetimes of long-lived components up to 2.6 μs were obtained for the excimer emission by multi-exponential fitting of photoluminescence decay curves. The polymers were tested in solution-processed OLEDs. Green thermally-activated-delayed-fluorescence OLEDs with polymers as hole transporting materials demonstrated lower turn-on voltage and enhanced charge balance in emission layer compared to device fabricated using the commercial hole-transporting material. Additionally, the phosphorescent OLEDs based on red phosphor as dopant and the synthesized polymer as a host materials were fabricated and characterized. The best device showed external quantum efficiency of 10.6%.

Revisiting carbazole-based polymer donors for efficient and thermally stable polymer solar cells: structural utility of coplanar π-bridged spacers

We develop a series of polymer donors containing carbazole-based units (CBT) to achieve high-performance (PCE of 15.54%) and thermally stable PSCs.

Vinylene-versus azomethine-bridged carbazole-based polymers for light emission and sensor applications

Two new carbazole-based soluble π-conjugated polymers were synthetized and investigated: P1 is a poly(p-phenylenevinylene) analogue and P2 is a poly-azomethine-type polymer. The macromolecular structures of P1 and P2 were confirmed by nuclear magnetic resonance and infrared spectroscopies. The effect of vinylene (in P1) and azomethine (in P2) π-linkers on thermal, optical and electrical properties of the two macromolecules was mainly studied. The differential scanning calorimetry and thermogravimetric analyses showed that both polymers are amorphous and better thermal stability was observed in the case of the azomethine containing polymer. The photophysical behavior of these π-conjugated systems were investigated by UV–visible absorption and photoluminescence spectroscopies. Schottky single-layer diodes and Organic Field-Effect Transistors (OFETs) using P1 and P2 as active layers were elaborated in order to study the electrical properties of these polymeric materials. P1 is a semi-conducting and fluorescent polymer, with a yellowish-green emission and a charge carrier mobility of 5.1 10−6 m²/V.s making it a good candidate for organic light emitting devices (OLED) applications. However, the poly-azomethine P2, in its neutral state, is of little interest when compared to the polyvinylene derivative, due to its very low charge transport capacity and negligible fluorescence intensity. We demonstrate in this study that the electrical and optical properties of the poly-azomethine P2 can be dramatically improved by nitrogen protonation of the azomethine linkers. Indeed, under exposure to trifluoroacetic acid (TFA) vapors, an emitted fluorescence that is a linear function of the amount of TFA added to the P2 solution was observed and a charge carrier mobility of 7 10−5 m²/V.s was achieved. This opens the way for these azomethine-containing carbazole-based polymers to promising applications in electrical and fluorescence turn-on sensors.

Polycarbazole and Its Derivatives: Synthesis and Applications. A Review of the Last 10 Years.

Polycarbazole and its derivatives have been extensively used for the last three decades, although the interest in these materials briefly decreased. However, the increasing demand for conductive polymers for several applications such as light emitting diodes (OLEDs), capacitators or memory devices, among others, has renewed the interest in carbazole-based materials. In this review, the synthetic routes used for the development of carbazole-based polymers have been summarized, reviewing the main synthetic methodologies, namely chemical and electrochemical polymerization. In addition, the applications reported in the last decade for carbazole derivatives are analysed. The emergence of flexible and wearable electronic devices as a part of the internet of the things could be an important driving force to renew the interest on carbazole-based materials, being conductive polymers capable to respond adequately to requirement of these devices.

Synthesis of carbazole-based polymer derived N-enriched porous carbon for dyes sorption

A (N-vinyl carbazole)-based polymer, namely PPVK, was subsequently synthesized by free radical polymerization and oxidative polymerization. This material exhibits permanent porosity, good physicochemical stability, and plenty of nitrogen units. All these features make PPVK promising precursor for constructing N-enriched porous carbon. Using KOH as the activating agent, porous carbon material was prepared and its adsorption performance was also evaluated. Due to the high Brunauer–Emmett–Teller surface area (1832 m2 g−1) and abundant nitrogen atoms, the porous carbon, CPVK-800, displays adsorption capacity of 1074 mg g−1 for Rhodamine B, which is far higher than that reported for commercial activated carbon (0.36 mmol g−1). Kinetic investigations indicate that the adsorption behaviour follows the Langmuir isotherm model and pseudo-second-order kinetics. Besides the cationic dye rhodamine B, CPVK-800 also can be used to adsorption removal of anionic dye methyl orange, with uptake of 739 mg g−1. Findings in this study highlight the potential of using carbonaceous polymer as an effective adsorbent for organic dyes.

Saturated Red Electroluminescence From Thermally Activated Delayed Fluorescence Conjugated Polymers.

Two sets of conjugated polymers with anthraquinone groups as pendant acceptors were designed and synthesized. The acceptor is tethered to an diphenylamine group via a phenylene bridge, constructing a thermally activated delayed fluorescence (TADF) unit, which is embedded into the polymer backbone through its donor fragment, while the backbone is composed of dibenzothiophene-S, S-dioxide and 2, 7-fluorene or 2, 7-carbazole groups. The polymers show distinct TADF characteristics, confirmed by transient photoluminescence spectra and theoretical calculations. The carbazole-based polymers exhibit shorter delay lifetimes and lower energy emission relative to the fluorene-based polymers. The non-doped organic light-emitting diodes fabricated via solution processing approach produce efficient red emissions with the wavelengths of 625–646 nm. The carbazole containing polymer with 2% molar content of the TADF unit exhibits the best maximum external quantum efficiency of 13.6% and saturated red electroluminescence with the Commission Internationale de l'Eclairage coordinates of (0.62, 0.37).

Effects of Hydrogen Bonds between Polymeric Hole-Transporting Material and Organic Cation Spacer on Morphology of Quasi-Two-Dimensional Perovskite Grains and Their Performance in Light-Emitting Diodes.

Perovskite is emerging as a novel emitter in solution-processed light-emitting diodes (LEDs). In these LEDs, morphology, especially the grain size of perovskite, plays a key role in determining electroluminescence performance. Several studies have shown that sizes of the perovskite grains can be controlled by the contact angle between the perovskite solution and the substrate. In this work, we found that in the quasi-two-dimensional (2D) system, the perovskite grain size can be substantially refined when there are hydrogen bonding between the perovskite's organic spacer and the substrates. In fact, for quasi-2D perovskite, with the presence of such hydrogen bond, its effects on the perovskite grain size overshadow the contact angle's effect. We demonstrated that perovskite with refined grains can form amine- or carbazole-based polymers which can form N···H hydrogen bonding with the perovskite's organic spacer. Using these polymers as hole-transporting layers on poly(3,4-ethylenedioxythiophene):polystyrene sulfonate, external quantum efficiency of CsPbBr3-based LEDs can be enhanced from 1.5 to 10.0% without passivation treatment. This work suggests that bonding between perovskite precursors and the substrate can have significant influence on the morphology of the final perovskite grains and their optoelectronic performance.

An all-optical photorefractive miktoarm star polymer synthesized via a combination of RAFT polymerization and click reaction

Aiming to obtain effective calix[4]resorcinarene (CRA)-based photorefractive (PR) materials, three star polymers CRA-PCAH4, CRA-PCAH8 and CRA-PCAH4-PCH4 were prepared via a combination of reversible addition-fragmentation chain transfer (RAFT) polymerization and click reaction. CRA-PCAH4 and CRA-PCAH8 bearing only carbazole-azo-nitrobenzene-based polymeric arms exhibited poor solubility in low boiling point solvents because of the strong interchain electrostatic interactions. While the miktoarm star polymer CRA-PCAH4-PCH4, which was prepared based on CRA-PCAH4 by introducing some carbazole-based polymer arms (PCH) as buffering chains to isolate the nonlinear optical (NLO) components in the CRA core, exhibited good solubility in tetrahydrofuran (THF). A composite based on CRA-PCAH4-PCH4 showed much better PR performance than that of the corresponding PCAH arm tested via a two-beam coupling (TBC) experiment under zero electric field without pre-poling.

Optimizing the property of cross-linked carbazole-based polymer for efficient hole transport in bulk-heterojunction photovoltaic device

Thin films made of cross-linked carbazole pendants of poly(ethylmethacrylate) deposited on indium tin oxide (ITO) was assessed for potential use as hole transport layer (HTL) in a fabricated photovoltaic cell configuration (ITO/PCDTBT/PCBM/Al). Before measurement, the film was designed to have uniform molecular weight, cross-linked carbazole for high electron mobility, high transmittance at the visible wavelength range and smoothness in morphology. Results showed that the film provided 70 times more of current value at open circuit voltage than without the film under light illumination, at optimized thickness from 15 to 25 cycles of deposition at 25 mV/s using cyclic voltammetry.

Applications of Copolymers Consisting of 2,6-di(9H-carbazol-9-yl)pyridine and 3,6-di(2-thienyl)carbazole Units as Electrodes in Electrochromic Devices.

A series of carbazole-based polymers (PdCz, P(dCz2-co-dTC1), P(dCz2-co-dTC2), P(dCz1-co-dTC2), and PdTC) were deposited on indium tin oxide (ITO) conductive electrodes using electrochemical polymerization. The as-prepared P(dCz2-co-dTC2) displayed a high ΔT (57.0%) and multichromic behaviors ranging from yellowish green, greenish gray, gray to purplish gray in different redox states. Five organic electrochromic devices (ECDs) were built using dCz- and dTC-containing homopolymers and copolymers as anodic materials, and poly(3,4-(2,2-dimethylpropylenedioxy)thiophene) (PProdot-Me2) as the cathodic material. The P(dCz2-co-dTC2)/PProdot-Me2 ECD presented remarkable electrochromic behaviors from the bleached to colored states. Moreover, P(dCz2-co-dTC2)/PProdot-Me2 ECD displayed a high optical contrast (ΔT, 45.8%), short switching time (ca. 0.3 s), high coloration efficiency (528.8 cm2 C−1) at 580 nm, and high redox cycling stability.

Poly(tris(4-carbazoyl-9-ylphenyl)amine)/Three Poly(3,4-ethylenedioxythiophene) Derivatives in Complementary High-Contrast Electrochromic Devices.

A carbazole-based polymer (poly(tris(4-carbazoyl-9-ylphenyl)amine) (PtCz)) is electrosynthesized on an indium tin oxide (ITO) electrode. PtCz film displays light yellow at 0.0 V, earthy yellow at 1.3 V, grey at 1.5 V, and dark grey at 1.8 V in 0.2 M LiClO4/ACN/DCM (ACN/DCM = 1:3, by volume) solution. The ΔT and coloration efficiency (η) of PtCz film are 30.5% and 54.8 cm2∙C−1, respectively, in a solution state. Three dual-type electrochromic devices (ECDs) are fabricated using the PtCz as the anodic layer, poly(3,4-ethylenedioxythiophene) (PEDOT), poly(3,3-dimethyl-3,4-dihydro-thieno[3,4-b][1,4]dioxepine) (PProDOT-Me2), and poly(3,4-(2,2-diethylpropylenedioxy)thiophene) (PProDOT-Et2) as the cathodic layers. PtCz/PProDOT-Me2 ECD shows high ΔTmax (36%), high ηmax (343.4 cm2·C−1), and fast switching speed (0.2 s) at 572 nm. In addition, PtCz/PEDOT, PtCz/PProDOT-Me2, and PtCz/PProDOT-Et2 ECDs show satisfactory open circuit memory and long-term stability.

Synthesis, Chemosensory Properties, and Self-Assembly of Terpyridine-Containing Conjugated Polycarbazole through RAFT Polymerization and Heck Coupling Reaction.

We report the responsive fluorescence chemosensory phenomena of a carbazole-functionalized crosslinked polymer (PCaT) with pendent terpyridine (tpy) groups as receptors of metal ions. The polymer was synthesized using Heck polymerization between 3,6-dibromide groups in a carbazole-based polymer (PC2Br) and divinyl tpy monomer. The effects of the polymeric structure on the optical and chemosensory properties of the PCaT were compared with those of a carbazole-tpy alternating conjugated polymer (PCT). Photoluminescence titrations demonstrated that the PCaT and PCT had the high sensing ability toward Fe3+ ions, with Stern–Volmer constants of 8.10 × 104 and 6.68 × 104 M−1, respectively. The limit of detection (LOD) toward Fe3+ of the PCaT and PCT was estimated to be 1.31 × 10−6 and 1.81 × 10−6 M, respectively, and the superior LOD of the PCaT was ascribed to its lowly crosslinked structure. The fluorescence of the solutions of these polymers that were quenched by Fe3+ ions recovered when trace CN− anions were added because of the high stability constant of the CN−–Fe3+ complex. Micellar aggregates with a mean diameter of approximately 239.5 nm were formed by dissolving the PCaT in tetrahydrofuran (THF) solution. Our results suggest that the PCaT is a promising material for chemosensory applications.

Three Carbazole-Based Polymers as Potential Anodically Coloring Materials for High-Contrast Electrochromic Devices.

Three carbazole-based conjugated polymers (poly(3,6-di(2-thienyl)carbazole) (PDTC), poly(2,7-bis(carbazol-9-yl)-9,9-spirobifluorene) (PS2CBP), and poly(3,6-bis(N-carbazole)-N-ethylcarbazole) (PCEC)) are synthesized using electrochemical polymerization. The spectroelectrochemical studies indicate that the PDTC, PS2CBP, and PCEC films show reversible electrochromic behaviors in their redox states, and the PS2CBP film shows a distinct color transition with four various colors (gray at 0 V, grayish-green at 1.0 V, moss green at 1.2 V, and foliage green at 1.4 V). The maximum optical contrast of the PS2CBP and PCEC films is 39.83% at 428 nm and 32.41% at 420 nm, respectively, in an ionic liquid solution. Dual-type electrochromic devices (ECDs) that employ PDTC, PS2CBP, or PCEC film as an anodic layer, and PProDOT-Et2 film as a cathodic layer, were constructed. The as-prepared PCEC/PProDOT-Et2 ECD shows high optical contrast (38.25% at 586 nm) and high coloration efficiency (369.85 cm2 C−1 at 586 nm), and the PS2CBP/PProDOT-Et2 ECD shows high optical contrast (34.45% at 590 nm), good optical memory, and good long-term cycling stability.

Triphenyl phosphine oxide and carbazole-based polymer host materials for green phosphorescent organic light-emitting diodes

Four novel polymers, poly(3,6-9-decyl-carbazole-alt-1,3-benzene) (PB13CZ), poly(3,6-9-decyl-carbazole-alt-bis(4-phenyl) (phenyl) phosphine oxide) (PTPPO38CZ), poly(3,6-9-decyl-carbazole-alt-2,4-phenyl(diphenyl) phosphine oxide) (PTPPO13CZ) and poly(3,6-9-decyl-carbazole-alt-bis(3-phenyl) (phenyl) phosphine oxide) (PTTPO27CZ) were synthesized, and their thermal, photophysical properties and device applications were further investigated to correlate the chemical structures with the photoelectric performance of bipolar host materials for phosphorescent organic light emitting diodes. All of them show high thermal stability as revealed by their high glass transition temperatures and thermal decomposition temperatures at 5% weight loss. These polymers have wide band gaps and relatively high triplet energy levels. As a result, the spin coating method was used to prepare the green phosphorescent organic light emitting diodes with polymers PTPPO38CZ, PTPPO13CZ and PTTPO27CZ as the typical host materials. The green device of polymer PTPPO38CZ as host material shows electroluminescent performance with maximum current efficiency of 2.16 cd·A−1, maximum external quantum efficiency of 0.7%, maximum brightness of 1475 cd·m−2 and reduced efficiency roll-off of 7.14% at 600 cd·m−2, which are much better than those of the same devices hosted by polymers PTTPO27CZ and PTPPO13CZ.

A facile one-pot synthesis of hyper-branched carbazole-based polymer as a hole-transporting material for perovskite solar cells

A novel hyper-branched carbazole-based polymer is synthesized and used as hole-transporting material for PVSCs giving a PCE of 14.07%.

Orthogonally Processable Carbazole-Based Polymer Thin Films by Nitroxide-Mediated Polymerization.

Cross-linking of hole-transporting polymer thin films in organic light emitting diodes (OLEDs) has been shown to increase device efficacy when subsequent layers are deposited from solution. This improvement, due to resistance of the films to dissolution, could also be achieved by covalently grafting the polymer film to the substrate. Using nitroxide-mediated polymerization (NMP), we synthesized a novel poly(9-(4-vinylbenzyl)-9H-carbazole) (poly(VBK)) copolymer which can be cross-linked and also developed two simple methods for the grafting-to or grafting-from, also known as surface-initiated polymerization, of poly(VBK) to indium tin oxide (ITO) substrates. All three of these methods produced thin films that could be orthogonally processed; that is, they resisted dissolution when the spin-coating of a subsequent layer was simulated. Similar electrochemical behavior for the poly(VBK) films was observed regardless of the technique used, suggesting that all three techniques could be used in the engineering of organic electronic devices. We expect that all three methods would be worth investigating in the solution-based assembly of OLEDs and other organic electronic devices.