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

Experimental and Theoretical Studies on Indigo-Dye-Modified Conjugated Polymers

The present work reports the synthesis of indigo-dye-incorporated polyaniline (Indigo-PANI), poly(1-naphthylamine) (Indigo-PNA), poly(o-phenylenediamine) (Indigo-POPD), polypyrrole (Indigo-PPy), and polythiophene (Indigo-PTh) via an ultrasound-assisted method. The synthesized oligomers were characterized using FTIR, UV-visible spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), fluorescence studies, and thermogravimetric analysis (TGA). The experimental data were theoretically compared to analyze the vibrational and electronic spectra via time-dependent density-functional theory (TD-DFT) by applying the Becke, three-parameter, and Lee-Yang-Parr (B3LYP) method with a 6-311G (d,p) basis set. The experimental, theoretical vibrational, and electronic spectra were found to be in close agreement and confirmed the successful incorporation of indigo dye in PANI, PNA, POPD, PPy, and PTh. These studies confirmed that multifunctional oligomers could be synthesized through a facile technique by incorporating dye moieties to enhance their optoelectronic properties, allowing them to be utilized as near-infrared-emitting probes for photodynamic therapy.

The Failure of Molecular Imprinting in Conducting Polymers: A Case Study of Imprinting Picric Acid on Polycarbazole

The aims of this study were to investigate the potential of utilising molecularly imprinted polycarbazole layers to detect highly toxic picric acid (PA) and to provide information about their performance. Quantum chemical calculations showed that strong interactions occur between PA and carbazole (bond energy of approximately 31 kJ/mol), consistent with the theoretical requirements for effective molecular imprinting. The performance of the sensors, however, was found to be highly limited, with the observed imprinting factor values for polycarbazole (PCz) layers being 1.77 and 0.95 for layers deposited on Pt and glassy carbon (GC) electrodes, respectively. Moreover, the molecularly imprinted polymer (MIP) layers showed worse performance than unmodified Pt or GC electrodes, for which the lowest limit of detection (LOD) values were determined (LOD values of 0.09 mM and 0.26 mM, respectively, for bare Pt and MIP PCz/Pt, as well as values of 0.11 mM and 0.57 mM for bare GC and MIP PCz/GC). The MIP layers also showed limited selectivity and susceptibility to interfering agents. An initial hypothesis on the reasons for such performance was postulated based on the common properties of conjugated polymers.

Electroactive Polymers for On-Demand Drug Release

Conductive materials have played a significant role in advancing society into the digital era. Such materials are able to harness the power of electricity and are used to control many aspects of daily life. Conductive polymers (CPs) are an emerging group of polymers that possess metal-like conductivity yet retain desirable polymeric features, such as processability, mechanical properties, and biodegradability. Upon receiving an electrical stimulus, CPs can be tailored to achieve a number of responses, such as harvesting energy and stimulating tissue growth. The recent FDA approval of a CP-based material for a medical device has invigorated their research in healthcare. In drug delivery, CPs can act as electrical switches, drug release is achieved at a flick of a switch, thereby providing unprecedented control over drug release. In this review, recent developments in CP as electroactive polymers for voltage-stimuli responsive drug delivery systems are evaluated. The review demonstrates the distinct drug release profiles achieved by electroactive formulations, and both the precision and ease of stimuli response. This level of dynamism promises to yield "smart medicines" and warrants further research. The review concludes by providing an outlook on electroactive formulations in drug delivery and highlighting their integral roles in healthcare IoT.

A novel carbazole-based fluorometric and colorimetric sensor for the highly sensitive and specific detection of Cu2+ in aqueous solution

Based on the typical Suzuki coupling reaction and Schiff base reaction, a novel fluorescent molecular PCBW is synthesized and applied as a fluorescence and colorimetric sensor to detect Cu2+ in aqueous solution. The PCBW sensor presents the aggregation-caused quenching (ACQ) effect and at 1 × 10-5 mol L-1 it emits the strongest turquoise fluorescence in the DMSO-H2O system (fw = 40%). The sensor exhibits a 'turn-off' fluorescent characteristic by adding Cu2+, and its fluorescent intensity shows a reliable linear relationship with the Cu2+ concentration in the range of 0-6 × 10-6 mol L-1, with a detection limit of 1.19 × 10-8 mol L-1. Meanwhile, the PCBW sensor also exhibits the colorimetric sensing from colorless to light yellow. The sensor has good selectivity and anti-interference and its pH application range can be extended from 5 to 10. The intramolecular charge transfer (ICT) is speculated as the main fluorescence mechanism of PCBW. In addition, the sensor presents good reusability and is practicable to detect Cu2+ in diverse aqueous samples.

Vinylation of N-Heteroarenes through Addition/Elimination Reactions of Vinyl Selenones

A new protocol for the synthesis of N-vinyl azoles using vinyl selenones and azoles in the presence of potassium hydroxide was developed. This reaction proceeded under mild and transition metal-free conditions through an addition/elimination cascade process. Both aromatic and aliphatic vinyl selenones and various mono-, bi- and tri-cyclic azoles can be tolerated and give terminal N-vinyl azoles in moderate to high yields. A plausible mechanism is also proposed.

One-Step Electropolymerization of a Dicyanobenzene-Carbazole-Imidazole Dye to Prepare Photoactive Redox Polymer Films

To the best of our knowledge, this study reports the first direct electropolymerization of a dicyanobenzene-carbazole dye functionalized with an imidazole group to prepare redox- and photoactive porous organic polymer (POP) films in controlled amounts. The POP films were grown on indium-doped tin oxide (ITO) and carbon surfaces using a new monomer, 1-imidazole-2,4,6-tri(carbazol-9-yl)-3,5-dicyanobenzene (1, 3CzImIPN), through a simple one-step process. The structure and activities of the POP films were investigated as photoelectrodes for electrooxidations, as heterogeneous photocatalysts for photosynthetic olefin isomerizations, and for solid-state photoluminescence behavior tunable by lithium-ion concentrations in solution. The results demonstrate that the photoredox-POPs can be used as efficient photocatalysts, and they have potential applications in sensing.

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,C^2')-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.

Light-Driven Energy and Charge Transfer Processes between Additives within Electrospun Nanofibres

Electrospinning is a cost-effective and efficient method of producing polymeric nanofibre films. The resulting nanofibres can be produced in a variety of structures, including monoaxial, coaxial (core@shell), and Janus (side-by-side). The resulting fibres can also act as a matrix for various light-harvesting components such as dye molecules, nanoparticles, and quantum dots. The addition of these light-harvesting materials allows for various photo-driven processes to occur within the films. This review discusses the process of electrospinning as well as the effect of spinning parameters on resulting fibres. Building on this, we discuss energy transfer processes that have been explored in nanofibre films, such as Förster resonance energy transfer (FRET), metal-enhanced fluorescence (MEF), and upconversion. A charge transfer process, photoinduced electron transfer (PET), is also discussed. This review highlights various candidate molecules that have been used for photo-responsive processes in electrospun films.

Electronically Conductive, Multifunctional Polymer Binder for Highly Active, Stable, and Abundant Composite Electrodes for Oxygen Evolution

The electrolysis of water to form hydrogen and oxygen is a promising method to store renewable energy. This method requires electrodes that convert water into protons, electrons, and oxygen. We report a multifunctional polymer that conducts electrons and ions and may coreact with the electrocatalyst in the oxygen evolution reaction (OER). The electrodes were prepared in two steps from off-the-shelf reagents. They operate with low loadings of abundant catalysts and are among the most active (100 mA cm^-2 at 1.43 V vs RHE (1.41 V, iR-corrected)) and stable electrodes, reported to date under harsh conditions (85 °C, 6 M KOH, 120 h (0.69% loss over the first 14.5 h and then 0.61% loss over 105.5 h)). Control experiments on glassy carbon electrodes showed that the polycarbazole system significantly outperformed a Nafion system of the same catalyst loading. This simple strategy can be applied to other types of electrodes.

Polynaphthylimide–Azomethines Containing Triphenylamine or Carbazole Moieties with Tuned Optoelectronic Properties through Molecular Design

Polyazomethines containing electron-donor triphenylamine (TPA) or carbazole (Cbz) and electron-acceptor naphthyl(di)imide were synthesized and investigated with regard to thermal, optical and electronic features, with a focus on their modulation by molecular design. The polycondesation of an imido-based diamine with a Cbz- or TPA-based dialdehyde led to donor-acceptor polymers with good thermostability, up to 318 °C. These displayed good solubility in organic solvents, which enabled easy polymer processability in thin films with different molecular assemblies. The molecular order improved the charge carrier’s mobility, with a direct impact on the bandgap energy. The optical properties studied by UV–Vis absorption and fluorescence experiments showed solvent-dependence, characteristic for donor-acceptor systems. The structural parameters exerted a strong influence on the light-emissive behavior, with the prevalence of intrinsic or intramolecular charge transfer fluorescence contingent on the donor-acceptor strength and polymer geometry. All polymers showed good electroactivity, supporting both electrons and holes transport. The exchange of Cbz with TPA proved to be an efficient tool with which to decrease the bandgap energy, while that of naphthyl(di)imide with bis(naphthylimide) was beneficial for fluorescence enhancement. This study may contribute to a deeper understanding of the physico-chemistry of electronic materials so as to make them more competitive in the newest energy-related or other optoelectronic devices.

Poly(carbazole-co-1,4-dimethoxybenzene): Synthesis, Electrochemiluminescence Performance, and Application in Detection of Fe3+

In this study, four polycarbazole derivatives (PCMB-Ds) with different alkyl side chains were designed and synthesized via Wittig–Horner reaction. A novel solid-phase electrochemiluminescence (ECL) system was prepared by immobilizing PCMB-D on an indium tin oxide (ITO) electrode with polyvinylidene fluoride (PVDF) in the presence of tripropylamine (TPrA). It could be found that the increase in alkyl side chain length had little effect on the ECL signal of PCMB-D, while the increase in the degree of polymerization (DP) greatly enhanced the ECL signal. Furthermore, the P-3/ITO ECL sensor based on the polyoctylcarbazole derivative (P-3) with the best ECL performance was successfully constructed and detected Fe³⁺ under the optimal experimental conditions. The ECL signal steadily diminished with the increased concentration of Fe³⁺ because of the competition and complexation between Fe³⁺ and P-3 under the condition of pH 7.4. This P-3/ITO platform could realize a highly sensitive and selective detection of Fe³⁺ with a wide detection range (from 6 × 10⁻⁸ mol/L to 1 × 10⁻⁵ mol/L) and low detection limit of 2 × 10⁻⁸ mol/L, which could allow the detection of Fe³⁺ in multiple scenarios, and would have a great application prospect.

Electrodeposition and Characterization of Conducting Polymer Films Obtained from Carbazole and 2-(9H-carbazol-9-yl)acetic Acid

Electrochemical oxidation of electrolyte solutions containing carbazole (Cz) and 2-(9H-carbazol-9-yl)acetic acid (CzA) monomers was performed in acetonitrile solutions. Different Cz and CzA feed ratios were used to electrodeposit solid polymer films of various compositions, and to study the influence of the monomer ratio on the physicochemical properties (electroactivity, topography, adhesion, stiffness, wettability) of the polymer films. Thus, electrochemical oxidation led to the deposition of a solid film of micrometric thickness, but only for the solutions containing at least 30% of Cz. The proportion of Cz and CzA in the electrodeposited polymer films has little impact on the adhesion strength values measured by AFM. On the contrary, this proportion significantly modifies the stiffness of the films. Indeed, the stiffness of the polymer films varies from 9 to 24 GPa depending on the monomer ratio, which is much lower than the value obtained for unmodified polycarbazole (64 GPa). This leads to the absence of cracks in the films, which all have a fairly homogeneous globular structure. Moreover, among the different polymer films obtained, those prepared from 70:30 and 50:50 ratios in Cz:CzA monomer solutions seem to be the most interesting because these green films are conductive, thick, low in stiffness, do not show cracks and are resistant to prolonged immersion in water.

Weak Polyelectrolytes as Nanoarchitectonic Design Tools for Functional Materials: A Review of Recent Achievements

The ionization degree, charge density, and conformation of weak polyelectrolytes can be adjusted through adjusting the pH and ionic strength stimuli. Such polymers thus offer a range of reversible interactions, including electrostatic complexation, H-bonding, and hydrophobic interactions, which position weak polyelectrolytes as key nano-units for the design of dynamic systems with precise structures, compositions, and responses to stimuli. The purpose of this review article is to discuss recent examples of nanoarchitectonic systems and applications that use weak polyelectrolytes as smart components. Surface platforms (electrodeposited films, brushes), multilayers (coatings and capsules), processed polyelectrolyte complexes (gels and membranes), and pharmaceutical vectors from both synthetic or natural-type weak polyelectrolytes are discussed. Finally, the increasing significance of block copolymers with weak polyion blocks is discussed with respect to the design of nanovectors by micellization and film/membrane nanopatterning via phase separation.

Electrochromic Polymers Based on 1,4-Bis((9H-carbazol-9-yl)methyl)benzene and 3,4-Ethylenedioxythiophene Derivatives as Promising Electrodes for Flexible Electrochromic Devices

A 1,4-bis((9H-carbazol-9-yl)methyl)benzene (DCB)-containing homopolymer (P(DCB)) and four DCB- and ED-derivative (3,4-ethylenedioxythiophene (EDOT) and 3,4-ethylenedioxythiophene-methanol (EDm))-containing copolymers (P(DCB-co-ED), P(2DCB-co-ED), P(DCB-co-EDm), and P(2DCB-co-EDm)) were electropolymerized on ITO-polyethylene terephthalate (PET) substrates and their electrochromic performances were studied. DCB displays a lower Eonset than that of EDOT and EDm, conjecturing that the biscarbazole-containing DCB group shows a stronger electron-donating property than that of the ED derivatives. The P(2DCB-co-ED) film presents slate grey, dark khaki, and dark olive green at 0.0, 1.0, and 1.2 V. Bleaching-to-coloring switching studies of polymers show that P(2DCB-co-EDm) shows a high ΔT (31.0% at 725 nm) in solutions. Five dual-layer flexible electrochromic devices (ECDs) based on P(DCB), P(DCB-co-ED), P(2DCB-co-ED), P(DCB-co-EDm), and P(2DCB-co-EDm) as the anodic materials and PEDOT-PSS as the cathodic material are constructed. The P(2DCB-co-ED)/PEDOT-PSS flexible ECD shows a high ΔT (40.3% at 690 nm) and long-term electrochemical cycling stability, while the P(DCB-co-EDm)/PEDOT-PSS ECD shows a high ΔT (39.1% at 640 nm) and short response time (≤1.5 s). These findings offer us a new structural insight for the valuable design of conjugated polymers in high-contrast, flexible ECDs.

Development of Uniform Porous Carbons From Polycarbazole Phthalonitriles as Durable CO2 Adsorbent and Supercapacitor Electrodes

Advances in new porous materials have recognized great consideration in CO₂ capture and electrochemical energy storage (EES) applications. In this study, we reported a synthesis of two nitrogen-enriched KOH-activated porous carbons prepared from polycarbazole phthalonitrile networks through direct pyrolysis protocol. The highest specific surface area of the carbon material prepared by pyrolysis of p-4CzPN polymer reaches 1,279 m² g⁻¹. Due to the highly rigid and reticular structure of the precursor, the obtained c-4CzPN–KOH carbon material exhibits high surface area, uniform porosity, and shows excellent CO₂ capture performance of 19.5 wt% at 0°C. Moreover, the attained porous carbon c-4CzPN–KOH showed high energy storage capacities of up to 451 F g⁻¹ in aqueous electrolytes containing 6.0 M KOH at a current density of 1 A g^-1. The prepared carbon material also exhibits excellent charge/discharge cycle stability and retains 95.9% capacity after 2000 cycles, indicating promising electrode materials for supercapacitors.

Palladium-catalyzed carbene coupling polymerization: synthesis of E-poly(arylene vinylene)s

The Pd-catalyzed carbene coupling reaction of N-tosylhydrazones and benzyl bromides has been developed into a polymerization process for the first time, providing an efficient method for the synthesis of poly(arylene vinylene)s (PAVs). This method affords PAVs bearing E-vinylene units predominantly. It can also introduce a CF₃ group on each vinylene carbon atom in the polymer main chain. The polymerization has a broad scope and the resultant polymers exhibit interesting optical properties and good thermal stabilities.

Rapid and sensitive determination of nitrobenzene in solutions and commercial honey samples using a screen-printed electrode modified by 1,3-/1,4-diazines

In this work, a screen-printed electrode (SPE) modified by 1,3/1,4-diazines was prepared for the rapid and sensitive determination of nitrobenzene (NB). The obtained results indicated enhanced cathodic currents of direct NB reduction into hydroxylaminophenol on the diazine-modified SPEs. The enhanced effect was most likely due to the combination of complexation and collisional processes of diazines towards nitroaromatic compounds and also the diazine-modified electrodes' increased electroconductivity. The best electrochemical responses were obtained in square wave voltammetry mode by using the carbazolyl substituted diazines as a component of the sensitive layer, which was assembled by co-electropolymerization with the unsubstituted carbazole on the electrode during 5 cycles. The low detection limit estimated as 0.107 μM and wide linear range (1-1000 µM) enables NB in water and food samples to be determined. The developed modified electrode was applied in the analysis of commercial honey samples.

Direct formation of 4,5-disubstituted carbazoles via regioselective dilithiation

Carbazoles are widely exploited for their interesting photophysical and electronic properties, however bay (4,5-) functionalization is challenging, and previously inaccessible through carbazole C-H activation. We report a simple methodology which introduces a range of versatile 4,5-functionality, enabling the wider investigation of ring annulation and close proximity effects on carbazole properties.

Electrosynthesis of Electrochromic Polymer Membranes Based on 3,6-Di(2-thienyl)carbazole and Thiophene Derivatives

Five carbazole-containing polymeric membranes (PDTC, P(DTC-co-BTP), P(DTC-co-BTP2), P(DTC-co-TF), and P(DTC-co-TF2)) were electrodeposited on transparent conductive electrodes. P(DTC-co-BTP2) shows a high ΔT (68.4%) at 855 nm. The multichromic properties of P(DTC-co-TF2) membrane range between dark yellow, yellowish-green, gunmetal gray, and dark gray in various reduced and oxidized states. Polymer-based organic electrochromic devices are assembled using 2,2'-bithiophene- and 2-(2-thienyl)furan-based copolymers as anodic membranes, and poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid) (PEDOT-PSS) as the cathodic membrane. P(DTC-co-TF)/PEDOT-PSS electrochromic device (ECD) displays a high transmittance change (ΔT%) (43.4%) at 627 nm as well as a rapid switching time (less than 0.6 s) from a colored to a bleached state. Moreover, P(DTC-co-TF2)/PEDOT-PSS ECD shows satisfactory optical memory (the transmittance change is less than 2.9% in the colored state) and high coloration efficiency (512.6 cm2 C-1) at 627 nm.