Theoretical Studies of Symmetric Five-Membered Heterocycle Derivatives of Carbazole and Fluorene: Precursors of Conducting Polymers

Preparation of Carbazoles Involving 6π-Electrocyclization, Photoredox-, Electrochemical-, and Thermal Cyclization Reactions: Mechanistic Insights

Carbazole is a heterocyclic motif that can be found in a diverse array of natural and unnatural products displaying a wide range of biological and physiological properties. Furthermore, this heterocycle is part of electronic materials like photoconducting polymers and organic optoelectronic materials owing to its excellent photophysical characteristics. Consequently, the development of synthetic strategies for carbazole scaffolds holds potential significance in biological and material fields. In this regard, a variety of preparation methods has been developed to exploit their efficient and distinct formation of new C-C and C-heteroatom bonds under mild conditions and enabling broad substrate diversity and functional group tolerance. Therefore, this review focuses on the synthesis of a set of carbazole derivatives describing a variety of methodologies that involve direct irradiation, photosensitization, photoredox, electrochemical and thermal cyclization reactions.

Photoinduced [6π]-Electrocyclic Reaction of Mono-, Di-, and Trisubstituted Triphenylamines in Acetonitrile. A Steady-State Investigation

Direct irradiation of mono-, di-, and trisubstituted triphenylamine derivatives in acetonitrile as solvent with light of 254 nm has been systematically investigated, revealing that the exo/endo carbazole derivatives were formed as the main photoproducts from modest to good yields for triphenylamines substituted with electron-donor and neutral substituents. The kinetic profiles of the photoreaction were also recorded, and the consumption rate constants (k) were measured. These kinetic parameters show dependence on the nature of the substituents, and linear Hammett correlations were carried out to showcase the substituent effect. On the other hand, the spectroscopic behavior of the electron-rich substituted triphenylamines has been analyzed, suggesting that the fluorescence emission spectra display a mirror image of the lower energy absorption bands, while for those amines bearing electron-acceptor groups the formation of charge-transfer complexes and their fluorescence emissions constitute the main deactivation pathway of the photoreaction.

Novel pyrazolyazoindole derivatives as photoswitches: design, synthesis, and photoswitching behavior research combined with theoretical methods

Novel pyrazolyazoindole photoswitches with high to near-complete photoconversion, adjustable thermal half-lives, photochromic properties, and potential application value are developed.

Substrate-Controlled Regio- and Stereoselective Synthesis of ( Z)- and ( E)- N-Styrylated Carbazoles, Aza-carbazoles, and γ-Carbolines via Hydroamination of Alkynes

We report herein the substrate-controlled regio- and stereoselective hydroamination of carbazoles, aza-carbazoles, and γ-carbolines with functionalized aromatic as well as aliphatic alkynes in a KOH/DMSO system in good yields. The electronic effect of the substrates governs the stereochemistry of the product. Electron-donating alkynes provided ( Z)-stereoselective products, and electron-withdrawing alkynes provided ( E)-stereoselective products. This approach also provides an easy route for the synthesis of mono- and bis-hydroaminated product. The deuterium-labeling studies were also conducted to support the mechanistic pathway.

Facile Synthesis, Characterization of Poly-2-mercapto-1,3,4-thiadiazole Nanoparticles for Rapid Removal of Mercury and Silver Ions from Aqueous Solutions

Industrial pollution by heavy metal ions such as Hg2+ and Ag⁺ is a universal problem owing to the toxicity of heavy metals. In this study, a novel nano-adsorbent, i.e., poly-2-mercapto-1,3,4-thiadiazole (PTT), was synthesized and used to selectively adsorb mercury and silver ions from aqueous solutions. PTT nanoparticles were synthesized via chemical oxidative dehydrogenation polymerization under mild conditions. Oxidant species, medium, monomer concentration, oxidant/monomer molar ratio, and polymerization temperature were optimized to obtain optimum yields. The molecular structure and morphology of the nanoparticles were analyzed by ultraviolet-visible (UV-Vis), Fourier transform infrared (FT-IR), matrix-assisted laser desorption/ionization/time-of-flight (MALDI/TOF) mass and X-ray photoelectron (XPS) spectroscopies, wide-angle X-ray diffraction (WAXD), theoretical calculations and transmission electron microscopy (TEM), respectively. It was found that the polymerization of 2-mercapto-1,3,4-thiodiazole occurs through head-to-tail coupling between the S(2) and C(5) positions. The PTT nanoparticles having a peculiar synergic combination of four kinds of active groups, S⁻, ⁻SH, N⁻N, and =N⁻ with a small particle size of 30⁻200 nm exhibit ultrarapid initial adsorption rates of 1500 mg(Hg)·g-1·h-1 and 5364 mg(Ag)·g-1·h-1 and high adsorption capacities of up to 186.9 mg(Hg)·g-1 and 193.1 mg(Ag)·g-1, becoming ultrafast chelate nanosorbents with high adsorption capacities. Kinetic study indicates that the adsorption of Hg2+ and Ag⁺ follows the pseudo-second-order model, suggesting a chemical adsorption as the rate-limiting step during the adsorption process. The Hg2+ and Ag⁺-loaded PTT nanoparticles could be effectively regenerated with 0.1 mol·L-1 EDTA or 1 mol·L-1 HNO₃ without significantly losing their adsorption capacities even after five adsorption⁻desorption cycles. With these impressive properties, PTT nanoparticles are very promising materials in the fields of water-treatment and precious metals recovery.

Highly Productive Synthesis, Characterization, and Fluorescence and Heavy Metal Ion Adsorption Properties of Poly(2,5-dimercapto-1,3,4-thiadiazole) Nanosheets

Poly(2,5-dimercapto-1,3,4-thiadiazole) (PBT) nanosheets were synthesized by chemical oxidative synthesis under mild conditions. The media, oxidant species, monomer concentrations, oxidant/monomer molar ratio, and temperature were optimized to achieve higher yields and better performance. The molecular structure, morphology, and properties of the nanosheets were analyzed by Fourier transform infrared (FT-IR), ultraviolet-visible (UV-Vis), and fluorescence spectroscopies, wide-angle X-ray diffraction (WAXD), matrix-assisted laser desorption/ionization/time-of-flight (MALDI-TOF) mass spectrometry, X-ray photoelectron spectroscopy (XPS), scanning electronic microscopy (SEM), transmission electron microscopy (TEM), and simultaneous thermogravimetry and differential scanning calorimetry (TG-DSC). It was found that the polymerization of 2,5-dimercapto-1,3,4-thiadiazole occurs via dehydrogenation coupling between two mercapto groups to form the ⁻S⁻S⁻ bond. PBTs show the highest polymerization yield of up to 98.47% and form uniform nanosheets with a thickness of 89~367 nm. poly(2,5-dimercapto-1,3,4-thiadiazole) polymers (PBTs) exhibit good chemical resistance, high thermostability, interesting blue-light emitting fluorescence, and wonderful heavy metal ion adsorption properties. Particularly, the PBT nanosheets having a unique synergic combination of three kinds of active ⁻S⁻, ⁻SH, and =N⁻ groups with a moderate specific area of 15.85 m² g^-1 exhibit an ultra-rapid initial adsorption rate of 10,653 mg g^-1 h^-1 and an ultrahigh adsorption capacity of up to 680.01 mg g^-1 for mercury ion, becoming ultrafast chelate nanosorbents with a high adsorption capacity. With these impressive properties, PBT nanosheets are very promising materials in the fields of water treatment, sensors, and electrodes.

Functional small-molecules & polymers containing PC and AsC bonds as hybrid π-conjugated materials

Switch the pnictogen: functional materials containing PC and AsC fragments for optoelectronic applications. An example of a polymer containing arsaalkenes is presented.

Heteroleptic Cu-Based Sensitizers in Photoredox Catalysis

Photochemistry is an important tool in organic synthesis that has largely been underdeveloped in comparison to thermal activation. Recent advances in technology have ushered in a new era in synthetic photochemistry. The emergence of photocatalysis, which exploits sensitizers for the absorption of visible light, has provided organic chemists with a new route to the generation of radical intermediates for synthesis. Of particular interest is the development of Cu-based complexes for photocatalysis, which possess variable photophysical properties and can display complementary reactivity with common photocatalysts based on heavier transition metals such as Ru or Ir. Heteroleptic Cu-based sensitizers incorporating the presence of both a bisphosphine and diamine ligand bound to the copper center are a promising class of photocatalysts. Their synthesis is a single step, often involving only precipitation for purification. In addition, it was shown that the sensitizers could be formed in situ in the reaction mixture, simplifying the experimental setup. The heteroleptic nature of the Cu-complexes also affords opportunities to fine-tune properties. For example, structurally rigidified bisphosphines reinforce geometries about the metal center to extend the excited state lifetime. Variation of the diamine ligand can influence the excited state oxidation/reduction potentials and optical absorbances. The heteroleptic complex Cu(XantPhos)(neo)BF4 has demonstrated utility in the synthesis of helical polyaromatic carbocycles. The synthesis of [5]helicene, a relatively simple member of the helicene family, was improved from the existing UV-light mediated method by eliminating the formation of unwanted byproducts. In addition, the Cu-based sensitizers also promoted the formation of novel pyrene/helicene hybrids for materials science applications. The synthetic methods that were developed were augmented when combined with continuous flow technology. The irradiation of reaction mixtures as they are pumped through small diameter tubing provides a more homogeneous and increased photon flux compared with irradiation in round-bottom flasks or other batch reactors. The value of continuous flow methods is also evident when examining UV-light photochemistry, where the simple and safe experimental set-ups allow for further exploration of high energy light for synthetic purposes. The synthesis of functionalized complex carbazoles was also studied using both a visible light method exploiting a heteroleptic copper-based sensitizer and a UV-light mediated method. It was demonstrated that both the photocatalysis methods and UV light photochemistries were rendered more user-friendly, safe, and reproducible when using continuous flow methods. Interestingly, the two photochemical methods often afford contrasting selectivities as a result of their inherently different mechanisms. It can be expected that the complementarity of the various photochemical methods will be an asset to synthetic chemists as the field continues to evolve.

Intrinsically conducting polyaminoanthraquinone nanofibrils: interfacial synthesis, formation mechanism and lead adsorbents

Water-dispersible and self-stabilized conductive polyaminoanthraquinone nanofibirls synthesizedviainterfacial polymerization showed high adsorption capacities toward toxic lead.

Phenoxazine based units--synthesis, photophysics and electrochemistry

A few new phenoxazine-based conjugated monomers were synthesized, characterized, and successfully used as semiconducting materials. The phenoxazine-based oligomers have low ionization potentials or high-lying HOMO levels (~4.7 eV), which were estimated from cyclic voltammetry. Conjugated oligomers offer good film—forming, mechanical and optical properties connected with their wide application. These results demonstrate that phenoxazine-based conjugated mers are a promising type of semiconducting and luminescent structures able to be used as thin films in organic electronics.