Synthesis and properties of N-carbazole end-capped conjugated molecules

A series of novel N-carbazole end-capped π-conjugated molecules were synthesized by a divergent approach with the use of bromination, Suzuki cross-coupling, and Ullmann reactions and their physical properties were investigated. In dilute solution, UV-vis absorption spectra displayed bathochromic shift with respect to their conjugated backbones, and photoluminescence spectra showed emission maxima in the blue region. Thermal analysis revealed that they are thermally stable semi-crystalline and amorphous materials. All molecules exhibited good electrochemical stability with high-lying HOMO energy levels and have potential applications as hole-transporting and light-emitting layers in organic light-emitting diodes or as host materials for electrophosphorescent applications.     

A useful procedure for diiodination of carbazoles and subsequent efficient transformation to novel 3,6-bis(triethoxysilyl)carbazoles giving mesoporous materials

Bis(pyridine)iodonium tetrafluoroborate (IPy₂BF₄) was successfully used as a diiodination reagent for carbazole and its derivatives to give 3,6-diiodocarbazoles in excellent yield. Subsequent rhodium-catalyzed disilylation of 3,6-diiodocarbazoles with triethoxysilane gave the corresponding 3,6-bis(triethoxysilyl)carbazoles, which are precursors for sol-gel polymerization, in good yield.     

Changes in the reactivity of the fluorescent reagents carbazole-9-carbonyl chloride and 9-carbazolylacetic acid in the presence of cyclodextrins

Carbazole-9-carbonyl chloride (C9CC) and 9-carbazolylacetic acid (9CAA) were selected as model fluorescent reagents. The effect of different chemically modified cyclodextrins (CDs) added to the aqueous solutions of these reagents was studied in water and in buffered aqueous solutions at pH 4.5 and 8.8. The CDs employed were 2-hydroxypropyl-β-cyclodextrin (HP-βCD), 2,3-di-O-methyl-β-cyclodextrin (DM-βCD) and 2,3,6-tri-O-methyl-β-cyclodextrin (TM-βCD). The inclusion of these reagents inside the cavities of the CDs was verified and this process can affect the derivatization reaction because CDs can modify the reactivity of the guest molecules. The basic conditions necessary for the derivatization reaction between C9CC and amines lead to the formation of carbazole anion through hydrolysis followed by decarboxylation. In the presence of CDs, the hydrolysis-decarboxylation of carbazole-9-carbonyl chloride is faster than in buffered aqueous homogeneous solutions. The behaviour observed for these reagents in aqueous solutions of CDs was compared to the one observed in basic ethanolic solutions. These changes are particularly noticeable in the case of 2,3-di-O-methyl-β-CD and 2-hydroxypropyl-β-CD. The characteristics of the fluorescent reagents are compared to carbazole and 9-methylcarbazole as model compounds. This paper was presented at XIIIth International Cyclodextrin Symposium. Torino, Italy, May 14–17, 2006.     

Synthesis and structure–property relationship of carbazole‐alt‐benzothiadiazole copolymers

A series of four π‐conjugated carbazole‐alt‐benzothiadiazole copolymers (PCBT) were prepared by Suzuki cross‐coupling reaction between synthesized dibromocarbazoles as electron‐rich subunits and 4,7‐bis(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)?2,1,3‐benzothiadiazole as electron‐deficient subunits. The subunits were directly linked through 2,7‐ or 3,6‐ positions of the carbazole. In addition, the carbazole monomers have been N‐substituted by a branched or a linear side‐chain. The chemical structure of the copolymers and their precursors was confirmed by NMR and IR spectroscopies, and their molar masses were estimated by SEC. Thermal analysis under N₂ atmosphere showed no weight loss below 329°C, and no glass transition was observed in between 0 and 250°C. The band gaps of all PCBTs evaluated by optical spectroscopies and by cyclic voltammetry analysis were consistent with expectations and ranged between 2.2 and 2.3 eV. Finally, 2,7 and 3,6 linkages were shown to influence optical properties of PCBTs. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2059–2068     

REDOX ACTIVE,MULTI-CHROMOPHORE RU(II) POLYPYRIDYL-CARBAZOLE COPOLYMERS: SYNTHESIS AND CHARACTERIZATION

A novel diimine ligand, 2-(2-pyridyl) 4-carboxyquinoline (pcq) and its corresponding polypyridyl Ru(II) complex were synthesized, characterized, and covalently attached to a carbazole based copolymer via post polymer modification. The resulting modified electroactive and multi-chromophoric polymer was readily characterized by UV-visible, FT-IR, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and elemental and electrochemical analysis. Results from cyclic voltammetry and FT-IR analysis both confirmed the covalent attachment of redox active Ru(II) center into the polymer. The emission spectrum of the copolymer, in comparison to that of Ru(II) complex, demonstrated that the excited-state properties of the metal complex is maintained, in contrast to the electronic absorption spectrum, which is sensitive to the hydrophobic polymeric chain surrounding the redox sites. The thermal analysis suggested that this metallopolymer also possesses high thermal stability. The ruthenium content was also found to be 7%, which corresponds to 80% of the maximum loading, by elemental analysis.     

Synthesis of new bicarbazole-linked triazoles as non-cytotoxic reactive oxygen species (ROS) inhibitors

Abstract

Carbazole analogs 3 and 4 and a new library of bicarbazole-linked triazoles 6–11 were prepared via new synthetic methodology. Metal-catalyzed oxidative coupling reaction was utilized for the synthesis of bicarbazole acetylene 4 and different metals (Zn⁺², Co⁺², Fe⁺³, Ni⁺², Cu⁺², Mn⁺²) as catalyst were screened. Only Fe-catalyzed reaction was found to be excellent and gave homocoupled product 4. Cu-catalyzed 1,3-dipolar cycloaddition was also utilized to install triazole moiety for the synthesis of hybrid molecules 6–11. Based on reported anti-inflammatory activity of carbazole and triazole scaffolds, all compounds were screened for their reactive oxygen species (ROS) inhibitory potential. Results from these studies revealed triazole 9 as most active compound (IC₅₀ value of 7.6?±?0.1?µg/mL on human whole blood and 2.7?±?0.09?µg/mL on isolated neutrophils) using ibuprofen as a standard. Therefore, class described herein can serve as attractive structural element for further studies on ROS inhibition.     

Efficient white emitting copolymers based on bipolar fluorene-co-dibenzothiophene-S,S-dioxide-co-carbazole backbone

Efficient white light emitting polymers were synthesized based on poly(9,9-dioctylfluorene-co-dibenzothiophene-S,S-dioxide) as blue emitter and a bisphenylamine functionalized 2,1,3-benzothiadiazole (DPABT) as red emitter. It was found that the incorporation of hole-transporting carbazole moiety into polymer main chain could effectively reduce the hole injection barriers, which can lead to distinctly improved charge balance in the emissive layer. Additionally, the hole-transporting carbazole units may form efficient bipolar host with electron-transporting dibenzothiophene-S,S-dioxide units. The white light emitting diodes based on single polymer PFSOCzDPABT showed the maximum luminous efficiency of 3.3 cd/A with the maximum luminance of 10282 cd/m2 , and the luminous efficiency showed only 24% roll off at current density of 400 mA/cm2 . These Commission Internationale d’Enclairage (CIE) coordinates of the devices changed slightly with the driving voltages increasing from 8 V to 12 V, and were very close to National Television System Committee (NTSC) standard white light emission of (0.33, 0.33). The results indicated that the incorporating bipolar host and low band gap DPABT unit was a promising way to achieve efficient single white light emitting copolymers.     

Novel tri-carbazole modified fluorene host material for highly efficient solution-processed blue and green electrophosphorescent devices

A series of novel solution-processable small-molecule host materials: 2DPF-TCz, 2SBF-TCz, 27DPF-TCz, and 27SBF-TCz comprising a fluorene monomer as the rigid core and tri-carbazole as the periphery have been designed and synthesized, and their optical, electrochemical, and thermal properties have been fully characterized. The host materials exhibit high glass-transition temperatures (231–310 °C) and high triplet energy levels (2.61–2.73 eV). High-quality amorphous thin films can be obtained by spin-coating the host materials from solutions. It is found that the HOMO level of the host materials can be tuned by linking the tri-carbazole unit to the 2,7 positions of the fluorine core, resulting in appropriate HOMO energy levels (−5.36 to −5.23 eV) for improved hole-injection in the device. Solution-processed blue and green electrophosphorescent devices bases on the developed host materials exhibit high efficiencies of 21.2 and 34.8 cd A⁻¹, respectively.     

Synthesis,identification and study of electrical conductivity of the doped copolymer carbazole–phenol formaldehyde

The copolymer carbazole–phenol formaldehyde doped with 4 (4-hydroxy-phenyl azo)-benzene sulfonic acid (PABS), 2,5-dimethyl benzene sulfonic acid (PXSA) and 4-hydroxy-m-benzene disulfonic acid (PDSA) were prepared. These compounds are identified by FT-IR spectroscopy.The conductivity of copolymer carbazole–phenol formaldehyde doped with 4 (4-hydroxy-phenyl azo)-benzene sulfonic acid (PABS), 2,5-dimethyl benzene sulfonic acid (PXSA) and 4-hydroxy-m-benzene disulfonic acid (PDSA) was studied as a function of weight of the dopant compounds; an increase of conductance of the copolymer by doping with PABS is noted; the conductance became equal to 0.000595 ohm⁻¹ for 0.1 g higher conductance for the copolymer when it is doping with PABS.