Carbazole Subunits Research Articles

Indolo[3,2-b]indole-based multi-resonance emitters for efficient narrowband pure-green organic light-emitting diodes.

Organic light-emitting diodes (OLEDs) utilizing multi-resonance (MR) emitters show great potential in ultrahigh-definition display benefitting from superior merits of MR emitters such as high color purity and photoluminescence quantum yields. However, the scarcity of narrowband pure-green MR emitters with novel backbones and facile synthesis has limited their further development. Herein, two novel pure-green MR emitters (IDIDBN and tBuIDIDBN) are demonstrated via replacing the carbazole subunits in the bluish-green BCzBN skeleton with new polycyclic aromatic hydrocarbon (PAH) units, 5-phenyl-5,10-dihydroindolo[3,2-b]indole (IDID) and 5-(4-(tert-butyl)phenyl)-5,10-dihydroindolo[3,2-b]indole (tBuIDID), to simultaneously enlarge the π-conjugation and enhance the electron-donating strength. Consequently, a successful red shift from aquamarine to pure-green is realized for IDIDBN and tBuIDIDBN with photoluminescence maxima peaking at 529 and 532 nm, along with Commission Internationale de l'Eclairage (CIE) coordinates of (0.25, 0.71) and (0.28, 0.70). Furthermore, both emitters revealed narrowband emission with small full width at half-maximum (FWHM) below 28 nm. Notably, the narrowband pure-green emission was effectively preserved in corresponding devices, which afford elevated maximum external quantum efficiencies of 16.3% and 18.3% for IDIDBN and tBuIDIDBN.

Stable Inner 2H Tautomer of N-Confused-like Porphyrin Embedded with a Carbazole Subunit: Synthesis, Metal Coordination, and Magnetic and Anion Sensing Studies.

A new class of N-confused porphyrin 1 embedded with a carbazole subunit was prepared via [3 + 1] acid-catalyzed condensation of appropriate precursors. 1 underwent smooth metal complexation with Pd(II) and Cu(II) salts to provide the corresponding diamagnetic 1-Pd and paramagnetic 1-Cu, respectively. The single-crystal X-ray structure of 1-Pd is evident with a square-planar Pd-center through C-H activation of inverted pyrrole. Superconducting quantum interference device analysis combined with electron paramagnetic resonance (EPR) results provided insights into the paramagnetic nature of 1-Cu. Further, a ratiometric enhancement of near-IR fluorescence at 746 nm was found to be reversible upon adding CN- and F- ions. The solid-state structure of 1-Pd confirms that the anionic species is due to NH deprotonation.

Gold‐Catalyzed Cyclizations and [3+2]‐Annulation Cascades between 1,5‐Diyn‐3‐ols and Nitrones to Construct Carbazole Frameworks

AbstractGold‐catalyzed cascade reactions between 1,5‐diyn‐3‐ols and nitrones to deliver carbazole derivatives are described. Such cascade reactions are applicable to facile synthesis of polyaromatic compounds containing carbazole subunits. Notably, the reaction mechanism involves unexpected oxoarylations, rather than oxidative Mannich reactions as known for but‐1‐yn‐4‐ols. Our control experiments indicate that the presence of a second alkyne as in 1,5‐diyn‐3‐ols enables such oxoarylations due to a weak bonding between gold and this alkyne, rending the tethered alcohol less conformationally flexible.

Fluorene‐based donor‐acceptor‐type multifunctional polymer with bicarbazole pendant moiety for optoelectronic applications

AbstractSince limited examples are in the literature in which both organic light‐emitting diodes (OLEDs) and electrochromic (EC) applications were performed using the same conjugated polymer, we presented comprehensive EC and electroluminescence (EL) studies of fluorene‐based electroactive polymer (e.g., CFP6) consisting of a bicarbazole pendant moiety with quinoxaline as an acceptor bridge. CFP6 was synthesized by a Suzuki cross‐coupling polymerization reaction and utilized as an active and emissive layers of the electrochromic device (ECD) and OLED, respectively, due to its high photoluminescence quantum yield intensity and fine thin film forming capability. The optical, electrochemical, cyclic voltammetry measurements, and density functional theory calculations were realized. Electrochemical cross‐linking process was applied over the electroactive carbazole subunit of the CFP6 polymer. After the crosslinking process, EC performance was greatly improved. On the other hand, light emission and EL characteristics of OLEDs based on CFP6 emissive layer were realized in detail with six different device architectures to understand light output profile behavior. As a result, CFP6 emitted bright greenish yellow emission with a maximum brightness of 1777 cd/m2 at 215 mA/cm2 in the indium tin oxide (ITO)/poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)/CFP6:%10 4,4′‐bis(N‐carbazolyl)‐1,1′‐biphenyl (CBP)/Alq3/LiF/Al device architecture.

A Green Fluorescent Nitrogen‐Doped Aromatic Belt Containing a [6]Cycloparaphenylene Skeleton

The design and synthesis of nitrogen-doped aromatic belts with conjugated structures still remain a challenge. Here, we report the first nitrogen-doped aromatic belt with a [6]cycloparaphenylene skeleton, which is conveniently synthesized from the easily available calix[3]carbazole. The aromatic belt has a rigid conjugated structure and deep cavity, and it can encapsulate one dichloromethane both in solution and in the solid state. Interestingly, the aromatic belt shows strong green fluorescence with a quantum yield of 0.39 and exhibits a narrow HOMO-LUMO energy gap of 2.02 eV. The belt-shaped conjugated structure composed of three carbazole subunits has specific optoelectronic properties that will promote wide applications in supramolecular chemistry and materials science.

A Green Fluorescent Nitrogen‐Doped Aromatic Belt Containing a [6]Cycloparaphenylene Skeleton

AbstractThe design and synthesis of nitrogen‐doped aromatic belts with conjugated structures still remain a challenge. Here, we report the first nitrogen‐doped aromatic belt with a [6]cycloparaphenylene skeleton, which is conveniently synthesized from the easily available calix[3]carbazole. The aromatic belt has a rigid conjugated structure and deep cavity, and it can encapsulate one dichloromethane both in solution and in the solid state. Interestingly, the aromatic belt shows strong green fluorescence with a quantum yield of 0.39 and exhibits a narrow HOMO–LUMO energy gap of 2.02 eV. The belt‐shaped conjugated structure composed of three carbazole subunits has specific optoelectronic properties that will promote wide applications in supramolecular chemistry and materials science.

Functional Carbazole‐Fullerene Complexes: A New Perspective of Carbazoles Acting as Nano‐Octopus to Capture Globular Fullerenes

Fullerene host-guest constructs have attracted increasing attention owing to their molecular-level hybrid arrangements. However, the usage of simple carbazolic derivatives to bind with fullerenes is rare. In this research, three novel carbazolic derivatives, containing a tunable bridging linker and carbazole units for the capturing of fullerenes, are rationally designed. Unlike the general concave-convex interactions, fullerenes could interact with the planar carbazole subunits to form 2-dimensional hexagonal/quadrilateral cocrystals with alternating stacking patterns of 1 : 1 or 1 : 2 stoichiometry, as well as the controllable fullerene packing modes. At the meanwhile, good electron-transporting performances and significant photovoltaic effects were realized when a continuous C60⋅⋅⋅ C60 interaction channel existed. The results indicate that the introduction of such carbazolic system into fullerene receptor would provide new insights into novel fullerene host-guest architectures for versatile applications.

Strategic Synchronization of 7,7-Dimethyl-5,7-dihydroindeno[2,1-b]carbazole for Narrow-Band, Pure Violet Organic Light-Emitting Diodes with an Efficiency of > 5% and a CIE y Coordinate of < 0.03

A novel violet emitter, 1,3-bis[10,10-dimethyl-10H-indeno[2,1-b]]indolo[3,2,1-jk]indolo[1',2',3':1,7]indolo[3,2-b]carbazole (m-FLDID), was designed and synthesized by meta-oriented bis-fusion of two 7,7-dimethyl-5,7-dihydroindeno[2,1-b]carbazole (DMID) subunits for use in a pure violet organic light-emitting diode (OLED). Incorporation of the DMID subunits effectively reduced the nonradiative recombination rate, improving the photoluminescence quantum yield of the m-FLDID emitter. The meta-oriented bis-fusion of the two DMID subunits not only triggered an alternative distribution of the frontier orbitals but also effectively locked the π-conjugation chain, which ultimately resulted in a narrow-band, pure violet emission of the m-FLDID emitter. Doped m-FLDID devices possessed an external quantum efficiency (EQE) of > 5%, pure violet emission with a maximum at 407 nm, a narrow full width at half-maximum of 17 nm, and a Commission Internationale de l'éclairage y coordinate of less than 0.03. This is the first work reporting an EQE of > 5% and an extremely narrow emission spectrum for a pure violet emitter.

Full-Color, Narrowband, and High-Efficiency Electroluminescence from Boron and Carbazole Embedded Polycyclic Heteroaromatics.

Herein, we demonstrate that the strategic implementation of electron-accepting tricoordinate boron and electron-donating carbazole subunits into polycyclic aromatic hydrocarbons (PAHs) produces a family of attractive full-color luminophores that can emit narrowband and efficient thermally activated delayed fluorescence (TADF). A versatile modular design for these boron- and carbazole-embedded PAHs can facilitate the systematic modulation of their photophysical and optoelectronic properties. Organic light-emitting diodes that utilize these PAHs as TADF emitters demonstrate narrowband electroluminescence from blue to red, achieving high maximum external quantum efficiencies of 29.3%, 31.8%, and 22.0% for blue, green, and red, respectively.

Carbazole derivatives containing chalcone analogues targeting topoisomerase II inhibition: First principles characterization and QSAR modelling.

Recently, a series of carbazole derivatives containing chalcone analogues (CDCAs) were synthetized as potent anticancer agents and apoptosis inducers. These compounds target the inhibition of topoisomerase II and present cytotoxic activities. After comparison to experiment, we validated the use of B3LYP, a density functional theory-based approach, to describe the structure and molecular properties of the carbazole subunit and CDCAs compounds of interest. Then, we derived relationships between the chemical descriptors and activity of these carbazole derivatives using multi-parameter optimization and quantitative structure activity relationships (QSAR) approaches. For the QSAR studies, we used multiple linear regression and artificial neural network statistical modelling. Our predicted activities are in good agreement with the experimental ones. We found that the most important parameter influencing the activity of the considered compounds is the octanol-water partition coefficient, highlighting the importance of flexibility as a key molecular parameter to favor cell membrane crossing and enhance the action of these CDCAs against topoisomerase II. Our results provide useful guidelines for designing new oral active CDCAs medicaments for cytotoxic inhibition.

Design and Synthesis of Air-Stable p-Channel-Conjugated Polymers for High Signal-to-Drift Nitrogen Dioxide and Ammonia Sensing.

The development of high-performance-conjugated polymer-based gas sensors involves detailed structural tailoring such that high sensitivities are achieved without compromising the stability of the fabricated devices. In this work, we systematically developed a series of diketopyrrolopyrrole (DPP)-based polymer semiconductors by modifying the polymer backbone to achieve and rationalize enhancements in gas sensitivities and electronic stability in air. NO2- and NH3-responsive polymer-based organic field-effect transistors (OFETs) are described with improved air stability compared to all-thiophene conjugated polymers. Five DPP-fluorene-based polymers were synthesized and compared to two control polymers and used as active layers to detect a concentration of NO2 at least as low as 0.5 ppm. The hypothesis that the less electron-donating fluorene main-chain subunit would lead to increased signal/drift compared to thiophene and carbazole subunits was tested. The sensitivities exhibited a bias voltage-dependent behavior. The proportional on-current change of OFETs using a dithienyl DPP-fluorene polymer reached ∼614% for an exposure to 20 ppm of NO2 for 5 min, testing at a bias voltage of -33 V, among the higher reported NO2 sensitivities for conjugated polymers. Electronic and morphological studies reveal that introduction of the fluorene unit in the DPP backbone decreases the ease of backbone oxidation and induces traps in the thin films. The combination of thin-film morphology and oxidation potentials governs the gas-absorbing properties of these materials. The ratio of responses on exposure to NO2 and NH3 compared to drifts while taking the device through repeated gate voltage sweeps is the highest for two polymers incorporating electron-donating linkers connecting the DPP and thiophene units in the backbone, in this category of organic semiconductors. The responses to NO2 were much larger than that to NH3, indicating increased susceptibility to oxidizing vs reducing gases, and that the capability of oxidizing gases to induce additional charge density has a more dramatic electronic effect than when reducing gases create traps. This work demonstrates the capability of achieving improved stability with the retention of high sensitivity in conjugated polymer-based OFET sensors by modulating redox and morphological properties of polymer semiconductors by structural control.

Multigram scale synthesis of polycyclic lactones and evaluation of antitumor and other biological properties

An efficient four-step synthesis of tetracyclic lactones from 1,4-benzodioxine-2-carboxylic acid was developed. Ellipticine derivatives exhibit antitumor activity however only a few derivatives without carbazole subunit have been studied to date. Herein, several tetracyclic lactones were synthesized and biologically evaluated. Several compounds (2a, 3a, 4a and 5a) were found to be inhibitors of the Kras-Wnt pathway. The lactone 2a also exerted a potent inhibition of Tau protein translation and was shown to have capacity for CYP1A1-bioactivation. The results obtained are further evidence of the therapeutic potential of tetracyclic lactones related to ellipticine. Molecular modeling studies showed that compound 2a is inserted between helix α3 and α4 of the KRas protein making interactions with the hydrophobic residues Phe90, Glu91, Ile9364, Hie94, Leu133 and Tyr137and a hydrogen bond with residue Arg97.

Carbazole-based π-conjugated polyazomethines: Effects of catenation and comonomer insertion on optoelectronic features

A series of carbazole-based polyazomethines have been synthesized under micro-wave irradiation and without transition-metal based catalyst. The impact of both the catenation brought by the carbazole subunits and the insertion of a co-monomer, i.e. 3,4 ethylene dioxythiophene (EDOT), on the optical and electrochemical properties have been studied. Among the different polyazomethines synthesized, the best in terms of optical and electrochemical properties has been found to be the one with the azomethine function linked in positions 2,7 of carbazole subunits. Upon the insertion of the EDOT comonomer, an increase of the molecular weight and a red-shift in the absorption spectra has been observed, corresponding to a diminution of the electronic gap.

Synthesis of Methylene-Bridged Biscarbazole Alkaloids by using an Ullmann-type Coupling: First Total Synthesis of Murrastifoline-C and Murrafoline-E.

We describe the total synthesis of methylene-bridged biscarbazole alkaloids by using a late-stage Ullmann-type coupling of fully functionalised carbazole subunits. The carbazole derivatives were synthesised via a sequence of palladium(0)- and palladium(II)-catalysed coupling reactions. Our approach has provided bismurrayafoline-A, bismurrayafolinol, chrestifolines B-D, and the first total synthesis of murrastifoline-C and murrafoline-E.

New 4,4′-Bis(9-carbazolyl)–Biphenyl Derivatives with Locked Carbazole–Biphenyl Junctions: High-Triplet State Energy Materials

We synthesized a series of 4,4′-bis(9-carbazolyl)–biphenyl (CBP) derivatives, using methyl groups as spatially demanding groups, locking the angle between the carbazole subunit and the biphenyl backbone as potential matrix material for blue organic light-emitting diodes (OLEDs). The locked rotation was achieved by four methyl groups either in positions 1 and 8 of the carbazole subunit (1) or in positions 3, 5, 3′, and 5′ of the biphenyl subunit (2), and the fixed spatial arrangement was confirmed by X-ray analysis. The physical properties of CBP derivatives based on parent structure 2 were further tailored by electron-withdrawing CF3 groups in positions 3 and 6 (3) or positions 2 and 7 of the carbazole subunits (4) or alternatively by electron-donating CH3O groups in positions 2 and 7 (5) of the same building blocks. Increased triplet energies (ET) compared to that of the parent compound CBP were found for all synthesized CBP derivatives 1–5. Enhanced glass transition temperatures ranging between 129 and ...

Toward Purple-to-Green-to-Transmissive-to-Black Color Switching in Polymeric Electrochrome

A novel 3,4-ethylenedioxythiophene (EDOT)-based donor–acceptor electroactive monomer (HCQE) bearing carbazole subunit is synthesized, and then the corresponding polymer, poly(HCQE), is directly deposited onto ITO/glass surface via electrochemical process. Spectroelectrochemical studies demonstrate that poly(HCQE) is capable of showing both n- and p-doping processes. Hence, this low band polymer serves the multielectrochromic feature at three separate states (−0.4 to −2.0 V, −0.4 to 1.2 V, and 1.2 to 2.0 V) with a highly unique near colorless and colored states, fast switching times, redox switching stability, and exceptional transmittance change. To the best of our knowledge, this is the first report of a neutral state green multielectrochromic polymer exhibiting successive switching of colored-to-bleached-to-colored in three distinct regimes.

Electronic Structure of Carbazole-Based Phosphine Oxides as Ambipolar Host Materials for Deep Blue Electrophosphorescence: A Density Functional Theory Study

We report the results of Density Functional Theory calculations on a series of carbazole-based phosphine oxides that experimental data have shown to be promising ambipolar host molecules for deep blue electrophosphorescence. The hosts under investigation contain either 1, 2, or 3 carbazole subunits attached to the phenyl rings of a triphenylphosphoryl group, with the carbazoles acting as hole transporters/acceptors and the triphenylphosphoryl groups as electron transporters/acceptors. The results underline that, in addition to the strong inductive effect of the phosphoryl groups, the LUMO of these hosts is further stabilized by the molecular orbital interactions among the phenyl rings of the triphenylphosphoryl group, which is modulated by the electron-withdrawing inductive effects of the carbazole subunits. The lowest triplet state of the hosts correspond to localized transitions within the carbazole units, which leads to a high triplet energy on the order of 3 eV. We describe the important buffer role o...

Copolymer-Controlled Diameter-Selective Dispersion of Semiconducting Single-Walled Carbon Nanotubes

The ability of a series of strictly alternating copolymers to selectively enwrap single-walled carbon nanotubes (SWNTs) is investigated. Seven copolymers comprising either fluorene or carbazole subunits separated by naphthalene, anthracene, and anthraquinone spacers are obtained in good yields via a Suzuki cross-coupling protocol. The 1,5-linked naphthalene, anthracene, and anthraquinone units are introduced to favor a spiral conformation of the polymer backbone in order to improve its SWNT wrapping features. Particularly high yields of polymers are obtained using the naphthalene-1,5-ditriflate precursor, highlighting the potential of bifunctional aryltriflates as precursors of copolymers. All polymers disperse HiPco SWNTs in toluene. The obtained dispersions are purified by density gradient centrifugation and their compositions are analyzed by photoluminescence (PL) spectroscopy. In their dispersing ability the polymers display more or less pronounced SWNT diameter selectivity. In particular, poly(9,9-di...

Functionalized ferrocenes and ferroceniums: synthesis, crystal structures and electrochemical properties based on carbazole/phenothiazine-ferrocene conjugated molecules

Four new D-pi-D (or D-pi-D-pi-D) complexes 9-ethyl-3-E-((1-ferrocenyl)vinyl)-carbazole (1), 9-ethyl-3,6-E,E-((1,1-diferrocenyl)vinyl)- carbazole(2), 10-ethyl-3-E-((1-ferrocenyl)vinyl)-phenothiazine (3), 10-ethyl- 3,7-E,E- ((1,1-diferrocenyl)vinyl)-phenothiazine (4), have been obtained by solid-phase Wittig reactions and fully characterized. The four complexes were treated with iodine leading to four corresponding [D-pi-A](+) I(3)(-) ferrocenium triiodides (+)I(3)(-) (5), (+)I(3)(-) (6), (+)I(3)(-) (7) and 4(+)I(3)(-) (8), respectively. The results of single crystal X-ray diffraction analysis show that and display better coplanarity between the Fc and carbazole subunits than that between the phenothiazine and ferrocene moieties, which leads to a better pi-electron delocalization. Both the poor pi-electron in [D-pi-A](+) ferroceniums and the heavy iodine atom have a negative effect on the electrochemical properties. The complexes 1-8 undergo multi-step redox processes and show lower oxidation potentials compared with those of ferrocene. Density functional theory (DFT) calculations are performed and the experimental redox properties of the complexes are studied. The eight complexes show MLCT and pi-pi transitions in the UV-visible range in solution, which have been verified by TD-DFT theoretical calculations. In all cases the highest-lying occupied molecular orbitals of the eight complexes are mainly localized on the Fe d orbitals and show a greater Fe proportion than that of alkyl in the complexes, whereas the LUMOs and LUMO+1 are mainly from the pi orbitals of the conjugated vinyl carbazole or phenothiazine unit.

Synthesis, Electrochemical and Spectroscopic Investigations of New N-BEDOT Derivatives Containing Anil Substituted Carbazole Subunits

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