Carbazole Core Research Articles

Total Synthesis of Dictyodendrins B and E, and Formal Synthesis of Dictyodendrin C

AbstractA full account of the concise total syntheses of dictyodendrins B and E, and the formal synthesis of dictyodendrin C are described. A palladium‐catalysed Larock indole synthesis was used to form the highly substituted indole core, and a palladium‐mediated one‐pot consecutive Buchwald–Hartwig amination/C–H activation reaction was used to construct the key pyrrolo[2,3‐c]carbazole core. Unsuccessful synthetic strategies are also discussed.

Synthesis of carbazoles by copper-catalyzed intramolecular C-H/N-H coupling.

A Cu-catalyzed intramolecular C-H amination for the synthesis of carbazoles has been developed. The key to success is the installation of the picolinamide-based directing group, which is spontaneously removed after the coupling event. The Cu catalysis proceeded smoothly under Pd- and I(III)-free conditions, and its mild oxidation aptitude enables the rapid and concise construction of heteroatom-incorporated carbazole core π-systems.

Novel carbazole/anthracene hybrids for efficient blue organic light-emitting diodes

Two novel carbazole/anthracene hybrided molecules, namely 2-(anthracen-9-yl)-9-ethyl-9H-carbazole (AnCz) and 2,7-di(anthracen-9-yl)-9-ethyl-9H-carbazole (2AnCz), were designed and synthesized via palladium catalyzed coupling reaction. The anthracene was attached either at the 2-site (AnCz) or at both 2,7-sites (2AnCz) of the central carbazole core to tune the conjugation state and the optoelectronic properties of the resultant molecules. Both of them show good solubility in common organic solvents. They also possess relatively high HOMO levels (−5.39eV, −5.40eV) that would facilitate efficient hole injection and be favorable for high power efficiencies when used in organic light-emitting devices (OLEDs). AnCz and 2AnCz were used as non-doped emitter to fabricate OLEDs by vacuum evaporation. Good performance was achieved with maximum luminance efficiency of 2.61cdA−1 and CIE coordinates of (0.15, 0.12) for AnCz, and 9.52cdA−1 and (0.22, 0.37) for 2AnCz.

Fluorescent imaging of acidic compartments in living cells with a high selective novel one-photon ratiometric and two-photon acidic pH probe

Fluorescent imaging of acidic compartments in living cells was carried out successfully by a novel molecule (CAE) that contained a pyridine unit and a carbazole core. As the protonation of the pyridine N atom of CAE, pH-dependent absorption and fluorescence properties were shown with a pKa of 5.47 which matches the pH range of intracellular acidic compartments. Moreover, a large Stokes shift, a significant enhancement in ratios of I544nm/I460nm and a distinct two-photon turn-on character were exhibited in spectral analysis. Meanwhile, direct intracellular imaging and standard double-staining experiments of CAE and LTR (co-localization coefficient: 0.83) revealed that CAE is an effective one-photon ratiometric and two-photon acidic pH probe for imaging intracellular acidic compartments. The pH distribution pattern of intracellular acidic compartments can be obtained facilely by CAE. In especial, CAE possessed well membrane-permeability, brilliant selectivity among various bioanalyte and excellent counterstain compatibility with Hoechst 33342, MTR and LTR.

Synthesis, characterization and third-order nonlinear optical properties of novel hyperbranched donor–acceptor polyfluorenes based on 1,3,6,8-tertsubstituted carbazole core

Two novel hyperbranched donor–acceptor polyfluorenes based on 1,3,6,8-tertsubstituted carbazole core (4BrCzP1 and 4BrCzP2) were synthesized and characterized. The third order nonlinear optical properties of the materials were studied using Z-scan technique with femtosecond Ti: sapphire laser with delivering pulses of 140fs at 800nm. The nonlinear optical refractive index was 9.29×10−8esu for 4BrCzP1 and 3.19×10−7esu for 4BrCzP2, respectively. While the third order nonlinear susceptibility was 1.29×10−9esu for 4BrCzP1 and 4.33×10−9esu for 4BrCzP2, respectively. The experimental results indicated that the hyperbranched polyfluorenes was a promising candidate in the application of third order nonlinear optical materials.

Anchoring stability and photovoltaic properties of new D(-π-A)2 dyes for dye-sensitized solar cell applications

This study deals with the synthesis and characterization of two new di-anchoring dyes for applications in dye-sensitized solar cells. The materials were designed with a branched D(-π-A)2 structure containing (i) a rigid alkyl-functionalized carbazole core as the donor part, (ii) one (DYE1) or two (DYE2) thiophene units as the π-bridge and (iii) a cyano-acrylic moiety as acceptor and anchoring part. Electrochemical impedance spectroscopy indicated that the injected electron lifetime is higher in the case of DYE2, probably due to the length of the π-spacer that, in combination with the alkyl chain on the carbazole unit, hampers the charge recombination with the electrolyte. Stability tests on TiO2-sensitized films revealed that the di-anchoring remarkably slows down the desorption process, which conversely is evident for classic reference dyes. The highest power conversion efficiency reaches 5.01% in the case of DYE2 with a photovoltage of 0.70 V and a photocurrent of 10.52 mA cm−2, substantially deriving from a broader absorption with respect to DYE1, as also confirmed by IPCE measurements. These results support the efforts aimed at the structural engineering of D(-π-A)2 dyes to design new, more efficient and stable organic sensitizers.

ChemInform Abstract: Synthetic Approach for Constructing the 1‐Oxygenated Carbazole Core and Its Application to the Preparation of Natural Alkaloids.

AbstractStarting with the regioselective condensation of anilines with cyclohexane‐1,2‐diones, a convenient synthesis of 2‐methoxy substituted diarylamines (V) is demonstrated.

Synthetic Approach for Constructing the 1-Oxygenated Carbazole Core and Its Application to the Preparation of Natural Alkaloids

An efficient synthetic approach for the construction of the 1-oxygenated carbazole core is described. The condensation of cyclohexane-1,2-diones with a series of anilines yielded the corresponding 2-anilinocyclohex-2-en-1-ones, followed by the one-pot aromatization/methylation process of the latter to provide N-aryl-2-methoxyanilines. A palladium(II)-catalyzed cyclization of these N-aryl-2-methoxyanilines afforded the desired 1-methoxycarbazole frame in high overall yields. This protocol was implemented for the total synthesis of the naturally occurring glycozolicine and 6-meth­oxymurrayanine.

Carbazole and benzimidazole/oxadiazole hybrids as bipolar host materials for sky blue, green, and red PhOLEDs

Two novel bipolar host materials (CBzIm and COxaPh) comprising of a hole-transport (HT) carbazole core functionalized with electron-transport (ET) moieties (benzimidazole/oxadiazole) at C3 and C6 positions have been synthesized. Their thermal, photophysical, electrochemical properties, and carrier mobilities were characterized. Theoretical calculations revealed that the HOMO orbitals were generally delocalized over the hole- and electron-transport moieties for both CBzIm and COxaPh, whereas the LUMO orbitals distribution only involved one benzimidazole moiety in CBzIm instead of fully delocalization over the whole polar moieties for COxaPh, which is consistent with the observation of good hole mobilities for both hosts and better electron mobility for COxaPh over CBzIm. CBzIm with high ET (2.76eV) is suitable to serve as a blue phosphor host, where a sky blue phosphor (DFPPM)2Irpic exhibiting superior properties than those of popular blue emitter FIrpic was used to give highly efficient phosphorescent OLEDs, achieving a maximum external quantum efficiency (ηext) of 15.7%. The better π-delocalization of COxaPh led to a lower triplet energy (ET=2.65eV), which can be used to accommodate green and red phosphors, providing excellent device performance with ηext as high as 17.7% for green [(ppy)2Ir(acac)] and 20.6% for red [Os(bpftz)2(PPh2Me)2], respectively.

Synthesis and Properties of Methoxyphenyl-Substituted Derivatives of Indolo[3,2-b]carbazole

The synthesis and full characterization of new derivatives of indolo[3,2-b]carbazole with differently substituted phenyl groups at nitrogen atoms is reported. Comparative study on their thermal, optical electrochemical, and photoelectrical properties is presented. The synthesized compounds are electrochemically stable. Their highest occupied molecular orbital energy values range from -5.14 to -5.07 eV. The electron photoemission spectra of the films of synthesized materials revealed the ionization potentials of 5.31-5.47 eV. Hole drift mobility of the amorphous film of 5,11-bis(3-methoxyphenyl)-6-pentyl-5,11-dihydroindolo[3,2-b]carbazole exceed 10(-3) cm(2)/V·s at high electric fields, as it was established by xerographic time-of-flight technique. In contrast to diphenylamino substituted derivatives of carbazole, no effect of the position of methoxy groups on the photoelectrical properties was observed for the synthesized methoxyphenyl-substituted derivatives of indolo[3,2-b]carbazole. The indolo[3,2-b]carbazole core has a larger resonance structure that includes 3 phenyl rings, and thus the energy gap of the HOMO and LUMO π orbitals is lower as compared to that of carbazoles. With a larger energy difference between the phenyl substituents and the core moiety, the indolo[3,2-b]carbazole derivatives studied all have a weaker coupling between the phenyl group and a much weaker dependence of the molecular properties on the position of substituents on the phenyl groups as compared to those observed in substituted carbazoles.

Carbazole oligomers revisited: new additions at the carbazole 1- and 8-positions

In recent years low molecular weight carbazole-based materials have attracted much interest as hole-transporting and host materials for organic light emitting diode (OLED) applications. Herein we report the tri- and tetra-bromination of carbazole and the subsequent synthesis of novel carbazole oligomers substituted at the 1- and 8-positions. The oligomer series range from mono-carbazole (Cz-1) to quinque-carbazole (Cz-5) and we have carried out a comparative study of their thermal, optical, electrochemical and optoelectronic properties. The glass transition temperature increases as the carbazole core is enlarged (0 °C to 54 °C) and all oligomers exhibit excellent thermal stability with high thermal decomposition temperatures in the range of 442 °C to 494 °C. From optical data and Raman spectroscopy we observe negligible changes in the effective conjugation length as the number of peripheral carbazole units increases. However, the oxidation potential decreases as the number of carbazole units increase, in which Cz-5 exhibits the highest HOMO level (−5.19 eV) compared to other carbazole oligomers in the series. All carbazole materials emit deep blue photoluminescence ranging from 416 to 432 nm in the solid-state. Finally, electrophosphorescence was demonstrated from solution processable guest-host organic light- emitting diodes (OLEDs) fabricated using Cz(2–5) as the host materials with device configuration ITO/PEDOT/Cz1–5 : 10% Ir(mppy)3/TPBi/LiF/Al. The device efficiency decreases from Cz-3 to Cz-5. The best OLED device that incorporates Cz-3 as the host exhibits a turn-on voltage of 2.8 V, maximum brightness of 2310 cd m−2, maximum power efficiency of 33.6 lm W−1, maximum current efficiency 35.5 cd A−1 and EQE of 10.6%.

Molecular engineering of chromophores for combined second-harmonic and two-photon fluorescence in cellular imaging

A series of chromophores with enhanced second- and third-order nonlinear optical properties were engineered for use in combined second-harmonic and two-photon fluorescence microscopy. Electron-accepting moieties imparted nonlinear optical properties to the chromophores. The electron-rich carbazole core served as a template towards one- or two-dimensional chromophores. More efficient acceptor groups (pyridinium, benzazolium, benzothiazolium) on the carbazole donor core resulted in improved second- and third-order nonlinear optical properties. A selection of these chromophores was tested in a cellular environment with a multimodal multiphoton microscope. The structural differences of the chromophores resulted in high selectivity for mitochondria or the nucleus in two-photon fluorescence and ranging from no signal to high selectivity for mitochondria in the SHG channel.

Structural planarity and conjugation effects of novel symmetrical acceptor–donor–acceptor organic sensitizers on dye-sensitized solar cells

In this study two series of novel symmetrical acceptor–donor–acceptor organic sensitizers containing 3,6- and 2,7-functionalized carbazole cores, respectively, connected to two anchoring cyanoacrylic acid termini via thienyl linkers were synthesized. The effect of the molecular planarity originating from the 3,6- and 2,7-functionalized carbazole cores on the performance of corresponding solar cells were investigated. Molecular orbital analyses revealed the characteristics of the carbazole-based highest occupied molecular orbitals and acid-based lowest unoccupied molecular orbitals. Time-dependent density functional theory calculations allowed us to assign the electronic transitions (>90%) of the low energy bands. Among these new dyes, the highest power conversion efficiency of 4.82% was obtained in a dye-sensitized solar cell device under standard AM 1.5 sunlight with an open-circuit voltage of 0.61 V, a short-circuit photocurrent density of 12.66 mA cm −2 and a fill factor of 0.62.

The New Branched Multielectrochromic Materials: Enhancing the Electrochromic Performance via Longer Side Alkyl Chain

We describe the synthesis and structure–property relationships of two branched electroactive monomers containing carbazole core, 2,5-di(2-thienyl)-1H-pyrrole, differentiated by the length of side alkyl chains (DSNSC-1 and DSNSC-2). Structural identification of initial compounds and products were carried out by using FT-IR and 1H and 13C NMR spectroscopy. The electroactive materials DSNSC-1 and DSNSC-2 were directly coated on to ITO glass surface by using electrochemical polymerization process. The results clearly indicate that the length of side alkyl chain has a major impact on optical and electrochemical properties of these polymers. Poly-DSNC-2 with longer side alkyl chain exhibits a high contrast ratio (ΔT% = 68% at 850 nm), a response time of about 0.8 s, and high coloration efficiency (352 cm2 C–1) and retained its performance by 97.1% even after 5000 cycles.

Structure–property relationship in high triplet energy host materials with a phenylcarbazole core and diphenylphosphine oxide substituent

A series of high triplet energy host materials with a carbazole core and a diphenylphosphine oxide substituent were synthesized and the effect of the substitution position on the photophysical properties and device performances of the host material was investigated. The substitution position of the diphenylphosphine oxide on the phenyl ring was changed and the substitution at ortho position of the phenyl ring induced the intramolecular charge transfer complex formation. The intramolecular charge transfer complex formation in the ortho substituted compound improved the current density. A maximum quantum efficiency of 20.4% was obtained in the phenylcarbazole host material with the phosphine oxide at para position of the phenyl group and the efficiency was degraded in the ortho substituted host.

Synthesis and application of H-Bonded cross-linking polymers containing a conjugated pyridyl H-Acceptor side-chain polymer and various carbazole-based H-Donor dyes bearing symmetrical cyanoacrylic acids for organic solar cells

A series of novel hydrogen-bonded (H-bonded) cross-linking polymers were generated by complexing various proton-donor (H-donor) solar cell dyes containing 3,6- and 2,7-functionalized electron-donating carbazole cores bearing symmetrical thiophene linkers and cyanoacrylic acid termini with a proton-acceptor (H-acceptor) side-chain homopolymer carrying pyridyl pendants (with 1/2 M ratio of H-donor/H-acceptor). The supramolecular H-bonded structures between H-donor dyes and the H-acceptor side-chain polymer were confirmed by FTIR measurements. The effects of the supramolecular architecture on optical, electrochemical, and organic photovoltaic (OPV) properties were investigated. From DFT (density functional theory) calculations, the optimized geometries of organic dyes reflected that the carbazole cores of H-donor dyes were coplanar with the conjugated thiophenes and cyanoacrylic acids, which is essential for strong conjugations across the donor-acceptor units in D1–D4 dyes. Under 100 mW/cm 2 of AM 1.5 white-light illumination, bulk heterojunction (BHJ) OPV cell devices containing an active layer of H-bonded polymers ( PDFTP/D1–D4) as an electron donor blended with [6,6]-phenyl C 61-butyric acid methyl ester (PCBM) as an electron acceptor in a weight ratio of 1:1 were explored. From the preliminary investigations, the OPV device containing 1:1 weight ratio of H-bonded polymer PDFTP/D2 and PCBM showed the best power conversion efficiency (PCE) value of 0.31% with a short-circuit current ( J sc) of 1.9 mA/cm 2, an open-circuit voltage ( V oc) of 0.55 V, and a fill factor (FF) of 29%, which has a higher PCE value than the corresponding H-donor D2 dye (PCE = 0.15%) or H-acceptor PDFTP homopolymer (PCE = 0.02%) blended with PCBM in 1:1 weight ratio.

Rational Design of d-PeT Phenylethynylated-Carbazole Monoboronic Acid Fluorescent Sensors for the Selective Detection of α-Hydroxyl Carboxylic Acids and Monosaccharides

We have synthesized three new phenylethynylated carbazole boronic acid sensors, which were predicted to display novel d-PeT fluorescence transduction (PeT, photoinduced electron transfer; fluorophore as the electron donor of the electron transfer, ET) by DFT/TDDFT calculations. The d-PeT effect is characterized by a lower background fluorescence at acidic pH than at neutral pH, which is in stark contrast to the normal a-PeT effect (fluorophore as the electron acceptor of the ET) that shows a strong and undesired background fluorescence at acidic pH. Our experimental results confirmed the theoretical predictions and d-PeT was observed for two of the sensors (with p-dimethylaminophenylethynyl substitution at 6- position of the carbazole core). For the third sensor (with phenylethynyl substitution at 6- position of the carbazole core), however, not d-PeT but rather the normal a-PeT was observed. The discrepancy between the DFT/TDDFT calculations and the experimental observations can be rationalized using free energy changes (Rehm-Weller equations) and the rate constants for the ET (k(ET), Marcus equation). These new d-PeT boronic acid sensors show improved photophysical properties compared to the known d-PeT sensor reported previously by us. In particular, the fluorescence transduction efficiency of the new sensors was improved 8-fold when compared to the known d-PeT boronic acid sensors. Novel fluorescence enhancement/reduction was observed for one of the sensors upon binding with mandelic acid or tartaric acid at pH 5.6. The effect of pH as well as the bonding with analytes on the emission of the sensors were rationalized using DFT/TDDFT calculations. We believe that rational sensor design aided by DFT/TDDFT calculations as well as using free energy changes and electron transfer rate constants to study the emission properties of PeT sensors will become an essential tool in the design of new fluorophores or fluorescent sensors with predetermined photophysical properties.

Bent Ladder-Type Hexaphenylene with Carbazole Core and Spiro Linkage as Stable and Efficient Blue Emitter

A bent ladder-type hexaphenylene with a carbazole core and spiro-linkage is designed and synthesized by using the ortho-linked spirobifluorene. The design eliminates the possibility of forming a positional isomer. As a blue-emitter, the BLHPC shows good thermal and color stability. A simple light-emitting device fabricated from BLHPC exhibits a maximum current efficiency of 1.46 cd/A and a maximum luminance of 505 cd/m(2).

Synthesis of the pyrrolo[2,3-c]carbazole core of the dictyodendrins

The pyrrolo[2,3-c]carbazole , the common core of the marine alkaloids known as the dictyodendrins, has been synthesised. The sequence is based on a Suzuki cross-coupling reaction between the pyrrole fragment and the indole fragment , followed by tandem photochemical 6pi-electrocyclization/aromatisation.

Total Syntheses of Clausamines A−C and Clausevatine D

The first total syntheses of clausamines A-C and clausevatine D are reported. The key step involves a Diels-Alder reaction between an imine quinone and cyclic diene, allowing for the subsequent construction of the carbazole core in a regiospecific manner. Stereochemistry of the natural products is also discussed.