Carbazole Dimers Research Articles

Synthesis of π-Extended Carbazole Dimers Via Oxidative Cyclization Using DDQ and Sulfonic Acid and Elucidation of the Reaction Mechanism.

This paper describes the synthesis of various π-extended carbazole dimers via intramolecular oxidative cyclization using a chain precursor consisting of two carbazole units bridged by a nitrogen atom. A careful selection of the reaction conditions using 2,3-dichloro-5,6-dicyano-p-benzoquinone/sulfonic acid enabled the selective synthesis of a π-extended analogue with an angular (L-shape) structure in moderate yield. The preferential positions for the bonding of the two carbazole units in this π-extended derivative were determined by performing density functional theory calculations.

Geländer Molecules with Orthogonal Joints: Synthesis of Macrocyclic Dimers.

Orthogonal joints, understood as connections with an angle of 90°, were introduced in the design of the "Geländer" model compounds 1 and 2. The banister, consisting of a conjugated carbazole dimer linked by either 1,3-butadiyne (2) or a single thiophene (1), wraps around an axis composed of a phthalimide dimer due to the dimensional mismatch of both subunits, which are interconnected by phenylene rungs. The "Geländer" structure was assembled from a monomer comprising the 1,4-diaminobenzene rung with one amino substituent as part of a 4-bromo phthalimide subunit forming the orthogonal junction to the axis, and the other as part of a masked 2-ethynyl carbazole as orthogonal joint to the banister. The macrocycle was obtained by two sequential homocoupling steps. A first dimerization by a reductive homocoupling assembled the axis, while an oxidative acetylene coupling served as ring-closing reaction. The formed butadiyne was further derivatized to a thiophene, rendering all carbons of the model compound sp2 hybridized. Both helical structures were fully characterized and chirally resolved. Assignment of the enantiomers was achieved by simulation of chiroptical properties and enantiopure synthesis.

Investigation of electrochemical oxidative coupling of 3 and 6 substituted carbazoles

• Investigation of carbazole reactivity and electropolymerization mechanism. • Combination of fast electrochemistry experiments and molecular orbital calculations. • Investigation of the stability of radical cations and polarons formed by electro-oxidation of carbazoles. • Comparison of the stability of the dimers depending on the coupling positions. In this study, electrochemical behavior of different functionalized carbazoles has been studied through classical cyclic voltammetry, computational calculations, electrochemical simulations and more originally fast cyclic voltammetry. Indeed, fast electrochemistry is rarely used to study reactivity of such compounds even if it can bring very interesting information as shown in this work. Carbazoles were substituted with ethyl, tert -butyl and phenyl groups at 3 and 6 positions. Oxidation of 3-ethylcarbazole leads to very fast dimerization of formed radical cations (k dim = 1.5.10 7 M −1 .s −1 ) and electrochemical polymerization of this compound leads to a thick adherent conducting polymer film. This was also the case for 3-phenylcarbazole and 3,6-diphenylcarbazole when potential was brought over 1.7 V/SCE because of formation of very reactive radicals after oxidation process involving phenyl groups. For 3,6-diethylcarbazole, 3- tert -butylcarbazole, 3,6-ditert-butylcarbazole, as well as 3-phenylcarbazole and 3,6-diphenylcarbazole when potential is kept under 1.4 V/SCE, dimerization of radical cations is slower (k dim ≤ 1.5.10 6 M −1 .s −1 ) and no efficient electropolymerization occurs. A theoretical study of the same substituted carbazoles in their neutral and oxidized states was done using molecular orbital calculations (DFT method) to obtain additional information about carbazole reactivity. These numerical calculations were in perfect accordance with results of fast electrochemistry and electrochemical simulations regarding stability of radical cations. They demonstrated that monosubstituted carbazole dimers are probably obtained through 6-6′ coupling while 1-1′ coupling is the most favorable for disubstituted carbazole dimers.

Capture of Electrochemically Generated Fleeting Carbazole Radical Cations and Elucidation of Carbazole Dimerization Mechanism by Mass Spectrometry

The capture of reactive intermediates is important for the elucidation of reaction mechanisms. We report the first observation of electrochemically generated, short-lived radical cations of carbazole (t1/2 ≈ 97 μs) and two N-substituted carbazole derivatives by mass spectrometry. In addition, online investigation of the reactivity of electrochemically generated carbazole radical cations supports that the carbazole dimerization mechanism involves the reaction of one radical cation with one neutral molecule rather than the previously proposed coupling of two radical cations.

A theoretical study of carbazole dimers: Does carbazole form an excimer that undermines the performance of organic light emitting diodes?

AbstractCarbazole (Cz) dimers in various cofacial conformations, including staggered (Stg), anti, and syn, were explored by means of ab initio calculations at scaled opposite‐spin (SOS)‐MP2, SOS‐CIS(D0), and additional coupled cluster calculation levels. Similar to other π‐conjugated molecules, strong Cz excimers form in the syn conformation in both S1 and T1 states, leading to significantly reduced optical excitation energies. Upon excitation, the dimers in the Stg and anti‐conformations remain simple excited dimers, exhibiting similar optical energy gaps to those of the monomer. Being far more stable in the ground state, however, the Stg dimer is nearly isoenergetic to the syn dimer in the S1 state and even more stable in the T1 state. Given that the intermolecular interactions in the ground state are expected to govern the dimer conformations of Cz‐based materials in the solid‐state films of organic electronics, our results strongly demonstrate that the electronic excitation of Cz dimers do not necessarily lead to the strong excimer formation unless Cz molecules are forced to be arranged in the syn conformation.

Molecular base and interfacial enrichment of chain entangle in amorphous conjugated polymers: Role of racemic alkyl side groups

Abstract Clear structure characterization is the basics of performance analysis, which is difficult for the complex structure of amorphous conjugated polymers. In this work, we have given solid evidence in copolymer of fluorene and carbazole that the carbazole with racemic branched alkyl side chain tend to form chain entanglement in high concentration of solution and thin film. The single crystal structure of two racemic carbazole dimer with stronger π-π interaction, which 1HNMR peaks is well corresponding to that of racemic polymer at high concentration and proves the existence of chain entanglement in racemic polymer. The chain entanglement segment with high molecular weight and low energy level (estimated as about 3% and absent in the chiral polymer) have enriched at the interface during film fabrication, which induce strong charge trapping and excited state quenching during the working of optoelectronic devices. These chain entanglement would be well restrained by chiral substitution, which induce one order of magnitudes improvement of device brightness and efficiency. These results indicate that the chain entangle at interface and charge trapping play the key role of bad device performance, which help to explore the instability origin and performance promotion.

Conformational distortion in solution processable PVK:TcTa blends and the effect on extra warm white organic phosphorescent light emitting diodes

Abstract Organic semiconductors generally display significant conformational flexibility which results in significant energetic disorder. In this research, ultraviolet photoelectron spectra are compared with the Gaussian density of states obtained from the density functional theory on assembly of molecules optimized using molecular dynamic simulations. It was found out that spin-coated organic semiconductor, tris(4-carbazoyl-9-ylphenyl)amine (TcTa), displays significant conformational distortion from its minimum geometry with significant Gaussian broadening. Adding poly(vinylcarbazole) (PVK) into TcTa results in increased face to face stacking of carbazole moieties from PVK as evident from increased red-shifted of absorption of PVK. Despite reduction of energy barrier upon addition of TcTa into PVK, the current efficiency of the extra warm white organic light emitting diodes showed limited improvement probably from the increased triplet quenchers from the carbazole dimers.

Electrochemical, spectroelectrochemical and surface photovoltage study of ambipolar C60-EDOT and C60-Carbazole based conducting polymers

Ethylenedioxythiophene (EDOT) and Carbazole (CBZ) based conducting polymers holding pendant C60 Buckminster fullerene were formed by electrochemical induced dimerization of four structurally related monomers. Electrochemical and spectroelectrochemical characterization of the thin films clearly indicates the presence of EDOT and CBZ dimers as structural building blocks of the polymeric materials. Under positive applied potentials, all the synthesized conductive materials generate UV–visible-near IR absorption bands that denote the presence of two oxidized states in the electrochemical generated dimers. Also, the four polymeric films showed reversible reduction of the C60 units. The capacity of the materials for the production of photoelectric effects was analyzed by surface photovoltage spectroscopy, showing that the illumination of C60-CBZ polymers causes preferential separation of photogenerated charge carriers in the double-cable polymeric organic films.

Synthesis of Carbazole-Based Porphyrin Oligomers

Fused porphyrins show NIR absorption because they have larger p-conjugation system than regular porphyrins. General fused porphyrins have been synthesized by the peripheral oxidative fusion reaction of the porphyrin skeleton. On the other hand, we successfully synthesized carbazole-based porphyrin via the annulation reaction of butadiyne-bridged carbazole dimer and the subsequent oxidation of the isophlorin. The carbazole-based porphyrin shows strong NIR absorption due to the effect of the quadruple benzo-fusion. We have synthesized several carbazole-based porphyrins, and effective substituent effect was observed at the carbazole moieties. Therefore, we then tried to oligomerize the carbazole-based porphyrin at the carbazole moieties. Four kinds of carbazole-based diporphyrins were synthesized, and their photophysical properties were investigated. As a result, thiophene-bridged diporphyrin was found to show strong intramolecular electron coupling. Furthermore, cyclic porphyrin trimer and tetramer with thiophene linkages were synthesized. All the molecules show NIR absorption. It is worth to note that the spectra of oligomers show broad and red-shifted NIR band as compared to the monomer, which indicates strong intramolecular electronic interaction. Figure 1

Palladium Complexes of Carbazole-Based Chalcogenaisophlorins: Synthesis, Structure, and Solid-State NIR Absorption Spectra.

Annulation reactions of the butadiyne-bridged carbazole dimer 1 produced carbazole-based chalcogenaisophlorins 2-4, which were transformed into the corresponding palladium complexes 2Pd-4Pd. The structures were characterized by NMR spectroscopy and X-ray diffraction analysis. Metallation fixed the structures which displayed weak antiaromatic character derived from the 20π isophlorin framework. These complexes showed weak near-infrared (NIR) absorption typical for antiaromatic porphyrinoids in solution. In addition, 2Pd and 3Pd showed relatively strong solid-state NIR absorption. X-ray diffraction analyses of 2Pd and 3Pd revealed trimeric and dimeric stacked layered structures, respectively, and DFT calculations suggest that the solid-state NIR absorption is ascribed to intermolecular charge transfer.

Synthesis and properties of photocross-linkable carbazole dimers

New carbazole-based monomers with two reactive functional groups such as epoxypropyl, oxetanyl and vinyloxethyl were synthesized and their cationic photopolymerization was performed. The monomer containing epoxypropyl groups exhibited the highest conversion in photopolymerization (78%). The monomers and polymers exhibited ability of glass formation with the glass transition temperatures up to 98°C for low-molecular-weight compounds and those observed for polymers ranging from 89 to 150°C. The synthesized derivatives absorb electromagnetic irradiation in the range of 200–390nm with the band gaps of 3.14–3.16eV. The compounds exhibit blue photoluminescence with the intensity maxima at 400nm. The compounds were found to have high triplet energies of ca. 2.78eV. The electron photoemission spectra of the layers of the synthesized compounds revealed ionization potentials of 5.20–5.37eV. The time-of-flight hole drift mobilities of the layers of the compounds exceed 10−5cm2/V×s at high electric fields.

Nitrogen Oxide Inhibitory Trimeric and Dimeric Carbazole Alkaloids from Murraya tetramera.

Two new structurally unique trimeric carbazole alkaloids, murratrines A and B (1, 2), and 11 new carbazole dimers, murradines A-K (3-13), and four known analogues (14-17) were isolated from the leaves and stems of Murraya tetramera. The structures and relative configurations of 1-13 were elucidated on the basis of comprehensive 1D and 2D NMR spectroscopy, high-resolution mass spectrometry, and electronic circular dichroism (ECD) data analysis. Murratrines A and B (1, 2) both contain an unprecedented carbazole trimeric skeleton, and murradines A and D (3, 6) are the first natural C-1-C-3'-methyl-linked and C-6-C-3'-methyl-linked dimeric carbazole alkaloids, respectively. Compounds 4, 10, 14, 15, and 17 exhibited inhibition of nitric oxide production stimulated by lipopolysaccharide in BV-2 microglial cells with IC50 values in the range of 11.2-19.3 μM.

Influence of the anchoring number in a carbazole-based photosensitizer on the photovoltaic performance of p-type NiO dye sensitized solar cells

Carbazole dimer enhances the charge injection and reduces the charge recombination to exhibit superior p-type performance of DSSCs.

Synthesis of carbazole-based hetero-core-modified porphyrins

Cu(I)-mediated annulation reaction of a 1,1'-(1,3-butadiyne)-8,8'-(2,5-thiophene)-bridged carbazole dimer 10 with amines provided the N-substituted carbazole-based isophlorines 11a-11c. A similar annulation reaction with selenium in the presence of hydrazine monohydrate afforded hetero-core-modified isophlorine 12. The oxidation of 12 generated the corresponding 21-selena-23-thiaporphyrin 13, which exhibited NIR absorption. The intramolecular charge transfer from Se to S was confirmed by the (1)H NMR results along with DFT calculations.

Synthesis and Characterization of Carbazole‐Based Expanded Thiaporphyrins

Carbazole-based porphyrins: Oligothiophene-bridged carbazole dimers and trimers were synthesized as new expanded thiaporphyrins through a sequential coupling and annulation strategy. The structures and electronic properties of these new macrocycles were investigated by spectroscopic methods and DFT calculations and they have been found to exhibit NIR absorption upon NOSbF6 oxidation (see figure). As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Synthesis of Carbazole-Based Selenaporphyrin via Annulation

Cu(I)-mediated alkoxylation of doubly 1,3-butadiyne-bridged carbazole dimer 1, followed by acid-catalyzed cyclization, provided furan-bridged carbazole dimer 3, while annulation reaction of 1 with selenium in the presence of hydrazine monohydrate provided selenophene-bridged carbazole dimer 5a. Oxidation of isophlorin 5a afforded carbazole-based selenaporphyrin 5b, which possessed distinct aromaticity and produced intensified and red-shifted absorption bands in the near-IR region.

カルバゾール等の複素環を基盤とするπ共役系化合物の合成と物性

Suitable functionalization of carbazole, namely the combination with other π-electron systems, can modify the π-conjugation behavior, electron-donating ability or fluorescence properties, and then provide various photofunctional materials. Recently, we have synthesized various carbazole-based π-conjugated compounds such as carbazole-based cyclophanes (carbazolophanes), carbazole dimers, carbazole-thiophene dyads and oligomers, and carbazole-fullerene dyads, and studied their properties. This account reviews their synthesis, structures, and properties in detail.

Bicarbazoles: Systematic Structure–Property Investigations on a Series of Conjugated Carbazole Dimers

A large series of conjugated carbazole dimers, namely bicarbazoles 1-12, were synthesized by Suzuki-Miyaura, Sonogashira, Hay, and McMurry coupling reactions. In 1-12, the two carbazole moieties are linked at the 1-, 2-, or 3-position directly or via an acetylenic or olefinic spacer. The structure-property relationships, particularly the effects of the conjugation connectivity and the π-conjugated spacers on the electronic, photophysical, and electrochemical properties of 1-12, were studied by extensive UV-vis and fluorescence spectroscopic measurements, cyclic voltammetry (CV), and theoretical calculations as well as X-ray crystallographic analyses. The connection at the 1-position of carbazole ensures high extent of π-conjugation, while that at the 3-position enhances the electron-donating ability. Both acetylenic and olefinic spacers allow the extension of π-conjugation, and the latter also causes the increase of the donor ability. Moreover, the structural variations were found to affect the fluorescence quantum yields significantly, which are up to 0.84.

A boron-containing carbazole dimer: synthesis, photophysical properties and sensing properties

A novel boron-containing π-conjugated compound has been synthesized by the introduction of electron-acceptors (dimesitylboron groups) at the 3,3'-positions of a carbazole dimer (electron-donor). The compound possesses excellent electrochemical properties and high fluorescence quantum yields. In addition, is a sensitive fluorescence sensor with remarkable colour changes and the results could be confirmed through theoretical calculations of the compounds and [(n)Bu(4)N](+)(2)[·(F)(2)](2-). Our studies indicate that could be used as an excellent optoelectronic material in OLED devices and a ratiometric fluorescent chemosensor.

Impact of Linking Topology on the Properties of Carbazole Trimers and Dimers

Synthesis and properties of new glass-forming 2-, 2,7-substituted carbazole dimers and trimers exhibiting ambipolar charge carrier transport are reported. The results of thorough evaluation of thermal, optical, and photoelectrical properties of the carbazole derivatives are presented. Additionally, a comparative experimental and theoretical analysis of the 2,7-substituted carbazole trimer with the 3,6-substituted analogue is performed. 2,7-Di(9-carbazolyl)-9-(2-ethylhexyl)carbazole was found to show very high electron mobility (μe = 2 × 10−3 cm2 V−1 s−1 at an electric field of 1.8 × 105 V/cm) and reasonably high hole mobility (μh = 8 × 10−4 cm2 V−1 s−1 at an electric field of 1.8 × 105 V/cm). 2-Substituted carbazole dimers also demonstrate bipolar conductive properties although with significantly lower charge carrier mobility values. The obtained carrier mobility values for the 2,7-substituted carbazole compound were found to be nearly 2 orders of magnitude higher than those for 3,6-substituted carbazole counterpart. The pronounced differences in carrier mobility are justified by DFT calculations indicating extended π-conjugation and a twice as large transition dipole moment in the 2,7-disubstituted carbazole derivative. This is also supported by the optical properties of the 2,7-disubstituted carbazole compound showing up to 5 times larger radiative relaxation rates, 3-fold increase in the fluorescence quantum yield and absorbance, as well as the reduced electron−vibronic system coupling as compared to the 3,6-substituted analogue. The prolonged molecular geometry and extended π-conjugation of the 2,7-substituted carbazole derivative facilitate more ordered and dense molecular packing and thus enhance intermolecular coupling in the solid films contributing to more efficient carrier hopping.