Revisiting Indolo[3,2‐b]carbazole: Synthesis,Structures, Properties,and Applications

Indolo[3,2‐b]carbazole presents a π‐skeleton with a remarkable electronic structure and interesting potential applications. It is, however, also associated with ambiguity and controversy. Herein, new derivatives of indolo[3,2‐b]carbazole are reported and they have enabled a comprehensive study on the electronic structure of indolo[3,2‐b]carbazole and the development of a new n‐type organic semiconductor. Experimental and computational studies show that indolo[3,2‐b]carbazole has a largely localized p‐benzoquinonediimine moiety and significant antiaromaticity. When substituted with (4‐silylethynyl)phenyl groups, the indolo[3,2‐b]carbazole exhibits one‐dimensional π–π stacking and functions as an n‐type organic semiconductor in solution‐processed field effect transistors.     

Synthesis and alkylation of indolo[3,2-b]carbazoles

Double Fischer cyclisation was used to prepare indolo[3,2-b]carbazole and its 2,8-di-OMe, OH, Br and F-derivatives. N-monosubstituted derivatives of indolo[3,2-b]carbazole (methyl, hydroxymethyl, dimethylaminoethyl) were obtained starting from 5,11-di-Boc-indolo[3,2-b]carbazole.     

Structure elucidation of two tryptophan-derived, high affinity Ah receptor ligands

Background: Environmental contaminants, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and other structurally related ‘environmental hormones’, exert their harmful biological effects through the Ah receptor signaling pathway. Several naturally occurring substances also bind to this receptor, but its natural role is still obscure. Tryptophan derivatives of the indolo[3,2-b]carbazole type, earlier suggested by us to be endogenous ligands for the receptor, should be a powerful tool in understanding receptor function. We therefore: set out to determine their identity.Results: The two tryptophan-derived Ah receptor ligands have been chemically analyzed and characterized by means of mass spectrometry, ¹H NMR and ¹³C NMR. UV, infra-red and fluorescence spectra were also recorded. All data are in accordance with the two compounds being closely related indolo[3,2-b]carbazole derivatives. Evidence is presented that compound A (MW = 312) is the symmetrical 6,12-diformylindolo[3,2-b]carbazole, and compound B (MW = 284) is the monosubstituted 6-formylindolo[3,2-b]carbazole.Conclusions: The elucidation of the structures of the two high affinity Ah receptor ligands 6,12-diformylindolo[3,2-b]carbazole and 6-formylindolo[3,2-b]carbazole provides the necessary basis for further mechanistic studies of this important group of compounds, and will help in determining the natural role of the Ah receptor.     

Synthesis of 2,10,11-Trisubstituted Indolo[3,2-b]quinolines

A new method has been developed for the synthesis of derivatives of indolo[3,2-b]quinolines-11 based on N-oxidization of 2-nitro-10-substituted indolo[3,2-b]quinolines with subsequent conversion of the mixtures obtained into 2-nitro-11-substituted indolo[3,2-b]quinolinones-11. A series of 2-nitro-11-substituted indolo[3,2-b]quinolines was prepared.     

Synthesis,photophysical and electrochemical properties of novel 6,12-di(thiophen-2-yl) substituted indolo[3,2-b]carbazoles

Novel 5,11-dialkyl-6,12-di(thiophen-2-yl) substituted 5,11-dihydroindolo[3,2-b]carbazoles have been obtained and plausible ways for their further modifications via the Friedel–Crafts reaction are presented. The formylation of these indolo[3,2-b]carbazoles with dichloromethyl alkyl esters catalysed by Lewis acids leads to the formation of the corresponding 2,8-diformyl derivatives. Applicability of this formylation method for modification of indolo[3,2-b]carbazoles bearing electron-rich aromatic substituents at C-6 and C-12 has also been demonstrated. The Knoevenagel condensation of 2,8-dialdehydes with active methylene nitriles has been studied. The measurements of optical and redox properties for a number of new indolo[3,2-b]carbazoles have been performed.     

Study of Friedel-Crafts acetylation of indolobenzo[b]furans,indolobenzo[b]thiophenes,pyrrolocarbazole, and pyrrolophenothazine dioxide by1H NMR spectroscopy

The reactivity towards Friedel-Crafts acetylation of the new heterocyclic systems indolo[5,6-d]- and indolo[5,4-d]benzo-[d]furans, 3H pyrrolo[2,3-c]carbazole, indolo[7,6-d]-, indolo[4,5-d]- and indolo[5,4-d]benzo-[b]thiophenes and 3H-pyrrolo[2,3-c]phenothiazine-11,11-dioxide have been studied. Under acid conditions these heterocycles behave like indole to give dimerization products, but anomalies were observed in a number of cases. These principles have been established by detailed analysis of the ¹ H NMR spectra of the reaction products. Georgian Technical University, Tbilisi 380075. D. I. Mendeleev Russian Chemical Technological University, Moscow 125047. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1078–1091, August, 1995. Original article submitted June 12, 1995.     

Heterocycles [h]-fused onto 4-oxoquinoline-3-carboxylic acid, Part VI [1]. Synthesis and X-ray structure of model indolo[3,2-b]- and [2,3-b]pyrido[2,3-f]quinoxaline-3-carboxylic esters

Cyclocondensation reaction of ethyl 7,8-diamino-1-cyclopropyl-6-fluoro-4-oxo-1,4-dihydroquinoline-3-carboxylate with 1-methylisatin produced a separable mixture of the corresponding indolo[3,2-b]- and [2,3-b]pyrido[2,3-f]quinoxaline-3-carboxylates, of which the latter isomer predominates. On the other hand, interaction with 1H-isatin or 5-chloroisatin gave the respective indolo[2,3-b]pyrido[2,3-f]quinoxaline-3-carboxylates as the sole regiospecific products. The structures of these new pentacyclic derivatives are based on microanalytical, spectral (IR, MS, and NMR) and X-ray crystal structure data.     

Synthesis, photophysical and electrochemical properties and theoretical studies on three novel indolo[3,2-b]carbazole derivatives containing benzothiazole units

Three novel indolo[3,2-b]carbazoles derivatives were successfully synthesized by condensation reaction and structurally characterized by elemental analysis, mass spectrometry and proton nuclear magnetic resonance spectroscopy methods, which belong to donor-π-acceptor systems comprising an indolo[3,2-b]carbazole group as an electron donor and two benzothiazole rings as electron acceptors. The thermal, electrochemical and photophysical properties of the compounds were characterized by thermogravimetric analysis combined with electrochemistry, UV-vis absorption spectroscopy and fluorescence spectroscopy. On the other hand, the geometries, molecular orbitals, charge-injection and transport properties were determined by quantum chemical calculations. The results show that the compounds synthesized exhibit good thermal stability and high fluorescence quantum yields, indicating the potential application as optoelectronic materials.     

Triazole-fused indolo[2,3-a]carbazoles: synthesis,structures, and properties

The synthesis, structure, and photophysical and electrochemical properties of triazole fused indolo[2,3-a]carbazole derivatives 2 - 5 are reported. The key step involved in the synthesis of triazole fused indolo[2,3-a]carbazole derivatives is the Cadogan ring closing reaction. 2-Hexyl-5,6-dinitro-2H-benzo[d][1,2,3]triazoles having 4,7-diaryl capping were subjected to the Cadogan cyclization reaction to obtain compounds 2-5 . In contrast to thiadiazole-fused indolo[2,3-a]carbazole 1 , bromination of triazole-fused indolo[2,3-a]carbazole 4 afforded only meta-dibrominated product with respect to the nitrogen of fused pyrrole rings on treatment with both N-bromosuccinimide (NBS) and elemental bromine. These compounds showed positive solvatochromism in their emission spectra. Incorporation of electron-donating substituent in the indole moiety resulted in the elevation of the highest occupied molecular orbital (HOMO) level. Density functional theory (DFT) calculations were performed to support the experimental findings.     

Acetylation of indolobenzo[b]furans,pyrrolocarbazole, pyrrolophenothiazine dioxide and pyrroloacridine under Vilsmeier reaction conditions

The course of the Vilsmeier acetylation of new heterocyclic systems, namely, indolo[4,5-d]-, indolo[6,5-d]-, indolo[5,6-d]-, indolo[5,4-d]benzo[b]furans, 3H-pyrrolo[2,3-c]carbazole, 3H-pyrrolo[2,3-c]pheno-thiazine 11,11-dioxide, and 3H-pyrrolo[2,3-c]acridine depends on the type of fusion of the pyrrole ring. Angular heterocycles are acetylated at the -position of the pyrrole ring, while linear heterocycles under analogues conditions give dimerization products with a substituent at the nitrogen atom of the hydrogenated part of the dimer molecule. 3H-Pyrrolo[2,3-c]phenothiazine 11,11-dioxide and 3H-pyrrolo[2,3-c]acridine are not acetylated under Vilsmeier reaction conditions.Georgian Technical University, 380075 Tbilisi, Georgia. D. E. Mendeleev Russian Chemical Engineering University, 125047 Moscow. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1331–1336, October, 1996. Original article submitted August 19, 1996.     

Azaindolo[3,2,1-jk]carbazoles: New Building Blocks for Functional Organic Materials

The preparation and characterization of 12 azaindolo[3,2,1-jk]carbazoles is presented. Ring-closing C−H activation allowed for the convenient preparation of six singly and six doubly nitrogen-substituted indolo[3,2,1-jk]carbazole derivatives in which ten of the materials have not been described in the literature before. The detailed photophysical and electrochemical characterization of the developed materials revealed a significant impact of the incorporation of pyridine-like nitrogen into the fully planar indolo[3,2,1-jk]carbazole backbone. Furthermore, the nitrogen position decisively impacted intermolecular hydrogen bonding and thus the solid-state alignment. Ultimately, the versatility of the azaindolo[3,2,1-jk]carbazoles scaffold makes this class of materials an attractive new building block for the design of functional organic materials.     

A biomimetic synthesis of the indolo[3,2-j]phenanthridine alkaloid, calothrixin B

A biomimetic approach to calothrixin B via a hypothetical metabolite, 6-formylindolo[2,3-a]carbazole, is described. The construction of a suitable indolo[2,3-a]carbazole ring system was carried out using an allene-mediated electrocyclic reaction involving two [b]-bonds of indoles as the key step.     

Action of 1,2-diamines and o-aminophenols on 1-alkyl-3-carboxyindole-2-acetic acid anhydrides. Preparation of new ring systems

1-Alkyl-3-carboxyindole-2-acetic acid anhydrides (I) react with ethylenediamine and with o-phenylenediamine to give directly 10-alkylimidazo[3,2:1′,2′]pyrido[4,5-b]indol-5(1H)-ones (II) and 5,6-dihydro-5-alkyl-13H-indolo[2′,3′:4,5]pyrido[1,2-a]benzimidazol-13-one (V), respectively. However, anhydrides I react with o-aminophenol and with o-aminothiophenol to give carboxyindole-acetanilide derivatives IX, which can be cyclised to indolo[2′,3′:4,5]pyrido[2,1-b]benzoxazolone and indolo[2′,3′:4,5]pyrido[2,1-b]benzthiazolone (XI). Some derivatives of II and V were prepared to help in elucidating the structures.     

Molecular Engineering of Isomeric Benzofurocarbazole Donors for Photophysical Management of Thermally Activated Delayed Fluorescence Emitters

Benzofurocarbazole moieties are commonly used donor structures in the design of thermally activated delayed fluorescence (TADF) emitters. However, only 5 H-benzofuro[3,2-c]carbazole (34BFCz) has been reported and, to the best of our knowledge, no other benzofurocarbazole derivatives have been covered in the literature. In the present study, two further benzofurocarbazole moieties, 12 H-benzofuro[3,2-a]carbazole (12BFCz) and 7 H-benzofuro[2,3-b]carbazole (23BFCz), have been synthesized to investigate the effect of the donor structure on the photophysics and device parameters of TADF emitters. Two benzofurocarbazole-derived TADF emitters, 12-(2-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-12 H-benzofuro[3,2-a]carbazole (o12BFCzTrz) and 7-(2-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-7 H-benzofuro[2,3-b]carbazole (o23BFCzTrz), have been compared with 5-(2-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-5 H-benzofuro[3,2-c]carbazole (oBFCzTrz). The benzofurocarbazole donor structure governs the TADF characteristics, such as charge-transfer property and emission color. The 12BFCz donor has proved to be effective in blue-shifting the emission color, and 34BFCz has proven useful for improving the external quantum efficiency (EQE). The 12BFCz-derived o12BFCzTrz showed blue-shifted color coordinates of (0.159, 0.288), compared to (0.178, 0388) for o23BFCzTrz and (0.169, 0.341) for oBFCzTrz. The 34BFCz-derived oBFCzTrz exhibited an EQE of 22.9 %, compared to 19.2 % for o12BFCzTrz and 21.1 % for o23BFCzTrz.     

Synthesis of Indolo[3,2‐b]carbazoles via an Anomeric‐Based Oxidation Process: A Combined Experimental and Computational Strategy

Indolo[3,2‐b]carbazole is a molecule of great biological significance, as it is formed in vivo after consumption of cruciferous vegetables. The reaction of 1H‐indole and various aldehydes in the presence of a catalytic amount of N,2‐dibromo‐6‐chloro‐3,4‐dihydro‐2H‐benzo[e][1,2,4]thiadiazine‐7‐sulfonamide 1,1‐dioxide as an efficient and homogeneous catalyst in acetonitrile at 50°C produces 6,12‐disubstituted 5,7‐dihydroindolo[2,3‐b]carbazole with an in good to excellent yield. The presented technique offers a fast and robust method, by the use of inexpensive commercially available starting materials toward 6,12‐disubstituted 5,7‐dihydroindolo[2,3‐b]carbazole. A new anomeric‐based oxidation was kept in mind for the final step of the indolo[2,3‐b]carbazoles synthesis. The suggested anomeric‐based oxidation mechanism was supported by experimental and theoretical evidences.     

Synthesis of derivatives of a new heterocyclic system,indolo[2,3-f][1,7]naphthyridine

3-(N"-Aryl-N"-chloroacetyl)amino-2-formylindoles were converted into 3-amino-1-aryl-2-oxo-1,2-dihydropyrido[3,2-b]indoles, which were used to synthesize derivatives of a new heterocyclic system, namely, indolo[2,3-f][1,7]naphthyridine. The structures of the resulting compounds were proved by IR and ¹H NMR spectroscopy and mass spectrometry.     

Synthetic experiments related to the indole alkaloids V. mercuric acetate oxidation of 2-[2-(3-indolyl)ethyl]-1,2,3,4-tetrahydroisoquinolines and the formation of benz[a]indolo[3,2-h]quinolizine derivatives

Oxidation of 2-[2-(3-indolyl)ethyl]-1,2,3,4-tetrahydroisoquinoline (I) with mercuric acetate gave 5,6,8,9,14,14b-hexahydrobenz[a]indolo[3,2-h]quinolizine (IV) and 8,9-dihydro-14H-benz[a]indolo[3,2-h]quinolizin-7-ium iodide (VI), as well as starting material. The base (IV) was oxidized with iodine and potassium acetate to VI and on Palladium carbon - maleic acid dehydrogenation yielded 5,6-dihydro-14H-benz[a]indolo[3,2-h]-quinolizin-7-ium iodide (IX), and 14H-benz[a]indolo[3,2-h]quinolizin-7-ium iodide (X). Heating the iodide (VI) with Palladium-carbon brought about an irreversible rearrangement to VII and both these salts with base yielded the red anhydro base 8, 9-dihydrobenz[a]indolo[3,2-h]quinolizine (VIII). This base was also obtained from IV by oxidation in air. The corresponding 8, 9-dehydroanhydro base (XI), benz[a]indolo[3,2-h]quinolizine, was readily obtained from X and alkali. The quinolizinium salts (VI), (VII), and (IX), on catalytic, zinc dust and acetic acid, or sodium borohydride reduction, regenerated the base (IV). Selenium degradation of IV gave, among other products, 1-(2-ethylphenyl)-β-carboline. An analogous series of products was obtained with the 6, 7-dimethoxy derivative of I. Various other aspects of these and related transformations are described.     

Palladium-catalyzed amination and cyclization to heteroannellated indoles and carbazoles

New ortho-bromodiarylamines in the benzo[b]thiophene series were prepared by palladium-catalyzed amination, either in the benzene or in the thiophene ring. These were submitted to palladium-catalyzed cyclization, under different required conditions, to give several differently substituted thieno[3,2-c] or [2,3-b]carbazoles and indolo[3,2-b]benzo[b]thiophenes. This constitutes a novel synthetic route to both tetracyclic systems.     

New push-pull systems based on indolo[3,2-b]carbazole and 1,2,4,5-tetrazine: synthesis,photophysical, and charge transport properties

5,11-Dihydroindolo[3,2-b]carbazoles were for the first time modified with acceptor 1,2,4,5-tetrazine fragments. The photophysical and charge-transport properties of the synthesized donor-acceptor heterocyclic systems were studied. It was shown that the introduction of the 1,2,4,5-tetrazine moieties makes it possible to increase the hole and electron mobility by one and two orders of magnitude, respectively, as compared to analogous 5,11-dihydroindolo-[3,2-b]carbazole derivatives studied previously.

     

Hole-transporting glass-forming indolo[3,2-b]carbazole-based diepoxy monomer and polymers

Hole-transporting indolo[3,2-b]carbazole-based diepoxy monomer and polymers are reported. The polymers were prepared by polyaddition reaction of indolo[3,2-b]carbazole diepoxide with aromatic dithiols in the presence of triethylamine. Their number average molecular weights range from 11500 to 14310 and polydispersity indices are in the range of 2.96–3.08. Thermal, optical, photophysical, electrochemical and photoelectrical properties of the title compounds were studied. Both the monomer, 5,11-di-2,3-epoxypropyl-6-pentyl-5,11-dihydroindolo[3,2-b]carbazole and the polymers were found to form glasses with the glass transition temperatures ranging from 37 °C for the monomer to 99 °C for one of the polymers. Time-of-flight hole drift mobilities observed in the solid amorphous films of the monomer exceeded 10^?4 cm² V^?1 s^?1 at an electric field of 10⁶ V cm^?1.