Indolocarbazole Research Articles

Enhancing Spin-Orbit Coupling in an Indolocarbazole Multiresonance Emitter by a Sulfur-Containing Peripheral Substituent for a Fast Reverse Intersystem Crossing.

A fast reverse intersystem crossing (RISC) remains an ongoing pursuit for multiresonance (MR) emitters but faces formidable challenges, particularly for indolocarbazole (ICz) derived ones. Here, heavy-atom effect is introduced first to construct ICz-MR emitter using a sulfur-containing substitute, simultaneously enhancing both spin-orbit and spin-vibronic coupling to afford a fast RISC with a rate of 1.2×105s-1, nearly one order of magnitude higher than previous maximum values. The emitter also exhibits an extremely narrow deep-blue emission peaking at 456nm with full-width at half-maxima of merely 12nm and a photoluminescence quantum yield of 92%. Benefiting from its efficient triplet upconversion capability, this emitter achieves not only a high maximum external quantum efficiency (EQE) of 31.1% in organic light-emitting diodes but also greatly alleviates efficiency roll-off, affording record-high EQEs of 29.9% at 1000cdm-2 and 18.7% at 5000cdm-2 among devices with ICz-MR emitters.

Bisphosphonate-Anchored Self-Assembled Molecules with Larger Dipole Moments for Efficient Inverted Perovskite Solar Cells with Excellent Stability.

In the fabrication of inverted perovskite solar cells (PSCs), the wettability, adsorbability, and compactness of self-assembled monolayers (SAMs) on conductive substrates have critical impacts on the quality of the perovskite films and the defects at the buried perovskite-substrate interface, which control the efficiency and stability of the devices. Herein, three bisphosphonate-anchored indolocarbazole (IDCz)-derived SAMs, IDCz-1, IDCz-2, and IDCz-3, are designed and synthesized by modulating the position of the two nitrogen atoms of the IDCz unit to improve the molecular dipole moments and strengthen the π-π interactions. Regulating the work functions (WF) of FTO electrodes through molecular dipole moments and energy levels, the perovskite band bends upwards with a small offset for ITO/IDCz-3/perovskite, thereby promoting hole extraction and blocking electrons. As a result, the inverted PSC employing IDCz-3 as hole-collecting layer exhibits a champion PCE of 25.15%, which is a record efficiency for the multipodal SAMs-based PSCs. Moreover, the unencapsulated device with IDCz-3 can be stored for at least 1800 h with little degradation in performance.

Novel indolocarbazole-based bipolar host materials for fabricating green phosphorescent organic light-emitting diodes with high efficiency and low roll-off

Herein we report two novel host materials, viz., 2-(dibenzo [b,d]furan-2-yl)indolo [3,2,1-jk]carbazole (ICz-DBF) and 3-(indolo [3,2,1-jk]carbazol-2-yl)furo [2,3-b:5,4-b']dipyridine (ICz-PFP), for fabricating highly stable and efficient organic light-emitting diodes (OLEDs). Green phosphorescent OLEDs (PhOLEDs) based on ICz-DBF and ICz-PFP exhibited less efficiency roll-off than those based on 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) host, and especially, the ICz-DBF-based device achieved a high external quantum efficiency (EQE) of 20.5 %. Bipolar hosts composed of indolocarbazole (ICz) exhibit strong molecular rigidity, high triplet energy, and fast electron transport properties; therefore, they act as acceptors, but dibenzofuran (DBF) and dipyridofuran (PFP) substitutions endow them with controlled electron-donating characteristics. The bipolar properties of the new host materials were demonstrated by single-carrier device analysis, confirming the effectiveness of our research strategy for developing hosts for high-quality OLEDs.

Performance-improved narrowband near-ultraviolet emission from a simple butyl and cyanogen substituted indolocarbazole

High-efficiency narrowband near-ultraviolet (NUV) organic light-emitting diodes with high color purity have currently encountered great challenges. Here, using butyl (Bu) and cyanogen (CN) substituted strategy in the simplest polycyclic aromatic hydrocarbons of indolocarbazole (ICz), two simple emitters of BuICz and BuICzCN were demonstrated. This simple strategy was observed to enable both emitters to realize NUV emission at 380–381 nm with a small full width at half maximum (FWHM) of 21–23 nm and high photoluminescent quantum efficiency of 50%–59% in toluene solution. Furthermore, the BuICzCN doped devices exhibited a slightly blueshifted narrowband NUV electroluminescence at 388 nm with a small FWHM of 32.3 nm but a higher external quantum efficiency of 3.92% in comparison with the BuICz doped devices. This work provides a path to realize high-performance narrow-band NUV emission.

Generation of streptocarbazoles with cytotoxicities by pathway engineering and insights into their biosynthesis.

Indolocarbazoles (ICZs) are a group of antitumor agents, with several analogs used in clinical trials. Therefore, the identification of novel ICZ compounds is important for drug discovery. Streptocarbazoles harbor unique N-glycosidic linkages (N13-C1' and N12-C3'), distinguishing them from the representative ICZ compound staurosporine; however, their biosynthesis remains unclear. In this study, two new streptocarbazoles (1 and 3) with cytotoxic activities were obtained by manipulating the staurosporine biosynthetic gene cluster spc followed by heterologous expression. The biosynthetic pathway of streptocarbazoles was proposed, and their productions were improved through the overexpression of the key enzymes involved. This study enriches the structural diversity of ICZ compounds and would facilitate the discovery of new streptocarbazoles via synthetic biological strategies.

Tuneable stimuli-responsive behaviour, spectroscopic signatures and redox properties of indolo[3,2-b]carbazole-based diradicals.

During the last decade, there has been an increasing interest in the rationalisation of how structural changes stabilise (or destabilise) diradical systems. Demonstrated herein is that indolocarbazole (ICz) diradicals, substituted with dicyanomethylene (DCM) groups, are useful motifs for dynamic covalent chemistry by self-assembling from isolated monomers to cyclophane structures. The comparison of ICz-based systems substituted with DCM groups in para- or meta-positions (p-ICz-CN and m-ICz-CN) and their short-chain carbazole analogues (p-Cz-CN and m-Cz-CN) may identify new potential design strategies for stimuli-responsive materials. The principal objectives of this investigation are the elucidation of (i) the connection between diradical character and the cyclophane stability, (ii) the spatial disposition of the cyclophane structures, (iii) the monomer/cyclophane interconversion both in solution and solid state in response to external stimuli and (iv) the impact that the different π-conjugation and electronic communication between the DCM terminals exerts on the electronic adsorption of the diradicals and their redox behavior. The spontaneous nature of the cyclophane structure is supported by the negative relative Gibbs free energies calculated at 298 K and experimentally by UV-Vis and Raman spectroscopy of the initial yellow solid powder. The conversion to monomeric species having diradical character was demonstrated by variable-temperature (VT) EPR, UV-Vis, Raman and IR measurements, resulting in appreciable chromic changes. In addition, electrochemical oxidation and reduction convert the cyclophane dimer (m-ICz-CN)2 to the monomer monocations and dianions, respectively. This research demonstrates how the chemical reactivity and physical properties of π-conjugated diradicals can be effectively tuned by subtle changes in their chemical structures.

End-capped engineering of carbazole based dopant free hole transporting material with improved power conversion efficiency

Perovskite solar cells (PSCs) belonging to third-generation of solar cells are reported to have better power conversion efficiency, cost-effectiveness, and many other benefits. This computational investigation focuses on designing five indolo(3,2-b) carbazole (ICZ) central core containing small hole transport materials (HTMs) to discover photovoltaic properties as donors for perovskite solar cells accompanied by enhanced charge mobility. New HTMs with A–π–D–π–A skeleton has been designed by thiophene-bridged end-capped acceptor engineering on reference molecule (ICZ-R). Absorption spectra, frontier MOs, density of state analysis, molecular electrostatic potential surfaces, transition density matrix, non-covalent interactions, iso-surface maps, and planarity parameters were analyzed through different softwares for better-predicting performance of perovskite solar cells. All tailored HTMs showed better absorption profiles. Among them, ICZ-D3 exhibited the maximum absorbance λmax at 695 nm in dichloromethane solvent and the greatest full-width half maximum (313.93 nm). ICZ-D2 showed the lowest Eg of 1.62 eV, and the highest dipole moment (8.35 D) in the solvent phase, showing admirable solubility. Designed HTMs exhibited decelerated HOMO values (−4.62 to −5.25), lower values of binding energies (0.0323–0.388 <0.542 eV), better intrinsic charge transfer percentage (10.74–72.71%>7.88), lower hardness (0.81–1.11 <1.78 eV) and greater softness values (0.90–1.23 >0.56 eV) as compared to ICZ-R. All designed HTMs demonstrated higher estimated VOC and power conversion efficiency (PCE=11.81–25.90%) than ICZ-R, leading to fruitful applications. ICZ-D4 resulted in the highest PCE (25.90%) with better VOC (1.25 eV). These outstanding findings paved a new way to develop better-performing HTMs for PSCs.

Theoretical models of staurosporine and analogs uncover detailed structural information in biological solution

Staurosporine and its analogs (STA-analogs) are indolocarbazoles (ICZs) compounds able to inhibit kinase proteins in a non-specific way, while present antimicrobial and cytostatic properties. The knowledge of molecular features associated to the complexation, including the ligand shape in solution and thermodynamics of complexation, is substantial to the development of new bioactive ICZs with improved therapeutic properties. In this context, the empirical approach of GROMOS force field is able to accurately reproduce condensed phase physicochemical properties of molecular systems after parameterization. Hence, through parameterization under GROMOS force field and molecular simulations, we assessed STA-analogs dynamics in aqueous solution, as well as its interaction with water to probe conformational and structural features involved in complexation to therapeutic targets. The coexistence of multiple conformers observed in simulations, and confirmed by metadynamics calculations, expanding the conformational space knowledge of these ligands with potential implications in understanding the ligand conformational selection during complexation. Also, changes in availability to H-bonding concerning the different substituents and water can reflect on effects at complexation free energy due to variation at the desolvation energetic costs. Based on these results, we expect the obtained structural data provide systemic framework for rational chemical modification of STA-analogs.

Improving anion sensing ability of the indolocarbazole-based fluorescence turn-on sensor by increasing salicylaldehyde response unit

Detection abilities on tested subjects of sensors should be closely connected to the sensing unit numbers. Herein, two anion sensors ICZ-o-1S and ICZ-o-2S were synthesized by using indolo (2,3-a) carbazoles as fluorescent chromophore and salicylaldehyde as recognition site. Though UV–Vis and fluorescent ways, it demonstrated that F− can induce the sensor solutions becoming colored from colorless to yellow green, and can endow them with bright green turn-on fluorescence, proving their sensitive and selective sensing on F−. Accordingly, the F ion sensing studies including anti-interference abilities against to other anions on fluorescence response, stoichiometric ratios of sensor-F− in 1 : 1 and 1 : 2, –OH deprotonation sensing mechanism confirmed by 1H NMR titration and theoretical calculation were fully covered. Most importantly, fluoride ion detection limits achieved by ICZ-o-1S and ICZ-o-2S were 1.8 × 10−7 M and 6.0 × 10−8 M, respectively, the latter with two sensing units exhibited 3 times lower detection limit outcompeted to the former with only one sensing unit, rendering the sensor design strategy of improving detecting ability by increasing sensing unit number was rational. The practical application of F− detection in water-containing environment calibrated from the standard curve between the fluorescence intensity of sensor-F− system and the changing F− concentration was conducted. In addition, the accuracy of the sensor on detecting F− was evaluated by the spiked recovery experiment, therefore, the fast and convenient F− concentration detection based on the fluorescence color RGB values of the tested sensor-sample mixture was investigated. Consequently, the results obtained by these two sensors should deliver effective supports on designing high-performance sensors featuring naked-eye and fluorescence turn-on anion sensing by altering the response unit numbers.

Orbital Symmetry Engineering in Fused Polycyclic Heteroaromatics toward Extremely Narrowband Green Emissions with an FWHM of 13nm.

Multiresonance (MR) molecules generally face spectral broadening issues with redshifted emissions. Thus, green emitters with full widths at half maximum (FWHMs) of <20nm are rarely reported, despite being highly desired. Herein, by properly fusing indolo(3,2,1-jk)carbazole (ICZ) and naphthalene moieties, green MR emitters are reported, which have FWHMs of merely 13nm (0.064eV) and 14nm (0.069eV) in dichloromethane, accompanied by high photoluminescence quantum yields of >95%, which represent not only the smallest FWHMs among all green MR emitters but also the first green emitters based on ICZ MR derivatives. Theoretical studies reveal that the orbital interactions between the antisymmetric sites of the segments play an important role in extending the conjugation length in the fusion architectures while simultaneously maintaining a small FWHM. The corresponding organic light-emitting diodes exhibit green emission peaks at 508-509nm and the first green electroluminescence FWHM of <20nm ever reported. Benefiting from the preferential horizontal dipole orientation, a high maximum external quantum efficiency of up to 30.9% is obtained, which remains at 28.9% and 23.2% under luminances of 1000 and 10000 cdm-2 , respectively, outperforming most reported green devices based on narrowband emitters.

Tuning the Diradical Character of Indolocarbazoles: Impact of Structural Isomerism and Substitution Position.

In this study, a set of 10 positional indolocarbazole (ICz) isomers substituted with dicyanomethylene groups connected via para or meta positions are computationally investigated with the aim of exploring the efficiency of structural isomerism and substitution position in controlling their optical and electronic properties. Unrestricted density functional theory (DFT), a spin-flip time-dependent DFT approach, and the multireference CASSCF/NEVPT2 method have been applied to correlate the diradical character with the energetic trends (i.e., singlet–triplet energy gaps). In addition, the nucleus-independent chemical shift together with ACID plots and Raman intensity calculations were used to strengthen the relationship between the diradical character and (anti)aromaticity. Our study reveals that the substitution pattern and structural isomerism represent a very effective way to tune the diradical properties in ICz-based systems with meta-substituted systems with a V-shaped structure displaying the largest diradical character. Thus, this work contributes to the elucidation of the challenging chemical reactivity and physical properties of diradicaloid systems, guiding experimental chemists to produce new molecules with desirable properties.

Afterglows from the indolocarbazole families

Indolocarbazoles (ICZs) and their derivates were immensely studied in the fields of organic opto-electronics, sensors and anti-cancer agents. However, the afterglow researches, the comprehensive syntheses and crystal structures of the isomeric ICZs remained shortages. Currently, the organic afterglows were mainly focused on the crystalline states, showing restrictions and inconveniences in practical applications, the organic amorphous afterglows were more favorable but were limitedly documented. Herein, the syntheses, single crystal structures, afterglow studies and data protection applications of the ICZ families with five isomers were together presented for the first time. For these ICZ crystals, the planar configurations and high void rates made them prone to stack and vulnerable to the O2 and humidity, affected by these factors, they were hard to radiate phosphorescence at room temperature, which can be more easily aroused at 77 K. By doping the ICZ into PVA, a rigid and confined environment was built by the hydrogen bond interaction between the –NH and –OH unit in the ICZ and PVA chain, greatly hindering the molecular motion, O2 and humidity quenchers. Consequently, the triplet states were efficiently stabilized, the nonradiative transitions were highly suppressed, blooming the phosphorescence of these ICZs at room temperature, the brilliant afterglow can be straight witnessed by the naked eyes. Impressively, the highest photoluminescence efficiency of 31.06% was obtained by the ICZ–o, the longest afterglow lasting time and phosphorescent lifetime of 35 s and 2.32 s were achieved by the ICZ–p2, rivaling to the reported organic amorphous afterglows. It’s believed that the synthetic, crystal structural and afterglow studies of the ICZ families should find a promising avenue for developing new organic amorphous afterglow materials and their applications.

Evaluation of Indolocarbazoles from Streptomyces sanyensis as a Novel Source of Therapeutic Agents against the Brain-Eating Amoeba Naegleria fowleri.

Naegleria fowleri is an opportunistic pathogenic free-living amoeba which is able to rapidly colonize the central nervous system (CNS) and causes a lethal infection known as primary amoebic meningoencephalitis (PAM). Furthermore, more than 98% of the known cases of PAM are fatal and affect mainly children under 12 and young adults. Until now, no fully effective therapeutic agents against N. fowleri are available and hence the urgent need to find novel agents to treat PAM. At present, PAM therapy is based on the combination of amphotericin B, miltefosine, among others, with unwanted toxic effects. Recently, our team isolated various indolocarbazoles (ICZs) from the culture of a mangrove strain of Streptomyces sanyensis which showed activity against kinetoplastids and the Acanthamoeba genus. Hence, in this study, the activity of the previously isolated ICZs, staurosporine (STS), 7-oxostaurosporine (7OSTS), 4′-demethylamino-4′-oxostaurosporine, and streptocarbazole B, was evaluated against two type strains of N. fowleri. Furthermore, the performed activity assays revealed that STS was the most active ICZ presenting an inhibitory concentration 50 (IC50) of 0.08 ± 0.02 µM (SI 109.3). Moreover, STS induced programmed cell death (PCD) in the treated amoebae by triggering DNA condensation, mitochondrial disfunction, cell membrane disruption, and reactive oxygen species (ROS) generation. Therefore, STS could be a promising therapeutic agent against PAM.

Antikinetoplastid Activity of Indolocarbazoles from Streptomyces sanyensis.

Chagas disease and leishmaniasis are neglected tropical diseases caused by kinetoplastid parasites of Trypanosoma and Leishmania genera that affect poor and remote populations in developing countries. These parasites share similar complex life cycles and modes of infection. It has been demonstrated that the particular group of phosphorylating enzymes, protein kinases (PKs), are essential for the infective mechanisms and for parasite survival. The natural indolocarbazole staurosporine (STS, 1) has been extensively used as a PKC inhibitor and its antiparasitic effects described. In this research, we analyze the antikinetoplastid activities of three indolocarbazole (ICZs) alkaloids of the family of staurosporine STS, 2–4, and the commercial ICZs rebeccamycin (5), K252a (6), K252b (7), K252c (8), and arcyriaflavin A (9) in order to establish a plausive approach to the mode of action and to provide a preliminary qualitative structure–activity analysis. The most active compound was 7-oxostaurosporine (7OSTS, 2) that showed IC50 values of 3.58 ± 1.10; 0.56 ± 0.06 and 1.58 ± 0.52 µM against L. amazonensis; L. donovani and T. cruzi, and a Selectivity Index (CC50/IC50) of 52 against amastigotes of L. amazonensis compared to the J774A.1 cell line of mouse macrophages.

A novel fluorene–indolocarbazole hybrid chromophore to assemble high efficiency deep-blue fluorescent emitters with extended device lifetime

In this work, a novel rigid chromophore was synthesized by the fusion of 9,9-dimethyl-9H-fluorene with indolocarbazole (ICz) for the development of deep-blue fluorescent emitters with high efficiencies and long lifetimes.

Indolocarbazole (IC) Derivatives as Promising p‐type Organic Semiconductors: A First‐Principle Study of Their Anisotropic Charge Mobilities

AbstractWe present a detailed theoretical study of the structural, charge transport, and optical properties of three indolocarbazole derivatives, viz., 11, 12‐Dihydroindolo[2, 3‐a]carbazole (DIC), 5, 10‐dimethyl‐5,10‐dihydrobenzo[a]indolo[2, 3‐c]carbazole (DMDBIC), and 2,11‐dimethoxydibenzo[2, 3:5,6]pyrrolizino[1, 7‐bc]indolo[1, 2,3‐lm]carbazole (DMDPIC). DFT calculations along with previously reported x‐ray crystal structures reveal that the studied compounds are planar and do not undergo significant changes in structure upon oxidation or reduction. The maximum hole anisotropic charge mobilities for DIC was found to be 0.338 cm2 V−1 s−1 at Φ=175.89° and 355.81° and the maximum electron mobility was 0.181 cm2 V−1 s−1 at Φ=85.94° and 265.85°. For DMDBIC, the predicted maximum anisotropic hole, and electron mobility was 0.501 cm2 V−1 s−1 and 0.775 cm2 V−1 s−1, respectively at Φ=56.72° and 236.63°, while for DMDPIC the predicted maximum anisotropic hole and electron mobility as 1.586 cm2 V−1 s−1 and 0.594 cm2 V−1 s−1, respectively at Φ=0° and 180.0°. The calculated mobilities show that these compounds may be suitable candidates as a p‐type organic semiconductor with better stability than acene compounds.

English

Indolocarbazole (ICZ) alkaloid constitutes a group of natural products which manifested powerful biological activity, especially anticancer. However, it was laborious to find ICZs-yield organism when anticancer activity was adopted as selection target. The specificity of 6 primer pairs was detected and the results revealed that primer rebBN1/rebBC1 possessed preferable specificity because indolocarbazole-producers DNA was exclusively amplified and no target fragment was amplified from any of indolocarbazole nonproducers. Therefore, primer rebBN1/rebBC1 could specifically identify indolocarbazole-producers from microorganism strains.&nbsp; &nbsp; Key words: Indolocarbazole, rebBN1/rebBC1, ICZs-producing microorganism screening. &nbsp

Cloning, Characterization and Heterologous Expression of the Indolocarbazole Biosynthetic Gene Cluster from Marine-Derived Streptomyces sanyensis FMA

The indolocarbazole (ICZ) alkaloids have attracted much attention due to their unique structures and potential therapeutic applications. A series of ICZs were recently isolated and identified from a marine-derived actinomycete strain, Streptomyces sanyensis FMA. To elucidate the biosynthetic machinery associated with ICZs production in S. sanyensis FMA, PCR using degenerate primers was carried out to clone the FAD-dependent monooxygenase gene fragment for ICZ ring formation, which was used as a probe to isolate the 34.6-kb DNA region containing the spc gene cluster. Sequence analysis revealed genes for ICZ ring formation (spcO, D, P, C), sugar unit formation (spcA, B, E, K, J, I), glycosylation (spcN, G), methylation (spcMA, MB), as well as regulation (spcR). Their involvement in ICZ biosynthesis was confirmed by gene inactivation and heterologous expression in Streptomyces coelicolor M1152. This work represents the first cloning and characterization of an ICZ gene cluster isolated from a marine-derived actinomycete strain and would be helpful for thoroughly understanding the biosynthetic mechanism of ICZ glycosides.

ChemInform Abstract: A Novel Synthesis of 2,2′-Bisindole and Its Application for the Synthesis of Indolo(2,3-a)carbazole Derivatives.

ChemInform Abstract: A Novel Synthesis of 2,2′-Bisindole and Its Application for the Synthesis of Indolo(2,3-a)carbazole Derivatives.

ChemInform Abstract: Some New Selenium-Containing Analogues of Pyridocarbazoles and Indolocarbazoles

Pyridocarbazole moiety is found for example in alkaloids from the ellipticine 1 series and indolocarbazole in tjipanozole 2 and staurosporine 3.