Bromine atom introduction improves the F- sensing ability of an indolo[3,2-b]carbazole-salicylaldehyde-based fluorescence turn-on sensor

The heavy-atom effect usually quenches fluorescence, but scarcely enhances it. Herein, fluorescence turn-on sensors without or with a bromine atom for F- detection are presented, achieving fast response time within 1 min, and the LODs of 1.9 × 10-7 and 8.5 × 10-8 M, reflecting that halogen atom introduction is beneficial for F- detection ability improvement. The sensing mechanism of -OH unit deprotonation is confirmed based on the results of a 1 : 2 stoichiometric ratio, 1H NMR titration and TD-DFT calculation. The water environment F- detection and spiked recovery experiments demonstrate their potential for real sample detection.

New Molecular Design, Step-Saving Synthesis, and Applications of Indolocarbazole Core-Based Oligo(hetero)arenes

In this work, we have successfully synthesized 15 new examples (LLA01-06; LinLi01-10) of small-molecule hole-transporting materials (HTM) using the less explored indolocarbazole (ICbz) as core moiety. Different from previously reported ICbz HTMs, LinLi01-10 exhibit new molecular designs in which 3,4-ethylenedioxythiophene (EDOT) units are inserted as crucial π-spacers and fluorine atoms are introdcued into end-group molecules. These substantially improve the materials solubility and device power conversion efficiencies (PCEs) while fabricated in perovskite solar cells (PSC). More importantly, LinLi01-10 are generated by a sustainable synthetic approach involving the use of straightforward C-H/C-Br couplings as key transformations, thus avoiding additional synthetic transformations including halogenation and borylation reactions called substrate prefunctionalizations usually required in Suzuki reactions. Most HTM molecules can be purified simply by reprecipitations instead of conducting column chromatography. In contrast to LLA01-06 without additional EDOT moieties, PSC devices using LinLi01-10 as hole-transport layers display promising PCEs of up to 17.5 %. Interestingly, PSC devices employing seven of the LinLi01-10 as hole-transport molecules, respectively, are all able to show an immediate >10 % PCE (t=0) without any device oxidation/aging process that is necessary for the commercial spiro-OMeTAD based PSCs.

Versatile access to nitrogen-rich π-extended indolocarbazoles via a Pictet–Spengler approach

A bidirectional Pictet-Spengler Reaction allows easy access to nitrogen-rich aromatics with seven fused rings. Photophysical measurements and computational methods show significant differences to parent N-heteropolycycles with fewer nitrogen atoms.

Powder X-ray diffraction as a powerful tool to exploit in organic electronics: shedding light on the first N,N',N''-trialkyldiindolocarbazole

The first crystal structure of a fully N-alkylated diindolocarbazole derivative, namely, 5,8,14-tributyldiindolo[3,2-b;2',3'-h]carbazole (1, C36H39N3), has been determined from laboratory powder X-ray diffraction (PXRD) data. A complex trigonal structure with a high-volume unit cell of 12987 Å3 was found, with a very long a(=b) [52.8790 (14) Å] and a very short c [5.36308 (13) Å] unit-cell parameter (hexagonal setting). The detailed analysis of the intermolecular interactions observed in the crystal structure of 1 highlights its potential towards the implementation of this core as a semiconductor in organic thin-film transistor (OTFT) devices. Since the molecule has a flat configuration reflecting its π-conjugated system, neighbouring molecules are found to stack atop each other in a slipped parallel fashion via π-π stacking interactions between planes of ca 3.30 Å, with a centroid-centroid distance between the aromatic rings corresponding to the shortest axis of the unit cell (i.e. c). The alkylation of the three N atoms proves to be a decisive feature since it favours the presence of C-H...π interactions in all directions, which strengthens the crystal packing. As a whole, PXRD proves to be a valuable option for the resolution of otherwise inaccessible organic crystal structures of interest in different areas.

High-performance five-ring-fused organic semiconductors for field-effect transistors

Organic molecular semiconductors have been paid great attention due to their advantages of low-temperature processability, low fabrication cost, good flexibility, and excellent electronic properties. As a typical example of five-ring-fused organic semiconductors, a single crystal of pentacene shows a high mobility of up to 40 cm² V^-1 s^-1, indicating its potential application in organic electronics. However, the photo- and optical instabilities of pentacene make it unsuitable for commercial applications. But, molecular engineering, for both the five-ring-fused building block and side chains, has been performed to improve the stability of materials as well as maintain high mobility. Here, several groups (thiophenes, pyrroles, furans, etc.) are introduced to design and replace one or more benzene rings of pentacene and construct novel five-ring-fused organic semiconductors. In this review article, ∼500 five-ring-fused organic prototype molecules and their derivatives are summarized to provide a general understanding of this catalogue material for application in organic field-effect transistors. The results indicate that many five-ring-fused organic semiconductors can achieve high mobilities of more than 1 cm² V^-1 s^-1, and a hole mobility of up to 18.9 cm² V^-1 s^-1 can be obtained, while an electron mobility of 27.8 cm² V^-1 s^-1 can be achieved in five-ring-fused organic semiconductors. The HOMO-LUMO levels, the synthesis process, the molecular packing, and the side-chain engineering of five-ring-fused organic semiconductors are analyzed. The current problems, conclusions, and perspectives are also provided.

End-Group Modifications with Bromine and Methyl in Nonfullerene Acceptors: The Effect of Isomerism

The development of isomeric molecules has been widely exploited in molecular structures associated with organic solar cells (OSC) and is an effective pathway to finely tune the photoelectric properties and device performance. The molecular properties of nonfullerene acceptors and the morphology of blend films can be effectively controlled by manipulating isomeric substituent positions on benzene-fused end-capping groups (EG) in acceptors. Here, three isomeric EGs were designed and synthesized which simultaneously possess an electron-withdrawing bromine and an electron-donating methyl substituent. By linking three isomeric EGs, (Br,Me), (Br,Me)-1, and (Br,Me)-2 each with the BTP-CHO core, three isomeric small-molecule acceptors (SMA) were obtained. The power conversion efficiency (PCE) of PM6:BTP-(Br,Me)-1-based OSCs is 13.43%, is much higher than that of PM6:BTP-(Br,Me)- (11.92%) and PM6:BTP-(Br,Me)-2- (11.08%) based devices. Our results show that isomeric EGs can provide strategies to tune the absorption spectra of SMAs, intramolecular charge transfer (ICT) and electron mobility of organic semiconductor device, and ultimately increase the performance of nonfullerene acceptors.

Fused Pyrazine- and Carbazole-Containing Azaacenes: Synthesis and Properties

A new family of azaacenes has been designed and synthesized by incorporating the electron-withdrawing sp² -hybridized nitrogen of pyrazine and electron-donating nitrogen of carbazole in a molecular skeleton. Two different conjugated lengths of 8-ring aza-nonacene and 10-ring aza-undecene have been achieved by an efficient condensation reaction. The unique optoelectronic properties of these molecules were investigated using both experimental and theoretical techniques. The azaacenes show visible-region absorption and near-infrared (NIR) fluorescence. These compounds can serve as hole-transport semiconductors for solution-processed organic field-effect transistors (OFETs). Single-crystal transistor devices of one of the aza-nonacenes exhibit hole charge transport behavior with a hole mobility of 0.07 cm² /Vs and an on/off current ratio of 1.3x10⁶ .

Mechanoluminescence or Room-Temperature Phosphorescence: Molecular Packing-Dependent Emission Response

Mechanoluminescence (ML) and room-temperature photophosphorescence (RTP) were achieved in polymorphisms of a triphenylamine derivative with ortho-substitution. This molecular packing-dependent emission afforded crucial information to deeply understand the intrinsic mechanism of different emission forms and the possible packing-function relationship. With the incorporation of solid-state ¹³ C NMR spectra of single crystals, as well as the analysis of crystal structures, the preferred packing modes for ML and/or RTP were investigated in detail, which can guide the reasonable design of organic molecules with special light-emission properties.

Design and Characterization of New D-A Type Electrochromic Conjugated Copolymers Based on Indolo[3,2-b]Carbazole, Isoindigo and Thiophene Units

Two new donor–acceptor (D–A) type organic conjugated random copolymers were successfully synthesized by three-component Stille coupling polymerization of indolo[3,2-b]carbazole (ICZ), isoindigo (IID) and thiophene units, namely PITID-X (X = 1 and 2), with the controlled monomer feed ratios of 3:1:4 and 1:1:2, respectively. The strategy of incorporating different alkyl-branched donor/acceptor units and raw material feed ratios facilitated the improvement of optical properties, solubility, conjugated structure, and electrochromic performance. Cyclic voltammetry, UV-vis-NIR absorption spectra, kinetic and colorimetric measurements of the spray-coated films were recorded in the fabricated three-electrode cells. The results showed that PITID-2, whose optical/electrical properties were better than that of PITID-1, was the candidate electrochromic material due to low band gap of 1.58 eV accompanying the color changing from cyan (neutral state) to gray (oxidized state). The copolymer also illustrated fast bleaching/coloration response time of 2.04/0.33 and 1.35/1.50 s in a 4 s time interval, high coloration efficiency of 171.52 and 153.08 cm² C⁻¹ and stable optical contrast of 18% and 58% at the wavelength of 675 and 1600 nm, respectively.

[1 + 2 + 3] Annulation as a General Access to Indolo[3,2- b]carbazoles: Synthesis of Malasseziazole C

A formal [1 + 2 + 3] annulation of methyleneindolinones with o-alkenyl arylisocyanides has been developed for the general and efficient synthesis of both symmetrical and unsymmetrical indolo[3,2- b]carbazoles. The chemoselectivity of this domino reaction was tuned by a tethered alkenyl group, which enables successive formation of three new bonds and two rings from readily accessible starting materials in a single operation. Furthermore, this methodology was used as a key step in the synthesis of the alkaloid malasseziazole C.

Organic field-effect optical waveguides

Integrating electronics and photonics is critically important for the realization of high-density and high-speed optoelectronic circuits. However, it remains challenging to achieve this target due to the difficulty of merging many different areas of science and technology. Here, we show an organic integrated optoelectronic device, namely, organic field-effect optical waveguide, integrating field-effect transistor and optical waveguide together. In such device, the propagation of optical waveguide in the active organic semiconductor can be tuned by the third terminal—the gate electrode of transistor, giving a controllable modulation depth as high as 70% and 50% in parallel and perpendicular directions of charge transport versus optical waveguide, respectively. Also, the optical waveguide with different directions can turn the field-effect of the device with the photodependence ratio up to 14800. The successful integration of active field-effect transistor with semiconductor waveguide modulator expands opportunities for creating scalable integration of electronics and photonics in a chip.

Despite recent advances in organic optoelectronics development, integration of electronics and photonics in a chip remains a challenge. Here, the authors demonstrate organic field-effect optical waveguides that control propagating photons by the electric field produced in an organic transistor.

Chemistry and Properties of Indolocarbazoles

The indolocarbazoles are an important class of nitrogen heterocycles which has evolved significantly in recent years, with numerous studies focusing on their diverse biological effects, or targeting new materials with potential applications in organic electronics. This review aims at providing a broad survey of the chemistry and properties of indolocarbazoles from an interdisciplinary point of view, with particular emphasis on practical synthetic aspects, as well as certain topics which have not been previously accounted for in detail, such as the occurrence, formation, biological activities, and metabolism of indolo[3,2- b]carbazoles. The literature of the past decade forms the basis of the text, which is further supplemented with older key references.

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 and characterization of novel donor–acceptor type neutral green electrochromic polymers containing an indolo[3,2-b]carbazole donor and diketopyrrolopyrrole acceptor

Indolocarbazole bearing donor–acceptor type polymers have rarely been reported in the electrochromic field despite them having considerable development in the applications of organic photoelectric devices. In this paper, two novel soluble electrochromic polymers, namely PDTCZ-1 and PDTCZ-2, were prepared by chemical polymerization including indolo[3,2-b]carbazole (IC) units as the donor, diketopyrrolopyrrole (DPP) units as the acceptor and bithiophene units as the bridging group. Through diverse characterization techniques such as cyclic voltammetry (CV), scanning electron microscopy (SEM), UV-vis spectroscopy and thermogravimetric analysis (TGA), it was found that PDTCZ-1 and PDTCZ-2 exhibited saturated green in the neutral state and pale green in the oxidized state with optical band gaps of 1.44 eV and 1.39 eV, respectively, as well as demonstrating fast switching speed, satisfactory coloration efficiency and favorable thermal stability. In addition, the proportion of donors to acceptors definitely exerted an influence on the electrochromic properties of the polymers. As the thiophene/IC/DPP ratio changed from 4/3/1 (PDTCZ-1) to 5/4/1 (PDTCZ-2), meaning an increase of the donor ratio, the polymer showed a reduced onset oxidation potential, decreased optical band gap and different dynamic parameters. The positive results suggest that PDTCZ-1 and PDTCZ-2 could be promising candidates as neutral green electrochromic materials and deserve more attention and penetrating research.

Two novel neutral green D–A type conjugated polymers were synthesized, illustrating satisfactory electrochromic properties, such as low band gaps, desirable color switches, excellent solubility and favorable thermal stability.

Nitration of 5,11-dihydroindolo[3,2-b]carbazoles and synthetic applications of their nitro-substituted derivatives

A new general approach to double nitration of 6,12-di(hetero)aryl-substituted and 6,12-unsubstituted 5,11-dialkyl-5,11-dihydroindolo[3,2-b]carbazoles by acetyl nitrate has been developed to obtain their 2,8-dinitro and 6,12-dinitro derivatives, respectively. A formation of mono-nitro derivatives (at C-2 or C-6) from the same indolo[3,2-b]carbazoles has also been observed in several cases. Reduction of 2-nitro and 2,8-dinitro derivatives with zinc powder and hydrochloric acid has afforded 2-amino- and 2,8-diamino-substituted indolo[3,2-b]carbazoles, while reduction of 6,12-dinitro derivatives under similar reaction conditions has been accompanied by denitrohydrogenation of the latter compounds into 6,12-unsubstituted indolo[3,2-b]carbazoles. Formylation of 6,12-dinitro derivatives has proved to occur only at C-2, while bromination of these compounds has taken place at both C-2 and C-8 of indolo[3,2-b]carbazole scaffold. Moreover, 6,12-dinitro-substituted indolo[3,2-b]carbazoles have been modified by the reactions with S- and N-nucleophiles. Notably, the treatment of 6,12-dinitro compounds with potassium thiolates has resulted in the displacement of both nitro groups, unlike potassium salts of indole or carbazole, which have caused substitution of only one nitro group.

Indolo[3,2-b]carbazole-based poly(arylene ethynylene)s

A novel family of indolo[3,2-b]carbazole (ICZ)-based polymers was designed and synthesized using Sonogashira cross-coupling reaction between three bisbromine indolo[3,2-b]carbazoles and 1,4-diethynylbenzene. The new polymers have an arylene ethynylene structure with ICZ moiety interconnected in the main chain by 2,8-, 3,9- or 6,12- positions. The polymers were obtained as partially soluble materials, in chlorinated, aromatic and aprotic polar solvents. The structure of the polymers was studied by spectroscopic methods such as Fourier transform infrared, proton and carbon-13 nuclear magnetic resonance, ultraviolet–visible and photoluminescence spectroscopies, thermogravimetry and molecular weights determined by gel permeation chromatography. Electrochemical properties were investigated by cyclic voltammetry using films cast on platinum disc working electrode. Optical and electronic properties were discussed from the viewpoint of the connection positions of ICZ units in the polymer chain.

An asymmetric naphthalimide derivative for n-channel organic field-effect transistors

A novel asymmetric naphthalimide derivative (IZ0) is synthesized and high electron mobility of 0.072 cm²V⁻¹s⁻¹and 0.22 cm²V⁻¹s⁻¹are achieved for IZ0 film and single crystal-based transistors, respectively.

Laterally expanded rylene diimides with uniform branched side chains for solution-processed air stable n-channel thin film transistors

Molecular packing motifs in solid states is the dominant factor affecting the n-channel organic field-effect transistors (OFETs). However, few systematic researches were performed in the different extensions of π-conjugated molecules with the uniform substitution effecting the molecular packing motifs. In this manuscript, OFET devices based on three latterally expanded rylene diimides end-functionalized with uniform 3-hexylundecyl substitution on the imide positions were systematically studied on the relationship of molecular stacking, film microstructure, and charge transport. As the π-conjugated systems expanded from doubly linked perylene diimide dimer (d-4CldiPDI, 1), triply linked perylene diimide dimer (t-4CldiPDI, 2), to hybrid array (NDI-PDI-NDI, 3), their corresponding molecular packing motifs exhibited a divide: the optimized molecular configuration became more planar and d (001) spacing distances became larger, which resulted in a larger π-π overlapping. Thus, an enhanced electron mobility was obtained. A typical n-channel field-effect characteristic was observed in thin film devices based on these molecules under ambient conditions. Especially, the hybrid system (3) with more planar and π-expanded aromatic backbone exhibited superior electron mobility approaching 0.44 cm(2) V(-1) s(-1) and on/off ratio of 10(6) after optimal annealing in this study.

High-performance air-stable single-crystal organic nanowires based on a new indolocarbazole derivative for field-effect transistors

A new indolocabazole derivative possessing an extended aromatic core and solubilizing long aliphatic chains effectively self-assembles and crystallizes within the nanoscale channels to form single-crystal nanowires via a direct printing method from an ink solution. Single-crystal organic nanowire transistor arrays based on the π-extended indolocarbazole derivative exhibit an excellent hole mobility of 1.5 cm² V⁻¹ s⁻¹ and outstanding environmental stability.