N-Glycosides of indigo, indirubin, and isoindigo: blue, red, and yellow sugars and their cancerostatic activity

Indigo, indirubin, and isoindigo derivatives have been used for centuries as pigments. Since the 1990s, a new aspect of the chemistry of this type of compounds is their activity against various types of cancer. N-Glycosides of indigo, indirubin, and isoindigo, blue, red, and yellow sugars, turned out to be of special interest because of their high cancerostatic activity and structural novelty. The present article provides an account on the synthesis and anticancer activity of these compounds.

Chiroptical Sensing of Amines With Isatins

Isatins are extensively researched compounds with diverse applications, particularly as synthetic precursors in pharmaceutical developments. However, their use as optical probes for enantioselective sensing of chiral amines has not been explored to date. Herein, we present a novel chiroptical assay with an optimized isatin that generates strong, red-shifted circular dichroism (CD) signals at approximately 380 nm upon ketimine formation with chiral amines. The intensity of the induced CD signal increases linearly with the enantiomeric excess of the analyte and thus allows quantitative chirality analysis. The general usefulness of this approach is demonstrated with a broad range of aliphatic and aromatic chiral amines, and by accurate determination of the enantiomeric composition of 10 samples.

Preparation of Novel Organic Polymer Semiconductor and Its Properties in Transistors through Collaborative Theoretical and Experimental Approaches

Conjugated polymer semiconductors based on donor-acceptor structures are commonly employed as core materials for optoelectronic devices in the field of organic electronics. In this study, we designed and synthesized a novel acceptor unit thiophene-vinyl-diketopyrrolopyrrole, named TVDPP, based on a four-step organic synthesis procedure. Stille coupling reactions were applied with high yields of polymerization of TVDPP with fluorinated thiophene (FT) monomer. The molecular weight and thermal stability of the polymers were tested and showed high molecular weight and good thermal stability. Theoretical simulation calculations and 2D grazing-incidence wide-angle X-ray scattering (GIWAXS) tests verified the planarity of the material and excellent stacking properties, which are favorable for achieving high carrier mobility. Measurements based on the polymer as an organic thin film transistor (OTFT) device were carried out, and the mobility and on/off current ratio reached 0.383 cm2 V-1 s-1 and 104, respectively, showing its great potential in organic optoelectronics.

Molecular Design Concept for Enhancement Charge Carrier Mobility in OFETs: A Review

In the last two decades, organic field-effect transistors (OFETs) have garnered increasing attention from the scientific and industrial communities. The performance of OFETs can be evaluated based on three factors: the charge transport mobility (μ), threshold voltage (Vth), and current on/off ratio (Ion/off). To enhance μ, numerous studies have concentrated on optimizing charge transport within the semiconductor layer. These efforts include: (i) extending π-conjugation, enhancing molecular planarity, and optimizing donor-acceptor structures to improve charge transport within individual molecules; and (ii) promoting strong aggregation, achieving well-ordered structures, and reducing molecular distances to enhance charge transport between molecules. In order to obtain a high charge transport mobility, the charge injection from the electrodes into the semiconductor layer is also important. Since a suitable frontier molecular orbitals' level could align with the work function of the electrodes, in turn forming an Ohmic contact at the interface. OFETs are classified into p-type (hole transport), n-type (electron transport), and ambipolar-type (both hole and electron transport) based on their charge transport characteristics. As of now, the majority of reported conjugated materials are of the p-type semiconductor category, with research on n-type or ambipolar conjugated materials lagging significantly behind. This review introduces the molecular design concept for enhancing charge carrier mobility, addressing both within the semiconductor layer and charge injection aspects. Additionally, the process of designing or converting the semiconductor type is summarized. Lastly, this review discusses potential trends in evolution and challenges and provides an outlook; the ultimate objective is to outline a theoretical framework for designing high-performance organic semiconductors that can advance the development of OFET applications.

A Rational Design of Isoindigo-Based Conjugated Microporous n-Type Semiconductors for High Electron Mobility and Conductivity

The development of n-type organic semiconductors has evolved significantly slower in comparison to that of p-type organic semiconductors mainly due to the lack of electron-deficient building blocks with stability and processability. However, to realize a variety of organic optoelectronic devices, high-performance n-type polymer semiconductors are essential. Herein, conjugated microporous polymers (CMPs) comprising isoindigo acceptor units linked to benzene or pyrene donor units (BI and PI) showing n-type semiconducting behavior are reported. In addition, considering the challenges of deposition of a continuous and homogeneous thin film of CMPs for accurate Hall measurements, a plasma-assisted fabrication technique is developed to yield uniform thin films. The fully conjugated 2D networks in PI- and BI-CMP films display high electron mobility of 6.6 and 3.5 cm2 V-1 s-1 , respectively. The higher carrier concentration in PI results in high conductivity (5.3 mS cm-1 ). Both experimental and computational studies are adequately combined to investigate structure-property relations for this intriguing class of materials in the context of organic electronics.

Solution-Processed Isoindigo- and Thienoisoindigo-Based Donor-Acceptor-Donor π-Conjugated Small Molecules: Synthesis, Morphology, Molecular Packing, and Field-Effect Transistor Characterization

Molecular design and precise control of thin-film morphology and crystallinity of solution-processed small molecules are important for enhancing charge transport mobility of organic field-effect transistors and gaining more insight into the structure-property relationship. Here, two donor-acceptor-donor (D-A-D) architecture small molecules TRA-IID-TRA and TRA-TIID-TRA comprising an electron-donating triarylamine (TRA) and two different electron-withdrawing cores, isoindigo (IID) and thienoisoindigo (TIID), respectively, were synthesized and characterized. Replacing the phenylene rings of central IID A with thiophene gives a TIID core, which reduces the optical band gap and upshifts the energy levels of frontier molecular orbitals. The single-crystal structures and grazing-incidence wide-angle X-ray scattering (GIWAXS) analysis revealed that TRA-TIID-TRA exhibits the relatively tighter π-π stacking packing with preferential edge-on orientation, larger coherence length, and higher crystallinity due to the noncovalent S···O/S···π intermolecular interactions. The distinctly oriented and connected ribbon-like TRA-TIID-TRA crystalline film by the solution-shearing process achieved a superior hole mobility of 0.89 cm² V^-1 s^-1 in the organic field-effect transistor (OFET) device, which is at least five times higher than that (0.17 cm² V^-1 s^-1) of TRA-IID-TRA with clear cracks. Eventually, rational modulation of fused core in the π-conjugated D-A-D small molecule provides a new understanding of structural design for enhancing the performance of solution-processed organic semiconductors.

Semiconducting Polymers for Neural Applications

Electronically interfacing with the nervous system for the purposes of health diagnostics and therapy, sports performance monitoring, or device control has been a subject of intense academic and industrial research for decades. This trend has only increased in recent years, with numerous high-profile research initiatives and commercial endeavors. An important research theme has emerged as a result, which is the incorporation of semiconducting polymers in various devices that communicate with the nervous system—from wearable brain-monitoring caps to penetrating implantable microelectrodes. This has been driven by the potential of this broad class of materials to improve the electrical and mechanical properties of the tissue–device interface, along with possibilities for increased biocompatibility. In this review we first begin with a tutorial on neural interfacing, by reviewing the basics of nervous system function, device physics, and neuroelectrophysiological techniques and their demands, and finally we give a brief perspective on how material improvements can address current deficiencies in this system. The second part is a detailed review of past work on semiconducting polymers, covering electrical properties, structure, synthesis, and processing.

Towards modulating the colour hues of isoindigo-based electrochromic polymers through variation of thiophene-based donor groups

This paper demonstrated that the hues of both neutral and oxidised colours of isoindigo-based donor–acceptor polymers could be tuned subtly by means of variation of the number and type of donor groups.

Enhanced Performance of Cyclopentadithiophene-Based Donor-Acceptor-Type Semiconducting Copolymer Transistors Obtained by a Wire Bar-Coating Method

Herein, we report the fabrications of high-performance polymer field-effect transistors (PFETs) with wire bar-coated semiconducting polymer film as an active layer. For an active semiconducting material of the PFETs, we employed cyclopentadithiophene-alt-benzothiadiazole (CDT-BTZ) that is a D-A-type-conjugated copolymer consisting of a repeated electron-donating unit and an electron-accepting unit, and the other two CDT-based D-A-type copolymer analogues are cyclopentadithiophene-alt-fluorinated-benzothiadiazole (CDT-FBTZ) and cyclopentadithiophene-alt-thiadiazolopyridine (CDT-PTZ). The linear field-effect mobility values obtained from the transfer curve of the PFETs fabricated with the spin-coating were 0.04 cm²/Vs, 0.16 cm²/Vs, and 0.31 cm²/Vs, for CDT-BTZ, CDT-FBTZ, and CDT-PTZ, respectively, while the mobility values measured from the PFETs with the wire bar-coated CDT-BTZ film, CDT-FBTZ film, and CDT-PTZ film were 0.16 cm²/Vs, 0.28 cm²/Vs, and 0.95 cm²/Vs, respectively, which are about 2 to 4 times higher values than those of the PFETs with spin-coated films. These results revealed that the aligned molecular chain is beneficial for the D-A-type semiconducting copolymer even though the charge transport in the D-A-type semiconducting copolymer is known to be less critical to the degree of disorder in film.

Charge injected proton transfer in indigo derivatives

In analogy with excited-state proton transfer, proton transfer is significantly facilitated in cationic and anionic molecules of indigo derivatives generated in field-effect transistors. We have prepared extended and truncated indigo derivatives and investigated their ambipolar transistor properties. Since the proton transfer reduces the energy gap from 2.2 to 0.4 eV, the proton transferred states are stabilized in the charge injected cationic and anionic states; the energy increase is as small as 0.5 eV, which is half of that in the neutral state. The intermolecular proton transfer enlarges the equilibrium N-H distance typically by 0.03 Å, and improves the donor and acceptor abilities by 0.2-0.4 eV, though the reorganization energy is practically unchanged. In addition, the transfer integrals along the hydrogen bonds are as large as one third of the columnar transfers, to facilitate the two-dimensional carrier conduction. The influence of proton transfer is most significant in indigo and truncated indigo derivatives, though isoindigo and quinacridone exhibit similar properties. Accordingly, indigo derivatives show much better donor and acceptor abilities than those expected from isolated molecules.

Recent progress of ultra-narrow-bandgap polymer donors for NIR-absorbing organic solar cells

Solution-processed near-infrared (NIR)-absorbing organic solar cells (OSCs) have been explored worldwide because of their potential as donor:acceptor bulk heterojunction (BHJ) blends. In addition, NIR-absorbing OSCs have attracted attention as high specialty equipment in next-generation optoelectronic devices, such as semitransparent solar cells and NIR photodetectors, owing to their feasibility for real-time commercial application in industry. With the introduction of NIR-absorbing non-fullerene acceptors (NFAs), the value of OSCs has been increasing while organic donor materials capable of absorbing light in the NIR region have not been actively studied yet compared to NIR-absorbing acceptor materials. Therefore, we present an overall understanding of NIR donors.

Recent advances in the application of isoindigo derivatives in materials chemistry

In this review, the data on the application of isoindigo derivatives in the chemistry of functional materials are analyzed and summarized. These bisheterocycles can be used in the creation of organic solar cells, sensors, lithium ion batteries as well as in OFET and OLED technologies. The potentials of the use of polymer structures based on isoindigo as photoactive component in the photoelectrochemical reduction of water, as matrix for MALDI spectrometry and in photothermal cancer therapy are also shown. Data published over the past 5 years, including works published at the beginning of 2021, are given.

Organic Semiconductors at the University of Washington: Advancements in Materials Design and Synthesis and toward Industrial Scale Production

Research at the University of Washington regarding organic semiconductors is reviewed, covering four major topics: electro-optics, organic light emitting diodes, organic field-effect transistors, and organic solar cells. Underlying principles of materials design are demonstrated along with efforts toward unlocking the full potential of organic semiconductors. Finally, opinions on future research directions are presented, with a focus on commercial competency, environmental sustainability, and scalability of organic-semiconductor-based devices.

Environmentally Benign Route for Scalable Preparation of 1-Imino-3-thioisoindolines-The Key Building Blocks for the Synthesis of Dithio- and Diamino-β-isoindigo Derivatives

A one-step, gram-scale protocol for the preparation of 1-imino-3-thioisoindolines and a novel one-pot two-step methodology of the synthesis of dithio- or diamino-β-isoindigo derivatives starting from phthalonitriles and sodium hydrosulfide in an aprotic dipolar solvent have been developed. It was demonstrated that the electronic properties of the substituent(s) in the phthalonitrile core play a critical role in β-isoindigo synthesis resulting either in the selective formation of dithio- or diamino-β-isoindigo chromophores. The N-acylated 1-imino-3-thioisoindolines can be used for the direct, easily scalable, and chromatography-free procedure for the preparation of a new class of N,N'-diacylamino-β-isoindigoid compounds. Properties of the monomeric as well as J-aggregated forms of dithio- and diamino-β-isoindigo were probed by the absorption and fluorescence spectroscopies. It was demonstrated that the tetracyano-diamino-β-isoindigo 3f can form a J-aggregate that absorbs at 793 nm and fluoresces at 824 nm. This aggregate is stable in N,N-dimethylformamide solution; however, it slowly dissociates in tetrahydrofuran or under sonication conditions. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations were employed to elucidate the electronic structures, spectroscopic properties, and aggregation of new dithio- and diamino-β-isoindigo derivatives.

Benzo/Naphthodifuranone-Based Polymers: Effect of Perpendicular-Extended Main Chain π-Conjugation on Organic Field-Effect Transistor Performances

For polymer semiconductors, the backbone structure plays an essential role in determining their physicochemical properties and charge transport behaviors. In this work, two donor-acceptor-type polymers (P-BDF and P-NDF) based on benzodifuranone (BDF) and naphthodifunarone (NDF) as electron-deficient moieties and indaceno-dithiophene as electron-rich groups are designed, synthesized and, for the first time, applied in organic field-effect transistor. P-BDF and P-NDF differ from their backbone structures while P-BDF has a more planar backbone conformation due to its smaller conjugated core size and P-NDF features a perpendicular-extended main chain structure. As a result, P-BDF polymer exhibits bathochromic optical absorption, deeper molecular orbital energy levels, and more importantly, closer π-stacking and stronger aggregation in the solid state and thus affords a more promising hole mobility of up to 0.85 cm² V^-1 s^-1 in OFET devices, while that of the P-NDF-based devices is only 0.55 cm² V^-1 s^-1 . The results suggest the great potential of BDF/NDF-type chromophores in constructing novel organic semiconductors and also indicate that the main chain coplanarity of polymer semiconductors is more essential than the sole extension of π-conjugations (especially at the perpendicular direction of polymer main chains) for the design of high-performance OFET materials.

Indolonaphthyridine: A Versatile Chromophore for Organic Electronics Inspired by Natural Indigo Dye

Organic electronics is an exciting field of research offering innovative technologies from roll-to-roll inkjet-printed solar cells to foldable displays for cellphones and televisions. These functional devices exploit the flexible nature of conjugated organic materials, both polymeric and molecular, to absorb and emit light and to facilitate transport of charge carriers. A major driving force of development within the field is the creation of novel high-performance building blocks, providing a fruitful and ever-growing library of materials for tailored applications. Most of these building blocks contain chromophores that are entirely synthetic, yet there exist many naturally occurring building blocks, which have been relatively overlooked, despite their innate high stability and inexpensive nature. Indigo is the most produced dye worldwide and has one of the richest histories of all known textile dyes, dating before 4000 BC. Indigo's superior photostability has been linked to fast, favorable deactivation pathways following light absorption. But through one straightforward reaction, the chromophore of indigo can be transformed to a new chromophore with remarkable optoelectronic properties.In this Account, we discuss this chromophore, indolonaphthyridine, and give an overview of our research into the synthesis and optoelectronics properties of functional organic electronic materials derived from it. The unit's strong, fused planar construction contains bis-imide functional groups in similarity to the field-favorite diketopyrrolopyrrole, and similarly requires solubilizing with long alkyl chains, the installation of which is nontrivial and achieved using a protecting group strategy. Our solubilized indolonaphthyridine monomer allows us to copolymerize it with simple archetypal comonomers (thiophene, benzothiadiazole, etc.), in contrast to the other research groups working on the chromophore, who employ complex alkylated comonomer units. We discovered materials with extraordinary performance in organic photovoltaics, affording power conversion efficiencies up to 4.1% in the near-IR region of the spectrum. In organic field-effect transistors, the copolymers exhibited ambipolar transport and notable n-type mobilities up to 3.1 cm²/(V s), well above the benchmark set by silicon (1 cm²/(V s)). The strong absorption in the near-IR allowed us to explore the use of the polymers as contrast agents in photoacoustic imaging, an emerging technique capable of achieving deep tissue penetration without the need for ionizing radiation, while maintaining high contrast and high accuracy responses. Finally, we discuss an exciting aspect of the photophysics of molecular indolonaphthyridine: its ability to undergo singlet fission. Moreover, most singlet fission materials exhibit poor ambient stability; however our molecular indolonaphthyridines exhibit superior stability. It is our hope that this Account showcases the remarkable potential of this relatively unexplored, versatile chromophore and leads to wider adoption in the future.

Synthesis of N-substituted 3-(2-aryl-2-oxoethyl)-3-hydroxyindolin-2-ones and their conversion to N-substituted (E)-3-(2-aryl-2-oxoethylidene)indolin-2-ones: synthetic sequence, spectroscopic characterization and structures of four 3-hydroxy compounds and five oxoethylidene products

An operationally simple and time-efficient approach has been developed for the synthesis of racemic N-substituted 3-(2-aryl-2-oxoethyl)-3-hydroxyindolin-2-ones by a piperidine-catalysed aldol reaction between aryl methyl ketones and N-alkylisatins. These aldol products were used successfully as strategic intermediates for the preparation of N-substituted (E)-3-(2-hetaryl-2-oxoethylidene)indolin-2-ones by a stereoselective dehydration reaction under acidic conditions. The products have all been fully characterized by 1H and 13C NMR spectroscopy, by mass spectrometry and, for a representative selection, by crystal structure analysis. In each of (RS)-1-benzyl-3-hydroxy-3-[2-(4-methoxyphenyl)-2-oxoethyl]indolin-2-one, C24H21NO4, (Ic), and (RS)-1-benzyl-3-{2-[4-(dimethylamino)phenyl]-2-oxoethyl}-3-hydroxyindolin-2-one, C25H24N2O3, (Id), inversion-related pairs of molecules are linked by O-H...O hydrogen bonds to form R22(10) rings, which are further linked into chains of rings by a combination of C-H...O and C-H...π(arene) hydrogen bonds in (Ic) and by C-H...π(arene) hydrogen bonds in (Id). The molecules of (RS)-1-benzyl-3-hydroxy-3-[2-oxo-2-(pyridin-4-yl)ethyl]indolin-2-one, C22H18N2O3, (Ie), are linked into a three-dimensional framework structure by a combination of O-H...N, C-H...O and C-H...π(arene) hydrogen bonds. (RS)-3-[2-(Benzo[d][1,3]dioxol-5-yl)-2-oxoethyl]-1-benzyl-3-hydroxyindolin-2-one, C24H19NO5, (If), crystallizes with Z' = 2 in the space group P-1 and the molecules are linked into complex sheets by a combination of O-H...O, C-H...O and C-H...π(arene) hydrogen bonds. In each of (E)-1-benzyl-3-[2-(4-fluorophenyl)-2-oxoethylidene]indolin-2-one, C23H16FNO2, (IIa), and (E)-1-benzyl-3-[2-oxo-2-(thiophen-2-yl)ethylidene]indolin-2-one, C21H15NO2S, (IIg), the molecules are linked into simple chains by a single C-H...O hydrogen bond, while those of (E)-1-benzyl-3-[2-oxo-2-(pyridin-4-yl)ethylidene]indolin-2-one, C22H16N2O2, (IIe), are linked by three C-H...O hydrogen bonds to form sheets which are further linked into a three-dimensional structure by C-H...π(arene) hydrogen bonds. There are no hydrogen bonds in the structures of either (E)-1-benzyl-3-[2-(4-methoxyphenyl)-2-oxoethylidene]indolin-2-one, C24H19NO3, (IIc), or (E)-1-benzyl-5-chloro-3-[2-(4-chlorophenyl)-2-oxoethylidene]indolin-2-one, C23H15Cl2NO2, (IIh), but the molecules of (IIh) are linked into chains of π-stacked dimers by a combination of C-Cl...π(arene) and aromatic π-π stacking interactions.

Synthesis of Poly(bisisoindigo) Using a Metal-Free Aldol Polymerization for Thin-Film Transistor Applications

Typical syntheses of conjugated polymers rely heavily on organometallic reagents and metal-catalyzed cross-coupling reactions. Here, we show that an environmentally benign aldol polymerization can be used to synthesize poly(bisisoindigo), an analog of polyisoindigo with a ring-fused structural repeat unit. Owing to its extended conjugation length, poly(bisisoindigo) absorbs across the UV/vis/NIR spectrum, with an absorption tail that reaches 1000 nm. Due to the four electron-deficient lactam units on each repeat unit, poly(bisoindigo) possesses a low-lying LUMO, which lies at -3.94 eV relative to vacuum. Incorporation of the ring-fused monomer unit also lowered the overall torsional strain in the polymer backbone (relative to polyisoindigo), and the polymer was successfully used in prototype unipolar n-channel organic thin-film transistors.

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.

Aza-Based Donor-Acceptor Conjugated Polymer Nanoparticles for Near-Infrared Modulated Photothermal Conversion

It is highly desired that synthesis of photothermal agents with near-infrared (NIR) absorption, excellent photostability, and high photothermal conversion efficiency are essential for potential applications. In this work, three (D-A) conjugated polymers (PBABDF-BDTT, PBABDF-BT, and PBABDF-TVT) based on aza-heterocycle, bis(2-oxo-7-azaindolin-3-ylidene)benzodifurandione (BABDF) as the strong acceptor, and benzodithiophene-thiophene (BDTT), bithiophene (BT), and thiophene-vinylene-thiophene (TVT) as the donors, were designed and synthesized. The conjugated polymers showed significant absorption in the NIR region and a maximum absorption peak at 808 nm by adjusting the donor and acceptor units. Their photothermal properties were also investigated by using poly(ethylene glycol)-block-poly(hexyl ethylene phosphate) (mPEG-b-PHEP) to stabilize the conjugated polymers. Photoexcited conjugated polymer (PBABDF-TVT) nanoparticles underwent non-radiative decay when subjected to single-wavelength NIR light irradiation, leading to an excellent photothermal conversion efficiency of 40.7%. This work indicated the aza-heterocycle BABDF can be a useful building block for constructing D-A conjugated polymer with high conversion efficiency.

Conversion of curved assemblies into two dimensional sheets

The design and preparation of organic two dimensional (O2D) sheets and their conversion to curved nanostructures is in its infancy. To convert a flat structure into a curved structure, the molecule must have multiple interaction possibilities and an in-built twist. The conjugated small molecule iso-Indigo (i-Indigo) comprises two phenyl rings that are twisted (the dihedral angle is 15°) at the junction. The i-Indigo has been connected with moieties that impart hydrogen bonding and van der Waals interactions. Due to the presence of the π cloud in i-Indigo, π-π interactions are also present in the molecule. While all three interactions are in operation, rings and toroids are formed. Upon addition of hydrogen bonding competing solvents, the rings and toroids unravel to form O2D sheets. Control molecules that don't have hydrogen bonding moieties and π-π interactions form random assemblies. Please note that the rings, toroids and O2D sheets are formed in a single solvent by simple dissolution, unlike previous approaches that involve multiple steps and solvents.

Isatin and its derivatives: a survey of recent syntheses, reactions, and applications

Isatin (1H-indole-2,3-dione) and its derivatives represent an important class of heterocyclic compounds that can be used as precursors for drug synthesis. Since its discovery, a lot of research work has been done regarding the synthesis, chemical properties, and biological and industrial applications of isatin. In this review, we have reported several novel methods for the synthesis of N-, C2-, and C3-substituted and spiro derivatives of isatin. The isatin moiety also shows important chemical reactions such as oxidation, ring expansion, Friedel-Crafts reaction and aldol condensation. These reactions, in turn, produce several biologically viable compounds like 2-oxindoles, tryptanthrin, indirubins, and many more. We have also summarized some recently reported biological activities exhibited by isatin derivatives, like anti-cancer, anti-bacterial, anti-diabetic and others. Special attention has been paid to their anti-cancer activity, and various anti-cancer targets such as histone deacetylase, carbonic anhydrase, tyrosine kinase, and tubulin have been discussed in detail. Other applications of isatin derivatives, such as in the dye industry and in corrosion prevention, have also been discussed.

Dithieno[3,2-a:3',2'-j][5,6,11,12]chrysene diimides: a versatile electron-deficient building block for polymeric semiconductors

In this work, dithieno[3,2-a:3',2'-j][5,6,11,12]chrysene diimides (DTCDI), an electron-deficient π-building block, were firstly incorporated into polymer main chains by using the 3,9-positions of chrysene and the α,α'-positions of thiophene units of DTCDI to connect with the 2,2'-bithiophene unit, affording copolymers P1 and P2, respectively. Due to their different connection ways the two polymers feature different optoelectronic properties.

Recent Advances in Isoindigo-Inspired Organic Semiconductors

Over the past decade, isoindigo has become a widely used electron-deficient subunit in donor-acceptor organic semiconductors, and these isoindigo-based materials have been widely used in both organic photovoltaic (OPV) devices and organic field effect transistors (OFETs). Shortly after the development of isoindigo-based semiconductors, researchers began to modify the isoindigo structure in order to change the optoelectronic properties of the resulting materials. This led to the development of many new isoindigo-inspired compounds; since 2012, the Kelly Research Group has synthesized a number of these isoindigo analogues and produced a variety of new donor-acceptor semiconductors. In this Personal Account, recent progress in the field is reviewed. We describe how the field has evolved from relatively simple donor-acceptor small molecules to structurally complex, highly planarized polymer systems. The relevance of these materials in OPV and OFET applications is highlighted, with particular emphasis on structure-property relationships.

New insights into the design of conjugated polymers for intramolecular singlet fission

Singlet fission (SF), a multiple exciton generation process that generates two triplet excitons after the absorption of one photon, can potentially enable more efficient solar cell designs by harvesting energy normally lost as heat. While low-bandgap conjugated polymers are highly promising candidates for efficient SF-based solar cells, few polymer materials capable of SF have been reported because the SF process in polymer chains is poorly understood. Using transient spectroscopy, we demonstrate a new, highly efficient (triplet yield of 160-200%) isoindigo-based donor-acceptor polymer and show that the triplet pairs are directly emissive and exhibit a time-dependent energy evolution. Importantly, aggregation in poor solvents and in films significantly lowers the singlet energy, suppressing triplet formation because the energy conservation criterion is no longer met. These results suggest a new design rule for developing intramolecular SF capable low-bandgap conjugated polymers, whereby inter-chain interactions must be carefully engineered.

Centrosymmetric Thiophenemethyleneoxindole-Based Donor-Acceptor Copolymers for Organic Field-Effect Transistors

Two novel, donor-acceptor-type π-conjugated polymers (P1 and P2) with 3'-(thieno[3,2-b]thiophene-2,5-diylbis(methan-1-yl-1-ylidene))bis-(indolin-2-one) (ITTI) as the acceptor and thiophene/bithiophene as the donor are designed and synthesized by palladium-catalyzed Stille coupling. The optical and electrochemical properties of these polymers are characterized and further implemented into organic field-effect transistors (OFET). Both polymers exhibit excellent thermal stability, broad UV-vis absorption, and high highest occupied molecular orbital energy levels. Thermal annealing induces a well-ordered structure, a highly planar π-system (oxygen-sulfur interaction), and a bathochromic shift in the polymers; furthermore, significant enhancement of the long wavelength intensity is also observed. Both polymers exhibit p-type charge transport behavior, with hole mobilities up to 0.51 cm² V^-1 s^-1 for P1 and 0.65 cm² V^-1 s^-1 for P2. This work demonstrates that ITTI can be a promising building block for the construction of donor-acceptor polymers with high-performance OFETs.

π-Conjugation expanded isoindigo derivatives and the donor-acceptor conjugated polymers: synthesis and characterization

Two π-conjugation expanded isoindigo derivatives (DIID-PhCO and TIID-PhCO) composed of up to 18 rings and two donor-acceptor conjugated polymers based on DIID-PhCO were synthesized. Both polymers are ambipolar semiconductors with balanced hole and electron mobilities up to 0.10 and 0.14 cm² V^-1 s^-1, respectively, under ambient conditions.

Fused electron deficient semiconducting polymers for air stable electron transport

Conventional semiconducting polymer synthesis typically involves transition metal-mediated coupling reactions that link aromatic units with single bonds along the backbone. Rotation around these bonds contributes to conformational and energetic disorder and therefore potentially limits charge delocalisation, whereas the use of transition metals presents difficulties for sustainability and application in biological environments. Here we show that a simple aldol condensation reaction can prepare polymers where double bonds lock-in a rigid backbone conformation, thus eliminating free rotation along the conjugated backbone. This polymerisation route requires neither organometallic monomers nor transition metal catalysts and offers a reliable design strategy to facilitate delocalisation of frontier molecular orbitals, elimination of energetic disorder arising from rotational torsion and allowing closer interchain electronic coupling. These characteristics are desirable for high charge carrier mobilities. Our polymers with a high electron affinity display long wavelength NIR absorption with air stable electron transport in solution processed organic thin film transistors.

Semiconducting polymers are usually prepared by transition metal mediated coupling reactions that cause problems for sustainability and biological applications. Here the authors synthesise fused electron deficient polymers that are air stable and have high electron affinities, via metal free aldol polymerisation reactions.

Molecular ordering of A(D–A′–D)2-based organic semiconductors through hydrogen bonding after simple cleavage of tert-butyloxycarbonyl protecting groups

Molecular ordering of organic semiconductors comprising a newly designed A(D–A′–D)₂ system was achieved through hydrogen bonding after removal of tert-butyloxycarbonyl substituents.

An efficient lactone-to-lactam conversion for the synthesis of thiophene Pechmann lactam and the characterization of polymers thereof

We proposed an efficient methodology for Pechmann lactone-to-lactam conversion for various molecular applications.

Molecular-level architectural design using benzothiadiazole-based polymers for photovoltaic applications

A series of low band gap, planar conjugated polymers, P1 (PFDTBT), P2 (PFDTDFBT) and P3 (PFDTTBT), based on fluorene and benzothiadiazole, was synthesized. The effect of fluorine substitution and fused aromatic spacers on the optoelectronic and photovoltaic performance was studied. The polymer, derived from dithienylated benzothiodiazole and fluorene, P1, exhibited a highest occupied molecular orbital (HOMO) energy level at -5.48 eV. Density functional theory (DFT) studies as well as experimental measurements suggested that upon substitution of the acceptor with fluorine, both the HOMO and lowest unoccupied molecular orbital (LUMO) energy levels of the resulting polymer, P2, were lowered, leading to a higher open circuit voltage and short circuit current with an overall improvement of more than 110% for the photovoltaic devices. Moreover, a decrease in the torsion angle between the units was also observed for the fluorinated polymer P2 due to the enhanced electrostatic interaction between the fluorine substituents and sulfur atoms, leading to a high hole mobility. The use of a fused π-bridge in polymer P3 for the enhancement of the planarity as compared to the P1 backbone was also studied. This enhanced planarity led to the highest observed mobility among the reported three polymers as well as to an improvement in the device efficiency by more than 40% for P3.

3D-Printed OFETs of the 1,4-bis(3-phenylquinoxalin-2-yl)benzene-based polymer semiconductors

In this study, we polymerized a 1,4-bis(3-phenylquinoxalin-2-yl)benzene unit with DPP and isoindigo units to produce four new polymers and deeply investigated the influence of DPP and isoindigo units on the semiconductor characteristics, band gap, and orientation properties of these polymers.

Synthesis and organic field effect transistor properties of isoindigo/DPP-based polymers containing a thermolabile group

The effect of hydrogen bonding and π–π intermolecular stacking on the physical properties and device performance.

The optimization of donor-to-acceptor feed ratios with the aim of obtaining black-to-transmissive switching polymers based on isoindigo as the electron-deficient moiety

The polymers based on isoindigo, thiophene and ProDOT were synthesized and characterized. Black to transmissive polymers were obtained by controlling the feed ratios of the units.

One-pot homopolymerization of thiophene-fused isoindigo for ambient-stable ambipolar organic field-effect transistors

The homopolymer that was directly obtained via one-pot polymerization exhibited much higher ambipolar transport behavior than the copolymer.

Conjugated Thiophene-Fused Isatin Dyes through Intramolecular Direct Arylation

We report on the design, synthesis, and properties of innovative, planar, π-conjugated compounds in which a thiophene ring is fused with the skeleton of the naturally occurring dye isatin. The synthesis is achieved in high yields making use of an intramolecular direct arylation reaction as the key step, making the overall process potentially scalable. The synthetic sequence has been demonstrated also for an isatin bearing fluorine substituents on the aromatic ring. NMR and X-ray studies demonstrate the crosstalk occurring between the fused, coplanar, and conjugated moieties, making these novel dyes with a donor-acceptor character. Cyclic voltammetry and UV-vis studies confirm very interesting HOMO-LUMO levels and energy gaps for the new compounds.