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π‐Extended dithienopyrrolobenzothiadiazole‐isoindigo‐based conjugated polymers were synthesized and well characterized by using various analysis techniques like infrared (IR), 1H NMR, UV–Visible spectroscopy, thermogravimetric analysis, cyclic voltammetry analysis, and gel permeation chromatography. The bandgap of synthesized polymers, P‐1, P‐2, and P‐3, were determined to be 1.95, 1.91, and 1.93 eV, respectively. These polymers exhibited robust thermal stability up to 290°C. The highest occupied molecular orbital energy levels were below −5.0 eV for all polymers, while the lowest unoccupied molecular orbital energy levels ranged from −3.5 to −3.3 eV. The measured space charge limited current hole mobilities for polymers, P‐1, P‐2, and P‐3, were 1.02 ± 0.47 × 10−1, 1.17 ± 0.47 × 10−1, and 2.51 ± 0 0.47 × 10−2 cm2 V−1 s−1, respectively. [ABSTRACT FROM AUTHOR]

A newly synthesized N,N′-dipropyl-substituted isoindigo derivative, namely, 1-propyl-3-(1-propyl-1,2-dihydro-2-oxo-3H-indol-3-ylidene)-1,3-dihydro-2H-indol-2-one, C22H22N2O2, was found to have three polymorphic forms (denoted Forms I, II and III) under various crystallization conditions. Crystal structure analysis indicated that Form III had a significantly different molecular conformation from the other two polymorphs. Their different packing arrangements were correlated with differences in the intermolecular interactions. Thermal measurements revealed that Forms I and II are enantiotropically related, and Form II exhibits thermally dynamic behaviour. [ABSTRACT FROM AUTHOR]

Artificial synapses have gained great interest in the past few years because of their importance in deep learning and image recognition. To fulfill device miniaturization and reduce the energy consumption of device operation, a series of silane‐based photoactive/conjugated self‐assembled molecules (CSAMs), including isoindigo (IID), diketopyrrolopyrrole, and benzodithiophene, are used as the charge‐trapping layers in synaptic phototransistors. The devices comprising CSAM demonstrate excellent short‐term/long‐term memory behaviors and can emulate the paired‐pulse facilitation (PPF) function. Notably, the IID‐based device shows the highest photoresponse, and this performance is highly related to the charge transfer efficiency and the photophysics lifetimes derived from the time‐resolved photoluminescence and the transient absorption characterizations. Therefore, IID produces the highest PPF ratios of 139% to blue light and 144% to green light. In addition, the energy consumption of 0.029 fJ at an operating voltage of −0.1 mV is achieved, which is the lowest value in synaptic phototransistors so far. Notably, neural networks of supervised and unsupervised learning algorithms are demonstrated in the device studied to process a pattern recognition system. Collectively, using conjugated self‐assembled materials as a charge‐trapping layer is a promising way for synaptic phototransistor applications to reduce energy consumption and fulfill the device miniaturization. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Isoindigo (IID) is widely used as organic dye and conjugated unit in opto‐electronic materials. Functionalization of IID to increase its structural complexity is demanding for obtaining diversity properties. Herein, we developed a direct C—H/N—H activation method of IIDs via double alkyne annulations and synthesized π‐extended IIDs with two pairs of 5/7 membered rings. The structure of the π‐extended IIDs was characterized and confirmed by 1H NMR, 13C NMR, HRMS and X ray crystal analysis. Their physical properties were characterized by UV‐vis absorption, cyclic voltammetry and thermogravimetric analysis. The absorption coefficient of the annulated products enhanced significantly compared with the non‐annulated analogue. [ABSTRACT FROM AUTHOR]

A Sonogashira coupling reaction leads to the formation of a serendipitous product C with the 3,3'‐(ethane‐1,2‐diylidene)bis(indolin‐2‐one) unit. To our knowledge, our study provides the first example demonstrating that electron transfer between isoindigo and triethylamine can be thermally activated and can be employed in synthesis. The physical properties of C suggest that it possesses decent photo‐induced electron‐transfer capabilities. Under the illumination of 136 mW cm−2 intensity, C yields ≈2.4 mmol gcat−1 (per gram of catalyst) of CH4 and ≈0.5 mmol gcat−1 of CO in 20 h in the absence of additional metal, co‐catalyst, and amine sacrificial agent. The primary kinetic isotope effect suggests that the bond cleavage of water is a rate‐determining step in the reduction. Moreover, the CH4 and CO production can be boosted as the illuminance increases. This study demonstrates that organic donor‐acceptor conjugated molecules are potential photocatalysts for CO2 reduction. [ABSTRACT FROM AUTHOR]

Microscopic particles (MPs) are used to scatter and reflect UV light. It is well established that inorganic MPs such as TiO2 and ZnO produce carcinogens. Therefore, organic MPs are explored for UV absorption. Conjugated chromophores with differing lipophilicity usually self‐assemble into nanoscopic structures. In our previous experiments, unsymmetrical i‐Indigo was found to self‐assemble into 500 nm particles. We hypothesized that the size of the self‐assembled particles can be increased by increasing the lipophilicity difference between the side chains. Toward this objective, we have chosen the i‐Indigo core with TEG and alkyl chains as side chains. As a result, the i‐Indigo molecules were found to self‐assemble into 3 μ spheres in solution. By substituting side chains with different lipophilicity, i‐Indigo microparticles with the size of 5 μ are prepared. A careful analysis showed that the spheres are similar to a soccer ball, and they deflate upon drying on the substrate surface. The judiciously chosen side chain binds with a metal‐ion (Cs+) and forms nanoscopic assemblies. After Cs+ binding, the size of the particles is decreased drastically to 100 nm. The simple addition of ions converts microscopic assemblies into nanoscopic assemblies. [ABSTRACT FROM AUTHOR]

Power sources that can be charged anytime and anywhere are highly desirable for mobile devices. The most suitable device for achieving such wireless charging is a photocapacitor, which utilizes light as a renewable energy source instead of electricity from the grid. Sunlight on Earth is intermittent and unstable, so photocapacitors that can be charged by the day or room light and near‐infrared (near‐IR) radiation are needed to ensure the uninterrupted operation of the equipment. We employ a single dye‐sensitized solar cell as a photocapacitor without adding any additional charge storage components to reduce the cost and complexity of device manufacturing. To realize such photocapacitors, this work presents a family of new isoindigo‐based D‐π‐A photoactive dyes with good visible and near‐IR absorption. Notably, LF15 has a higher molar absorbance coefficient and enhanced dye‐loading than LF23, which is consistent with the higher photocurrent of photocapacitors based on the former. Photocapacitors based on these three dyes achieve photovoltages up to 0.74 V, area‐specific capacitances of 2.87 mF cm−2, and excellent charge‐discharge stability. The devices can be charged in both visible and near‐IR conditions, exhibiting typical capacitor behavior. [ABSTRACT FROM AUTHOR]

Conjugated polymers are of great interest owing to their potential in stretchable electronics to function under complex deformation conditions. To improve the performance of conjugated polymers, various structural designs have been proposed and these conjugated polymers are specially applied in exotic optoelectronics. In this work, a series of all‐conjugated block copolymers (PII2T‐b‐PNDI2T) comprising poly(isoindigo–bithiophene) (PII2T) and poly(naphthalenediimide–bithiophene) (PNDI2T) are developed with varied compositions and applied to electret‐free phototransistor memory. Accordingly, these memory devices present p‐type transport capability and electrical‐ON/photo‐OFF memory behavior. The efficacy of the all‐conjugated block copolymer design in improving the memory‒photoresponse properties in phototransistor memory is revealed. By optimizing the composition of the block copolymer, the corresponding device achieves a wide memory window of 36 V and a high memory ratio of 7 × 104. Collectively, the results of this study indicate a new concept for designing electret‐free phototransistor memory by using all‐conjugated block copolymer heterojunctions to mitigate the phase separation of conjugated polymer blends. Meanwhile, the intrinsic optoelectronic properties of the constituent conjugated polymers can be well‐maintained by using an all‐conjugated block copolymer design. [ABSTRACT FROM AUTHOR]

Four novel isoindigo–thiophene D–A–D–type precursors are synthesized by Stille coupling and electrosynthesized to yield corresponding hybrid polymers with favorable electrochemical and electrochromic performances. Intrinsic structure–property relationships of precursors and corresponding polymers, including surface morphology, band gaps, electrochemical properties, and electrochromic behaviors, are systematically investigated. The resultant isoindigo–thiophene D–A–D–type polymer combines the merits of isoindigo and polythiophene, including the excellent stability of isoindigo–based polymers and the extraordinary electrochromic stability of polythiophene. The low onset oxidation potential of precursors ranges from 1.10 to 1.15 V vs. Ag/AgCl, contributing to the electrodeposition of high–quality polymer films. Further kinetic studies illustrate that isoindigo–thiophene D–A–D–type polymers possess favorable electrochromic performances, including high optical contrast (53%, 1000 nm), fast switching time (0.8 s), and high coloration efficiency (124 cm2 C−1). These features of isoindigo–thiophene D–A–D–type conjugated polymers could provide a possibility for rational design and application as electrochromic materials. [ABSTRACT FROM AUTHOR]

Iron‐catalyzed dimerization of various isatin derivatives is described for the efficient synthesis of 3,3′‐biindolinylidene‐diones (isoindigos). The reaction provides easy access to self‐coupled and cross‐coupled 3,3′‐indolinylidene‐diones that have high relevance to biology and materials. This Fe(0)‐ or Fe(II)‐catalyzed dimerization reaction tolerates a wide range of functionalities, such as fluoro, chloro, bromo, alkenyl, nitrile, ether, ester, pyrrolyl, indolyl and carbazolyl groups, including cyclic and acyclic alkyls as well as an alkyl‐bearing fatty‐alcohol moiety. Especially, the coupling between two distinct isatins provided excellent selectivity for the cross‐dimerization with trace of self‐couplings. The single‐crystal X‐ray diffraction study established the molecular structure of eight dimerized products. A preliminary mechanistic study of the Fe‐catalyzed dimerization supported the radical pathway for the reaction. [ABSTRACT FROM AUTHOR]

Oxygenation/oxidative self‐coupling of indole are performed to obtain isatin and isoindigo in the absence of metal catalysts. Iodine‐DMSO is used to synthesize isatin whereas Iodine‐DMSO‐K2S2O8 combination is used for isoindigo synthesis directly from indole in a single step. Though several methods are known for isatin synthesis from indole, most of them use large quantity of oxidants or metal catalyzed. Moreover, the primary existing process for the synthesis of isoindigo is the condensation of isatin and oxindole in the presence of an acid catalyst. But this method provides isoindigo derivatives directly from indoles. A plausible mechanism is also proposed based on the various control experiments which indicate that both the reactions proceed via radical route. It is also observed that oxygen atoms of isatin and isoindigo come from water molecule and DMSO. [ABSTRACT FROM AUTHOR]

Herein, the synthesis of a novel isoindigo‐based conjugated polymer using Suzuki and Stille polycondensation reactions is reported. It is shown that the polymer obtained using various reactions possesses different performance in photovoltaic devices. In particular, polymers synthesized using Suzuki and Stille polycondensation demonstrate 2.7% and 4.1% efficiency in organic solar cells, and 12.6% and 15.1% in perovskite solar cells, respectively. The observed difference in the performances of devices is attributed to the appearance of defects in the polymer obtained via Suzuki reaction. Using high‐performance liquid chromatography it is demonstrated that the origin of the polymer quality deterioration is the poor stability of isoindigo‐based monomer under conditions of Suzuki polycondensation. Revealing this aspect allows one to figure out a more effective approach for the synthesis of high‐quality isoindigo‐based polymers for organic electronics. [ABSTRACT FROM AUTHOR]

The past few decades have witnessed the tremendous development of semiconducting polymers in electronic applications, which is inextricably related to the diversity of polymer structure. The change of polymer structure significantly influences the polymer packing, thin film morphology, and other optoelectronic properties, thus meeting the need for different device applications. With the development of synthetic chemistry and theoretical computation, many high‐performance building blocks and polymers have emerged. Among them, isoindigo‐ and isoindigo derivatives‐based polymers are widely studied in various fields of organic electronics, and many of them showed excellent properties. This review summarizes the synthetic tactics of isoindigo‐derived monomers and polymers. Moreover, the structural modification strategies of polymers are discussed in detail, including the modification of isoindigo derivatives and the regulation of polymer type. Using isoindigo‐derived polymers, various applications, such as organic field‐effect transistors, chemical sensors, organic electrochemical transistors, organic phototransistors, organic photovoltaics, organic thermoelectrics, organic spin valves, and biophotonic applications, are introduced to illustrate the important effects of structural modification. [ABSTRACT FROM AUTHOR]

Isoindigo (IID) has been developed as an electron deficient moiety for high-performance conjugated organic materials, especially for constituting donor–acceptor (D-A) type conjugated polymers. To further enhance the planarity of IID unit to promote the associated intramolecular charge transfer (ICT) effect of the derived polymers, various of structural modifications have been performed in recent years. Herein, two heterocyclic ring-fused IID core structures, tetrafluorobenzene-centered IID (FBIID) and pyrazine-centered IID (PzIID), were developed and copolymerized with two common electron-rich moieties, 2,2′-bithiophene (2 T) and (E)-1,2-bis(thiophen-2-yl)ethene (TVT). The properties and structure-mobility relationship of the prepared four D-A type polymers, PFBIID-2 T, PFBIID-TVT, PPzIID-2 T, and PPzIID-TVT are systematically studied to elucidate the effect of the spacer structure in the heterocyclic ring-fused IID units. Both the simulation results and experimental analyses show that the PzIID-based polymers possess much higher planarity and mobility than the FBIID-based ones because of the less substituents on the pyrazine spacer, which reduces the steric hindrance within the structure. Finally, we show that the distinctly different planarity between FBIID and PzIID results in significantly different field-effect transistor (FET) mobility. Owing to the higher planarity and improved stacking and crystallinity of the polymer chains, the PzIID-derived polymers deliver much higher hole mobilities (μhs) of > 3 × 10 −4 (cm2 V−1 s−1) than the FBIID-derived polymers that show no conspicuous charge-transporting properties. This result clearly highlights the crucial role of the spacer structure in designing the heterocyclic ring-fused IID core structures. [ABSTRACT FROM AUTHOR]

Direct arylation methods have been used to polymerize thienylmethylene oxindoles (TEIs) and 3,3-bis[[(2-ethylhexyl)oxy]methyl]-3,4-dihydro-2H-thieno-[3,4-b][1,4]dioxepin (ProDOT) for new donor-acceptor conjugated polymers. The polymers exhibited blue hues in neutral-state with distinct color-to-transmissive reversible electrochromic switching under applied potentials from 0 V to +1.5 V, and showed high coloration efficiencies (436–438 cm2·C−1) in near-infrared regions with high switching speeds around 1–2 s under ambient conditions. [ABSTRACT FROM AUTHOR]

Donor‐acceptor (D−A) polymers have excellent electronic and optical properties that allow for their use in multiple areas of research, ranging from field‐effect transistors to biosensing. However, traditional chemical polymerization strategies to form D−A polymers often require extensive purification and generate large amounts of waste. Electro‐copolymerization of complex isoindigo‐based copolymers is explored as a way to overcome traditional synthetic challenges. Herein, the electropolymerization and characterization of four isoindigo‐based D−A copolymers are studied with: II‐EDOT‐T3, II‐Thio‐T3, II‐Thio‐T3‐TTDT2, and II‐EDOT‐T3‐TTDT2. Scanning electron microscopy (SEM) and energy dispersive X‐ray (EDX) analysis are used to confirm the composition of the polymers. Electrochemical impedance measurements show electron‐transport resistance (Re) values as low as 74.7 Ω at selected potentials, indicating that highly conductive copolymers are present. These p‐doped polymers exhibit absorption bands within the near‐infrared region (NIR) with optical band gaps as low as 0.790 eV. Results confirm the electro‐synthesized D−A copolymers exhibit excellent optical properties in the solid state and enhanced conductivity relative to conventional polymers; thus, affording materials with uses in a broad spectrum of applications. [ABSTRACT FROM AUTHOR]

Although isoindigo (IID)-based polymers can realize high charge mobility, these materials are currently confined to fullerene-based organic solar cells (OSCs). Herein, we designed a pair of alternative D-π-A type copolymers, PE71 and PE72, to expand the application in non-fullerene OSCs, where benzo[1,2-b:4,5-b′]thiophene (BDT), thieno[3,2-b]thiophene (TT) and IID units were used as D, A and π-bridge, respectively. The aim of optimizing the length of alkyl chains on TT bridge is to ensure polymer solubility, crystallinity as well as miscibility with acceptor molecules. We find that PE71 and PE72 exhibit similar optical and electronic properties, but PE71 with shorter hexyl chain tends to aggregate into fiber-like structure. In the end, Y6 is selected as the electron acceptor because of suitable energy levels and complementary absorption spectrum. Finally, PE71:Y6 device realizes a power conversion efficiency (PCE) of 12.03%, which is obviously higher than that of PE72:Y6 device (9.74%) and is also the highest value for IID-based photovoltaic polymers. The charge transport, molecular aggregation, film morphology and energy loss analysis were systematically investigated. The improved photovoltaic performance of PE71:Y6 mainly originates from the better interpenetrating network structure toward facilitating exciton seperation and free charge carrier transportation. Our results indicate that IID-based D-π-A polymers can also be utilized in non-fullerene OSCs and the alkyl chains on the thieno [3,2-b]thiophene π-bridge have a vital effect on the photovoltaic performance. [ABSTRACT FROM AUTHOR]

To optimize the energy levels of the structural framework of isoindigo polymers, a series of asymmetric isoindigo based low bandgap polymers with chlorine, fluorine and thiazole substituents was constructed and their optical, electrochemical and photovoltaic properties were comparatively evaluated for the impact of different substitutions. In comparison with the polymer based on 2,2'‐bithiophene and isoindigo unit (PTi) with non‐substituted bithiophene as the donor moiety, the highest occupied molecular orbital energy level for the newly synthesized polymers is significantly decreased, and in turn an improvement of the open‐circuit voltage (VOC) is noted in the corresponding photovoltaic devices. More importantly, combined with a low bandgap of 1.32 eV, the energy losses (Eloss) could be reduced to 0.61 eV for polymer based on chlorinated 2,2'‐bithiophene and isoindigo unit (PCl). In addition, the halogen moieties are observed to be superior in device fabrication and give better values than the thiazole substituent. Both fluorinated and chlorinated polymer donors exhibited improved performance compared with the original polymer PTi. Consequently, this work not only presents the influence of different electron withdrawing substituents on the physicochemical and photovoltaic performance, but also backs the concept of how to reduce the energy loss via the heteroatom effect. © 2020 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Triethylene glycol, a common side chain, is attached to two different dye moieties, diketopyrrolopyrrole (DPP) and isoindigo (II), and their bromo derivative monomers are copolymerized, respectively, with common bisstannyl alkylated bithiophene via Stille coupling. The resulting donor–acceptor low‐bandgap copolymers, namely, PTDPP‐DT and PTII‐DT, are rationally deigned and synthesized conjugated polymeric systems suitable for doping. Both polymers are successfully investigated as single‐component and composite‐system‐based electrochemical transistors and light‐emitting electrochemical cells. A PTDPP‐DT thin film exhibits relatively high electrical conductivity of up to 80 S cm−1 in the electrochemically doped state, whereas PTII‐DT thin film prevents the macroscopic charge transport due to a large‐scale crystalline disorientation. Upon evaluating both polymers as active conjugated materials in light‐emitting electrochemical cells, they both exhibit emission under efficient electron/hole doping conditions. [ABSTRACT FROM AUTHOR]

Singlet fission (SF) holds the potential to boost the maximum power conversion efficiency of photovoltaic devices. Internal conversion (IC) has been considered as one of the major competitive deactivation pathways to transform excitation energy into heat. Now, using time‐resolved spectroscopy and theoretical calculation, it is demonstrated that, instead of a conventional IC pathway, an unexpected intramolecular singlet fission (iSF) process is responsible for excited state deactivation in isoindigo derivatives. The 1TT state could form at ultrafast rate and nearly quantitatively in solution. In solid films, the slipped stacked intermolecular packing of a thiophene‐functionalized derivative leads to efficient triplet pair separation, giving rise to an overall triplet yield of 181 %. This work not only enriches the pool of iSF‐capable materials, but also contributes to a better understanding of the iSF mechanism, which could be relevant for designing new SF sensitizers. [ABSTRACT FROM AUTHOR]

Singlet fission (SF) holds the potential to boost the maximum power conversion efficiency of photovoltaic devices. Internal conversion (IC) has been considered as one of the major competitive deactivation pathways to transform excitation energy into heat. Now, using time‐resolved spectroscopy and theoretical calculation, it is demonstrated that, instead of a conventional IC pathway, an unexpected intramolecular singlet fission (iSF) process is responsible for excited state deactivation in isoindigo derivatives. The 1TT state could form at ultrafast rate and nearly quantitatively in solution. In solid films, the slipped stacked intermolecular packing of a thiophene‐functionalized derivative leads to efficient triplet pair separation, giving rise to an overall triplet yield of 181 %. This work not only enriches the pool of iSF‐capable materials, but also contributes to a better understanding of the iSF mechanism, which could be relevant for designing new SF sensitizers. [ABSTRACT FROM AUTHOR]

Highlights: A donor–acceptor–donor (D–A–D) conjugated small molecule IID-ThTPA with narrow singlet–triplet energy gap is synthesized via acceptor-oriented molecular design. IID-ThTPA nanoparticles exhibit not only competitive photothermal conversion efficiency (35.4%), but also a dramatically high singlet oxygen quantum yield (84.0%). IID-ThTPA nanoparticles enable superior cooperative tumor PTT/PDT eradicating capability both in vitro and in vivo.Simultaneous photothermal therapy (PTT) and photodynamic therapy (PDT) is beneficial for enhanced cancer therapy due to the synergistic effect. Conventional materials developed for synergistic PTT/PDT are generally multicomponent agents that need complicated preparation procedures and be activated by multiple laser sources. The emerging monocomponent diketopyrrolopyrrole (DPP)-based conjugated small molecular agents enable dual PTT/PDT under a single laser irradiation, but suffer from low singlet oxygen quantum yield, which severely restricts the therapeutic efficacy. Herein, we report acceptor-oriented molecular design of a donor–acceptor–donor (D–A–D) conjugated small molecule (IID-ThTPA)-based phototheranostic agent, with isoindigo (IID) as selective acceptor and triphenylamine (TPA) as donor. The strong D–A strength and narrow singlet–triplet energy gap endow IID-ThTPA nanoparticles (IID-ThTPA NPs) high mass extinction coefficient (18.2 L g−1 cm−1), competitive photothermal conversion efficiency (35.4%), and a dramatically enhanced singlet oxygen quantum yield (84.0%) comparing with previously reported monocomponent PTT/PDT agents. Such a high PTT/PDT performance of IID-ThTPA NPs achieved superior tumor cooperative eradicating capability in vitro and in vivo. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This personal account describes the pursuit of non‐fullerene acceptors designed from simple and accessible organic pi‐conjugated building blocks and assembled through efficient direct (hetero)arylation cross‐coupling protocols. Initial materials development focused on isoindigo and diketopyrrolopyrrole organic dyes flanked by imide‐based terminal acceptors. Efficiencies in solution‐processed organic solar cells were modest but highlighted the potential of the material design. Materials performance was improved through structural engineering to pair perylene diimide with these organic dyes. Optimization of active layer processing and solar cell device fabrication identified the perylene diimide flanked diketopyrrolopyrrole structure as the best framework, with fullerene‐free organic solar cells achieving power conversion efficiencies above 6 %. This material has met our criteria for a simple wide band gap fullerene alternative for pairing with a range of donor polymers. [ABSTRACT FROM AUTHOR]

Diketopyrrolopyrrole and isoindigo are commercially important dyes that have recently found broad application as electron acceptor and light‐absorbing groups in organic semiconductors. Their self‐assembly into specific supramolecular structures to control optoelectronic properties has been hampered by limited options for substitution and their high propensity for crystallization. Reported here is a molecular design that directs self‐assembly into previously elusive columnar mesophases of π‐π stacking cores. Although attachment of bis(trisoctyloxyphenyl)‐1,3,5‐triazine groups to both ends of diketopyrrolopyrrole‐thiophene and isoindigo cores generated mesomorphic dyes of similar overall shapes and dimensions, distinct differences in their mesomorphism and optoelectronic properties were observed. Piling up after all: Diketopyrrolopyrrole and isoindigo have long resisted self‐assembly into columnar π‐π stacks but their conversion into board‐shaped planar structures supports columnar mesomorphism over a wide temperature range. The presented generic molecular design has little effect on the optical and electronic properties of the dye cores but provides ample opportunity for tuning self‐assembly. [ABSTRACT FROM AUTHOR]

Abstract: A library of N,N-substituted isoindigo derivatives were prepared by reaction of isoindigo with a variety of alkylating agents in the presence of MeONa under mild conditions in yields of 65-80%. A new, more efficient synthesis of (3Z,3′Z)-3,3′-(ethane-1,2-diylidene)bis(indolin-2-one) is described by reaction of oxindole with glyoxal at reflux in methanol—a small library of N,N′-substituted derivatives were also prepared in 60-70% yield.Graphical abstract: [ABSTRACT FROM AUTHOR]

A gold‐catalyzed dimerization of 3‐diazooxindoles was developed, delivering isoindigos as products. The reaction shows broad substrate scope and functional group tolerance by affording various substituted isoindigos. Moreover, the method also exhibited high efficiency on a gram‐scale reaction. [ABSTRACT FROM AUTHOR]

ABSTRACT: The synthesis, characterization, and solar cell application of newly developed two semiconducting polymers containing phenanthro[1,2‐b:8,7‐b′]dithiophene (PDT) and an isoindigo (IID) unit are described. In addition, a relationship between substitution position of side chains and molecular weights of the polymers and their solar cell performance are also discussed. Because of the installation of alkyl side chains onto sterically less hindered positions, PDT‐IID copolymers 12OD‐2 and 8OD‐2 have stronger intermolecular interaction than that of the previously reported copolymer 12OD. In low‐Mn polymers 12OD‐2 and 8OD‐2 formed high‐crystalline thin film with higher face‐on ratio than that of 12OD, but their unsuitable large‐scale phase separation suppressed their efficient photocurrent generation, leading to poor PCE of 2–3%. However, the surface morphology of 12OD‐2 and 8OD‐2 blended films are drastically improved by increasing Mn, which leads to the enhancement of Jsc and higher PCE of up to 4.3%. However, high‐Mn polymers 12OD‐2 and 8OD‐2 formed high‐crystalline film with about 10–15% lower face‐on ratio than that of high‐Mn polymer 12OD, leading to poor hole transporting ability, and thus lower Jsc and PCE. From this result, too much strong intermolecular interaction promotes the formation of unsuitable edge‐on orientation in blended films. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1757–1767 [ABSTRACT FROM AUTHOR]

Abstract: The first isoindigo (bi)radicals were obtained by proton coupled oxidation of their 4‐hydroxyaryl substituted precursors. Optical and magnetic spectroscopic studies revealed a singlet open‐shell biradicaloid electronic ground state for the bisphenoxyl‐isoindigo (<s2>=1.20) with a small singlet–triplet energy gap of 0.065 eV and a large biradical character of y=0.79 that was corroborated by temperature‐dependent EPR spectroscopy and quantum chemical calculations. The concept of kinetic blocking of the radical centers and delocalization of spin density into the electron‐withdrawing chromophore core of isoindigo offers an entry into a new class of exceptionally stable open‐shell functional materials based on organic colorants. [ABSTRACT FROM AUTHOR]

Poly(isoindigo- alt-3,4-difluorothiophene) (PIID[2F]T) analogues used as 'polymer acceptors' in bulk-heterojunction (BHJ) solar cells achieve >7 % efficiency when used in conjunction with the polymer donor PBFTAZ (model system; copolymer of benzo[1,2- b:4,5- b′]dithiophene and 5,6-difluorobenzotriazole). Considering that most efficient polymer-acceptor alternatives to fullerenes (e.g. PC61BM or its C71 derivative) are based on perylenediimide or naphthalenediimide motifs thus far, branched alkyl-substituted PIID[2F]T polymers are particularly promising non-fullerene candidates for 'all-polymer' BHJ solar cells. [ABSTRACT FROM AUTHOR]

Poly(isoindigo- alt-3,4-difluorothiophene) (PIID[2F]T) analogues used as 'polymer acceptors' in bulk-heterojunction (BHJ) solar cells achieve >7 % efficiency when used in conjunction with the polymer donor PBFTAZ (model system; copolymer of benzo[1,2- b:4,5- b′]dithiophene and 5,6-difluorobenzotriazole). Considering that most efficient polymer-acceptor alternatives to fullerenes (e.g. PC61BM or its C71 derivative) are based on perylenediimide or naphthalenediimide motifs thus far, branched alkyl-substituted PIID[2F]T polymers are particularly promising non-fullerene candidates for 'all-polymer' BHJ solar cells. [ABSTRACT FROM AUTHOR]

A high-yield and simple synthesis of certain aminomethylisatins bearing dye fragments via the Mannich reaction of isatin with amino-containing azobenzenes was reported. It was found that the absence of electron-donating groups in azo-dye molecule prevents aminomethylation of isatin. The effect of the incorporation of an isatin moiety with an azobenzene dye in one molecule on its absorption and electrochemical behavior was studied using UV spectroscopy and cyclic voltammetry. [ABSTRACT FROM AUTHOR]

This study investigates the effect of the molecular structure of three different donor units, naphthalene (Np), bithiophene (BT), and thiophene-vinylene-thiophene (TVT), in isoindigo (IIG)-based donor -acceptor conjugated polymers (PIIG-Np, PIIG-BT and PIIG-TVT) on the charge carrier mobility of organic field-effect transistors (OFETs). The charge transport properties of three different IIG-based polymers strongly depend on donor units. PIIG-BT OFETs showed 50 times higher hole mobility (0.63 cm2 V−1 s−1) than PIIG-TVT and PIIG-Np ones of ≈ 0.01 cm2 V−1 s−1 with CYTOP dielectric though the BT units have less planarity than the TVT and Np units. The reasons for the different mobility in IIG-based polymers are studied by analyzing the energy structure by absorption spectra, calculating transport levels by density functional theory, investigating the in- and out-of-plane crystallinity of thin film by grazing-incidence wide-angle X-ray scattering, and extracting key transport parameters via low-temperature measurements. By combining theoretical, optical, electrical, and structural analyses, this study finds that the large difference in OFET mobility mainly originates from the transport disorders determined by the different microcrystal structure, rather than the intrinsic transport properties in isolated chains for different polymers. [ABSTRACT FROM AUTHOR]

The article describes the synthesis and characterization of a conjugated polymer with alternating isoindigo (II) and naphthalene (NT) units (PII-NT) and a small molecule. Topics covered include the factors limiting the development of p-type polymers for organic solar cells, the possible reason behind the low molecular weight of PII-NT and the measurement of the oxidation and reduction onset potentials of PII-NT.

Two novel side-chain conjugated polymers, PTBT-TID and PTBT-TTID, based on the new synthetic thiophene- benzne-thiophene (TBT) unit, side-chain isoindigo (ID) unit, and the introduced thiophene π-bridge, have been designed and synthesized. The photophysical, electrochemical and photovoltaic properties of the two polymers have been systematically investigated. The two polymers possess relatively good solubility as well as excellent thermal stability up to 380°C, and all of the polymer solar cell (PSC) devices based on the two polymers obtain high open circuit voltage (Voc) of about 0.8 V. The polymer solar cells based on the polymer PTBT-TID show relatively higher efficiencies than the PTBTTTID- based ones, due to the broader absorption spectrum, a relatively higher hole mobility, a lower HOMO (the highest occupied molecular orbital) energy level, a stronger IPCE (the incident photon to current conversion efficiency) response and a better microphase separation, Consequently, the device based on PTBT-TID:PC61BM (1:2, by weight) gives the best power conversion efficiency (PCE) of 2.04%, with a short-circuit current density (Jsc) of 5.39 mA·cm–2, an open-circuit voltage (Voc) of 0.83 V, and a fill factor (FF) of 0.45. [ABSTRACT FROM AUTHOR]

ABSTRACT Two novel ID-based water-soluble conjugated polymers (+)-PIDPV and (−)-PIDPV were synthesized by Heck coupling reaction. These two polyelectrolytes are both consisted of isoindigo units and phenylenevinylene units. In the UV-vis absorption spectra, both (+)-PIDPV and (−)-PIDPV exhibit broad absorption bands that almost cover the whole visible region. Photophysical investigations reveal that the fluorescence of water-soluble PPV can be efficiently quenched by oppositely charged PIDPV at a very low concentration. Cationic PPV shows an efficient quenching effect with ΚSV = 1.01 × 106 M−1 in the presence of (−)-PIDPV while the anionic PPV gives a lager quenching constant with ΚSV = 1.71 × 106 M−1 in the presence of (+)-PIDPV. Furthermore, the blend films of water-soluble PPVs and oppositely charged PIDPV also exhibit excellent quenching effect. These properties suggest that (+)-PIDPV and (−)-PIDPV are promising materials in the application of ionic photoactive layer in the organic solar cells. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 2223-2237 [ABSTRACT FROM AUTHOR]

Two solution-processable small organic molecules, (E)-6,6'-bis(4-(diphenylamino)phenyl)-1,1'-bis(2-ethylhexyl)-(3,3'-biindolinylidene)-2,2'-dione (coded as S10) and (E)-6,6'-di(9H-carbazol-9-yl)-1,1'-bis(2-ethylhexyl)-(3,3'-biindolinylidene)-2,2'dione (coded as S11) were successfully designed, synthesized and fully characterized. S10 and S11 are based on a donor-acceptor-donor structural motif and contain a common electron accepting moiety, isoindigo, along with different electron donating functionalities, triphenylamine and carbazole, respectively. Ultraviolet-visible absorption spectra revealed that the use of triphenylamine donor functionality resulted in an enhanced intramolecular charge transfer transition and reduction of optical band gap, when compared with its carbazole analogue. Both of these materials were designed to be donor semiconducting components, exerted excellent solubility in common organic solvents, showed excellent thermal stability, and their promising optoelectronic properties encouraged us to scrutinize charge-carrier mobilities using solution-processable organic field effect transistors. Hole mobilities of the order of 2.2 × 10-4 cm²/Vs and 7.8 × 10-3 cm²/Vs were measured using S10 and S11 as active materials, respectively. [ABSTRACT FROM AUTHOR]

ABSTRACT Reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization is becoming an important technique to synthesize the latex of block copolymers. A previous study showed that in the synthesis of polystyrene- b-poly(butyl acrylate)- b-polystyrene triblock copolymer via RAFT emulsion polymerization using amphiphilic oligo(acrylic acid-styrene) macroRAFT as surfactant and mediator, the molecular weight distribution could be much broadened to PDI higher than 2. In this study, an in-depth investigation was performed to decrease PDI. It was found that long-chain branches could be formed in the synthesis of triblock block copolymer, leading to the appearance of a higher molecular weight shoulder in the GPC curve of the final product. The lower neutralization degree of acrylic acid (AA) units on the macroRAFT and shorter AA chains would help to suppress the formation the long-chain branches, leading to PDI around 1.5. It is evidenced that the successful suppression is due to the promotion of radical entry as a result of decreased interfacial transport impedance. It is also evidenced that the presence of styrene during the polymerization of butyl acrylate could promote the formation of long chain branches. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1464-1473 [ABSTRACT FROM AUTHOR]

ABSTRACT New isoindigo and di(thienyl)ethylene-containing π-extended conjugated polymers with different branched side chains were synthesized to investigate their physical properties and device performance in thin-film transistors and photovoltaic cells. 11-Butyltricosane (S3) and 11-heptyltricosane (S6) groups were used as side-chain moieties tethered to isoindigo units. The linking groups between the polymer backbone and bifurcation point in the branched side chain differ in the two polymers (i.e., PIDTE-S3 and PIDTE-S6). The polymers bearing S6 side chains showed much better charge transport behavior than those with S3 side chains. Thermally annealed PIDTE-S6 film exhibited an outstanding hole mobility of 4.07 cm2 V−1 s−1 under ambient conditions. Furthermore, bulk heterojunction organic photovoltaic cells made from a blend film of PIDTE-S3 and (6,6)-phenyl C61-butyric acid methyl ester demonstrated promising device performance with a power conversion efficiency in the range of 4.9-5.0%. © 2015 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 2015, 53, 1226-1234 [ABSTRACT FROM AUTHOR]

[Figure not available: see fulltext.] In this review we generalize and analyze information about reactions between isatin and three-, four-, and five-coordinate phosphorus compounds, published between 1966 and 2014. [ABSTRACT FROM AUTHOR]

Two new solution-processible platinum(II) polyyne polymers P1 and P2 bridged by diketopyrrolopyrrole and isoindigo units have been synthesized via the CuI-catalyzed dehydrohalogenation reaction of the platinum(II) chloride precursors and the corresponding diacetylene ligands. The photophysical and electrochemical properties of P1 and P2 were investigated. These metallo-organic polymers have relatively narrow bandgaps of around 1.58-1.70 eV and broad absorption bands which are favorable for harvesting solar energy. [ABSTRACT FROM AUTHOR]

The synthesis of a new thieno[3,2- b]thiophene isoindigo (iITT) based monomer unit, and its subsequent incorporation into a series of alternating copolymers is reported. Copolymerisation with benzothiadiazole, bithiophene and thiophene comonomer units by palladium catalysed cross coupling gives three new narrow band gap semiconducting polymers for OFET applications. Extending the fused nature of the isoindigo core serves to further enhance molecular orbital overlap along the polymer backbones and facilitate good charge transport characteristics thus demonstrating the potential of extending the fused ring system that is attached to the isoindigo core. When used as the semiconducting channel in top-gate/bottom-contact OFET devices, good ambipolar properties are observed, with hole and electron mobilities up to 0.4 cm2/Vs and 0.7 cm2/Vs respectively. The three new polymers show good stability, with high temperature annealing showing an increase in the crystallinity of the polymers which corresponds directly to charge carrier mobility improvement as shown by X-ray diffraction, atomic force microscopy and photothermal deflection spectroscopy. [ABSTRACT FROM AUTHOR]

Depending on the structure of the substituent at the nitrogen atom of the heterocycle, reaction of isoindigo derivatives with hydrazine hydrate leads to the formation of either oxindole derivatives, or to a substituted isatin-3-hydrazone. [ABSTRACT FROM AUTHOR]

A selected set of substituted pyridone-annelated isoindigos 3a-f has been synthesized via interaction of 5- and 6-substituted oxindoles 2a-f with 6-ethyl-1,2,9- trioxopyrrolo[3,2-f]quinoline-8-carboxylic acid (1) in acetic acid at reflux. Among these isoindigos, the 5'-chloro and 5'-bromo derivatives 3b and 3d show strong and selective antiproliferative activities against a panel of human hematological and solid tumor cell-lines, but not against noncancerous cells, suggesting their potential use as anticancer agents. In all the tested cell lines, compound 3b was a 25%-50% more potent inhibitor of cell growth than 3d, suggesting the critical role of the substitution at 5'-position of the benzo-ring E. The IC50 values after 48 hours incubation with the 5'-chloro compound 3b were 6.60 μM in K562, 8.21 μM in THP-1, 8.97 μM in HepG2, 11.94 μM in MCF-7 and 14.59 μM in Caco-2 cancer cells, while the IC50 values in noncancerous HEK-293 and L-929 were 30.65 μM and 40.40 μM, respectively. In addition, compound 3b induced higher levels apoptosis in K562 cells than 3d, as determined by annexin V/7-AAD flowcytometry analysis. Therefore, further characterization of the antitproliferative mechanisms of compounds 3b and 3d may provide a novel chemotherapeutic agents. [ABSTRACT FROM AUTHOR]

Three random conjugated polymers, RP-TiI, RP-2TiI and RP-TVTiI based on both thieno[3,4- c]pyrrole-4,6-dione and isoindigo units have been synthesized by Stille cross-coupling reaction. The optical and electrochemical properties of new polymers have been investigated. The resulted polymers showed broad absorption spectra and appropriate energy levels for polymer solar cell applications. The bulk heterojunction devices based on the blend of the polymer RP-TiI and PC61BM showed a power conversion efficiency of 1.75%. [ABSTRACT FROM AUTHOR]

The article discusses a study on the synthesis and characterization of phenothiazine-isoindigo copolymers for photovoltaic applications. Topics covered include the chemical structure of phenothiazine II (PPT-II) copolymers confirmed via its proton nuclear magnetic resonance (NMR) spectrum, the polydispersion and solubility of PPT-II, and the onsets of oxidation and reduction potential of PPT-II.

Two donor-acceptor copolymers (P1 and P2) containing isoindigo as the acceptor unit and the benzodithiophene and bisthiophene-dithieno[3,2-b:2′,3′-d]-pyrrole as the donor unit have been designed and synthesized by the Pd-catalyzed Stille coupling reaction. The copolymers show broad and flat absorption, exhibit good solubility, and thermal stability, but possess optical bandgaps of 1.62 and 1.42 eV, respectively, and different donor-acceptor distance, of which the former is shorter than the later. The power conversion efficiency of the polymer solar cells based on P2:PC61BM (1:1 wt%) reached 1.86% with open-circuit voltage of 0.54 V and a short-circuit current of 6.36 mA/cm2, under the illumination of AM 1.5, 100 mW/cm2. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

An efficient green condensation reaction has been developed for synthesis of trans-isoindigo derivatives using SBA-Pr-SOH with pore size of 6 nm as a heterogeneous nanoporous acid catalyst under solvent-free conditions. Isoindigo derivatives have many industrial applications, e.g., dyes, drugs, organic solar cells, and semiconductor memories. The antimicrobial activities of these compounds have also been tested. [ABSTRACT FROM AUTHOR]

A novel class of thieno[3,2-b]thiophene (TT) and isoindigo based copolymers were synthesized and evaluated as electron donor and hole transport materials in bulk-heterojunction polymer solar cells (BHJ PSCs). These π-conjugated donor-acceptor polymers were derived from fused TT and isoindigo structures bridged by thiophene units. The band-gaps and the highest occupied molecular orbital (HOMO) levels of the polymers were tuned using different conjugating lengths of thiophene units on the main chains, providing band-gaps from 1.55 to 1.91 eV and HOMO levels from −5.34 to −5.71 eV, respectively. The corresponding lowest unoccupied molecular orbital (LUMO) levels were appropriately adjusted with the isoindigo units. Conventional BHJ PSCs (ITO/PEDOT:PSS/active layer/interlayer/Al) with an active layer composed of the polymer and PC71BM were fabricated for evaluation. Power conversion efficiency from a low of 1.25% to a high of 4.69% were achieved with the best performing device provided by the D−π−A polymer with a relatively board absorption spectrum, high absorption coefficient, and more uniform blend morphology. These results demonstrate the potential of this class of thieno[3,2-b]thiophene-isoindigo-based polymers as efficient electron donor and hole transport polymers for BHJ PSCs. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 [ABSTRACT FROM AUTHOR]