Three polymorphs of a new N,N'-dipropylated isoindigo derivative.

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.

Enhanced N-type Semiconducting Performance of Asymmetric Monochlorinated Isoindigo-based Semiregioregular Polymers under Dynamic Forces.

The asymmetric monochlorination strategy not only effectively addresses the steric issues in conventional dichlorination but also enables the development of promising acceptor units and semiregioregular polymers. Herein, monochlorinated isoindigo (1CIID) is successfully designed and synthesized by selectively introducing single chlorine (Cl) atoms. Furthermore, the 1CIID copolymerizes with two donor counterparts, centrosymmetric 2,2'-bithiophene (2T) and axisymmetric 4,7-di(thiophen-2-yl)benzo[1,2,5]thiadiazole (DTBT), forming two polymers, P1CIID-2T and P1CIID-DTBT. These polymers exhibit notable differences in backbone linearity and dipole moments, influenced by the symmetry of their donor counterparts. In particular, P1CIID-2T, which contains a centrosymmetric 2T unit, demonstrates a linear backbone and a significant dipole moment of 10.20 D. These properties contribute to the favorable film morphology of P1CIID-2T, characterized by highly ordered crystallinity in the presence of fifth-order (500) X-ray diffraction peaks. Notably, P1CIID-2T exhibits a significant improvement in molecular alignment under dynamic force, resulting in over 8-fold improvement in the performance of organic field-effect transistor (OFET) devices, with superior electron mobility up to 1.22 cm2 V-1 s-1. This study represents the first synthesis of asymmetric monochlorinated isoindigo-based conjugated polymers, highlighting the potential of asymmetric monochlorination for developing n-type semiconducting polymers. Moreover, our findings provide valuable insights into the relationship between the molecular structure and properties.

Strategic Design of Hemi-Isoindigo Polymer for a Highly Sensitive and Selective All-Printed Flexible Nitrogen Dioxide Chemiresistive Sensor.

The study has developed two hemi-isoindigo (HID)-based polymers for printed flexible resistor-type nitrogen oxide (NO2 ) sensors: poly[2-ethylhexyl 3-((3'",4'-bis(dodecyloxy)-3,4-dimethoxy-[2,2':5',2'"-terthiophen]-5-yl)methylene)-2-oxoindoline-1-carboxylate] (P1) and poly[2-ethylhexyl 2-oxo-3-((3,3'",4,4'-tetrakis(dodecyloxy)-[2,2':5',2'"-terthiophen]-5-yl)methylene)indoline-1-carboxylate] (P2). These polymers feature thermally removable carbamate side chains on the HID units, providing solubility and creating molecular cavities after thermal annealing. These cavities enhance NO2 diffusion, and the liberated unsubstituted amide ─C(═O)NH─ groups readily form robust double hydrogen bonds (DHB), as demonstrated by computer simulations. Furthermore, both polymers possess elevated highest occupied molecular orbital (HOMO) energy levels of -4.74 and -4.77 eV, making them highly susceptible to p-doping by NO2 . Gas sensors fabricated from P1 and P2 films, anneal under optimized conditions to partially remove carbamate side chains, exhibit remarkable sensitivities of +1400% ppm-1 and +3844% ppm-1 , and low detection limit (LOD) values of 514 ppb and 38.9 ppb toward NO2 , respectively. These sensors also demonstrate excellent selectivity for NO2 over other gases.

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.

White Light to Near-IR Chargeable Single Component Photocapacitor Based on Donor-chromophore-Acceptor Dyes.

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.

Synthesis of 3,3'-(Ethane-1,2-diylidene)bis(indolin-2-one) Promoted by Thermally-activated Electron Transfer and Photoreduction of CO2 to CH4 and CO.

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.

Isoindigo-Thiophene D-A-D-Type Conjugated Polymers: Electrosynthesis and Electrochromic Performances.

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.

Enhancing the Performance of Electret-Free Phototransistor Memory by Using All-Conjugated Block Copolymer.

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.

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.

An Efficient Route to 3,3'-Biindolinylidene-diones by Iron-Catalyzed Dimerization of Isatins.

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.

From p- to n-Type Mixed Conduction in Isoindigo-Based Polymers through Molecular Design.

Organic mixed ionic and electronic conductors are of significant interest for bioelectronic applications. Here, three different isoindigoid building blocks are used to obtain polymeric mixed conductors with vastly different structural and electronic properties which can be further fine-tuned through the choice of comonomer unit. This work shows how careful design of the isoindigoid scaffold can afford highly planar polymer structures with high degrees of electronic delocalization, while subtle structural modifications can control the dominant charge carrier (hole or electron) when probed in organic electrochemical transistors. A combination of experimental and computational techniques is employed to probe electrochemical, structural, and mixed ionic and electronic properties of the polymer series which in turn allows the derivation of important structure-property relations for this promising class of materials in the context of organic bioelectronics. Ultimately, these findings are used to outline robust molecular-design strategies for isoindigo-based mixed conductors that can support efficient p-type, n-type, and ambipolar transistor operation in an aqueous environment.

Preparation and Electrochromic Properties of Benzodithiophene-Isoindigo Conjugated Polymers with Oligoethylene Glycol Side Chains.

Functional polymers featuring good processability in non-halogenated, benzene-free green solvents are highly desired due to health and environmental concerns. Herein, a series of novel D-A type conjugated polymers, PBDT-IIDs, are designed and successfully prepared by "green" functionalization of the polymers with highly hydrophilic, highly polar, highly flexible, and biocompatible oligoethylene glycol (OEG) side chains in order to improve the processability. These series polymers are named PBDT-IID2, PBDT-IID3, and PBDT-IID4, respectively, according to the number of oxygen atoms in the side chain. After confirmation by structural characterization, the basic properties of PBDT-IIDs are also investigated. With the increase in the OEG side chain length, the polymer PBDT-IID4 not only has good solubility in the halogen solvent chlorobenzene, but also exhibits excellent solubility in the green halogen-free solvent methyltetrahydrofuran (Me-THF). As a result, the green solvent Me-THF can also be applied to prepare PBDT-IIDs' electrochromic active layers, except for chlorobenzene and toluene. The electrochromism of PBDT IIDs under both positive and negative voltages has a practical application potential. The several controllable switches between dark green and khaki (0-0.6 V) are expected to show great potential in the field of military camouflage. Furthermore, according to the principle of red, green, and blue (RGB) mixing, light blue-green in the reduced state (-1.6 V) can be used in the preparation of complementary ECDs to provide one of the three primary colors (green).

Metallated Isoindigo-Porphyrin Covalent Organic Framework Photocatalyst with a Narrow Band Gap for Efficient CO2 Conversion.

Photocatalytic CO2 reduction into formate (HCOO-) has been widely studied with semiconductor and molecule-based systems, but it is rarely investigated with covalent organic frameworks (COFs). Herein, we report a novel donor-acceptor COF named Co-PI-COF composed of isoindigo and metallated porphyrin subunits that exhibits high catalytic efficiency (∼50 µmol formate g-1 h-1) at low-power visible-light irradiation and in the absence of rare metal cocatalysts. Density functional theory calculations and experimental diffuse-reflectance measurements are used to explain the origin of catalytic efficiency and the particularly low band gap (0.56 eV) in this material. The mechanism of photocatalysis is also studied experimentally and is found to involve electron transfer from the sacrificial agent to the excited Co-PI-COF. The observed high-efficiency conversion could be ascribed to the enhanced CO2 adsorption on the coordinatively unsaturated cobalt centers, the narrow band gap, and the efficient transfer of the charge originating from the postsynthetic metallation. It is anticipated that this study will pave the way toward the design of new simple and efficient catalysts for photocatalytic CO2 reduction into useful products.

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.

ß-Isoindigo-azaDIPYs: Fully Conjugated Hybrid Systems with Broad Absorption in the Visible Region.

A one-step synthetic pathway for the preparation of fully conjugated ß-isoindigo-azaDIPY hybrid chromophores comprised of ß-isoindigo and azadipyrromethene moieties is reported. The target compounds were characterized by spectroscopic, crystallographic, and theoretical methods and show unprecedented broad absorption across the visible region of the electromagnetic spectrum. The X-ray crystal structure of the octa(n-butyl)-ß-isoindigo-azaDIPY derivative revealed that a trans-configuration of the ß-isoindigo fragment accompanies a planar conjugated core.

Revealing the Nature of Singlet Fission under the Veil of Internal Conversion.

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 1 TT 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.

Molecular Design of Conjugated Small Molecule Nanoparticles for Synergistically Enhanced PTT/PDT.

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.

Synthesis and Density Functional Theory Studies of Azirinyl and Oxiranyl Functionalized Isoindigo and (3Z,3'Z)-3,3'-(ethane-1,2-diylidene)bis(indolin-2-one) Derivatives.

The design and synthesis of functionalized isoindigo compounds by reaction of isoindigo with (S)-glycidyl tosylate, epibromohydrin, 2-(bromomethyl)-1-(arylsulfonyl)aziridine, and 2-(bromomethyl)-1-(alkylsulfonyl)aziridine in the presence of MeONa proceed under mild conditions in moderate yields. (3Z,3'Z)-3,3'-(Ethane-1,2-diylidene)bis(1-(oxiran-2-ylmethyl)indolin-2-one), with an extended central olefin π-conjugated moiety was also reacted with methyl-oxiranes to give the corresponding N,N'-disubstituted derivative. Calculations with DFT and TD-DFT of hypothetical isoindigo-thiophene DA molecules with various electron withdrawing substituents, including aziridine, oxirane, nitrile, carbonyl, and sulfonate, indicated that the proximity and strength of the functional group have a significant effect on the HOMO, LUMO, vertical excitation energy, and oscillator strength of the π-π* transitions.

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.

Asymmetric Side-Chain Engineering of Isoindigo-Based Polymers for Improved Stretchability and Applications in Field-Effect Transistors.

Thus far, there is still no study systematically investigating the influence of asymmetric side-chain design on a polymer's stretchability and its associated stretchable device applications. Herein, three kinds of asymmetric side chains consisting of carbosilane side chain (Si-C8), siloxane-terminated side chain (SiO-C8), and decyltetradecane side chain (DT) are engineered in isoindigo-bithiophene (PII2T, P1-P3) and isoindigo-difluorobithiophene (PII2TF, P4-P6) conjugated polymers, and their structure-stretchability correlation is explored in field-effect transistor characterization. It is revealed that owing to the geometric difference between the side chains, different asymmetric side-chain combinations impose distinct influences on the molecular stacking and orientation of the derived polymers. Surprisingly, the combination of asymmetric side chains and backbone fluorination is shown to deliver the best stretchability and mechanical durability of the derived polymer. Consequently, P6 consisting of asymmetric Si-C8/DT side chains and fluorinated backbone possesses the best mobility preservation of 81% at 100% strain with the stretching force perpendicular to the charge-transporting direction. Moreover, it presents 90% mobility retention after 400 stretching-releasing cycles with 60% strain, greatly exceeding the value (36%) of the non-fluorinated counterpart (P3). Our results suggest that the rational design of asymmetric side chains and backbone fluorination provides an efficient way to enhance the intrinsic stretchability of conjugated polymers.