Rational design of benzotrithiophene-diketopyrrolopyrrole-containing donor-acceptor polymers for improved charge carrier transport

Iridium-Catalyzed [2 + 2 + 2] Cycloaddition of Bithiophen-Linked Diynes with Nitriles: Scope and Mechanistic Study with Quantum Chemical Calculation

We report a simple and atom-efficient method for the synthesis of bithiophene-fused isoquinolines by iridium-catalyzed [2 + 2 + 2] cycloaddition of bithiophene-linked diynes with nitriles. All three structural isomers of bithiophene-linked diynes underwent [2 + 2 + 2] cycloaddition, and the trend in the reactivity for cycloaddition was diyne 1 = diyne 3 > diyne 2. Dibenzothiophene-linked diyne also reacted with nitriles to form a variety of cycloadducts. Cycloaddition of bithiophene-linked diynes with alkynes and an isocyanate formed naphthodithiophenes and a 2-pyridone derivative, respectively. Cycloadducts bearing a 2-aminopyridine moiety and benzothiophene rings showed intense fluorescence at around 530 nm and gave a fluorescence quantum yield of 0.44. Furthermore, quantum chemical calculations provided insight into the origin of the difference in reactivity of three bithiophene-linked diynes. The different reactivities of the three diynes 1-3 are believed to originate from the step where an iridacyclopentadiene reacts with a coordinated nitrile to form azairidabicyclo[3.2.0]heptatriene. HOMOs of iridacyclopentadiene play a decisive role in this step.

Benzotrithiophene-based Covalent Organic Framework Photocatalysts with Controlled Conjugation of Building Blocks for Charge Stabilization

Covalent organic frameworks have recently shown high potential for photocatalytic hydrogen production. However, their structure-property-activity relationship has not been sufficiently explored to identify a research direction for structural design. Herein, we report the design and synthesis of four benzotrithiophene (BTT)-based covalent organic frameworks (COFs) with different conjugations of building units, and their photocatalytic activity for hydrogen production. All four BTT-COFs had slipped parallel stacking patterns with high crystallinity and specific surface areas. The change in the degree of conjugation was found to rationally tune the rate of photocatalytic hydrogen evolution. Based on the experimental and calculation results, the tunable photocatalytic performance could be mainly attributed to the electron affinity and charge trapping of the electron accepting units. This study provides important insights for designing covalent organic frameworks for efficient photocatalysts.

Tuning the nanostructure and molecular orientation of high molecular weight diketopyrrolopyrrole-based polymers for high-performance field-effect transistors

As a versatile class of semiconductors, diketopyrrolopyrrole (DPP)-based conjugated polymers are well suited for applications of next-generation plastic electronics because of their excellent and tunable optoelectronic properties via a rational design of chemical structures. However, it remains a challenge to unravel and eventually influence the correlation between their solution-state aggregation and solid-state microstructure. In this contribution, the solution-state aggregation of high molecular weight PDPP3T is effectively enhanced by solvent selectivity, and a fibril-like nanostructure with short-range and long-range order is generated and tuned in thin films. The predominant role of solvent quality on polymer packing orientation is revealed, with an orientational transition from a face-on to an edge-on texture for the same PDPP3T. The resultant edge-on arranged films lead to a significant improvement in charge transport in transistors, and the field-effect hole mobility reaches 2.12 cm² V^-1 s^-1 with a drain current on/off ratio of up to 10⁸. Our findings offer a new strategy for enhancing the device performance of polymer electronic devices.

Droplet-Based Techniques for Printing of Functional Inks for Flexible Physical Sensors

Printed electronics (PE) is an emerging technology that uses functional inks to print electrical components and circuits on variety of substrates. This technology has opened up new possibilities to fabricate flexible, bendable, and form-fitting devices at low-cost and fast speed. There are different printing technologies in use, among which droplet-based techniques are of great interest as they provide the possibility of printing computer-controlled design patterns with high resolution, and greater production flexibility. Nanomaterial inks form the heart of this technology, enabling different functionalities. To this end, intensive research has been carried out on formulating inks with conductive, semiconductive, magnetic, piezoresistive, and piezoelectric properties. Here, a detailed landscape view on different droplet-based printing technologies (inkjet, aerosol jet, and electrohydrodynamic jet) is provided, with comprehensive discussion on their working principals. This is followed by a detailed research overview of different functional inks (metal, carbon, polymer, and ceramic). Different sintering methods and common substrates being used in printed electronics are also discussed, followed by an in-depth review of different physical sensors fabricated by droplet-based techniques. Finally, the challenges facing the field are considered and a perspective on possible ways to overcome them is provided.

Synthesis and Electronic Properties of Diketopyrrolopyrrole-Based Polymers with and without Ring-Fusion

Diketopyrrolopyrroles (DPP) have been recognized as a promising acceptor unit for construction of semiconducting donor–acceptor (D–A) polymers, which are typically flanked by spacers such as thiophene rings via a carbon–carbon single bond formation. It may suffer from a decrease in the coplanarity of the molecules especially when bulky side chains are installed. In this work, the two N atoms in the DPP unit are further fused with C-3 of the two flanking thiophene rings, yielding a π-expanded, very planar fused-ring building block (DPPFu). A novel DPPFu-based D–A copolymer (PBDTT-DPPFu) was successfully synthesized, consisting of a benzo[1,2-b:4,5-b′]dithiophene (BDTT) unit as a donor and a DPPFu unit as an acceptor. For comparison, the unfused DPP-based counterpart PBDTT-DPP was also synthesized. Two dodecyl alkyl chains were attached to thiophene rings of DPP moieties to ensure good solubility of the DPPFu-based polymer. The influence of the ring-fusion effect on their structure, photophysical properties, electronic properties, molecular packing, and charge transport properties is investigated. Ring-fusion enhances the intermolecular interactions of PBDTT-DPPFu polymer chains as indicated by density functional theory calculation and analysis of electrostatic potential and van der Waals potential and results in significantly improved molecular packing for both the in-plane and out-of-plane directions as suggested by X-ray measurements. Finally, we correlate the molecular packing to the device performance by fabricating field-effect transistors based on these two polymers. The charge carrier mobility of the ring-fused polymer PBDTT-DPPFu is significantly higher as compared to the PBDTT-DPP polymer without ring-fusion, although PBDTT-DPPFu exhibited a much lower number-average molecular weight of 17 kDa as compared to PBDTT-DPP with a molecular weight of 108 kDa. The results from our comparative study provide a robust way to increase the interchain interaction by ring-fusion-promoted coplanarity.

Geometry Control of Source/Drain Electrodes in Organic Field-Effect Transistors by Electrohydrodynamic Inkjet Printing

In this work we study the influence of dielectric surface and process parameters on the geometry and electrical properties of silver electrodes obtained by electrohydrodynamic inkjet printing. The cross-section and thickness of printed silver tracks are optimized to achieve a high conductivity. Silver overprints with cross-section larger than 4 μm2 and thickness larger than 90 nm exhibit the lowest resistivity. To fabricate electrodes in the desired geometry, a sufficient volume of ink is distributed on the surface by applying appropriate voltage amplitude. Single and multilayer overprints are incorporated as bottom contacts in bottom gate organic field-effect transistors (OFETs) with a semiconducting polymer as active layer. The multilayer electrodes result in significantly higher electrical parameters than single layer contacts, confirming the importance of a careful design of the printed tracks for reliable device performance. The results provide important design guidelines for precise fabrication of electrodes in electronic devices by electrohydrodynamic inkjet printing.

A 2D donor–acceptor covalent organic framework with charge transfer for supercapacitors

A 2D covalent organic framework with intramolecular charge transfer, numerous redox-active groups and high electrical conductivity possesses a specific capacitance of 752 F g⁻¹ and an energy density of 57 W h kg⁻¹.

The Effects of Side Chains on the Charge Mobilities and Functionalities of Semiconducting Conjugated Polymers beyond Solubilities

Recent decades have witnessed the rapid development of semiconducting polymers in terms of high charge mobilities and applications in transistors. Significant efforts have been made to develop various conjugated frameworks and linkers. However, studies are increasingly demonstrating that the side chains of semiconducting polymers can significantly affect interchain packing, thin film crystallinity, and thus semiconducting performance. Ways to modify the side alkyl chains to improve the interchain packing order and charge mobilities for conjugated polymers are first discussed. It is shown that modifying the branching chains by moving the branching points away from the backbones can boost the charge mobilities, which can also be improved through partially replacing branching chains with linear ones. Second, the effects of side chains with heteroatoms and functional groups are discussed. The siloxane-terminated side chains are utilized to enhance the semiconducting properties. The fluorinated alkyl chains are beneficial for improving both charge mobility and air stability. Incorporating H bonding group side chains can improve thin film crystallinities and boost charge mobilities. Notably, incorporating functional groups (e.g., glycol, tetrathiafulvalene, and thymine) into side chains can improve the selectivity of field-effect transistor (FET)-based sensors, while photochromic group containing side chains in conjugated polymers result in photoresponsive semiconductors and optically tunable FETs.

A Quinacridone-Diphenylquinoxaline-Based Copolymer for Organic Field-Effect Transistors

In this work, we characterized poly(quinacridone-diphenylquinoxaline) (PQCTQx). PQCTQx was synthesized by a Suzuki coupling reaction and the synthesized PQCTQx was used as a polymeric semiconducting material in organic field-effect transistors (OFETs) to research the potential of using quinacridone derivatives. The measured field-effect mobility of the pristine PQCTQx film was 6.1 × 10⁻³ cm²/(V·s). A PQCTQx film heat-treated at 150 °C exhibited good field-effect performances with a hole mobility of 1.2 × 10⁻² cm²/(V·s). The improved OFET behaviors resulting from the mild thermal treatment was attributed to improved packing of the molecules in the film, as determined using X-ray diffraction, and to decreased channel resistance.

Molecular packing and morphological stability of dihydro-indeno[1,2-b]fluorenes in the context of their substitution pattern

The synthesis and structural characterization of a series of dihydroindeno[1,2-b]fluorene (IF) derivatives with various side chain substituents is reported.

Controlling the Surface Organization of Conjugated Donor-Acceptor Polymers by their Aggregation in Solution

The aggregation of conjugated polymers is found to have a significant influence on the surface organization of deposited films. Difluorobenzothiadiazole-based polymers show a strong pre-aggregation in solution, but the addition of 1,2,4-trichlorobenzene efficiently reduces such aggregates, leading to the transition of the surface organization from edge- to face-on orientation in deposited films.

Design directed self-assembly of donor-acceptor polymers

Donor-acceptor polymers with an alternating array of donor and acceptor moieties have gained particular attention during recent years as active components of organic electronics. By implementation of suitable subunits within the conjugated backbone, these polymers can be made either electron-deficient or -rich. Additionally, their band gap and light absorption can be precisely tuned for improved light-harvesting in solar cells. On the other hand, the polymer design can also be modified to encode the desired supramolecular self-assembly in the solid-state that is essential for an unhindered transport of charge carriers. This review focuses on three major factors playing a role in the assembly of donor-acceptor polymers on surfaces which are (1) nature, geometry and substitution position of solubilizing alkyl side chains, (2) shape of the conjugated polymer defined by the backbone curvature, and (3) molecular weight which determines the conjugation length of the polymer. These factors adjust the fine balance between attractive and repulsive forces and ensure a close polymer packing important for an efficient charge hopping between neighboring chains. On the microscopic scale, an appropriate domain formation with a low density of structural defects in the solution deposited thin film is crucial for the charge transport. The charge carrier transport through such thin films is characterized by field-effect transistors as basic electronic elements.

Diketopyrrolopyrrole-based polymer with a semi-fluorinated side chain for high-performance organic thin-film transistors

A semi-fluorinated DPP based polymer showed hole mobility about 3 times higher than did its non-fluorinated analogue.

Direct C–H arylation for various Ar-cored diketopyrrolopyrrole containing small molecules in solution-processed field-effect transistors

D–A–π–A–D small molecules Ar(DPPT₂)₂ are designed and synthesized by direct (hetero) C–H arylation, with hole mobility as high as 0.12 cm² V⁻¹ s⁻¹.

Dithieno[2,3-d;2′,3′-d]benzo[2,1-b;3,4-b‘]dithiophene: a novel building-block for a planar copolymer

A planar heteroacene building block, dithieno[2,3-d;2′,3′-d′]benzo[1,2-b;3,4-b′]dithiophene (DTmBDT), is reported via a facile synthetic procedure.

Tuning the optoelectronic properties of dual-acceptor based low-bandgap ambipolar polymers by changing the thiophene-bridge length

Dual-acceptor polymers based on DPP and TQ are prepared with very low bandgaps (0.6–0.9 eV) and ambipolar charge carrier transports.

Enhancing the organic thin-film transistor performance of diketopyrrolopyrrole–benzodithiophene copolymers via the modification of both conjugated backbone and side chain

A synthetic strategy for enhancing the OTFT performance of DPP–BDT copolymers is developed through the tuning of the bulky side chain position and modification of the conjugated backbone.

Bis(2-oxoindolin-3-ylidene)-benzodifuran-dione-based D–A polymers for high-performance n-channel transistors

Conjugated polymers based on a bis(2-oxoindolin-3-ylidene)-benzodifuran-dione (BIBDF) unit displayed promising performances for their application in organic thin-film transistors (OTFTs).

Synthesis of four-armed triphenylamine-based molecules and their applications in organic solar cells

Two wide band gap four-armed triphenylamine-based small molecule donors were synthesized and applied in organic solar cells.

Effects of cyano (CN)-groups on the planarity, film morphology and photovoltaic performance of benzodithiophene-based polymers

A class of polymers (POT-DH, POT-HCN and POT-DCN) were synthesized and they contain the same donor (BDT) and acceptor units but different numbers of cyano (CN)-groups, i.e. 0, 1 and 2.

Synthesis and photovoltaic properties of new donor–acceptor (D–A) copolymers based on benzo[1,2-b:3,4-b′:6,5-b′′] trithiophene donor and different acceptor units (P1 and P2)

A power conversion efficiency of about 5.26% has been achieved for the device based onP1:PC71BM.