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The doping levels of conjugated polymers significantly influence their conductivity, energetics, and optical properties. Recently, a highly conductive n‐doped polymer called poly (3,7‐dihydrobenzo[1,2‐b:4,5‐b′]difuran‐2,6‐dione) (poly(benzodifurandione), n‐PBDF) is discovered, opening new possibilities for n‐type conducting polymers in printed electronics and other fields. Controlling the doping level of n‐PBDF is of great interest due to its wide range of potential applications. Here controlled dedoping and redoping of n‐PBDF is reported and a mechanistic understating of such a process is provided. Dedoping occurs through electron transfer and proton capture, wherein the ionic dopants, tris(4‐bromophenyl)ammoniumyl hexachloroantimonate (Magic Blue), exhibit efficient proton capture ability and stronger interaction with n‐PBDF, resulting in high dedoping efficiency. Moreover, chemically dedoped PBDF can be redoped using various proton‐coupled electron transfer agents. By manipulating the doping levels of n‐PBDF thin films, ranging from highly doped to dedoped states, the system demonstrates controllable conductivity in five orders of magnitude, adjustable optical properties, and energetics. As a result, these characteristics demonstrate the potential applications of n‐PBDF in organic electrochemical transistors and thermoelectrics. [ABSTRACT FROM AUTHOR]

Recently, solution‐processable n‐doped poly(benzodifurandione) (n‐PBDF) has been made through in‐situ oxidative polymerization and reductive doping, which exhibited exceptionally high electrical conductivities and optical transparency. The discovery of n‐PBDF is considered a breakthrough in the field of organic semiconductors. In the initial report, the possibility of structural defect formation in n‐PBDF was proposed, based on the observation of structural isomerization from (E)‐2H,2′H‐[3,3′‐bibenzofuranylidene]‐2,2′‐dione (isoxindigo) to chromeno[4,3‐c]chromene‐5,11‐dione (dibenzonaphthyrone) in the dimer model reactions. In this study, we present clear evidence that structural isomerization is inhibited during polymerization. We reveal that the dimer (BFD1) and the trimer (BFD2) can be reductively doped by several mechanisms, including hydride transfer, forming charge transfer complexes (CTC) or undergoing an integer charge transfer (ICT) with reactants available during polymerization. Once the hydride transfer adducts, the CTC, or the ICT product forms, structural isomerization can be effectively prevented even at elevated temperatures. Our findings provide a mechanistic understanding of why isomerization‐derived structural defects are absent in n‐PBDF backbone. It lays a solid foundation for the future development of n‐PBDF as a benchmark polymer for organic electronics and beyond. [ABSTRACT FROM AUTHOR]

Recently, solution‐processable n‐doped poly(benzodifurandione) (n‐PBDF) has been made through in‐situ oxidative polymerization and reductive doping, which exhibited exceptionally high electrical conductivities and optical transparency. The discovery of n‐PBDF is considered a breakthrough in the field of organic semiconductors. In the initial report, the possibility of structural defect formation in n‐PBDF was proposed, based on the observation of structural isomerization from (E)‐2H,2′H‐[3,3′‐bibenzofuranylidene]‐2,2′‐dione (isoxindigo) to chromeno[4,3‐c]chromene‐5,11‐dione (dibenzonaphthyrone) in the dimer model reactions. In this study, we present clear evidence that structural isomerization is inhibited during polymerization. We reveal that the dimer (BFD1) and the trimer (BFD2) can be reductively doped by several mechanisms, including hydride transfer, forming charge transfer complexes (CTC) or undergoing an integer charge transfer (ICT) with reactants available during polymerization. Once the hydride transfer adducts, the CTC, or the ICT product forms, structural isomerization can be effectively prevented even at elevated temperatures. Our findings provide a mechanistic understanding of why isomerization‐derived structural defects are absent in n‐PBDF backbone. It lays a solid foundation for the future development of n‐PBDF as a benchmark polymer for organic electronics and beyond. [ABSTRACT FROM AUTHOR]

The field of electronic textiles currently lacks n‐type polymer fibers that can complement the more established p‐type polymer fibers. Here, a highly conductive n‐type polymer fiber is obtained via wet‐spinning of n‐doped poly(3,7‐dihydrobenzo[1,2‐b:4,5‐b']difuran‐2,6‐dione) (n‐PBDF). The electrical conductivity of the fibers increases from 1000 to 1600 S cm−1 with increased draw during processing and correlates well with Young's modulus. Wide‐angle X‐ray scattering reveals the existence of a bimodal orientation of the polymer chains, favoring parallel alignment to the fiber axis with increased draw. After 14 d in 80% humid air, fiber conductivity stabilizes maintaining 81% of the initial conductivity. Although the electrical conductivity drops slightly over time, the Seebeck coefficient increases, resulting in the highest thermoelectric power factor being measured at 91 µW m−1 K−2 for the most drawn fiber 14 d after its fabrication. A proof‐of‐concept two‐couple thermoelectric textile is crafted by embroidering bundles of n‐type PBDF fibers and p‐type PEDOT:PSS fibers. The device generates 2.40 nW at a 22 °C temperature gradient. This work represents the initial steps and a crucial advancement toward fabricating high‐performance n‐type polymer fibers that can complement their p‐type counterparts to close the existing performance gap. [ABSTRACT FROM AUTHOR]

Optoelectronic synapses can perceive and memorize visual information, making them appealing for future bionic eyes or vision automation. Organic field-effect transistors are a promising platform for optoelectronic synaptic devices thanks to their flexibility and biocompatibility. However, charge screening effects occurring at channel–dielectric interfaces hinder the implementation of programmable multilevel memories. Here, we report photonic organic synapses based on photon-modulated electrochemical doping in electrochemical transistors, where light can manipulate ion insertion into the photoactive layer composed of donor–acceptor heterojunction interfaces. This enables high-density multilevel conductance modulation at low operating voltages (<1 V) and the imitation of ion flux-driven synaptic activity of living systems. The devices can recognize different optical signals and mimic the learning processes of the human brain. By exploiting the integrated functions of perception, processing and memorization of visual information, a single-layer synapse array acts as an artificial retina enabling facial recognition without the use of a complex artificial neural network. An optoelectronic synapse is realized by incorporating a photoactive layer in an organic electrochemical transistor. Writing and erasing multiple conductance states allow optical signals to be recognized and the learning process of the human brain to be mimicked. [ABSTRACT FROM AUTHOR]

Control of the spin angular momentum (SAM) carried in a photon provides a technologically attractive element for next-generation quantum networks and spintronics1–5. However, the weak optical activity and inhomogeneity of thin films from chiral molecular crystals result in high noise and uncertainty in SAM detection. Brittleness of thin molecular crystals represents a further problem for device integration and practical realization of chiroptical quantum devices6–10. Despite considerable successes with highly dissymmetric optical materials based on chiral nanostructures11–13, the problem of integration of nanochiral materials with optical device platforms remains acute14–16. Here we report a simple yet powerful method to fabricate chiroptical flexible layers via supramolecular helical ordering of conjugated polymer chains. Their multiscale chirality and optical activity can be varied across the broad spectral range by chiral templating with volatile enantiomers. After template removal, chromophores remain stacked in one-dimensional helical nanofibrils producing a homogeneous chiroptical layer with drastically enhanced polarization-dependent absorbance, leading to well-resolved detection and visualization of SAM. This study provides a direct path to scalable realization of on-chip detection of the spin degree of freedom of photons necessary for encoded quantum information processing and high-resolution polarization imaging.We report a simple method to fabricate chiroptical flexible layers via supramolecular helical ordering of conjugated polymer chains, providing direct, scalable realization of on-chip detection of the spin degree of freedom of photons. [ABSTRACT FROM AUTHOR]

Depolymerization is a promising strategy for recycling waste plastic into constituent monomers for subsequent repolymerization1. However, many commodity plastics cannot be selectively depolymerized using conventional thermochemical approaches, as it is difficult to control the reaction progress and pathway. Although catalysts can improve the selectivity, they are susceptible to performance degradation2. Here we present a catalyst-free, far-from-equilibrium thermochemical depolymerization method that can generate monomers from commodity plastics (polypropylene (PP) and poly(ethylene terephthalate) (PET)) by means of pyrolysis. This selective depolymerization process is realized by two features: (1) a spatial temperature gradient and (2) a temporal heating profile. The spatial temperature gradient is achieved using a bilayer structure of porous carbon felt, in which the top electrically heated layer generates and conducts heat down to the underlying reactor layer and plastic. The resulting temperature gradient promotes continuous melting, wicking, vaporization and reaction of the plastic as it encounters the increasing temperature traversing the bilayer, enabling a high degree of depolymerization. Meanwhile, pulsing the electrical current through the top heater layer generates a temporal heating profile that features periodic high peak temperatures (for example, about 600 °C) to enable depolymerization, yet the transient heating duration (for example, 0.11 s) can suppress unwanted side reactions. Using this approach, we depolymerized PP and PET to their monomers with yields of about 36% and about 43%, respectively. Overall, this electrified spatiotemporal heating (STH) approach potentially offers a solution to the global plastic waste problem.A depolymerization method is described that uses electrified spatiotemporal heating to selectively generate monomers from the commodity plastics polypropylene and poly(ethylene terephthalate), allowing control over the pyrolysis of plastic waste and reducing the formation of side products. [ABSTRACT FROM AUTHOR]

Doping plays a critical role in organic electronics, and dopant design has been central in the development of functional and stable doping. In this study, there is departure from conventional molecular dopants and a new class of dopants are reported – aromatic ionic dopants (AIDs). AIDs consist of a pair of aromatic cation and anion that are responsible for molecular doping reaction and charge balancing separately. It is shown that the first AID made from cycloheptatrienyl (tropylium) cation and pentacyanocyclopentadienide anion (PCCp), abbreviated as T‐PCCp, can function as an effective p‐type dopant to dope polydioxythiophenes. Here, tropylium cation induces the doping reaction while the PCCp anion stabilizes the generated polarons and bipolarons. With T‐PCCp, a highly doped (≈120 S/cm) and stable system is achieved up to 150 °C, an orthogonal (sequential)solution processing resulting from the immiscibility of the dopant and the polymer host, and a high‐resolution direct micropatterning with laser writing resulted from a thermally activated doping process. [ABSTRACT FROM AUTHOR]

2D organic–inorganic hybrid halide perovskites are promising semiconductor materials for a variety of device applications. However, fundamental issues of charge transport through multiple quantum wells separated by bulky organic ligands remain unsolved. Herein, a mixture of π‐conjugated organic ligands, (2‐(3‴,4′‐dimethyl‐[2,2′:5′,2′:5″,2‴‐quaterthiophen]‐5‐yl)ethan‐1‐ammonium iodide) (4Tm) and 2‐([2,2′‐bithiophen]‐5‐yl)ethan‐1‐aminium iodide (2T), is used as spacer to form (4Tm)x(2T)2−xSnI4 2D perovskite thin films. The new strategy of alloying 2T into 4Tm ligands reduces the interlayer distance (barrier thickness) while maintaining the relatively small energy barrier height for the hybrid quantum wells, enhances interlayer interactions, and improves charge transport across adjacent perovskite layers. Moreover, solar cell devices fabricated with (4Tm)x(2T)2−xSnI4 exhibit improved photovoltaic properties and stability. [ABSTRACT FROM AUTHOR]

The electrochromism of a water‐soluble naturally oxidized electrochromic polymer, ox‐PPE, is harnessed for rapid and facile bacterial detection, discrimination, and susceptibility testing. The ox‐PPE solution shows distinct colorimetric and spectroscopic changes within 30 min when mixed with live bacteria. For the underlying mechanism, it is found that ox‐PPE responds to the reducing species (e.g., cysteine and glutathione) released by metabolically active bacteria. This reduction reaction is ubiquitous among various bacterial strains, with a noticeable difference that enables discrimination of Gram‐negative and Gram‐positive bacterial strains. Combining ox‐PPE with antibiotics, methicillin‐susceptible and methicillin‐resistant Staphylococcus aureus can be differentiated within 2.5 h. Proof‐of‐concept demonstration of ox‐PPE for antimicrobial susceptibility testing is carried out by incubating Escherichia coli with various antibiotics. The obtained minimum inhibition concentrations are consistent with the conventional culture‐based methods, but with the procedure time significantly shortened to 3 h. [ABSTRACT FROM AUTHOR]

The design of functional interfaces is central to both fundamental and applied research in materials science and energy technology. We introduce a new, broadly applicable technique for the precisely controlled high‐throughput preparation of well‐defined interfaces containing polyatomic species ranging from small ions to nanocrystals and large protein complexes. The mass‐dispersive deposition of ions onto surfaces is achieved using a rotating‐wall mass analyzer, a compact device which enables the separation of ions using low voltages and has a theoretically unlimited mass range. We demonstrate an efficient deposition of singly charged Au144(SC4H9)60 ions (33.7 kDa), which opens up exciting opportunities for the structural characterization of nanocrystals and their assemblies using transmission electron microscopy. Our approach also enables the high‐throughput deposition of mass‐selected ions from multicomponent mixtures, which is of interest to the controlled preparation of surface gradients and rapid screening of molecules in mixtures for a specific property. [ABSTRACT FROM AUTHOR]

The design of functional interfaces is central to both fundamental and applied research in materials science and energy technology. We introduce a new, broadly applicable technique for the precisely controlled high‐throughput preparation of well‐defined interfaces containing polyatomic species ranging from small ions to nanocrystals and large protein complexes. The mass‐dispersive deposition of ions onto surfaces is achieved using a rotating‐wall mass analyzer, a compact device which enables the separation of ions using low voltages and has a theoretically unlimited mass range. We demonstrate an efficient deposition of singly charged Au144(SC4H9)60 ions (33.7 kDa), which opens up exciting opportunities for the structural characterization of nanocrystals and their assemblies using transmission electron microscopy. Our approach also enables the high‐throughput deposition of mass‐selected ions from multicomponent mixtures, which is of interest to the controlled preparation of surface gradients and rapid screening of molecules in mixtures for a specific property. [ABSTRACT FROM AUTHOR]

The repetitive size change of the electrode over cycles, termed as mechanical breathing, is a crucial issue limiting the quality and lifetime of organic electrochromic devices. The mechanical deformation originates from the electron transport and ion intercalation in the redox active material. The dynamics of the state of charge induces drastic changes of the microstructure and properties of the host, and ultimately leads to structural disintegration at the interfaces. We quantify the breathing strain and the evolution of the mechanical properties of poly(3,4-propylenedioxythiophene) thin films in-situ using customized environmental nanoindentation. Upon oxidation, the film expands nearly 30% in volume, and the elastic modulus and hardness decrease by a factor of two. We perform theoretical modeling to understand thin film delamination from an indium tin oxide (ITO) current collector under cyclic load. We show that toughening the interface with roughened or silica-nanoparticle coated ITO surface significantly improves the cyclic performance. Though organic electrochromic devices are promising for various applications, their performance is limited by a cyclic change in volume of the material over time. Here, the authors study mechanical breathing in a model polymer and provide rules for the design of new mechanically-reliable materials. [ABSTRACT FROM AUTHOR]

Thermomechanical properties of polymers highly depend on their glass transition temperature (Tg). Differential scanning calorimetry (DSC) is commonly used to measure Tg of polymers. However, many conjugated polymers (CPs), especially donor–acceptor CPs (D–A CPs), do not show a clear glass transition when measured by conventional DSC using simple heat and cool scan. In this work, we discuss the origin of the difficulty for measuring Tg in such type of polymers. The changes in specific heat capacity (Δcp) at Tg were accurately probed for a series of CPs by DSC. The results showed a significant decrease in Δcp from flexible polymer (0.28 J g−1 K−1 for polystyrene) to rigid CPs (10−3 J g−1 K−1 for a naphthalene diimide‐based D–A CP). When a conjugation breaker unit (flexible unit) is added to the D–A CPs, we observed restoration of the Δcp at Tg by a factor of 10, confirming that backbone rigidity reduces the Δcp. Additionally, an increase in the crystalline fraction of the CPs further reduces Δcp. We conclude that the difficulties of determining Tg for CPs using DSC are mainly due to rigid backbone and semicrystalline nature. We also demonstrate that physical aging can be used on DSC to help locate and confirm the glass transition for D‐A CPs with weak transition signals. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1635–1644 [ABSTRACT FROM AUTHOR]

Electrochromic devices (ECDs) that modulate optical transmission or reflection in a controllable manner are attractive in energy-saving and colour-tuning applications. In this review, we discuss the key components, fundamental working principles and performance metrics of ECDs using layman's terms. We also highlight recent materials development of each component and illustrate how the structure–property relationships impact their processability, device performance and stability. We further introduce emerging materials that exhibit electrochromic properties, and discuss the transition from laboratory-scale, half-cell-based characterisations of electrochromic materials to the fabrication of solid-state electrochromic devices and evaluation of their performances. Finally, we lay out major challenges for fabricating large-scale and cost-effective ECDs, particularly the materials design and fabrication strategies for achieving chemically and electrochemically stable, high performance ECDs that can be produced by roll-to-roll techniques. [ABSTRACT FROM AUTHOR]

Blending two or more π-conjugated polymers together provides a means of manipulating charge transport properties and potentially improving the performance of organic thermoelectrics. Previous results have shown that π-conjugated polymer blends can display higher Seebeck coefficients than either of the individual polymers; however, significantly increased power factors and improved thermoelectric performance in polymer blends as compared to the individual polymers has not yet been demonstrated. The purpose of this work is to theoretically and experimentally probe how the electronic properties of the individual polymers influence the Seebeck coefficient, electrical conductivity, and power factor in polymer blends. Specifically, the influence of energetic disorder, energy offsets between the transport states in the two polymers, and charge-carrier localization lengths are investigated based on a theoretical model introduced by Arkhipov and Bässler. These calculations show that gains in the power factor should be attainable when the two polymers have a small (e.g., 0.1–0.2 eV) offset in their density of states (DOS) distributions and the polymer with the higher energy DOS has a wider DOS distribution and a larger localization length. Experimentally, power factors in an appropriate polymer blend are demonstrated to exceed the power factors of the individual polymers by nearly two-fold. Through the applied theoretical and experimental approach, this work provides guidance in regards to the energetics, density of states, and charge-carrier mobilities for designing higher performing organic thermoelectrics with π-conjugated polymer blends. [ABSTRACT FROM AUTHOR]

Incorporation of acceptor‐acceptor (A‐A) type moieties into donor‐acceptor (D‐A) type conjugated polymers becomes a new strategy to tune their electronic properties. In this work, we first demonstrate an efficient convergent route to prepare isoindigo‐based A‐A type building blocks ‐ bis‐isoindigos ‐ via the palladium‐catalyzed oxidative coupling. Bis‐isoindigo‐based polymers show high planarity and delocalized frontier molecular orbitals with lowered LUMO and intact HOMO energy levels, in comparison with their corresponding mono‐isoindigo counterparts. Moreover, fluorine substitution on donors only lowers HOMO levels of Bis‐IID polymers. This study asserts that the D‐A‐A strategy is effective in selectively tuning FMO energy levels of conjugated polymers, complementary to the D‐D‐A approach for the HOMO energy level tuning. Isoindigo‐based A‐A type building blocks, bis‐isoindigos, were synthesized by the palladium‐catalyzed oxidative coupling. Bis‐isoindigo‐based polymers show high planarity and delocalized frontier molecular orbitals with selective tuning ability of LUMO/HOMO levels, complementary to the D‐D‐A approach for the HOMO energy level tuning. [ABSTRACT FROM AUTHOR]

Chemical doping is widely used to manipulate the electrical and thermoelectric properties of organic semiconductors, yet intelligent design of polymer–dopant systems remains elusive. It is challenging to predict the electrical and thermoelectric properties of doped organic semiconductors due to the large number of variables impacting these properties, including film morphology, dopant and polymer energetics, dopant size, and degree of polaron delocalization. Herein, a series of dopants with varying sizes and electron affinities (EAs) are combined with polymers of differing ionization energies (IEs) to investigate how the difference between polymer IE and dopant EA influences the doping efficiency and electrical conductivity, and how the dopant size influences the thermoelectric properties. Our experiments demonstrate that at low doping levels the doping efficiency strongly depends on the difference between the polymer IE and dopant EA; the effectiveness of doping on increasing electrical conductivity drastically decreases at high loadings for the molybdenum dithiolene complexes, while FeCl3 remains effective at high loadings; and the large molybdenum complexes lead to more delocalized polarons as compared to FeCl3. To take advantage of the complementary doping characteristics of the molybdenum complexes and FeCl3, both dopants are employed simultaneously to reach high power factors at relatively low dopant concentrations. [ABSTRACT FROM AUTHOR]

Abstract: A scalable and green approach to manufacture semiconducting microfibers from polymer melts has been demonstrated. The polymer chains are highly aligned along the microfiber's long axis direction and exhibit highly anisotropic optical properties. In addition, the polymer microfibers show good flexibility and stretchability with a yield point around 10% under a reversible stress and can be stretched up to 180% without breaking. These features are desired for future flexible, stretchable, and conformable electronics. The origin of this stretchability is studied with diketopyrrolopyrrole derivatives using different conjugation break spacers and side chains. In addition, stretchable conducting microfibers can be obtained by doping with FeCl3, which are further evaluated as organic conductors and source/drain electrodes in organic field‐effect transistors. [ABSTRACT FROM AUTHOR]

Abstract: Semiconducting polymer thin films, which are usually formed by solution‐casting from their organic solutions, are critical in the development of flexible and printed electronics. To seek out a method that can further improve the electrical properties of semiconducting polymers and also be industrially applicable is of vital significance. In this study, the impact of zone annealing on the charge‐transport properties of diketopyrrolopyrrole‐based complementary semiconducting polymer blends in field‐effect transistor devices is investigated. An average mobility increased from 0.66 to 0.87 cm2 V−1 s−1, with a highest of 1.6 cm2 V−1 s−1, is observed. It is also demonstrated that zone annealing can be integrated with melt processing to realize a solvent‐free process for polymer thin films for organic field‐effect transistors (OFETs) and achieve improved charge transport characteristics with a record mobility of 0.54 cm2 V−1 s−1 among melt‐processed OFETs. This work provides an alternative, green, and sustainable processing method to advance polymer‐based organic electronics. [ABSTRACT FROM AUTHOR]

Porous materials are ubiquitous in nature and have found a wide range of applications because of their unique absorption, optical, mechanical, and catalytic properties. Large surface-area-to-volume ratio is deemed a key factor contributing to their catalytic properties. Here, it is shown that introducing tunable nanopores (50-700 nm) to organic semiconductor thin films enhances their reactivity with volatile organic compounds by up to an order of magnitude, while the surface-area-to-volume ratio is almost unchanged. Mechanistic investigations show that nanopores grant direct access to the highly reactive sites otherwise buried in the conductive channel of the transistor. The high reactivity of nanoporous organic field-effect transistors leads to unprecedented ultrasensitive, ultrafast, selective chemical sensing below the 1 ppb level on a hundred millisecond time scale, enabling a wide range of health and environmental applications. Flexible sensor chip for monitoring breath ammonia is further demonstrated; this is a potential biomarker for chronic kidney disease. [ABSTRACT FROM AUTHOR]

The first general open-flask synthesis of amine–boranes with inexpensive and readily available reagents, such as sodium borohydride, sodium bicarbonate, water, and the desired amines is described. Even amines bearing borane-reactive functionalities, such as alkene, alkyne, hydroxyl, thiol, ester, amide, nitrile, and nitro are well tolerated. Some of these novel amine–boranes represent stable molecules containing potentially incompatible electrophilic and nucleophilic centers in proximity. This convenient scalable synthesis provides a novel class of organic ligands for surface functionalization, as demonstrated by the formation of self-assembled layers of thiol- and alkoxysilane-bearing amine–boranes on gold and silica surfaces, respectively. [ABSTRACT FROM AUTHOR]

Increasing the flexibility of polymer chains is a common method of increasing the deformability of solid polymeric materials. Here, the effects of 'conjugation-break spacers' (CBSs)-aliphatic units that interrupt the sp2-hybridized backbone of semiconducting polymers-on the mechanical and photovoltaic properties of a diketopyrrolopyrrole-based polymer are described. Unexpectedly, the tensile moduli and cracking behavior of a series of polymers with repeat units bearing 0%, 30%, 50%, 70%, and 100% of the CBS are not directly related to the percent incorporation of the flexible unit. Rather, the mechanical properties are a strong function of the order present in the film as determined by grazing-incidence x-ray diffraction. The effect of the CBSs on the photovoltaic performance of these materials, on the other hand, is more intuitive: it decreases with increasing fraction of the flexible units. These studies highlight the importance of solid-state packing structure-as opposed to only the flexibility of the individual molecules-in determining the mechanical properties of a conjugated polymer film for stretchable, ultraflexible, and mechanically robust electronics. [ABSTRACT FROM AUTHOR]

Temperature-dependent (80-350 K) charge transport in polymer semiconductor thin films is studied in parallel with in situ X-ray structural characterization at equivalent temperatures. The study is conducted on a pair of isoindigo-based polymers containing the same π-conjugated backbone with different side chains: one with siloxane-terminated side chains (PII2T-Si) and the other with branched alkyl-terminated side chains (PII2T-Ref). The different chemical moiety in the side chain results in a completely different film morphology. PII2T-Si films show domains of both edge-on and face-on orientations (bimodal orientation) while PII2T-Ref films show domains of edge-on orientation (unimodal orientation). Electrical transport properties of this pair of polymers are also distinctive, especially at high temperatures (>230 K). Smaller activation energy ( EA) and larger pre-exponential factor ( μ0) in the mobility-temperature Arrhenius relation are obtained for PII2T-Si films when compared to those for PII2T-Ref films. The results indicate that the more effective transport pathway is formed for PII2T-Si films than for the other, despite the bimodally oriented film structure. The closer π-π packing distance, the longer coherence length of the molecular ordering, and the smaller disorder of the transport energy states for PII2T-Si films altogether support the conduction to occur more effectively through a system with both edge-on and face on orientations of the conjugated molecules. Reminding the 3D nature of conduction in polymer semiconductor, our results suggest that the engineering rules for advanced polymer semiconductors should not simply focus on obtaining films with conjugated backbone in edge-on orientation only. Instead, the engineering should also encounter the contribution of the inevitable off-directional transport process to attain effective transport from polymer thin films. [ABSTRACT FROM AUTHOR]

A series of isoindigo-based conjugated polymers (PII2F-C mSi, m = 3-11) with alkyl siloxane-terminated side chains are prepared, in which the branching point is systematically 'moved away' from the conjugated backbone by one carbon atom. To investigate the structure-property relationship, the polymer thin film is subsequently tested in top-contact field-effect transistors, and further characterized by both grazing incidence X-ray diffraction and atomic force microscopy. Hole mobilities over 1 cm2 V−1 s−1 is exhibited for all soluble PII2F-C mSi ( m = 5-11) polymers, which is 10 times higher than the reference polymer with same polymer backbone. PII2F-C9Si shows the highest mobility of 4.8 cm2 V−1 s−1, even though PII2F-C11Si exhibits the smallest π-π stacking distance at 3.379 Å. In specific, when the branching point is at, or beyond, the third carbon atoms, the contribution to charge transport arising from π-π stacking distance shortening becomes less significant. Other factors, such as thin-film microstructure, crystallinity, domain size, become more important in affecting the resulting device's charge transport. [ABSTRACT FROM AUTHOR]

Photoacoustic imaging holds great promise for the visualization of physiology and pathology at the molecular level with deep tissue penetration and fine spatial resolution. To fully utilize this potential, photoacoustic molecular imaging probes have to be developed. Here, we introduce near-infrared light absorbing semiconducting polymer nanoparticles as a new class of contrast agents for photoacoustic molecular imaging. These nanoparticles can produce a stronger signal than the commonly used single-walled carbon nanotubes and gold nanorods on a per mass basis, permitting whole-body lymph-node photoacoustic mapping in living mice at a low systemic injection mass. Furthermore, the semiconducting polymer nanoparticles possess high structural flexibility, narrow photoacoustic spectral profiles and strong resistance to photodegradation and oxidation, enabling the development of the first near-infrared ratiometric photoacoustic probe for in vivo real-time imaging of reactive oxygen species-vital chemical mediators of many diseases. These results demonstrate semiconducting polymer nanoparticles to be an ideal nanoplatform for developing photoacoustic molecular probes. [ABSTRACT FROM AUTHOR]

Solution processable semiconducting polymers have been under intense investigations due to their diverse applications from printed electronics to biomedical devices. However, controlling the macromolecular assembly across length scales during solution coating remains a key challenge, largely due to the disparity in timescales of polymer assembly and high-throughput printing/coating. Herein we propose the concept of dynamic templating to expedite polymer nucleation and the ensuing assembly process, inspired by biomineralization templates capable of surface reconfiguration. Molecular dynamic simulations reveal that surface reconfigurability is key to promoting template-polymer interactions, thereby lowering polymer nucleation barrier. Employing ionic-liquid-based dynamic template during meniscus-guided coating results in highly aligned, highly crystalline donor-acceptor polymer thin films over large area (>1 cm2) and promoted charge transport along both the polymer backbone and the π-π stacking direction in field-effect transistors. We further demonstrate that the charge transport anisotropy can be reversed by tuning the degree of polymer backbone alignment. [ABSTRACT FROM AUTHOR]

A generic method to solution‐process nanoporous electronic thin films is demonstrated by Ying Diao and co‐workers in article number 1701117. The fabricated nanoporous electronic devices exhibit highly sensitive detection of volatile organic compounds below 1 ppb and could potentially be applied for personalized health and environmental monitoring. [ABSTRACT FROM AUTHOR]

A three dimensional nature of the charge transport is more effectively described by using the bimodally oriented polymer semiconductor films than unimodally oriented ones as long as good π‐stacking is attained in molecular scale. This finding, reported by D. R. Lee, M. S. Kang, D. H. Kim, and co‐workers on page 4627, enables another design or engineering consideration for advancing polymer semiconductor systems. [ABSTRACT FROM AUTHOR]