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Materials that undergo shape morphing in response to external stimuli have numerous applications, e.g., in soft robotics and biomedical devices. Shape memory polymers utilize kinetically trapped states to, typically irreversibly, transfer between a programmed morphed shape and an equilibrium shape. Liquid crystal elastomers (LCEs), in turn, can undergo reversible actuation in response to several stimuli. This study combines the irreversible and reversible shape morphing processes to obtain LCEs that undergo shape‐programming via the shape memory effect and subsequent reversible actuation of the programmed shape. This is enabled by an LCE crosslinked via dynamic hydrogen bonds that break at high temperatures and reform upon cooling, endowing the shape memory effect, while mild thermal or photothermal stimulation yields the reversible actuation. Through this combination, proof‐of‐concept robotic application scenarios such as grippers that can adjust their shape for grabbing different‐sized objects and crawling robots that can morph their shape to adapt to constrained spaces, are demonstrated. It is anticipated that this work adds new diversity to shape‐programmable soft microrobotics. [ABSTRACT FROM AUTHOR]

A common way of determining the majority charge carriers of pristine and doped semiconducting polymers is to measure the sign of the Seebeck coefficient. However, a polarity change of the Seebeck coefficient has recently been observed to occur in highly doped polymers. Here, it is shown that the Seebeck coefficient inversion is the result of the density of states filling and opening of a hard Coulomb gap around the Fermi energy at high doping levels. Electrochemical n‐doping is used to induce high carrier density (>1 charge/monomer) in the model system poly(benzimidazobenzophenanthroline) (BBL). By combining conductivity and Seebeck coefficient measurements with in situ electron paramagnetic resonance, UV–vis–NIR, Raman spectroelectrochemistry, density functional theory calculations, and kinetic Monte Carlo simulations, the formation of multiply charged species and the opening of a hard Coulomb gap in the density of states, which is responsible for the Seebeck coefficient inversion and drop in electrical conductivity, are uncovered. The findings provide a simple picture that clarifies the roles of energetic disorder and Coulomb interactions in highly doped polymers and have implications for the molecular design of next‐generation conjugated polymers. [ABSTRACT FROM AUTHOR]

Shape‐changing polymeric materials have gained significant attention in the field of bioinspired soft robotics. However, challenges remain in versatilizing the shape‐morphing process to suit different tasks and environments, and in designing systems that combine reversible actuation and self‐healing ability. Here, we report halogen‐bonded liquid crystal elastomers (LCEs) that can be arbitrarily shape‐programmed and that self‐heal under mild thermal or photothermal stimulation. We incorporate halogen‐bond‐donating diiodotetrafluorobenzene molecules as dynamic supramolecular crosslinks into the LCEs and show that these relatively weak crosslinks are pertinent for their mechanical programming and self‐healing. Utilizing the halogen‐bonded LCEs, we demonstrate proof‐of‐concept soft robotic motions such as crawling and rolling with programmed velocities. Our results showcase halogen bonding as a promising, yet unexplored tool for the preparation of smart supramolecular constructs for the development of advanced soft actuators. [ABSTRACT FROM AUTHOR]

Shape‐changing polymeric materials have gained significant attention in the field of bioinspired soft robotics. However, challenges remain in versatilizing the shape‐morphing process to suit different tasks and environments, and in designing systems that combine reversible actuation and self‐healing ability. Here, we report halogen‐bonded liquid crystal elastomers (LCEs) that can be arbitrarily shape‐programmed and that self‐heal under mild thermal or photothermal stimulation. We incorporate halogen‐bond‐donating diiodotetrafluorobenzene molecules as dynamic supramolecular crosslinks into the LCEs and show that these relatively weak crosslinks are pertinent for their mechanical programming and self‐healing. Utilizing the halogen‐bonded LCEs, we demonstrate proof‐of‐concept soft robotic motions such as crawling and rolling with programmed velocities. Our results showcase halogen bonding as a promising, yet unexplored tool for the preparation of smart supramolecular constructs for the development of advanced soft actuators. [ABSTRACT FROM AUTHOR]

Operational stability is essential for the success of organic electrochemical transistors (OECTs) in bioelectronics. The oxygen reduction reaction (ORR) is a common electrochemical side reaction that can compromise the stability of OECTs, but the relationship between ORR and materials degradation is poorly understood. In this study, the impact of ORR on the stability and degradation mechanisms of thiophene‐based OECTs is investigated. The findings show that an increase in pH during ORR leads to the degradation of the polymer backbone. By using a protective polymer glue layer between the semiconductor channel and the aqueous electrolyte, ORR is effectively suppressed and the stability of the OECTs is significantly improved, resulting in current retention of nearly 90% for ≈2 h cycling in the saturation regime. [ABSTRACT FROM AUTHOR]

Photoisomerization of azobenzenes from their stable E isomer to the metastable Z state is the basis of numerous applications of these molecules. However, this reaction typically requires ultraviolet light, which limits applicability. In this study, we introduce disequilibration by sensitization under confinement (DESC), a supramolecular approach to induce the E-to-Z isomerization by using light of a desired color, including red. DESC relies on a combination of a macrocyclic host and a photosensitizer, which act together to selectively bind and sensitize E-azobenzenes for isomerization. The Z isomer lacks strong affinity for and is expelled from the host, which can then convert additional E-azobenzenes to the Z state. In this way, the host-photosensitizer complex converts photon energy into chemical energy in the form of out-of-equilibrium photostationary states, including ones that cannot be accessed through direct photoexcitation. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of thermal degradation on polyetheretherketone (PEEK) fibres. PEEK samples were aged at a constant temperature of 250 °C for 1–128 days and characterized with mechanical tests, FTIR (Fourier Transform Infrared Spectroscopy), DSC (Differential Scanning Calorimetry), rheology, TGA (Thermogravimetric Analysis), SEM (Scanning Electron Microscopy), and UV–Vis diffuse reflectance spectroscopy. The short-term thermal annealing had a positive effect on the mechanical properties, due to the formation and growth of secondary crystals. Crosslinking in the material was verified by rheological inspections. The crosslinking increased the mechanical strength and modulus but reduced the elongation at break of the fibres. FTIR tests showed that carbonyl and hydroxyl groups were slowly formed on the surface of the fibres while ring opening reactions took place. The thermal ageing reduced the thermal stability of PEEK. The decreased stability was observed in the decomposition onset temperature after 8 d and in the melting point and the glass transition temperature after 32 d. The first signs of degradation, crosslinking, embrittlement, and reduced thermal stability, were visible roughly after 8 d of ageing, whereas the deterioration in general usability occurred after 64 d. [ABSTRACT FROM AUTHOR]

The effects of UV irradiation on polyetheretherketone (PEEK) fibres were investigated in this study. PEEK fibres were manufactured with a melt spinning system and then artificially aged with simulated solar UV light. Fibres were then characterized by mechanical tests, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), rheology, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). PEEK, best known for its excellent thermal stability, suffered greatly from the effects of UV irradiation. The low UV stability manifested as embrittlement of the fibres in the mechanical tests, increased crosslinking rate in the rheological tests, formation of carbonyl and hydroxyl groups and changes in the nature of the carbon–hydrogen bonds in the FTIR, diminished thermal properties in TGA, and transverse cracks in the SEM photos. DSC was found to be an inaccurate technique for estimating the degradation level of PEEK fibres, whereas the carbonyl index measured by FTIR was found to be the most convenient technique. [ABSTRACT FROM AUTHOR]

Organic electrochemical transistors (OECTs) have the potential to revolutionize the field of organic bioelectronics. To date, most of the reported OECTs include p‐type (semi‐)conducting polymers as the channel material, while n‐type OECTs are yet at an early stage of development, with the best performing electron‐transporting materials still suffering from low transconductance, low electron mobility, and slow response time. Here, the high electrical conductivity of multi‐walled carbon nanotubes (MWCNTs) and the large volumetric capacitance of the ladder‐type π‐conjugated redox polymer poly(benzimidazobenzophenanthroline) (BBL) are leveraged to develop n‐type OECTs with record‐high performance. It is demonstrated that the use of MWCNTs enhances the electron mobility by more than one order of magnitude, yielding fast transistor transient response (down to 15 ms) and high μC* (electron mobility × volumetric capacitance) of about 1 F cm−1 V−1 s−1. This enables the development of complementary inverters with a voltage gain of >16 and a large worst‐case noise margin at a supply voltage of <0.6 V, while consuming less than 1 µW of power. [ABSTRACT FROM AUTHOR]

The charge‐transfer (CT) interactions between organic compounds are reflected in the (opto)electronic properties. Determining and visualizing crystal structures of CT complexes are essential for the design of functional materials with desirable properties. Complexes of pyranine (PYR), methyl viologen (MV), and their derivatives are the most studied water‐based CT complexes. Nevertheless, very few crystal structures of CT complexes have been reported so far. In this study, the structures of two PYRs‐MVs CT crystals and a map of the noncovalent interactions using 3D electron diffraction (3DED) are reported. Physical properties, e.g., band structure, conductivity, and electronic spectra of the CT complexes and their crystals are investigated and compared with a range of methods, including solid and liquid state spectroscopies and highly accurate quantum chemical calculations based on density functional theory (DFT). The combination of 3DED, spectroscopy, and DFT calculation can provide important insight into the structure‐property relationship of crystalline CT materials, especially for submicrometer‐sized crystals. [ABSTRACT FROM AUTHOR]

The most critical challenge faced in realizing a high efficiency photoelectrochemical water splitting process is the lack of suitable photoanodes enabling the transfer of four electrons involved in the complex oxygen evolution reaction (OER). Uranium oxides are efficient catalysts due to their wide range optical absorption (Eg ≈ 1.8–3.2 eV), high photoconductivity, and multiple valence switching among uranium centers that improves the charge propagation kinetics. Herein, thin films of depleted uranium oxide (U3O8) are demonstrated grown via chemical vapor deposition effectively accelerate the OER in conjunction with hematite (α‐Fe2O3) overlayers through a built‐in potential at the interface. Density functional theory simulations demonstrate that the multivalence of U and Fe ions induce the adjustment of the band alignment subject to the concentration of interfacial Fe ions. In general, the equilibrium state depicts a type II band edge as the favored alignment, which improves charge‐transfer processes as observed in transient and X‐ray absorption (TAS and XAS) spectroscopy. The enhanced water splitting photocurrent density of the heterostructures (J = 2.42 mA cm−2) demonstrates the unexplored potential of uranium oxide in artificial photosynthesis. [ABSTRACT FROM AUTHOR]

The self-assembled monolayer (SAM)technique was employed to fabricate a two-layer donor–acceptorfilm on the surface of TiO2. The approach is based on usingdonor and acceptor compounds with anchoring groups of different lengths.The acceptor, a fullerene derivative, has a carboxyl anchor attachedto the fullerene moiety via a short linker that places the fullereneclose to the surface. The donor, a porphyrin derivative, is equippedwith a long linker that can penetrate between the fullerenes and keepporphyrin on top of the fullerene layer. The two-layer fullerene–porphyrinstructures were deposited on a mesoporous film of TiO2nanoparticlesby immersing the TiO2film sequentially into fullereneand porphyrin solutions. Transient absorption spectroscopy studiesof the samples revealed that after the selective photoexcitation ofporphyrin a fast (<5 ps) intermolecular electron transfer (ET)takes place from porphyrin to the fullerene layer, which confirmsthe formation of the interlayer donor–acceptor interface. Furthermore,in the second step of ET the fullerene anions donate electrons tothe TiO2nanoparticles. The latter reaction is relativelyslow with an average time constant of 230 ps. It involves roughlyhalf of the primary generated charges, and the second half relaxesby the interlayer charge recombination. The resulting state with aporphyrin cation and electron in TiO2has an extremelylong lifetime and recombines with an average time constant of 23 ms. [ABSTRACT FROM AUTHOR]