Fast Photoswitchable Order-Disorder Transitions in Liquid-Crystalline Block Co-oligomers

Unusual photo-tunable mechanical transformation of azobenzene terminated aliphatic polycarbonate

Human substance needsśś have been enriched by the development of smart-responsive materials possessing unique responsiveness and mechanical variability. However, acquiring these features in photoresponsive energy-driven elastomers is challengeable but highly desirable. Here, we report fabrication of physically-crosslinked elastomers based on an aliphatic polycarbonate terminated with one azobenzene derivative as the end group. Upon irradiation of UV light, the aliphatic polycarbonate shows unusual mechanical transformation from trans-azobenzene-rich elasticity to cis-azobenzene-rich plasticity, which is contrary to the photo-triggered mechanics of other azopolymers. This indicates that stronger interaction may be established between the terminated cis-azobenzenes and the benzene rings in the side chain of polymer, leading to a higher crosslinking density appeared in the cis-azobenzene-rich sample. This azobenzene-terminated polymer is an energy-driven elastomer, which has photo-switchable supramolecular interactions, showing photo-tunable mechanical properties (the half-life period of the cis-azobenzene is 16.9 h). More interestingly, the photoinduced mechanical change occurs at room temperature, enabling the aliphatic polycarbonate to behave as non-thermally switchable ultra-strong adhesive for different substrates, which is specifically suitable for smart dressings to promote wound healing. This switchable mechanical feature of elastomers may be a reference for smart elastomers towards advanced applications.

Moderate Active Hydrogen Generation over a Ni2P/CoP Heterostructure for One-Step Electrosynthesizing of Azobenzene with High Selectivity

Through hydrogenation and N-N coupling, azobenzene can be produced via highly selective electrocatalytic nitrobenzene reduction, offering a mild, cost-effective, and sustainable industrial route. Inspired by the density functional theory calculations, the introduction of H* active Ni2P into CoP, which reduces the water dissociation energy barrier, optimizes H* adsorption, and moderates key intermediates' adsorption, is expected to assist its hydrogenation ability for one-step electrosynthesizing azobenzene. A self-supported NiCo@Ni2P/CoP nanorod array electrode was synthesized, featuring NiCo alloy nanoparticles within a Ni2P/CoP shell. By virtue of the thermodynamically optimal Ni2P/CoP heterostructure, along with overall fast electron transport in a core-shell integrated electrode, NiCo@Ni2P/CoP with abundant interfacial structure attains a great nitrobenzene conversion of 94.3%, especially prominent azobenzene selectivity of 97.2%, and Faradaic efficiency of 94.1% at -0.9 V (vs Hg/HgO). High-purity azobenzene crystals can also self-separate under refrigeration postelectrolysis. This work provides an energy-efficient and scalable pathway for the economical preparation of azobenzene in the electrocatalytic nitrobenzene hydrogenation.

Self-assembled nanostructured membranes with tunable pore size and shape from plant-derived materials

Nanostructured materials derived from sustainable sources are of interest as viable alternatives to traditional petroleum-derived sources in membrane applications due to environmental concerns. Here, we present the development of pore size-tunable nanostructured polymer membranes based on a plant-derived material. The membranes were fabricated using a tri-functional amine as the templating core species and a cross-linkable ligand synthesized from rose oil-derived citronellol. The self-assembly of a supramolecular complex between the template core and the ligand forms a hexagonally packed columnar (Colh) mesophase, the dimensions of which can be precisely controlled by changing the stoichiometric ratio between these constituents. Within the hexagonal mesophase stoichiometric range, the pore size of the nanostructured membranes can be tuned from 1.0 to 1.3 nm, with a step size of approximately 0.1 nm. The membranes exhibited a clear distinction in molecular size selectivity, as demonstrated by dye adsorption experiments. The membrane fabricated with a ligand-to-core ratio of 3 to 1 demonstrated shape-based selectivity, exhibiting a higher permeability for propeller-shaped penetrants and highlighting its potential for shape-selective transport. We anticipate that this straightforward approach, using plant-derived materials, can contribute to important sustainability aspects while enhancing the performance of current state-of-the-art nanostructured membranes by enabling precise control over pore size.

Ionic nanoporous membranes from self-assembled liquid crystalline brush-like imidazolium triblock copolymers

There is a need to generate mechanically and thermally robust ionic nanoporous membranes for separation and fuel cell applications. Herein, we report a general approach to the preparation of ionic nanoporous membranes through custom synthesis, self-assembly, and subsequent chemical manipulations of ionic brush block copolymers. We synthesized polynorbornene-based triblock copolymers containing imidazolium cations balanced by counter anions in the central block, side-chain liquid crystalline units, and sidechain polylactide end blocks. This unique platform comprises: (1) imidazolium/bis(trifluoromethanesulfonyl)imide (TFSI) as the middle block, which has an excellent ion-exchange ability, (2) cyanobiphenyl liquid crystalline end block, a sterically hindered hydrophobic segment, which is chemically stable and immune to hydroxide attack, (3) polylactide brush-like units on the other end block that is easily etched under mild alkaline conditions and (4) a polynorbornene backbone, a lightly crosslinked system that offers mechanical robustness. These membranes retain their morphology before and after backbone crosslinking as well as etching of polylactide sidechains. The ion exchange performance and dimensional stability of these membranes were investigated by water uptake capability and swelling ratio. Moreover, the length of the carbon spacer in the imidazolium/TFSI central block moiety endowed the membrane with improved ionic conductivity. The ionic nanoporous materials are unusual due to their singular thermal, mechanical, alkaline stability and ion transport properties. Applications of these materials include electrochemical actuators, solid-state ionic nanochannel biosensors, and ion-conducting membranes.

Overcoming the entropy of polymer chains by making a plane with terminal groups: a thermoplastic PDMS with a long-range 1D structural order

Due to its unique physical and chemical properties, polydimethylsiloxane (PDMS) is widely used in many applications, in which covalent cross-linking is commonly used to cure the fluidic polymer. The formation of a non-covalent network achieved through the incorporation of terminal groups that exhibit strong intermolecular interactions has also been reported to improve the mechanical properties of PDMS. Through the design of a terminal group capable of two-dimensional (2D) assembly, rather than the generally used multiple hydrogen bonding motifs, we have recently demonstrated an approach for inducing long-range structural ordering of PDMS, resulting in a dramatic change in the polymer from a fluid to a viscous solid. Here we present an even more surprising terminal-group effect: simply replacing a hydrogen with a methoxy group leads to extraordinary enhancement of the mechanical properties, giving rise to a thermoplastic PDMS material without covalent cross-linking. This finding would update the general notion that less polar and smaller terminal groups barely affect polymer properties. Based on a detailed study of the thermal, structural, morphological and rheological properties of the terminal-functionalized PDMS, we revealed that 2D assembly of the terminal groups results in networks of PDMS chains, which are arranged as domains with long-range one-dimensional (1D) periodic order, thereby increasing the storage modulus of the PDMS to exceed its loss modulus. Upon heating, the 1D periodic order is lost at around 120 °C, while the 2D assembly is maintained up to ∼160 °C. The 2D and 1D structures are recovered in sequence upon cooling. Due to the thermally reversible, stepwise structural disruption/formation as well as the lack of covalent cross-linking, the terminal-functionalized PDMS shows thermoplastic behavior and self-healing properties. The terminal group presented herein, which can form a 'plane', might also drive other polymers to assemble into a periodically ordered network structure, thereby allowing for significant modulation of their mechanical properties.

Multiple Azoarenes Based Systems - Photoswitching, Supramolecular Chemistry and Application Prospects

In the recent decades, the investigations on photoresponsive molecular systems with multiple azoarenes are quite popular in diverse perspectives ranging from fundamental understanding of multiple photoswitches, supramolecular chemistry, and various application prospects. In fact, several insightful and conceptual designs of such systems were investigated with architectural distinctions. In particular, the demonstration of applications such as data storage with the help of multistate or orthogonal photoswitches, light modulation of catalysis via cooperative switching, sensors using supramolecular host-guest interactions, and materials such as liquid crystals, grating, actuators, etc. are some of the milestones in this area. Herein, we cover the recent advancements in the research areas of multiazoarenes containing systems that have been classified into Type-1 {linear, non-linear, and core-based (A)}, Type-2 {tripodal C₃ -symmetric (C3)} and Type-3 {macrocyclic (M)} structural motifs.