Baihao Shao

Hydrogels are indispensable for the development of next‐generation bioelectronics, soft robotics, and biomedical devices, where their mechanical properties determine performance and reliability. Among strategies to enhance hydrogel mechanics, phase separation enables controlled heterogeneity resulting in gel networks that are reinforced by more than just covalent bonds and polymer entanglements. By regulating the demixing of polymer‐rich and solvent‐rich domains, phase separation leads to architectures that couple strength, elasticity, and dynamic responsiveness. This article reviews the recent advances in designing high‐performance phase‐separated hydrogels by linking phase separation behavior within polymer networks to emergent properties such as toughness, fatigue resistance, adhesion, and stimuli‐responsiveness. We highlight how mesoscale organization governs multifunctional performance and demonstrate how these principles help resolve the key trade‐offs in critical applications, such as high‐pressure hemostatic sealants, low‐impedance bioelectronics, perfusable tissue engineering scaffolds, and adaptive soft robotics. Finally, we discuss critical challenges, including in situ characterization and scalability, and future opportunities like machine‐learning‐guided design, which are essential to translate phase separation from a materials heuristic into design rules for reliable, high‐performance hydrogel materials.

Pumping ions against a concentration gradient through protein-based transporters is a cornerstone of numerous biological processes. Mimicking this function by using artificial receptors remains a daunting challenge, mainly because of the difficulties in balancing between the requirement for high binding affinities and precise and on-demand ion capture and release properties. We report a trimeric hydrazone photoswitch-based receptor that converts light energy into work by actively transporting chloride anion against a gradient through a dichloromethane liquid membrane, functioning as a molecular pump. The system manifests ease of synthesis, bistability, excellent photoswitching properties, and superb ON-OFF binding properties (difference of up to six orders of magnitude).

In this work we apply a combination of steady state and time resolved luminescence and absorption spectroscopies to investigate the excited-state dynamics of a recently developed molecular photoswitch, belonging to the hydrazone family. The outstanding properties of this molecule, involving fluorescence toggling, bistability, high isomerization quantum yield and non-negligible two-photon absorption cross section, make it very promising for numerous applications. Here we show that the light induced Z/E isomerization occurs on a fast Z-form depends on solvent polarity, suggesting a partial charge transfer nature of its low lying excited state. Time-resolved luminescence measurements evidence the presence of a main emission component in the 500–520 nm spectral range, attributed to the Z-isomer, and a very short living blue-shifted emission, attributed to the E-isomer. Finally, transient absorption measurements performed upon far-red excitation are employed as an alternative method to determine the two-photon absorption cross-section of the molecule.

Two hydrazones featuring a unique excitation wavelength-dependent dual fluorescence emission have been developed.

The proliferation of light-activated switches in recent years has enabled their use in a broad range of applications encompassing an array of research fields and disciplines. All current systems, however, have limitations (e.g., from complicated synthesis to incompatibility in biologically relevant media and lack of switching in the solid-state) that can stifle their real-life application. Here we report on a system that packs most, if not all, the desired, targeted and sought-after traits from photochromic compounds (bistability, switching in various media ranging from serum to solid-state, while exhibiting ON/OFF fluorescence emission switching, and two-photon assisted near-infrared light toggling) in an easily accessible structure.

Strain has been used as a tool to modulate the reactivity (e.g., mechanochemistry) and thermal isomerization kinetics of photochromic compounds. Macrocylcization is used to build-up strain in such systems, and in general the reactivity and rates increase with the decrease in macrocycle size. To ascertain the effect of strain on recently reported bistable hydrazone photoswitches, we incorporated them into macrocycles having varying aliphatic linker lengths (C3−C7), and studied their switching behavior, and effect of macrocycle size on thermal isomerization rate. Surprisingly, while the systems with C3-C5 linkers behave as expected (i.e., the rate is faster with smaller linker), the isomerization rate in the systems with larger aliphatic linkers (C6-C8) is enhanced up to four orders of magnitude. NMR spectroscopy, X-ray crystallography and DFT calculations were used to elucidate this unexpected behavior, which based on our analyses results from the build-up of Pitzer (torsional), Prelog (transannular) and Baeyer (large angle) strain in the longer linkers.