Photoswitchable materials

Achieving multiple fluorescence changes in a single luminogenic system is desirable but challenging. Here, the authors report a chromone-based aggregation-induced emission luminogen, with six distinct thermal and photoswitchable states.

Strong light-matter interactions demonstrated considerable potential to control photochemical reactions, but further experimental testing is needed. Here, the authors demonstrate that electronically degenerate states of E and Z-isomers of azopyrrole photoswitch couple to a single cavity mode, thereby tuning the coupling conditions from strong to weak.

Photoswitches are useful in a range of applications, with designing molecules with desirable properties remaining a key challenge. Here, the authors report hemiphosphoindigo chromophores enabling chiroptical and in-water photoswitching with high thermal stabilities, fatigue resistance and isomer enrichment in the photostationary state.

Steric hindrance in crystals can prevent activity of photochromic compounds. Here, the authors show reversible isomerization in spiropyran crystals even in the presence of photoinduced mechanical strain using ultrafast spectroscopy techniques.

Azobenzenes undergo reversible light-induced photoisomerization, resulting in marked spectroscopic, electronic, and mechanical changes, but their sensitivity towards solvents is not fully understood. Here, the authors report how irradiation of an azopyridine photoswitch with UV light in dichloromethane triggers protonation of the pyridine moiety through photodecomposition of the solvent, consequently accelerating thermal back isomerization and abolishing singlet-triplet rotation mechanisms.

It is a synthetic challenge to modulate the backbone heteroatom of donor-acceptor Stenhouse adducts limiting their photoswitchable properties. Here, the authors address the challenge with the introduction of an amino functionality into the photoswtich backbone and investigate their resulting photoswitch isomerization.

Metal–organic crystals with dynamic behaviours like bending and jumping offer promise in applications such as smart devices and flexible electronics. Here, the authors develop a Zn-based crystal exhibiting photomechanical effects under UV light, revealing insights into its structural transformation and mechanical properties.

A growing portfolio of Ru-based single-crystal optical actuators is forging a new class of photonic materials that hold prospects for quantum technologies but complete photoconversion into each SO₂-isomeric state is rarely achieved. Here, the authors report the photoisomerization of trans-[Ru(SO₂)(NH₃)₄(4-bromopyridine)]tosylate₂.

Crystals that undergo mechanical motion in response to light are of great interest for the development of photoactuating smart materials, but their disintegration hinders the characterization of accompanying structural changes. Here, two iso-structural photoreactive metal-organic crystals are found to undergo [2 + 2] cycloaddition under UV light in a single-crystal-to-single-crystal manner, enabling detailed characterization of their photomechanical behaviours.

Selectively extracting U(VI) from seawater is challenging. Here, authors propose a dynamically matched spatial coordination strategy to improve the extraction of U(VI). With the size-matching and the spatial coordination, uranium species are precisely captured in confined coordination space.

Metal–organic frameworks functionalized with photoresponsive molecules are of interest as materials with photoswitchable electronic properties, but designing such MOFs remains challenging. Here, the authors use in silico molecular design to explore photoswitchable MOF candidates that incorporate spiropyran photoswitches at controlled positions and with defined intermolecular distances and orientations.

Controlling the number of molecular switches and their relative positioning within porous materials is critical to their functionality and properties. Here the authors systematically control the number of spiropyran units in a covalent organic framework using a mixed-linker synthetic strategy which resulted in one photoresponsive unit per pore.

Light and redox switches are of interest for responsive materials, actuators and robotics. Here the authors integrated a redox- and photoresponsive switch into a polymer hydrogel enabling reversible redox-switching with high spatio-temporal precision.

The development of photoresponsive energy-driven elastomers with unique responsiveness and mechanical variability is challenging. Here, the authors describe elastomers based on reversible cis-trans isomerization transition of azobenzene terminated aliphatic polycarbonate, allowing mechanical transformation for smart photo/thermal switchable adhesion and wound healing as medical dressings.

Photoresponsive hydrogels are of interest as candidates for materials that compute. Here the authors design a NAND logic gate based on the interactions of self-trapped laser beams in a hydrogel system.

The amplification of molecular motion along length scales for macroscopic muscle-like functions provides attractive opportunities ranging from soft actuators to responsive biomedical materials. Here, the authors design a photoswitch amphiphile based on an overcrowded alkene-derived core and develop supramolecular polymer-based artificial muscles.

Rotaxanes equipped with actuators hold great potential for developing highly functional molecular machines, and could enhance our ability to study and manipulate biological and artificial membranes. Here, the authors introduce a rotaxane with a ring that features two azobenzene photoswitches, and demonstrate that photoswitching can be used to reversibly modulate lipid bilayer structure. This capability was exploited for the light-triggered release of sulforhodamine B from large unilamellar vesicles.

Azo compounds are widely used in the photo-induced regulation in biological systems. Here, the authors develop a nanosystem comprising an azo-fluorescent switch, in which the visible light-responsiveness enables the control of the system and monitorization using fluorescence imaging.

Building stimuli-responsive supramolecular materials enables spatiotemporal control over complex systems, and is a promising strategy for a range of applications. Here, mixing adenosine 5’-triphosphate (ATP) with an azobenzene-guanidium compound possessing photodependent nucleotide binding affinity is shown to result in the spontaneous photo-reversible self-assembly of these compounds into micrometer-sized fluorescent aggregates that display dynamic responses to several chemical, physical and biological stimuli.

Thioindigos are reversible photoswitches with spatial control over the conformational change, yet have very limited solubility in most solvents. Here, the authors report a method for the insertion of thioindigos into polymer chains, allowing the formation of visible light responsive hydrogels.

Hemiindigo derivatives can act as photoswitches, but their applicability is limited by synthetic challenges. Here, the authors report the synthesis of modified photoswitches and demonstrate four-state switching, chemical fueling, and reversible inscription into transparent polymers.