Photoswitching CO2 Capture and Release in a Photochromic Diarylethene Metal–Organic Framework

We demonstrate herein a promising pathway towards low‐energy CO₂ capture and release triggered by UV and visible light. A photosensitive diarylethene ligand was used to construct a photochromic diarylethene metal–organic framework (DMOF). A local photochromic reaction originating from the framework movement induced by the photoswitchable diarylethene unit resulted in record CO₂‐desorption capacity of 75 % under static irradiation and 76 % under dynamic irradiation.     

Synthesis and photoswitching properties of bent-shaped liquid crystals containing azobenzene monomers

Three novel bent-shaped monomers, namely 1,3-phenylene bis-{4-[4-(n-allyloxyalkyloxy)phenylazo]benzoate} 5a–c, containing azobenzene as side arms, resorcinol as central units and terminal double bonds as polymerisable functional groups were synthesised and characterised. The mesophase behaviour was investigated by polarising optical microscopy, differential scanning calorimetry and X-ray diffraction measurements and it was found that all three compounds display SmA_intercal mesophases. These bent-shaped molecules exhibit strong photoisomerisation behaviour in solutions in which trans to cis isomerisation takes about 50 seconds whereas the reverse process takes almost 31 hours.     

Photochromic Free MOF-Based Near-Infrared Optical Switch

We demonstrate herein an all-optical switch based on stimuli-responsive and photochromic-free metal–organic framework (HKUST-1). Ultrafast near-infrared laser pulses stimulate a reversible 0.4 eV blue shift of the absorption band with up to 200 s⁻¹ rate due to dehydration and concomitant shrinking of the structure-forming [Cu₂C₄O₈] cages of HKUST-1. Such light-induced switching enables the remote modulation of intensities of photoluminescence of single crystals of HKUST-1 as well visible radiation passing through the crystal by 2 order of magnitude. This opens up the possibility of utilyzing stimuli-responsive MOFs for all-optical data processing devices.     

A Light‐Responsive Metal–Organic Framework Hybrid Membrane with High On/Off Photoswitchable Proton Conductivity

Mimicking biological proton pumps to achieve stimuli‐responsive protonic solids has long been of great interest for their diverse applications in fuel cells, chemical sensors, and bio‐electronic devices. Now, dynamic light‐responsive metal–organic framework hybrid membranes can be obtained by in situ encapsulation of photoactive molecules (sulfonated spiropyran, SSP), as the molecular valve, into the cavities of the host ZIF‐8. The configuration of SSP can be changed and switched reversibly in response to light, generating different mobile acidic protons and thus high on/off photoswitchable proton conductivity in the hybrid membranes and device. This device exhibits a high proton conductivity, fast response time, and extremely large on/off ratio upon visible‐light irradiation. This approach might provide a platform for creating emerging smart protonic solids with potential applications in the remote‐controllable chemical sensors or proton‐conducting field‐effect transistors.     

Fused Bis(hemi-indigo): Broad-Range Wavelength-Independent Photoswitches

Wavelength-independent conversion of organic photoswitches in the photostationary state is a rare phenomenon that opens up a way for many practical applications. In this work, three fused bis(hemi-indigo) derivatives with different substitution patterns were synthesized and their photoswitching was investigated by optical spectroscopy, real-time NMR spectroscopy and TD-DFT calculations. We disclosed that the Z-E photoisomerization of the meta-bis(hemi-indigo) derivative was remarkably independent of the irradiation wavelength from UV up to yellow light. The wavelength-independent forward photoswitching together with the inhibited backward photoisomerization, high thermal stability of the photoinduced isomers as well as significant overlap between the photoswitch absorption and the solar spectrum allows to suggest bis(hemi-indigo) derivatives as promising candidates for molecular solar thermal energy storage (MOST) systems.     

Structural Optimization of Photoswitch Ligands for Surface Attachment of α‐Chymotrypsin and Regulation of Its Surface Binding

A modified gold surface that allows photoregulated binding of α‐chymotrypsin has previously been reported. Here the development of this surface is reported, through the synthesis of a series of trifluoromethyl ketones and α‐keto esters containing the azobenzene group and a surface attachment group as photoswitch inhibitors of α‐chymotrypsin. All of the compounds are inhibitors of the enzyme, with activity that can be modulated by photoisomerization. The best photoswitch shows a reversible change in IC₅₀ inhibition constant of >5.3 times on photoisomerization. The trifluoromethyl ketone 1 exhibited excellent photoswitching and was attached to a gold surface in a two‐step procedure involving an azide–alkyne cycloaddition. The resulting modified surface bound α‐chymotrypsin to a degree that could be modulated by UV/Vis irradiation, showing “slow‐tight” enzyme binding as observed for inhibitors in solution.     

Photoswitching the Efficacy of a Small‐Molecule Ligand for a Peptidergic GPCR: from Antagonism to Agonism

For optical control of GPCR function, we set out to develop small‐molecule ligands with photoswitchable efficacy in which both configurations bind the target protein but exert distinct pharmacological effects, that is, stimulate or antagonize GPCR activation. Our design was based on a previously identified efficacy hotspot for the peptidergic chemokine receptor CXCR3 and resulted in the synthesis and characterization of five new azobenzene‐containing CXCR3 ligands. G protein activation assays and real‐time electrophysiology experiments demonstrated photoswitching from antagonism to partial agonism and even to full agonism (compound VUF16216). SAR evaluation suggests that the size and electron‐donating properties of the substituents on the inner aromatic ring are important for the efficacy photoswitching. These compounds are the first GPCR azo ligands with a nearly full efficacy photoswitch and may become valuable pharmacological tools for the optical control of peptidergic GPCR signaling.     

cis/trans photoisomerization of secondary thiopeptide bonds

The reversible cis/trans photoisomerization of secondary thiopeptide bonds has been systematically studied with UV-visible absorption, capillary electrophoresis, 1H NMR spectroscopy, and circular dichroism methods. It was found that the concentration of the cis conformers could be increased from less than 1 % in the thermal equilibrated solution to up to 20 % in the photostationary state. The rotational barriers of the thiopeptide bond and the pH dependence of the isomerization rates were also studied. The quantum yields of the trans-->cis and the cis-->trans processes were determined from photokinetic analysis.