Reversible Photocontrol of Biological Systems by the Incorporation of Molecular Photoswitches

Remarkable Increase in the Rate of Trans-Cis Photoisomerization of Os(II)-Terpyridine Complexes via Oxidation and Reduction

Luminescent homoleptic Os(II)-terpyridine complexes comprising stilbene-appended naphthalene, anthracene, and pyrene motifs are designed in this work, and their photophysical, electrochemical, and photoisomerization behaviors are extensively investigated. All complexes exhibit intense spin-allowed singlet metal-to-ligand charge transfer (1MLCT) bands in the visible (496-500 nm) and weaker spin-forbidden singlet-to-triplet 3MLCT transitions in the 600-700 nm range. They display moderate emission at room temperature with lifetimes in the range of 84.5-112.5 ns. Electrochemical studies reveal a reversible Os2+/Os3+ oxidation couple within 0.93-0.96 V, alongside multiple reversible or quasi-reversible reduction peaks associated with terpyridine units in between -1.10 and -1.85 V. The stilbene motifs facilitate reversible trans-cis photoisomerization under alternative treatment with visible and UV light, enabling the complexes to function as photomolecular switches in the near-infrared domain. Interestingly, a remarkable increase in the rate of photoisomerization has been achieved via oxidation as well as reduction of the complexes, which, in turn, induces multistep switching involving reversible oxidation-reduction and trans-cis isomerization. Computational investigations are also conducted on all three conformations {trans-trans (t-t), trans-cis (t-c), and cis-cis (c-c)} of the complexes to gain insight into their electronic structures and for accurate assignment of their absorption and emission spectral bands.

Optogenetics with Atomic Precision─A Comprehensive Review of Optical Control of Protein Function through Genetic Code Expansion

Conditional control of protein activity is important in order to elucidate the particular functions and interactions of proteins, their regulators, and their substrates, as well as their impact on the behavior of a cell or organism. Optical control provides a perhaps optimal means of introducing spatiotemporal control over protein function as it allows for tunable, rapid, and noninvasive activation of protein activity in its native environment. One method of introducing optical control over protein activity is through the introduction of photocaged and photoswitchable noncanonical amino acids (ncAAs) through genetic code expansion in cells and animals. Genetic incorporation of photoactive ncAAs at key residues in a protein provides a tool for optical activation, or sometimes deactivation, of protein activity. Importantly, the incorporation site can typically be rationally selected based on structural, mechanistic, or computational information. In this review, we comprehensively summarize the applications of photocaged lysine, tyrosine, cysteine, serine, histidine, glutamate, and aspartate derivatives, as well as photoswitchable phenylalanine analogues. The extensive and diverse list of proteins that have been placed under optical control demonstrates the broad applicability of this methodology.

Glucose-derived receptors for photo-controlled binding of amino acid esters in water

Selective receptors of amino acids in aqueous media are highly sought after as they may enable the creation of novel diagnostic and sensing tools. Photoswitchable receptors are particularly attractive for such purposes as their response and selectivity towards bioanalytes can be modulated using light. Herein we report glucose-based photoswitchable receptors of amino-acid methyl esters and biogenic amines in water. The tetra-ortho-fluoroazobenzene unit in the receptors structure allows to control the distance between their binding sites using light. The Z-isomers of both receptors, having these sites in closer proximity, bind lysine, ornithine and arginine esters significantly stronger compared to E-isomers, where the binding sites are further apart.

Challenging and new opportunities for prodrug technology

Research on prodrug technology has opened new avenues for site-directed chemotherapy rather than systemic chemotherapy. This distinctive strategy allows drug delivery to be activated by light-, irradiation-, or ultrasound (US)-tunable chemistries, which have been termed photopharmacology, radiopharmacology, and sonopharmacology, respectively. Prodrugs have emerged as a main strategy for improving pharmacokinetics, reducing side effects, and thus enhancing the therapeutic efficacy of drugs. This review summarizes stimuli-responsive drug release systems and the latest progress in exogenous stimuli-responsive prodrug activation, e.g., light, irradiation, and US, with a focus on the activation of small molecule prodrugs, antibody‒drug conjugates, and prodrug nanosystems. In addition, challenges encountered by Pt drugs and Pt(IV) prodrug nanotherapeutics are summarized and discussed. Moreover, this review presents the current state of precise treatment and discusses the opportunities and challenges for the clinical translation of these strategies.

Ionic control of small GTPase HRas using calmodulin

HRas is a small GTPase that plays physiologically important roles in various intracellular signal transduction processes, such as cell growth and proliferation. The structure and action mechanisms of HRas have been well characterized, leading to its widespread use as a molecular switch in bionanomachines. Calmodulin (CaM), a calcium ion-binding protein, acts as an ion-binding molecular switch and activates the target enzymes. We previously demonstrated that the fusion protein of HRas (M13-HRas) with the CaM target peptide M13 at the N-terminus of HRas exhibits reversible regulation of GTPase activity and the interaction between M13-HRas and the downstream signalling factor Raf by calcium ions with CaM. In this study, we prepared two new HRas fusion proteins with the M13 peptide at the C-terminus (HRas-M13) and both termini (M13-HRas-M13) of HRas and analysed the calcium-dependent regulation of HRas function. M13-HRas-M13 more efficiently controlled GTPase, interaction with Raf and the HRas regulator GEF by calcium ions with CaM.

Coupling Rotary Motion to Helicene Inversion within a Molecular Motor

Towards complex coupled molecular motions, the remote handedness inversion of a helicene moiety was achieved by a rotary molecular motor. The use of a specifically engineered dynamic helicene stator in a novel overcrowded-alkene second-generation molecular motor based on a fluorinated dibenzofluorene fragment allows for an unprecedented control over helicity inversion. This is achieved by the mechanical coupling of the rotation of the rotor to the helicene inversion of the stator half via a remote chirality transmission process. Thus, the unidirectional rotary motion generated upon irradiation is used to invert the dynamic stereochemistry of a helicene, leading to a 6-step cycle with eight intermediates. In this cycle, both alternation between P and M configurations of the helicene stator and dynamic thermal interconversion (paddling motion) can be achieved. In-depth computational and spectroscopic studies were performed to support the associated mechanism. The control over coupled motion and dynamic helicity offers prospects for the development of complex responsive systems.

A Photocontrolled Molecular Rotor Based on Azobenzene-Strapped Mixed (Phthalocyaninato)(Porphyrinato) Rare Earth Triple-Decker

Effectively regulating the rotary motions of molecular rotors through external stimuli poses a tremendous challenge. Herein, a new type of molecular rotor based on azobenzene-strapped mixed (phthalocyaninato)(porphyrinato) rare earth triple-decker complex Azo-1 is reported. Electronic absorption and 1H NMR spectra manifested the reversible isomerization of the rotor Azo-1 between the trans configuration and the cis configuration. The rotational behavior of phthalocyanine rotator in two configurations were investigated by VT-1H NMR experiments, and the results indicated that the phthalocyanine rotator possessed a smaller rotational energy barrier in the cis isomer than in the trans isomer, which was also supported by DFT calculations. This result demonstrates that the rotation of phthalocyanine rotator in (phthalocyaninato)(porphyrinato) rare earth triple-decker complex can be successfully modulated by photo-isomerization via altering irradiation.

Compartmentalizing Donor-Acceptor Stenhouse Adducts for Structure-Property Relationship Analysis

The development of photoswitches that absorb low energy light is of notable interest due to the growing demand for smart materials and therapeutics necessitating benign stimuli. Donor-acceptor Stenhouse adducts (DASAs) are molecular photoswitches that respond to light in the visible to near-infrared spectrum. As a result of their modular assembly, DASAs can be modified at the donor, acceptor, triene, and backbone heteroatom molecular compartments for the tuning of optical and photoswitching properties. This Perspective focuses on the electronic and steric contributions at each compartment and how they influence photophysical properties through the adjustment of the isomerization energetic landscape. An emphasis on current synthetic strategies and their limitations highlights opportunities for DASA architecture, and thus photophysical property expansion.

Spatiotemporal Control Over Circadian Rhythms With Light

Circadian rhythms are endogenous biological oscillators that synchronize internal physiological processes and behaviors with external environmental changes, sustaining homeostasis and health. Disruption of circadian rhythms leads to numerous diseases, including cardiovascular and metabolic diseases, cancer, diabetes, and neurological disorders. Despite the potential to restore healthy rhythms in the organism, pharmacological chronotherapy lacks spatial and temporal resolution. Addressing this challenge, chrono-photopharmacology, the approach that employs small molecules with light-controlled activity, enables the modulation of circadian rhythms when and where needed. Two approaches-relying on irreversible and reversible drug activation-have been proposed for this purpose. These methodologies are based on photoremovable protecting groups and photoswitches, respectively. Designing photoresponsive bioactive molecules requires meticulous structural optimization to obtain the desired chemical and photophysical properties, and the design principles, detailed guidelines and challenges are summarized here. In this review, we also analyze all the known circadian modulators responsive to light and dissect the rationale following their construction and application to control circadian biology from the protein level to living organisms. Finally, we present the strength of a reversible approach in allowing the modulation of the circadian period and the phase.

Membrane-targeted push-pull azobenzenes for the optical modulation of membrane potential

We introduce a family of membrane-targeted azobenzenes (MTs) with a push-pull character as a new tool for cell stimulation. These molecules are water soluble and spontaneously partition in the cell membrane. Upon light irradiation, they isomerize from trans to cis, changing the local charge distribution and thus stimulating the cell response. Specifically, MTs photoisomerization induces clear and reproducible depolarization. The most promising species, MTP2, was extensively studied. Time-resolved spectroscopy techniques provide insights into the excited state evolution and a complete understanding of its isomerization reaction. Molecular Dynamics simulations reveal the spontaneous and stable partitioning of the compound into the cellular membrane, without significant alterations to the bilayer thickness. MTP2 was tested in different cell types, including HEK293T cells, primary neurons, and cardiomyocytes, and a steady depolarization is always recorded. The observed membrane potential modulation in in-vitro models is attributed to the variation in membrane surface charge, resulting from the light-driven modulation of the MT dipole moment within the cell membrane. Additionally, a developed mathematical model successfully captures the temporal evolution of the membrane potential upon photostimulation. Despite being insufficient for triggering action potentials, the rapid light-induced depolarization holds potential applications, particularly in cardiac electrophysiology. Low-intensity optical stimulation with these modulators could influence cardiac electrical activity, demonstrating potential efficacy in destabilizing and terminating cardiac arrhythmias. We anticipate the MTs approach to find applications in neuroscience, biomedicine, and biophotonics, providing a tool for modulating cell physiology without genetic interventions.

Enzyme fragment complementation driven by nucleic acid hybridization sans self-labeling protein

A modified enzyme fragment complementation assay has been designed and validated as a turn-on biosensor for nucleic acid detection in dilute aqueous solution. The assay is target sequence-agonistic and uses fragments of NanoBiT, the split luciferase reporter enzyme, that are esterified enzymatically at their C-termini to steramers, sterol-linked oligonucleotides. The Drosophila hedgehog autoprocessing domain, DHhC, serves as the self-cleaving enzyme for the NanoBiT-steramer bioconjugations. Unlike current approaches, the final bioconjugate generated by DHhC and used for nucleic acid detection is free of self-labeling passenger protein. In the presence of single stranded (ss) DNA or RNA template with adjacent segments complementary to the Nano-BiT steramer oligonucleotides, the two NanoBiT fragments associate productively, reconstituting NanoBiT's luciferase activity. In samples containing ssDNA or RNA template at low nM concentrations, NanoBiT luminescence exceeded background signal by 30- to 60-fold. The steramer probe sequences used to prepare these sensors are unconstrained in length and composition. In the absence of sequence constraints of the probe element and without the added bulk of a self-labeling protein, these NanoBiT-steramer bioconjugates open new applications in the programmable detection of small fragments of coding and noncoding DNA and RNA.

Supramolecular Control of the Photoisomerization of a Coumarin-Based Photoswitch

The complex formation of the cationic stilbene-type photoswitch CP with the anionic macrocycles carboxylato-pillar[5]arene (WP5) and carboxylato-pillar[6]arene (WP6) has been investigated in aqueous solution by optical spectroscopic, NMR and isothermal calorimetric experiments and theoretical calculations. Subsequently, the photoisomerization reactions of the supramolecular complexes formed have been studied. CP consists of a 7-diethylamino-coumarin fluorophore and an N-methylpyridinium unit, which are connected via an ethene bridge. The trans isomer of CP is fluorescent, and its cis isomer is dark. The binding constants of the WP6 complexes of the two photoisomers of CP are larger by 2 orders of magnitude than those of the respective complexes with WP5, and trans-CP forms more stable complexes with the individual pillararenes than the cis isomer. As shown by NMR spectroscopic measurements and theoretical calculations, the two isomers of CP form external complexes with WP5 and inclusion complexes with WP6. On complexation with WP6, the quantum yields of both the trans-to-cis and cis-to-trans photoisomerization reactions of CP increase significantly, and the fluorescence quantum yield of trans-CP is also enhanced. These changes are due to the suppression of the TICT deactivation process, which is characteristic of 7-dialkylamino-coumarin derivatives.

Ni(II)-Directed Supramolecular Metallogel: Stimuli Responsiveness and Semiconducting Device Fabrication

Metal-organic gels (MOGs) are a type of supramolecular complex that have become highly intriguing due to their synergistic combination of inorganic and organic elements. We report the synthesis and characterization of a Ni-directed supramolecular gel using chiral amino acid L-DOPA (3,4-dihydroxy phenylalanine) containing ligand, which coordinates with Ni(II) to form metal-organic gels with exceptional properties. The functional Ni(II)-gel was synthesized by heating nickel(II) acetate hexahydrate and the L-DOPA containing ligand in DMSO at 70 °C. The rheological tests have verified the gel with its mechanical stability, while a SEM image has shown a spherical aggregate morphology. The gel is photo-responsive in nature and exhibits gel to sol transformation upon adsorption of toxic gases like NH3 or H2S. Notably, electrical conductivity of the gel was observed in electronic metal-semiconductor (MS) junctions' devices with a measured conductivity of 0.9×10-6 Sm-1. These devices also exhibited Schottky barrier diode characteristics, underscoring the multifunctional potential of the Ni(II)-gel.

Synthesis of Tetra-ortho-Methoxylated Azobenzene Photoswitches via Sequential Catalytic C-H Activation and Methoxylation

Functionalized tetra-ortho-methoxyazobenzenes have been prepared in a two-step approach based on palladium-catalyzed C-H ortho bromination of azobenzenes, followed by copper-catalyzed methoxylation. The method has shown a broad tolerance to different functional groups that could not be incorporated by previous strategies. With this two-step transition metal-catalyzed strategy, we achieved overall yields that range from good to excellent and enable the exploitation of these highly coveted photoswitches. The superior robustness of this scaffold for solid phase peptide synthesis (SPPS) applications when compared to its chlorinated counterpart has been demonstrated after extensive treatments with piperidine while bound to a RinkAmide ChemMatrix resin, showcasing their potential for use in the synthesis of red-light-operated peptides.

Photoluminescence Switching in Quantum Dots Connected with Carboxylic Acid and Thiocarboxylic Acid End-Group Diarylethene Molecules

We contrast the switching of photoluminescence (PL) of PbS quantum dots (QDs) cross-linked with photochromic diarylethene molecules with different end groups, 4,4'-(1-cyclopentene-1,2-diyl)bis[5-methyl-2-thiophenecarboxylic acid] (1C) and 4,4'-(1-cyclopentene-1,2-diyl)bis[5-methyl-2-thiophenethiocarboxylic acid] (2T). Our results show that the QDs cross-linked with the carboxylic acid end group molecules (1C) exhibit a greater amount of switching in photoluminescence intensity compared to QDs cross-linked with the thiocarboxylic acid end group (2T). We also demonstrate that regardless of the molecule used, greater switching amounts are observed for smaller quantum dots. Varying these parameters allows for the fabrication of photoswitches with tunable PL change. We relate these observations to the differences in the HOMO energy levels between the QDs and the photochromic molecules. Our findings demonstrate how the size of the QDs and the energy levels of the linker ligands influences the charge tunneling rate and thus the PL switching performance in tunneling-based photoswitches.

Protacs in cancer therapy: mechanisms, design, clinical trials, and future directions

Cancer develops as a result of changes in both genetic and epigenetic mechanisms, which lead to the activation of oncogenes and the suppression of tumor suppressor genes. Despite advancements in cancer treatments, the primary approach still involves a combination of chemotherapy, radiotherapy, and surgery, typically providing a median survival of approximately five years for patients. Unfortunately, these therapeutic interventions often bring about substantial side effects and toxicities, significantly impacting the overall quality of life for individuals undergoing treatment. Therefore, urgent need of research required which comes up with effective treatment of cancer. This review explores the transformative role of Proteolysis-Targeting Chimeras (PROTACs) in cancer therapy. PROTACs, an innovative drug development strategy, utilize the cell's protein degradation machinery to selectively eliminate disease-causing proteins. The review covers the historical background, mechanism of action, design, and structure of PROTACs, emphasizing their precision in targeting oncogenic proteins. The discussion extends to the challenges, nanotechnology applications, and ongoing clinical trials, showcasing promising results and clinical progress. The review concludes with insights into patents, future directions, and the potential impact of PROTACs in addressing dysregulated protein expression across various diseases. Overall, it provides a concise yet comprehensive overview for researchers, clinicians, and industry professionals involved in developing targeted therapies.

Computational Characterization of the DAD Photoisomerization: Functionalization, Protonation, and Solvation Effects

Photoswitches are becoming increasingly popular in pharmacology due to the possibility of modifying their activity with light. Hence, it is crucial to understand the photophysics of these compounds to identify promising light-activated drugs. We focused our study on DAD, an azobenzene derivative that, according to a previous experimental investigation, can restore visual function in blind mice due to trans-cis photoisomerization upon light absorption. With the present computational study, we aim to characterize the absorption spectrum of DAD, and to understand its photoisomerization mechanism by means of conformational search analysis, quantum mechanical (QM) and hybrid QM/continuum calculations, and classical molecular dynamics simulations. Moreover, we explored the effect of the derivation (DAD vs azobenzene), the protonation (DAD vs DADH22+, the two possible protonation states) and the solvation (vacuum vs water) on the photoisomerization. Similarly to azobenzene, we showed that the photoisomerization of both protonation states of DAD begin with the population of the bright S2 state. Then, it crosses to the S1 surface and relaxes along the rotation of the azo dihedral to a S1/S0 crossing point. The latter is close to a transition state that connects the trans and cis geometries on the ground state. Finally, our results suggested that amino derivation, nonprotonation and water solvation could improve the quantum yield of the photoisomerization.

Noncanonical Amino Acid Tools and Their Application to Membrane Protein Studies

Methods rooted in chemical biology have contributed significantly to studies of integral membrane proteins. One recent key approach has been the application of genetic code expansion (GCE), which enables the site-specific incorporation of noncanonical amino acids (ncAAs) with defined chemical properties into proteins. Efficient GCE is challenging, especially for membrane proteins, which have specialized biogenesis and cell trafficking machinery and tend to be expressed at low levels in cell membranes. Many eukaryotic membrane proteins cannot be expressed functionally in E. coli and are most effectively studied in mammalian cell culture systems. Recent advances have facilitated broader applications of GCE for studies of membrane proteins. First, AARS/tRNA pairs have been engineered to function efficiently in mammalian cells. Second, bioorthogonal chemical reactions, including cell-friendly copper-free "click" chemistry, have enabled linkage of small-molecule probes such as fluorophores to membrane proteins in live cells. Finally, in concert with advances in GCE methodology, the variety of available ncAAs has increased dramatically, thus enabling the investigation of protein structure and dynamics by multidisciplinary biochemical and biophysical approaches. These developments are reviewed in the historical framework of the development of GCE technology with a focus on applications to studies of membrane proteins.

An ab initio study on the photoisomerization in 2-styrylpyridine

We report results of a theoretical study on photoinduced processes in 2-styrylpyridine. The geometries and the relative energies of the possible conformers were investigated using the second-order Møller-Plesset (MP2) and algebraic diagrammatic construction to second-order (ADC(2)) methods and the cc-pVTZ basis set. The complete active space self consistent field (CASSCF) method is used for locating the minimum-energy conical intersection (MECI) geometries between the S0 and S1 states. In addition to the twisted-pyramidalized MECI points along the trans and cis isomerization pathways, S1/S0 cooperating-ring MECI and cyclized-ring MECI structures, lying on the cyclization pathways of cis-2-styrylpyridine, were also located. Except the twisted pyramidalized CI2 and cyclized Cyc-CI3, all the other MECI points are found to be accessible from either one or more Franck-Condon points. The possibilities for the cis-trans isomerization and cyclization processes are discussed along the image-dependent pair potential (IDPP) paths.

Effect of the Protic vs. Non-Protic Molecular Environment on the cis to trans Conformation Change of Phototrexate Drug

The therapeutical applicability of the anticancer drug phototrexate, a photoswitchable derivative of the antimetabolite dihydrofolate reductase inhibitor methotrexate, highly depends on the stability of its bioactive isomer. Considering that only the cis configuration of phototrexate is bioactive, in this work, the effect of the molecular environment on the stability of the cis isomer of this drug has been investigated. UV-vis absorption and fluorescence-based solvent relaxation methods have been used. Protic methanol and non-protic dimethylsulfoxide were used as medium-ranged permittivity solvents. The results showed a decreased rate of cis → trans conversion and enhanced stabilities of the cis isomer in methanol. Temperature-dependent measurements of the isomerization rate reflect the increased activation energy in methanol.

Study of Azobenzene-modified Black Phosphorus for Potential Tumor Therapy

Exploring the interaction between black phosphorus (BP)-based hybrid systems and target proteins is of great significance for understanding the biological effects of 2D nanomaterials at the molecular level. Density functional theory (DFT) calculations revealed that different terminal groups of the azobenzene (AB) motif in BP@AB hybrids can affect the extent of interfacial charge transfer between the BP sheet and AB-derivatives, which determines the electrostatic interaction with proteins and hence biofunctions of BP@AB hybrids. With the advantage of AB modification, BP@AB hybrids displayed antitumor effects and induced production of cellular reactive oxygen species and apoptosis in cancer cells. Through the proteomics profiling, cellular ribosome and lipid metabolic processes were screened out as the target pathways of the BP@AB-NH2 in HeLa cells, while the BP@AB-S-S-AB system mainly targets the ERBB and PPAR signaling pathways. Molecular docking simulations revealed that due to the positive charge, ribosomal pathway proteins enriched in negatively charged amino acids such as lysine and arginine are preferentially adsorbed and bound by BP@AB-NH2 hybrids. Whereas for BP@AB-S-S-AB, receptors containing narrow and long pocket domains are more likely to bind with BP@AB-S-S-AB by van der Waals forces for the rod-like hybrids. Different biomolecule targeting and action modes of BP@AB hybrids have been rationalized by different electrostatic environments and matching of geometric configurations, shedding insight for designing efficient and targeted modification of a 2D nanomaterial-based strategy for cancer therapy.

Azobenzene-Tagged Photopeptides Exhibiting Excellent Selectivity and Light-Induced Cytotoxicity in MCF-7 Cells over HeLa and A549

The precise regulation of proteasome activity has become a focal point in current research, particularly its implications in cancer treatment. Bortezomib is used for treating multiple myeloma and is found to be ineffective against solid tumors. A spatiotemporal control over the proteasome is one of the solutions to resolve these issues using external stimuli, such as light. Thus, we designed and synthesized azobenzene-containing tripeptide vinyl sulfones 1, 2, 3, and 4, as the azobenzene moiety can impart E↔Z isomerism upon exposure to UV light. Further, the hydrophobicity of these peptides was fine-tuned by systematically varying the size of hydrophobic amino acids at the P1, P2, and P3 positions. The light-induced Z isomers of these photopeptides showed excellent cellular potency in HeLa, MCF-7, and A549 cell lines. Photopeptide 4 with valine at the proximal position, phenylalanine at P2, and leucine at the P1 positions exhibited 19.3- and 6.6-fold cellular potency in MCF-7 and A549 cells, respectively.

Photoinduced Isomerization of [N2]2- in a Bimetallic Lutetium Complex

The first lanthanide dinitrogen photoswitch [(C5Me4H)2(THF)Lu]2(μ-η2:η2-N2), 1, is reported. 1 is a unique example of controlled isomerization between side-on and end-on coordination modes of [N2]2- in a bimetallic lutetium dinitrogen complex that results in photochromism. Near-infrared light (NIR) was used to promote this effect, as evidenced by single X-ray diffraction (XRD) connectivity and Raman data, generating the [N2]2- end-on bound isomer, [(C5Me4H)2(THF)Lu]2(μ-η1:η1-N2), 2. Although different ligands and coordinating solvents were studied to replicate and control the optical properties in 1/2, only the original configuration with C5Me4H ligands and THF as the coordinating solvent worked. Supported by the first-principles calculations, the electronic structures along with the mechanistic details of the side-on to end-on isomerization were unraveled. Preliminary reactivity studies show that 2 formed with NIR light reacts with anthracene, generating dihydroanthracene and anthracene dimers, indicating new redox reaction pathways.

Light-Responsive Smart Nanoliposomes: Harnessing the Azobenzene Moiety for Controlled Drug Release under Near-Infrared Irradiation

The azobenzene moiety is an intriguing structure that deforms under UV and visible light, indicating a high potential for biomedical applications. However, its reaction to UV radiation is problematic because of its high energy and low tissue penetration. Unlike previous research on azobenzene structures in photoresponsive materials, this study presents a novel method for imparting photostimulation-responsive properties to liposomes by incorporating the azobenzene moiety and extending the light wavelength with up-conversion nanoparticles. First, the azobenzene structure was incorporated into a phospholipid molecule to create Azo-PSG, which could spontaneously form vesicle assemblies in aqueous solutions and isomerizes within 1 h of light exposure. Furthermore, orthogonal up-conversion nanoparticles with a core-shell structure were created by sequentially growing lanthanide rare earths in the shell layer, which efficiently converts near-infrared light into ultraviolet (400 nm) and blue-green (540 nm) light. Combining these core-shell structured up-conversion nanomaterials with Azo-PSG molecules resulted in the creation of a near-infrared light-responsive smart nanoliposome system. Under near-infrared light irradiation, UCNPs emit UV and blue-green light, causing conformational changes in Azo-PSG molecules that allow drug release within 6 h. The reversible structural shift of Azo-PSG in response to light stimulation holds enormous promise for improving drug release techniques. This novel technique also expands the usage of UV-responsive compounds beyond their constraints of low penetration and high biotoxicity, allowing for rapid medication release under NIR light.

Expanding the Genetic Code of Bioelectrocatalysis and Biomaterials

Genetic code expansion is a promising genetic engineering technology that incorporates noncanonical amino acids into proteins alongside the natural set of 20 amino acids. This enables the precise encoding of non-natural chemical groups in proteins. This review focuses on the applications of genetic code expansion in bioelectrocatalysis and biomaterials. In bioelectrocatalysis, this technique enhances the efficiency and selectivity of bioelectrocatalysts for use in sensors, biofuel cells, and enzymatic electrodes. In biomaterials, incorporating non-natural chemical groups into protein-based polymers facilitates the modification, fine-tuning, or the engineering of new biomaterial properties. The review provides an overview of relevant technologies, discusses applications, and highlights achievements, challenges, and prospects in these fields.

Effect of Leaving Centrosymmetric Character on Spectral Properties in Mono-, Bi-, and Triphotonic Absorption Spectroscopies

Numerical simulations of the absorption bands of photoswitch E-o-tetrafluoroazobenzene in DMSO solution under one-, two-, and three-photon absorption conditions combined with the analysis of the behavior of transition probability under distortion of planarity reveal many similarities between the mono- and triphoton spectroscopic behaviors with a two-photon spectrum being set apart. The position of the absorption peak for the studied nπ* and ππ* transitions appears shifted to lower energies (longer wavelengths) than the conventional estimate based on vertical excitation from the ground-state potential energy minimum.

Strategies to control humidity sensitivity of azobenzene isomerisation kinetics in polymer thin films

Azobenzenes are versatile photoswitches that garner interest in applications ranging from photobiology to energy storage. Despite their great potential, transforming azobenzene-based discoveries and proof-of-concept demonstrations from the lab to the market is highly challenging. Herein we give an overview of a journey that started from a discovery of hydroxyazobenzene's humidity sensitive isomerisation kinetics, developed into commercialization efforts of azobenzene-containing thin film sensors for optical monitoring of the relative humidity of air, and arrives to the present work aiming for better design of such sensors by understanding the different factors affecting the humidity sensitivity. Our concept is based on thermal isomerisation kinetics of tautomerizable azobenzenes in polymer matrices which, using pre-defined calibration curves, can be converted to relative humidity at known temperature. We present a small library of tautomerizable azobenzenes exhibiting humidity sensitive isomerisation kinetics in hygroscopic polymer films. We also investigate how water absorption properties of the polymer used, and the isomerisation kinetics are linked and how the azobenzene content in the thin film affects both properties. Based on our findings we propose simple strategies for further development of azobenzene-based optical humidity sensors.

A chemical platform for the efficient screening of arylazopyrazole-based photoswitchable CENP-E inhibitors using mild cyclization reactions

A set of arylazopyrazole-based inhibitors targeting the mitotic motor protein CENP-E was discovered through the chemical platform using the quantitative cyclization of 1,3-diketone intermediate with various hydrazines under mild conditions. Through this efficient platform, the structure-activity relationship pertaining to the pyrazole photoswitch in photoswitchable CENP-E inhibitors not only in vitro but also in cells was successfully clarified.

Advancements of prodrug technologies for enhanced drug selectivity in pharmacotherapies

The therapeutic effects of many pharmacotherapies have been explored, but disadvantages such as low drug specificity, drug resistance and side effects makes their effective delivery to target sites a great challenge. Consequently, a distinctive prodrug-based technology have emerged as an effective treatments because of their distinctive advantages, such as high drug loading capacity, precise targeting, reduced side effects and spatial and temporal controllability. In particular, the use of gamma/X-ray-mediated strategies in radiotherapy is a new strategy that could enable the precise drug release from implanted devices. This review presents readers with the current state of prodrug therapy and reports the design protocols of rational and effective prodrugs for clinical use.

Recent Progress in Regulating the Activity of Enzymes with Photoswitchable Inhibitors

Photoregulation of biomolecules has become crucial tools in chemical biology, because light enables access under mild conditions and with delicate spatiotemporal control. The control of enzyme activity in a reversible way is a challenge. To achieve it, a facile approach is to use photoswitchable inhibitors. This review highlights recent progress in photoswitchable inhibitors based on azobenzenes units. The progress suggests that the incorporation of an azobenzene unit to a known inhibitor is an effective method for preparing a photoswitchable inhibitor, and with these photoswitchable inhibitors, the activity of enzymes can be regulated by optical control, which is valuable in both basic science and therapeutic applications.

Pushing the limits of ultrafast diffraction: Imaging quantum coherences in isolated molecules

Quantum coherence governs the outcome and efficiency of photochemical reactions and ultrafast molecular dynamics. Recent ultrafast gas-phase X-ray scattering and electron diffraction have enabled the observation of femtosecond nuclear dynamics driven by vibrational coherence. However, probing attosecond electron dynamics and coupled electron-nuclear dynamics remains challenging. This article discusses advances in ultrafast X-ray scattering and electron diffraction, highlighting their potential to resolve attosecond charge migration and vibronic coupling at conical intersections. Novel techniques, such as X-ray scattering with orbital angular momentum beams and combined X-ray and electron diffraction, promise to selectively probe coherence contributions and visualize charge migration in real-space. These emerging methods could further our understanding of coherence effects in chemical reactions.

Visible and near-infrared light-induced photoclick reactions

Photoclick reactions combine the advantages offered by light-driven processes, that is, non-invasive and high spatiotemporal control, with classical click chemistry and have found applications ranging from surface functionalization, polymer conjugation, photocrosslinking, protein labelling and bioimaging. Despite these advances, most photoclick reactions typically require near-ultraviolet (UV) and mid-UV light to proceed. UV light can trigger undesirable responses, including cellular apoptosis, and therefore, visible and near-infrared light-induced photoclick reaction systems are highly desirable. Shifting to a longer wavelength can also reduce degradation of the photoclick reagents and products. Several strategies have been used to induce a bathochromic shift in the wavelength of irradiation-initiating photoclick reactions. For instance, the extension of the conjugated π-system, triplet-triplet energy transfer, multi-photon excitation, upconversion technology, photocatalytic and photoinitiation approaches, and designs involving photocages have all been used to achieve this goal. Current design strategies, recent advances and the outlook for long wavelength-driven photoclick reactions are presented.

"On-the-Fly" Nonadiabatic Dynamics Simulation on the Ultrafast Photoisomerization of a Molecular Photoswitch Iminothioindoxyl: An RMS-CASPT2 Investigation

Iminothioindoxyl (ITI) is a new class of photoswitch that exhibits many excellent properties including well-separated absorption bands in the visible region for both conformers, ultrafast Z to E photoisomerization as well as the millisecond reisomerization at room temperature for the E isomer, and switchable ability in both solids and various solvents. However, the underlying ultrafast photoisomerization mechanism at the atomic level remains unclear. In this work, we have employed a combination of high-level RMS-CASPT2-based static electronic structure calculations and nonadiabatic dynamics simulations to investigate the ultrafast photoisomerization dynamics of ITI. Based on the minimum-energy structures, minimum-energy conical intersections, linear interpolation internal coordinate paths, and nonadiabatic dynamics simulations, the overall photoisomerization scenario of ITI upon excitation is established. Upon excitation around 416 nm, the molecule will be excited to the S2 state considering its close energy to the experimentally measured absorption maximum and larger oscillator strength, from which ultrafast decay of S2 to S1 state can take place efficiently with a time constant of 62 fs. However, the photoisomerization is not likely to complete in the S2 state since the dihedral associated with the Z to E isomerization changes little during the relaxation. Upon relaxing to the S1 state, the molecule will decay to the S0 state ultrafast with a time constant of 232 fs. In contrast, the decay of the S1 state is important for the isomerization considering that the dihedral related to the isomerization of the hopping structures is close to 90°. Therefore, the S1/S0 intersection region should be important for the isomerization of ITI. Arriving at the S0 state, the molecule can either go back to the original Z reactant or isomerize to the E products. At the end of the 500 fs simulation time, the E configuration accounts for nearly 37% of the final structures. Moreover, the photoisomerization mechanism is different from the isomerization mechanism in the ground state; i.e., instead of the inversion mechanism in the ground state, the photoisomerization prefers the rotation mechanism. Our results not only agree well with previous experimental studies but also provide some novel insights that could be helpful for future improvements in the performance of the ITI photoswitches.

A photoswitchable CENP-E inhibitor with single blue-green light to control chromosome positioning in mitotic cells

Reversibly photoswitchable chemical tools have aided in the development of novel approaches in the biomedical field. The visible region of light should be ideal for the biological application of this approach because of its low phototoxicity and deep penetration depth compared to ultraviolet light. Herein, we report a photoswitchable centromere-associated protein E (CENP-E) inhibitor, which is controllable with low-energy blue-green light (around 500 nm) illumination. This photoswitchable tool enabled us to control CENP-E-driven chromosome movements and positioning at subcellular resolutions with low phototoxic effects. This study can contribute to the development of a unique technique for chromosome engineering.

Reversible and size-controlled assembly of reflectin proteins using a charged azobenzene photoswitch

Disordered proteins often undergo a stimuli-responsive, disorder-to-order transition which facilitates dynamic processes that modulate the physiological activities and material properties of cells, such as strength, chemical composition, and reflectance. It remains challenging to gain rapid and spatiotemporal control over such disorder-to-order transitions, which limits the incorporation of these proteins into novel materials. The reflectin protein is a cationic, disordered protein whose assembly is responsible for dynamic color camouflage in cephalopods. Stimuli-responsive control of reflectin's assembly would enable the design of biophotonic materials with tunable color. Herein, a novel, multivalent azobenzene photoswitch is shown to be an effective and non-invasive strategy for co-assembling with reflectin molecules and reversibly controlling assembly size. Photoisomerization between the trans and cis (E and Z) photoisomers promotes or reduces Coulombic interactions, respectively, with reflectin proteins to repeatedly cycle the sizes of the photoswitch-reflectin assemblies between 70 nm and 40 nm. The protein assemblies formed with the trans and cis isomers show differences in interaction stoichiometry and secondary structure, which indicate that photoisomerization modulates the photoswitch-protein interactions to change assembly size. Our results highlight the utility of photoswitchable interactions to control reflectin assembly and provide a tunable synthetic platform that can be adapted to the structure, assembly, and function of other disordered proteins.

Accessing a Diverse Set of Functional Red-Light Photoswitches by Selective Copper-Catalyzed Indigo N-Arylation

The ability to correlate the structure of a molecule with its properties is the key to the rational and accelerated design of new functional compounds and materials. Taking photoswitches as an example, the thermal stability of the metastable state is a crucial property that dictates their application in molecular systems. Indigos have recently emerged as an attractive motif for designing photoswitchable molecules due to their red-light addressability, which can be advantageous in biomedical and material applications. The lack of synthetic techniques to derivatize the abundant parent dye and a thorough understanding of the impact of structural factors on the photochemical and thermal properties hinder broad applications of this emerging photoswitch class. Herein, we report an efficient copper-catalyzed indigo N-arylation that enables the installation of a wide variety of aryl moieties carrying useful functional groups. The exclusive selectivity for monoarylation likely originates from a bimetallic cooperative mechanism through a binuclear copper-indigo intermediate. Functional N-aryl-N'-alkylindigos were prepared and shown to photoisomerize efficiently under red light. Moreover, this design allows for the modulation of thermal half-lives through N-aryl substituents, while the N'-alkyl groups enable the independent attachment of functional moieties without affecting the photochromic properties. A strong correlation between the structure of the N-aryl moiety and the thermal stability of the photogenerated Z-isomers was achieved by multivariate linear regression models obtained through a data-science workflow. This work thus builds an avenue leading to versatile red-light photoswitches and a general method for structure-property correlation that is expected to be broadly applicable to the design of photoresponsive molecules.

A high-affinity, cis-on photoswitchable beta blocker to optically control β2-adrenergic receptors in vitro and in vivo

This study introduces (S)-Opto-prop-2, a second-generation photoswitchable ligand designed for precise modulation of β2-adrenoceptor (β2AR). Synthesised by incorporating an azobenzene moiety with propranolol, (S)-Opto-prop-2 exhibited a high PSScis (photostationary state for cis isomer) percentage (∼90 %) and a favourable half-life (>10 days), facilitating diverse bioassay measurements. In vitro, the cis-isomer displayed substantially higher β2AR binding affinity than the trans-isomer (1000-fold), making (S)-Opto-prop-2 one of the best photoswitchable GPCR (G protein-coupled receptor) ligands reported so far. Molecular docking of (S)-Opto-prop-2 in the X-ray structure of propranolol-bound β2AR followed by site-directed mutagenesis studies, identified D1133.32, N3127.39 and F2896.51 as crucial residues that contribute to ligand-receptor interactions at the molecular level. In vivo efficacy was assessed using a rabbit ocular hypertension model, revealing that the cis isomer mimicked propranolol's effects in reducing intraocular pressure, while the trans isomer was inactive. Dynamic optical modulation of β2AR by (S)-Opto-prop-2 was demonstrated in two different cAMP bioassays and using live-cell confocal imaging, indicating reversible and dynamic control of β2AR activity using the new photopharmacology tool. In conclusion, (S)-Opto-prop-2 emerges as a promising photoswitchable ligand for precise and reversible β2AR modulation with light. The new tool shows superior cis-on binding affinity, one of the largest reported differences in affinity (1000-fold) between its two configurations, in vivo efficacy, and dynamic modulation. This study contributes valuable insights into the evolving field of photopharmacology, offering a potential avenue for targeted therapy in β2AR-associated pathologies.

Detour to success: photoswitching via indirect excitation

Photoswitchable molecules that undergo nanoscopic changes upon photoisomerisation can be harnessed to control macroscopic properties such as colour, solubility, shape, and motion of the systems they are incorporated into. These molecules find applications in various fields of chemistry, physics, biology, and materials science. Until recently, research efforts have focused on the design of efficient photoswitches responsive to low-energy (red or near-infrared) irradiation, which however may compromise other molecular properties such as thermal stability and robustness. Indirect isomerisation methods enable photoisomerisation with low-energy photons without altering the photoswitch core, and also open up new avenues in controlling the thermal switching mechanism. In this perspective, we present the state of the art of five indirect excitation methods: two-photon excitation, triplet sensitisation, photon upconversion, photoinduced electron transfer, and indirect thermal methods. Each impacts our understanding of the fundamental physicochemical properties of photochemical switches, and offers unique application prospects in biomedical technologies and beyond.

Solar Azo-Switches for Effective E→Z Photoisomerization by Sunlight

Natural photoactive systems have evolved to harness broad-spectrum light from solar radiation for critical functions such as light perception and photosynthetic energy conversion. Molecular photoswitches, which undergo structural changes upon light absorption, are artificial photoactive tools widely used for developing photoresponsive systems and converting light energy. However, photoswitches generally need to be activated by light of specific narrow wavelength ranges for effective photoconversion, which limits their ability to directly work under sunlight and to efficiently harvest solar energy. Here, focusing on azo-switches-the most extensively studied photoswitches, we demonstrate effective solar E→Z photoisomerization with photoconversions exceeding 80 % under unfiltered sunlight. These sunlight-driven azo-switches are developed by rendering the absorption of E isomers overwhelmingly stronger than that of Z isomers across a broad ultraviolet to visible spectrum. This unusual type of spectral profile is realized by a simple yet highly adjustable molecular design strategy, enabling the fine-tuning of spectral window that extends light absorption beyond 600 nm. Notably, back-photoconversion can be achieved without impairing the forward solar isomerization, resulting in unique light-reversible solar switches. Such exceptional solar chemistry of photoswitches provides unprecedented opportunities for developing sustainable light-driven systems and efficient solar energy technologies.

Getting a molecular grip on the half-lives of iminothioindoxyl photoswitches

Visible-light-operated photoswitches are of growing interest in reversibly controlling molecular processes, enabling for example the precise spatiotemporal focusing of drug activity and manipulating the properties of materials. Therefore, many research efforts have been spent on seeking control over the (photo)physical properties of photoswitches, in particular the absorption maxima and the half-life. For photopharmacological applications, photoswitches should ideally be operated by visible light in at least one direction, and feature a metastable isomer with a half-life of 0.1-10 seconds. Here we present our efforts towards the engineering of the half-life of iminothioindoxyl (ITI) photoswitches, a recently discovered class of visible-light-responsive photochromes, whose applicability was hitherto limited by half-lives in the low millisecond range. Through the synthesis and characterization of a library of ITI photoswitches, we discovered variants with a substantially increased thermal stability, reaching half-lives of up to 0.2 seconds. Based on spectroscopic and computational analyses, we demonstrate how different substituent positions on the ITI molecule can be used to tune its photophysical properties independently to fit the desired application. Additionally, the unique reactivity of the ITI derivative that featured a perfluoro-aromatic ring and had the most long-lived metastable state was shown to be useful for labeling of nucleophilic functional groups. The present research thus paves the way for using ITI photoswitches in photopharmacology and chemical biology.

Photocontrolled Reversible Amyloid Fibril Formation of Parathyroid Hormone-Derived Peptides

Peptide fibrillization is crucial in biological processes such as amyloid-related diseases and hormone storage, involving complex transitions between folded, unfolded, and aggregated states. We here employ light to induce reversible transitions between aggregated and nonaggregated states of a peptide, linked to the parathyroid hormone (PTH). The artificial light-switch 3-{[(4-aminomethyl)phenyl]diazenyl}benzoic acid (AMPB) is embedded into a segment of PTH, the peptide PTH25-37, to control aggregation, revealing position-dependent effects. Through in silico design, synthesis, and experimental validation of 11 novel PTH25-37-derived peptides, we predict and confirm the amyloid-forming capabilities of the AMPB-containing peptides. Quantum-chemical studies shed light on the photoswitching mechanism. Solid-state NMR studies suggest that β-strands are aligned parallel in fibrils of PTH25-37, while in one of the AMPB-containing peptides, β-strands are antiparallel. Simulations further highlight the significance of π-π interactions in the latter. This multifaceted approach enabled the identification of a peptide that can undergo repeated phototriggered transitions between fibrillated and defibrillated states, as demonstrated by different spectroscopic techniques. With this strategy, we unlock the potential to manipulate PTH to reversibly switch between active and inactive aggregated states, representing the first observation of a photostimulus-responsive hormone.

Deciphering the shape selective conformational equilibrium of E- and Z-locked azobenzene-tetraethylammonium ion in regulating photo-switchable K+-ion channel blocking

The search for photo-switchable optopharmacological agents that can block ion channels has been a prevalent area owing to its prime advantages of reversibility and specificity over the traditional blockers. However, the quest for a higher blocking ability shown by a less stable photo-isomer to perfectly suit the requirement of the optopharmacological agents is still ongoing. To date, only a marginal improvement in terms of blocking ability is observed by the less stable E-isomer of para-substituted locked azobenzene with TEA (LAB-TEA) for the K+-ion channel. Thus, rationalization of the limitation for achieving high activity by the E-isomer is rather essential to aid the improvement of the efficiency of photoswitchable blocker drugs. Herein, we report a molecular-level analysis on the mechanism of blocking by E- and Z-LAB-TEA with the bacterial KcsA K+-ion channel using Molecular Dynamics (MD) simulation and Quantum Mechanical (QM) calculations. The positively charged TEA fragment engages in stronger electrostatic interactions, while the neutral LAB fragment engages in weaker dispersive interactions. The binding free energy calculated by Molecular Mechanics Poisson-Boltzmann Surface Area (MMPBSA) for E-LAB-TEA (-22.3 kcal mol-1) shows less thermodynamic preference for binding with K+-ion channels than Z-LAB-TEA (-21.6 kcal mol-1) corroborating the experimental observation. The correlation between the structure and the binding ability of E- and Z-isomers of LAB-TEA indicates that the channel gate is narrow and acts as a bottleneck for the entry of the binder molecule inside the large cavity. Upon irradiation, the Z-isomer converts into a less stable but long and planar E-isomer (ΔE of photoisomerism = 7.0 kcal mol-1, at SA2-CASPT2(6,4)/6-31+G(d)//CASSCF(6,4)/6-31+G(d)), which is structurally more suitable to fit into the narrow channel gate rather than the curved and non-planar Z-LAB-TEA. Thus, a reduction in the ionic current is observed owing to the preferential entry and subsequent blocking by E-LAB-TEA. Discontinuing the irradiation leads to conversion to the Z-isomer, the curved nature of which hinders its spontaneous release outside the cavity, thereby contributing only a small increase in the ionic current.

Copper indium sulfide quantum dots enabling quantitative visible light photoisomerisation of (E)-azobenzene chromophores

Azobenzene derivatives have long been studied for their photochromic behaviour. One of the greatest challenges in this field is the quantitative (E) to (Z) photoconversion triggered by visible light irradiation. In this work, the synthesis and characterization of CuInS2 quantum dots (CIS-QDs) appended with azobenzene units are reported: quantitative (E) → (Z) isomerisation is obtained by visible light (e.g., λex = 533 nm). Interestingly, catalytic amounts of CIS-QDs allow the full photoconversion of ungrafted (E)-azobenzene derivatives into the corresponding (Z)-isomers using visible light. This peculiar behaviour is associated with the direct complexation of the (Z)-isomer on the QD surface.

A Site-Specific Cross-Linker for Visible-Light Control of Proteins

There is a need for photochemical tools that allow precise control of protein structure and function with visible light. We focus here on the s-tetrazine moiety, which can be installed at a specific protein site via the reaction between dichlorotetrazine and two adjacent sulfhydryl groups. Tetrazine's compact size enables structural mimicry of native amino acid linkages, such as an intramolecular salt bridge or disulfide bond. In this study, we investigated tetrazine installation in three different proteins, where it was confirmed that the cross-linking reaction is highly efficient in aqueous conditions and site-specific when two cysteines are located proximally: the S-S distance was 4-10 Å. As shown in maltose binding protein, the tetrazine cross-linker can replace an interdomain salt bridge crucial for xenon binding and serve as a visible-light photoswitch to modulate 129Xe NMR contrast. This work highlights the ease of aqueous tetrazine bioconjugation and its applications for protein photoregulation.

Photocontrol of small GTPase Ras fused with a photoresponsive protein

The small GTPase Ras plays an important role in intracellular signal transduction and functions as a molecular switch. In this study, we used a photoresponsive protein as the molecular regulatory device to photoregulate Ras GTPase activity. Photo zipper (PZ), a variant of the photoresponsive protein Aureochrome1 developed by Hisatomi et al. was incorporated into the C-terminus of Ras as a fusion protein. The three constructs of the Ras-PZ fusion protein had spacers of different lengths between Ras and PZ. They were designed using an Escherichia coli expression system. The Ras-PZ fusion proteins exhibited photoisomerization upon blue light irradiation and in the dark. Ras-PZ dimerized upon light irradiation. Moreover, Ras GTPase activity, which is accelerated by the Ras regulators guanine nucleotide exchange factors and GTPase-activating proteins, is controlled by photoisomerization. It has been suggested that light-responsive proteins are applicable to the photoswitching of the enzymatic activity of small GTPases as photoregulatory molecular devices.

An ultrawide-range photochromic molecular fluorescence emitter

Photocontrollable luminescent molecular switches capable of changing emitting color have been regarded as the ideal integration between intelligent and luminescent materials. A remaining challenge is to combine good luminescence properties with wide range of wavelength transformation, especially when confined in a single molecular system that forms well-defined nanostructures. Here, we report a π-expanded photochromic molecular photoswitch, which allows for the comprehensive achievements including wide emission wavelength variation (240 nm wide, 400-640 nm), high photoisomerization extent (95%), and pure emission color (<100 nm of full width at half maximum). We take the advantageous mechanism of modulating self-assembly and intramolecular charge transfer in the synthesis and construction, and further realize the full color emission by simple photocontrol. Based on this, both photoactivated anti-counterfeiting function and self-erasing photowriting films are achieved of fluorescence. This work will provide insight into the design of intelligent optical materials.

ATP/azobenzene-guanidinium self-assembly into fluorescent and multi-stimuli-responsive supramolecular aggregates

Building stimuli-responsive supramolecular systems is a way for chemists to achieve spatio-temporal control over complex systems as well as a promising strategy for applications ranging from sensing to drug-delivery. For its large spectrum of biological and biomedical implications, adenosine 5'-triphosphate (ATP) is a particularly interesting target for such a purpose but photoresponsive ATP-based systems have mainly been relying on covalent modification of ATP. Here, we show that simply mixing ATP with AzoDiGua, an azobenzene-guanidium compound with photodependent nucleotide binding affinity, results in the spontaneous self-assembly of the two non-fluorescent compounds into photoreversible, micrometer-sized and fluorescent aggregates. Obtained in water at room temperature and physiological pH, these supramolecular structures are dynamic and respond to several chemical, physical and biological stimuli. The presence of azobenzene allows a fast and photoreversible control of their assembly. ATP chelating properties to metal dications enable ion-triggered disassembly and fluorescence control with valence-selectivity. Finally, the supramolecular aggregates are disassembled by alkaline phosphatase in a few minutes at room temperature, resulting in enzymatic control of fluorescence. These results highlight the interest of using a photoswitchable nucleotide binding partner as a self-assembly brick to build highly responsive supramolecular entities involving biological targets without the need to covalently modify them.

Photoswitchable positive allosteric modulators of metabotropic glutamate receptor 4 to improve selectivity

Metabotropic glutamate receptors (mGlu) regulate multiple functions in the nervous systems and are involved in several neurological disorders. However, selectively targeting individual mGlu subtypes with spatiotemporal precision is still an unmet need. Photopharmacology can address this concern through the utilization of photoswitchable compounds such as optogluram, which is a positive allosteric modulator (PAM) of mGlu4 that enables the precise control of physiological responses using light but does not have an optimal selectivity profile. Optogluram analogs were developed to obtain photoswitchable PAMs of mGlu4 receptor with an improved selectivity. Among them, optogluram-2 emerged as a photoswitchable ligand for mGlu4 receptor with activity as both PAM and allosteric agonists. It presents a higher selectivity and offers improved photoswitching of mGlu4 activity. These improved properties make optogluram-2 an excellent candidate to study the role of mGlu4 with a high spatiotemporal precision in systems where mGlu4 can be co-expressed with other mGlu receptors.

Pyrene Functionalized Norbornadiene-Quadricyclane Fluorescent Photoswitches: Characterization of their Spectral Properties and Application in Imaging of Amyloid Beta Plaques

This study presents the synthesis and characterization of two fluorescent norbornadiene (NBD) photoswitches, each incorporating two conjugated pyrene units. Expanding on the limited repertoire of reported photoswitchable fluorescent NBDs, we explore their properties with a focus on applications in bioimaging of amyloid beta (Aβ) plaques. While the fluorescence emission of the NBD decreases upon photoisomerization, aligning with what has been previously reported, for the first time we observed luminescence after irradiation of the quadricyclane (QC) isomer. We deduce how the observed emission is induced by photoisomerization to the excited state of the parent isomer (NBD) which is then the emitting species. Thorough characterizations including NMR, UV-Vis, fluorescence, X-ray structural analysis and density functional theory (DFT) calculations provide a comprehensive understanding of these systems. Notably, one NBD-QC system exhibits exceptional durability. Additionally, these molecules serve as effective fluorescent stains targeting Aβ plaques in situ, with observed NBD/QC switching within the plaques. Molecular docking simulations explore NBD interactions with amyloid, unveiling novel binding modes. These insights mark a crucial advancement in the comprehension and design of future photochromic NBDs for bioimaging applications and beyond, emphasizing their potential in studying and addressing protein aggregates.

Photochromic luminescence of organic crystals arising from subtle molecular rearrangement

Photoluminescence (PL) colour-changing materials in response to photostimulus play an increasingly significant role in intelligent applications for their programmability. Nevertheless, current research mainly focuses on photochemical processes, with less attention to PL transformation through uniform aggregation mode adjustment. Here we show photochromic luminescence in organic crystals (e.g. dimethyl terephthalate) with PL varying from dark blue to purple, then to bright orange-red, and finally to red. This change is attributed to the emergence of clusters with red emission, which is barely achieved in single-benzene-based structures, thanks to the subtle molecular rearrangements prompted by light. Crucial to this process are the through-space electron interactions among molecules and moderate short contacts between ester groups. The irradiated crystals exhibit reversible PL transformation upon sufficient relaxation, showing promising applications in information storage and smart optoelectronic devices. This research contributes to the development of smart photochromic luminescent materials with significant PL colour transformations through molecular rearrangement.