Search

Light-responsive liquid crystal elastomers (LCEs) are stimuli-responsive materials that facilitate the conversion of light energy into a mechanical response. In this work, a novel polysiloxane-based LCE with donor-acceptor Stenhouse adduct (DASA) side-chains is synthesized using a late-stage functionalization strategy. It is demonstrated that this approach does not compromise the molecular alignment observed in the traditional Finkelmann method. This easy, single-batch process provides a robust platform to access well-aligned, light-responsive LCE films with thickness ranging from 400 µm to a 14-layer stack that is 5 mm thick. Upon irradiation with low-intensity broadband visible light (100-200 mW cm-2), these systems undergo 2D planar actuation and complete bleaching. Conversely, exposure to higher-intensity visible light induces bending followed by contraction (300 mW cm-2). These processes are repeatable over several cycles. Finally, it is demonstrated how light intensity and the resulting heat generation influences the photothermal stationary state equilibrium of DASA, thereby controlling its photoresponsive properties. This work establishes the groundwork for advancement of LCE-based actuators beyond thin film and UV-light reliant systems.

ABSTRACT The synthesis of new photochromic lactone‐fused naphthopyrans substituted with arylethenyl groups is discussed. Brief exposure of solutions of these colorless compounds to the UV light results in the generation of intense hues, which spontaneously return to the uncolored state within seconds after removing the light source. As anticipated, introducing the ethenyl bonds caused a bathochromic shift in the absorption spectrum of the opened colored photoisomers, however, due to non‐uniform absorption across the visible spectrum, the perceived color ranged from red to brownish‐red. [ABSTRACT FROM AUTHOR]

Cholesteric liquid crystals (CLCs) with chiral nanostructures take on great significance in light modulation for optical devices, especially involving the features of circularly polarized and dynamic structural colors. However, on‐demand self‐assembly by photoprogramming still remains a challenge that is ascribed to the unpredictable variation of the helical superstructures in the existing CLCs induced by light‐driven chiral switches. Here, novel binary chiral systems are designed to construct visible‐light‐actuated CLCs with multi‐degrees of freedom, including adjustable circular polarization, bidirectional photochromism, and manipulable photonic bands. Such systems consist of an o‐fluoroazobenzene‐containing chiral switch and an inert chiral dopant, whose interaction dominates the strategies of chiral cooperation or conflict to determine the CLC handedness as well as shift direction of the selective reflection. Particularly, the precise tuning range of the structural color is tailored by programmable helical twisting power to enable diverse paradigms of light‐actuated patterning. The unprecedented quantitative manipulation of circularly polarized structural colors offers unique photonic attributes for applications in information encoding and multiplexed communication. [ABSTRACT FROM AUTHOR]

Nucleosidic diarylethenes (DAEs) have evolved from an emerging class of photochromes into a well‐established option for integrating photochromic functionalities into biological systems. However, a comprehensive understanding of how chemical structure influences their photochromic properties remains essential. While structural features, such as an inverse connection between the aryl residues and the ethene bridge, are well‐documented for classical DAEs, their application to nucleosidic DAEs has been underexplored. In this study, we address this gap by developing three distinct types of inverse nucleosidic DAEs–semi‐inverse thiophenes, semi‐inverse uridines and inverse uridines. We successfully synthesized these compounds and conducted comprehensive analyses of their photostationary states, thermal stability, reversibility, and reaction quantum yields. Additionally, we conducted an in‐depth comparison of their photochromic properties with those of their normal‐type counterparts. Among the synthesized compounds, seven semi‐inverse thiophenes exhibited the most promising characteristics. Notably, these compounds demonstrated excellent fatigue resistance, with up to 96 % retention of photochromic activity over 40 switching cycles, surpassing the performance of all comparable nucleosidic DAEs reported to date. These findings hold significant promise for future applications in various fields. [ABSTRACT FROM AUTHOR]

We report the synthesis and characterization of library of new 2,3–disubstituted norbornadiene/quadricyclane couples. For the first time, the para–tolylsulfone moiety was employed as electron–withdrawing substituent in combination with a variety of different electron donors as counterparts. Comprehensive characterization was conducted for every interconversion couple. By comparison with structurally related molecules published before we established the tosyl moiety as suitable alternative to previously investigated ester functionalities by providing similar photophysical properties. The photo–induced interconversion behavior was investigated via UV/Vis‐ and NMR–spectroscopy. The UV/Vis experiments were carried out exclusively in acetonitrile, whereas several solvents were investigated in the NMR studies. A detailed description and comparison of the isomerization behavior is provided, while examining relevant optical properties like λmax and λonset. Thereby, an enhanced red‐shift up to λmax=394 nm combined with an λonset value of 469 nm could be generated which is necessary for potential applications. [ABSTRACT FROM AUTHOR]

The functionality and efficiency of proteins within a biological membrane are highly dependent on both the membrane lipid composition and the physiochemical properties of the solution. Lipid mesophases are directly influenced by changes in temperature, pH, water content or due to individual properties of single lipids such as photoswitchability. In this work, we were able to induce light- and temperature-driven mesophase transitions in a model membrane system containing a mixture of 1,2-dipalmitoyl-phosphatidylcholine phospholipids and azobenzene amphiphiles. We observed reversible and reproducible transitions between the lamellar and Pn3m cubic phase after illuminating the sample for 5 min with light of 365 and 455 nm wavelengths, respectively, to switch between the cis and trans states of the azobenzene N=N double bond. These light-controlled mesophase transitions were found for mixed complexes with up to 20% content of the photosensitive molecule and at temperatures below the gel-to-liquid crystalline phase transition temperature of 33°C. Our results demonstrate the potential to design bespoke model systems to study the response of membrane lipids and proteins upon changes in mesophase without altering the environment and thus provide a possible basis for drug delivery systems.

Here we report the design, synthesis, and photoresponsive behavior of supramolecular liquid crystalline (LC) materials based on benzenetricarboxamide and di‐ortho substituted azobenzene. Differential scanning calorimetry, polarized optical microscopy, and wide‐angle X‐ray scattering studies confirm the formation of columnar tetragonal mesophase at room‐temperature. Photoisomerization studies reveal the visible light responsiveness of compounds in solution. Furthermore, we demonstrate supramolecular gel formation, which undergoes irreversible gel‐sol transformation upon blue light irradiation, highlighting its potential for light‐triggered applications in the field of drug delivery, energy storage etc. [ABSTRACT FROM AUTHOR]

New approaches for the integration of chemical and physical stimuli to control the dynamics of artificial enzymatic reaction networks (ERNs) are needed. Here, we present a general approach to convert a light stimulus into a time‐programmed pH response. We developed and characterized a panel of photoswitchable inhibitors of urease. Urease activity, now regulated by light via the photoinhibitors, leads to an increase in pH upon hydrolysis of urea into ammonia. Careful choice of characteristics of light, and concentrations of enzyme, substrate, and photoinhibitor, allowed us to control the timing of the pH transition. Furthermore, as all enzymes have an activity–pH profile, the urease photoinhibitor system can be used to regulate the activities of other enzymes in small reaction networks. [ABSTRACT FROM AUTHOR]

Owing to their property to alter their surface‐activity upon the irradiation with light, photoswitchable surfactants have gained tremendous interest in colloidal science. Their mere addition to a colloidal system allows, e. g., to obtain control over polyelectrolytes, micro‐ and nanoscale particles or emulsions. Most literature examples focus on azobenzene‐based, or related, systems, which employ a photoisomerization reaction for switching. Other structures, such as spiropyrans, play a subordinate role, although they have gained increasing attention over the past few years. In this perspective article, we want to provide an overview about existing systems of photoswitchable surfactants. We address the issue that alternative photoswitches are given less attention, and what benefits surfactants could possess that are based on said switchable units. With our contribution, we want to broaden the view on stimuli‐responsive surfactants – and to provide a guideline for the design of novel structures. [ABSTRACT FROM AUTHOR]

RNA‐based tools for biological and pharmacological research are raising an increasing interest. Among these, RNA aptamers whose biological activity can be controlled via illumination with specific wavelengths represent an important target. Here, we report on a proof‐of‐principle study supporting the viability of a systematic use of Morita‐Baylis‐Hillman adducts (MBHAs) for the synthesis of light‐responsive RNA building blocks. Accordingly, a specific acetylated MBHA derivative was employed in the functionalization of the four natural RNA bases as well as two unnatural bases (5‐aminomethyl uracil and 5‐methylaminomethyl uracil). The results reveal a highly selective functionalization for both unnatural bases. The conjugation products were then investigated spectroscopically, photochemically and computationally. It is shown that when a single light‐responsive unit is present (i. e. when using 5‐methylaminomethyl uracil), the generated unnatural uracil behaves like a cinnamic‐framework‐based photochemical switch that isomerizes upon illumination through a biomimetic light‐induced intramolecular charge transfer mechanism driving a barrierless and, therefore, ultrafast reaction path. [ABSTRACT FROM AUTHOR]

Stimuli responsive optical materials are attractive for many areas, from healthcare to art design. However, creating intricate color‐changing patterns for visual information is still a challenge. This work describes the preparation of mechanochromic structural colored intricate pictures imprinted in cholesteric liquid crystal elastomers by using a chiral isosorbide molecular photoswitch. The photoswitch contains a photoisomerizable cinnamate moiety and was incorporated in a main chain liquid crystal oligomer with photopolymerizable acrylate end groups. After coating, the structural colored film was irradiated with ultraviolet (UV) light in air causing E/Z isomerization of the cinnamate units leading to a redshift of the structural color of the film. A grayscale photomask was used to spatially control the photoisomerization reaction and imprint colorful pictures such as portraits and landscapes, in the cholesteric liquid crystal films with high resolution. Photopolymerization in a nitrogen atmosphere led to a mechanochromic cholesteric liquid crystal elastomer with striking structural colors that blueshift upon strain. The sharp details of the patterns were preserved even under deformation and the system returned to the initial state upon strain removal. Our work offers a simple photoswitch approach to prepare stimuli responsive optical polymers imprinted with color‐changing pictures of unprecedented complexity. [ABSTRACT FROM AUTHOR]

Time‐resolved photofluorochromism constitutes a powerful approach to enhance information encryption security but remains challenging. Herein, we report a strategy of using hydrogen bonds to regulate the time for initiating photofluorochromism. In our strategy, copolymers containing negative photochromic spiropyran (NSP), naphthalimide, and multiple hydrogen‐bonding (UPy) units are designed, which display photo‐switchable fluorescence resonance energy transfer (FRET) process from naphthalimide donor to the NSP acceptor. Interestingly, the FRET is locked via the dynamic hydrogen‐bonding interaction between ring‐opened NSP and UPy moieties, resulting in time‐dependent fluorescence. The change in fluorescence can be finely regulated via UPy fraction in the polymers. Besides the novel time‐dependent fluorescence, the polymers also take advantage of visible‐light triggerable, excellent photostability, photoreversibility, and processability. We demonstrate that these properties enable them many application opportunities such as fluorescent security labels and multilevel information encryption patterns. [ABSTRACT FROM AUTHOR]

Herein, we report monomeric and dimeric norbornadiene‐quadricyclane molecular photoswitch systems intended for molecular solar thermal applications. A series of six new norbornadiene derivatives conjugated with benzothiadiazole as the acceptor unit and dithiafulvene as the donor unit were synthesized and fully characterized. The photoswitches were evaluated by experimentally and theoretically measuring optical absorption profiles and thermal conversion of quadricyclane to norbornadiene. Computational insight by density functional theory calculations at the M06‐2X/def2‐SVPD level of theory provided geometries, storage energies, UV‐vis absorption spectra, and HOMO‐LUMO levels that are used to describe the function of the molecular systems. The studied molecules exhibit absorption onset ranging from 416 nm to 595 nm due to a systemic change in their donor‐acceptor character. This approach was advantageous due to the introduction of benzothiadiazole and the dimeric nature of molecular structures. The best‐performing system has a half‐life of 3 days with quantum yields over 50 %. [ABSTRACT FROM AUTHOR]

Optoacoustic (or photoacoustic) imaging promises micron‐resolution noninvasive bioimaging with much deeper penetration (>cm) than fluorescence. However, optoacoustic imaging of enzyme activity would require loud, photostable, NIR‐absorbing molecular contrast agents, which remain unknown. Most organic molecular contrast agents are repurposed fluorophores, with severe shortcomings of photoinstability or phototoxicity under optoacoustic imaging, as consequences of their slow S1→S0 electronic relaxation. We now report that known fluorophores can be rationally modified to reach ultrafast S1→S0 rates, without much extra molecular complexity, simply by merging them with molecular switches. Here, we merge azobenzene switches with cyanine dyes to give ultrafast relaxation (<10 ps, >100‐fold faster). Without even adapting instrument settings, these azohemicyanines display outstanding improvements in signal longevity (>1000‐fold increase of photostability) and signal loudness (>3‐fold even at time zero). We show why this simple but unexplored design strategy can still offer stronger performance in the future, and can also increase the spatial resolution and the quantitative linearity of photoacoustic response over extended longitudinal imaging. By bringing the world of molecular switches and rotors to bear on problems facing optoacoustic agents, this practical strategy will help to unleash the full potential of optoacoustic imaging in fundamental studies and translational uses. [ABSTRACT FROM AUTHOR]

Styrylbenzazoles form a promising yet under‐represented class of photoswitches that can perform a light‐driven E‐Z isomerization of the central alkene double bond without undergoing irreversible photocyclization, typical of the parent stilbene. In this work, we report the synthesis and photochemical study of 23 styrylbenzazole photoswitches. Their thermal stabilities, quantum yields, maximum absorption wavelengths and photostationary state (PSS) distributions can be tuned by changing the benzazole heterocycle and the substitution pattern on the aryl ring. In particular, we found that push‐pull systems show large redshifts of the maximum absorption wavelengths and the highest quantum yields, whereas ortho‐substituted styrylbenzazole photoswitches exhibit the most favorable PSS ratios. Taking advantage of both design principles, we produced 2,6‐dimethyl‐4‐(dimethylamino)‐styrylbenzothiazole, a thermally stable and efficient P‐type photoswitch which displays negative photochromism upon irradiation with visible light up to 470 nm to obtain a near‐quantitative isomerization with a very high quantum yield of 59 %. Furthermore, 4‐hydroxystyrylbenzoxazole was demonstrated to be a pH‐sensitive switch which exhibits a 100 nm redshift upon deprotonation. Ortho‐methylation of its benzothiazole analogue improved the obtained PSS ratio in its deprotonated state from E : Z=53 : 47 to E : Z=18 : 82. We anticipate that this relatively unexplored class of photoswitches will form a valuable expansion of the current family of photoswitches. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Donor‐Acceptor Stenhouse Adduct (DASA), a class of push‐pull negative photochrome, has received large interest lately owing to its versatile synthesis, modularity and excellent photoswitching in solutions. From a technological perspective, it is imperative for this class of photoswitches to work robustly in solid state, e. g. thin films. We feature a molecular framework for the optimized design of DASAs by introducing a new thioindoline donor (D3) and assessing its performance against known 2nd generation indoline‐based donors. The systematic structure‐function investigations suggest that to achieve robust reversible photoswitching, a ground state with low charge separation is desired. DASAs with stronger electron donors and a larger charge separation in the ground state result in a low population of the photothermalstationary state (PTSS) and reduced photostability. The DASA with thioindoline donor (D3A3) seems to be a special case among the donor series as it causes a red shift (ca. 15 nm), however with less polarization of the ground state and marginally better photostability as compared to the unsubstituted 2‐methyl indoline (D1A3). We also emphasize the consideration of the key additional factors that can modulate the red‐light photoswitching properties of DASA chromophores in polymer thin films, which might not be dominant in homogenous solution state. [ABSTRACT FROM AUTHOR]

Proteases are involved in many essential biological processes. Dysregulation of their activity underlies a wide variety of human diseases. Photopharmacology, as applied on various classes of proteins, has the potential to assist protease research by enabling spatiotemporal control of protease activity. Moreover, it may be used to decrease side-effects of protease-targeting drugs. In this review, we discuss the current status of the chemical design of photoactivatable proteases inhibitors and their biological application. Additionally, we give insight into future possibilities for further development of this field of research. [ABSTRACT FROM AUTHOR]

Supramolecular polymers offer tremendous potential to produce new "smart" materials, however, there remains a need to develop systems that are responsive to external stimuli. In this work, visible‐light responsive hydrogen‐bonded supramolecular polymers comprising photoresponsive supramolecular synthons (I–III) consisting of two hydrogen bonding motifs (HBMs) connected by a central ortho‐tetrafluorinated azobenzene have been characterized by DOSY NMR and viscometry. Comparison of different hydrogen‐bonding motifs reveals that assembly in the low and high concentration regimes is strongly influenced by the strength of association between the HBMs. I, Incorporating a triply hydrogen‐bonded heterodimer, was found to exhibit concentration dependent switching between a monomeric pseudo‐cycle and supramolecular oligomer through intermolecular hydrogen bonding interactions between the HBMs. II, Based on the same photoresponsive scaffold, and incorporating a quadruply hydrogen‐bonded homodimer was found to form a supramolecular polymer which was dependent upon the ring‐chain equilibrium and thus dependent upon both concentration and photochemical stimulus. Finally, III, incorporating a quadruply hydrogen‐bonded heterodimer represents the first photoswitchable AB type hydrogen‐bonded supramolecular polymer. Depending on the concentration and photostationary state, four different assemblies dominate for both monomers II and III, demonstrating the ability to control supramolecular assembly and physical properties triggered by light. [ABSTRACT FROM AUTHOR]

Photoswitches are molecules that can absorb light of specific wavelengths and undergo a reversible transformation between their trans and cis isomeric forms. In phenylazo photoswitches, it is common for the less stable cis (Z) isomer to convert back to the more stable trans (E) isomer either through photochemical or thermal means. In this research, we designed new derivatives of phenylazothiazole (PAT) photoswitches, PAT‐Fn, which feature fluorine substituents on their phenyl component. These derivatives can reversibly isomerize under visible light exposure with the enrichment of E and Z isomers at photostationary state (PSS). Surprisingly, we observed an unconventional phenomenon when these PAT‐Fn (n≧2) photoswitches were in their cis isomeric state in the absence of light. Instead of the anticipated transformation from cis to trans isomer, these compounds converted to an oligomeric compound. Our detailed experimental investigation and theoretical calculations, indicated the crucial role of fluorine substituents and the distinctive geometric arrangement of the cis isomer in driving the unexpected oligomerization process originating from the cis isomeric state. [ABSTRACT FROM AUTHOR]

Gene transcription patterns can be perturbed by modulating epigenetic marks using photoresponsive probes. Photoswitches and photocages offer unprecedented precision in studying (RNA) epigenetics from in vitro to downstream events in vivo. RNA epigenetics is in its infancy, but provides a new multi-layer code where precise intervention may contribute to its deciphering. Optochemical tools have become potent instruments for understanding biological processes at the molecular level, and the past decade has witnessed their use in epigenetics and epitranscriptomics (also known as RNA epigenetics) for deciphering gene expression regulation. By using photoresponsive molecules such as photoswitches and photocages, researchers can achieve precise control over when and where specific events occur. Therefore, these are invaluable for studying both histone and nucleotide modifications and exploring disease-related mechanisms. We systematically report and assess current examples in the field, and identify open challenges and future directions. These outstanding proof-of-concept investigations will inspire other chemical biologists to participate in these emerging fields given the potential of photochromic molecules in research and biomedicine. [ABSTRACT FROM AUTHOR]

Antibiotic resistance is an escalating global health threat. Due to their diverse mechanisms of action and evasion of traditional resistance mechanisms, peptides hold promise as future antibiotics. Their ability to disrupt bacterial membranes presents a potential strategy to combat drug‐resistant infections and address the increasing need for effective antimicrobial treatments. Amphipathic α‐helical peptides possess a distinctive molecular structure with both charged/hydrophilic and hydrophobic regions that interact with the bacterial cell membrane, disrupting its structural integrity. The α‐helical amphipathic peptide aurein 1.2, secreted by the Australian frog Litoria aurea, is one of the shortest known antimicrobial peptides, spanning only 13 amino acids. The primary objective of this study was to investigate stapled and photoswitchable modifications of short helical peptides employing biocompatible chemistry, utilising aurein 1.2 as a model system. We developed various stapled versions of aurein 1.2 using biocompatible conjugation chemistry between dicyanopyridine and 1,2‐aminothiols. While the commonly employed stapling pattern for longer staples is i, i + 7, we observed superior helicity in peptides stapled at positions i, i + 8. Molecular dynamics simulations confirmed both stapling patterns to support an α‐helical peptide conformation. Additionally, we utilised a cysteine‐selective photosensitive staple, perfluoro azobenzene, to explore photoswitchable variants of aurein 1.2. A double‐cysteine variant stapled at i, i + 7 indeed exhibited a change in overall helicity induced by light. We further demonstrated the applicability of this staple to attach to cysteine residues in i, i + 7 positions of a helix in a model protein. While some of the stapled variants displayed substantial increase in helicity, minimal inhibitory concentration assays revealed that none of the stapled aurein 1.2 variants exhibited increased antimicrobial activity compared to the wildtype. [ABSTRACT FROM AUTHOR]

A smart window is an optical dimming device with intelligent functions that can control its relevant performances through external stimuli, achieving functions such as privacy protection and temperature regulation. Light is an ideal stimulus for regulating smart windows, which is noninvasive and allows self‐adaptable manipulation of materials. This review highlights recent significant achievements in smart windows constructed by photo‐responsive liquid crystals (LCs) systems that can undergo the transition between different phases. The smart windows based on photo‐responsive LCs are used in a plethora of areas, including privacy protection, absorption glass, building decoration, energy saving, and climate modulation applications. The review concludes with a brief perspective on some significant challenges and opportunities for the future development of photo‐responsive smart windows, which is crucial for expanding the applications of smart windows and improving their performances. [ABSTRACT FROM AUTHOR]

Merocyanines (MC) usually adopt ring opened zwitterionic structures that are interconvertible with their ring‐closed spiropyran photoisomers. By methylating the phenolate oxygen, and thereby blocking the ring‐closure reaction, a cis/trans‐only MC photoswitch was obtained, yielding a perfect candidate for a detailed examination of the cis/trans isomerization mechanism for this class of compounds. This photoswitch displays outstanding properties including excellent photoreaction quantum yields and photoswitching turnovers. Due to the central polymethine bridge of MC, in principle eight cis (C)/trans/(T) isomers are possible. Density Functional Theory (DFT) calculations revealed the CCT and TTT‐isomers of the studied compound as most stable cis and trans ground state isomers, respectively. UV/vis transient absorption studies combined with conical intersection computations with the complete active space self‐consistent field (CASSCF) method show that both trans/cis‐ and cis/trans‐photoisomerizations are initiated by a rotation of the central doubled bond fragment. A hot ground state species is then formed, which undergoes a second isomerization. Thus, the cis/trans reaction proceeds via a CCT‐CTT‐TTT sequence and the reverse reaction via TTT‐TCT‐CCT. [ABSTRACT FROM AUTHOR]

Photochromism is a reversible phenomenon wherein a material undergoes a change in color upon exposure to light. In organic photochromes, this effect often results from light‐induced isomerization reactions, leading to alterations in either the spatial orientation or electronic properties of the photochrome. The incorporation of photochromic moieties into biomolecules, such as proteins or nucleic acids, has become a prevalent approach to render these biomolecules responsive to light stimuli. Utilizing light as a trigger for the manipulation of biomolecular structure and function offers numerous advantages compared to other stimuli, such as chemical or electrical treatments, due to its non‐invasive nature. Consequently, light proves particularly advantageous in cellular and tissue applications. In this review, we emphasize recent advancements in the field of photochromic nucleosides and oligonucleotides. We provide an overview of the design principles of different classes of photochromes, synthetic strategies, critical analytical challenges, as well as structure–property relationships. The applications of photochromic nucleic acid derivatives encompass diverse domains, ranging from the precise photoregulation of gene expression to the controlled modulation of the three‐dimensional structures of oligonucleotides and the development of DNA‐based fluorescence modulators. Moreover, we present a future perspective on potential modifications and applications. [ABSTRACT FROM AUTHOR]

The exceptional thermal stability of diarylethene closed isomers enabled many applications but also prevented utilization in photochromic systems that require rapid thermal reversibility. Herein, we report the diaryltriazolium (DAT+) photoswitch undergoing thermal cycloreversion within a few milliseconds and absorption of the closed form in the near‐infrared region above 900 nm. Click chemistry followed by alkylation offers modular and fast access to the electron‐deficient DAT+ scaffold. In addition to excellent fatigue resistance, the introduced charge increases water solubility, rendering this photoswitch an ideal candidate for exploring biological applications. [ABSTRACT FROM AUTHOR]

Triarylhydrazones represent an attractive class of photochromic compounds offering many interesting features including high molar absorptivity, good addressability, and extraordinary thermal stability. In addition, unlike most other hydrazone‐based photoswitches, they effectively absorb light above 365 nm. However, previously prepared triaryhydrazones suffer from low quantum yields of the Z→E photoisomerization. Here, we have designed a new subclass of naphthoyl‐benzothiazole hydrazones that balance the most beneficial features of previously reported naphthoyl‐quinoline and benzoyl‐pyridine triarylhydrazones. These preserve the attractive absorption characteristics, exhibit higher thermal stability of the metastable form than the former and enhance the rate of the Z→E photoisomerization compared to the later, as a result of the weakening of the intramolecular hydrogen bonding between the hydrazone hydrogen and the benzothiazole moiety. Introducing the benzothiazole motif extends the tunability of the photochromic behaviour of hydrazone‐based switches. [ABSTRACT FROM AUTHOR]

Molecular solar thermal systems (MOSTs) are molecular systems based on couples of photoisomers (photoswitches), which combine solar energy conversion, storage, and release. In this work, we address the catalytically triggered energy release in the promising MOST couple phenylethylesternorbornadiene/quadricyclane (PENBD/PEQC) on a Au(111) surface in a combined liquid‐phase and surface science study. We investigated the system by photoelectrochemical infrared reflection absorption spectroscopy (PEC‐IRRAS) in the liquid phase, conventional IRRAS and synchrotron radiation photoelectron spectroscopy (SRPES) in ultra‐high vacuum (UHV). Au(111) is highly active towards catalytically triggered energy release. In the liquid phase, we did not observe any decomposition of the photoswitch, no deactivation of the catalyst within 100 conversion cycles and we could tune the energy release rate of the heterogeneously catalyzed process by applying an external potential. In UHV, submonolayers of PEQC on Au(111) are back‐converted to PENBD instantaneously, even at 110 K. Multilayers of PEQC are stable up to ~220 K. Above this temperature, the intrinsic mobility of the film is high enough that PEQC molecules come into direct contact with the Au(111) surface, which catalyzes the back‐conversion. We suggest that this process occurs via a singlet–triplet mechanism induced by electronic coupling between the PEQC molecules and the Au(111) surface. [ABSTRACT FROM AUTHOR]

This work reports the 23000‐ and 9200‐fold enhancement of the 15N nuclear spin polarization of cis and trans isomers of azobenzene, correspondingly, as compared to the thermal NMR signals at 9.4 T by exploiting signal amplification by reversible exchange (SABRE) and parahydrogen molecules at 400 nT simultaneously with light irradiation. Only cis‐azobenzene gains substantial hyperpolarization of its 15N spins directly from parahydrogen in SABRE through coherent polarization transfer. Consequently cis‐trans photoisomerization at ultralow magnetic field preserves the SABRE‐derived nuclear hyperpolarization of cis‐azobenzene resulting in hyperpolarization of trans‐azobenzene as well, despite its direct coordination with the SABRE Ir‐complex being sterically hindered. Moreover, the proposed approach, which we called photo‐SABRE, allows to hyperpolarize the long‐lived spin order of trans‐isomer 15N spins with a lifetime of about 25 minutes, which greatly exceeds their relaxation times at high (10 seconds) and low (200 seconds) magnetic field. Since this spin order in 15N2‐trans‐azobenzene is collectively formed by nuclei of different kinds, it can be detected by both 15N or 1H NMR spectroscopy. [ABSTRACT FROM AUTHOR]

The phosphate‐coordination triple helicates A2L3 (A=anion) with azobenzene‐spaced bis‐bis(urea) ligands (L) have proven to undergo a rare in situ photoisomerization (without disassembly of the structure) rather than the typically known, stepwise "disassembly‐isomerization‐reassembly" process. This is enabled by the structural self‐adaptability of the "aniono" assembly arising from multiple relatively weak and flexible hydrogen bonds between the phosphate anion and bis(urea) units. Notably, the Z→E thermal relaxation rate of the isomerized azobenzene unit is significantly decreased (up to 20‐fold) for the triple helicates compared to the free ligands. Moreover, the binding of chiral guest cations inside the cavity of the Z‐isomerized triple helicate can induce optically pure diastereomers, thus demonstrating a new strategy for making light‐activated chiroptical materials. [ABSTRACT FROM AUTHOR]

A huge variety of synthetic molecular machines and their components are developed, and their actuation at the molecular level is demonstrated and used in microscopic molecular systems and macroscopic materials. Not only the actuation but also their mechanical responses are critical to the applications. In other words, a molecular machine or a machine part insensitive to mechanical forces can produce mechanical work by another external stimulus even under mechanical loading as an actuator, whereas that sensitive to mechanical forces can be controlled to generate motions by mechanical forces as a mechanophore. To explore the mechanical response empirically, a molecular machine or a part of it has to be chemically incorporated in a polymer chain, through which elongational forces can be applied to the embedded molecule. Here, the mechanochemistry of component parts is reviewed for artificial molecular machines represented by photoswitches and mechanically interlocked architectures using polymer mechanochemistry. [ABSTRACT FROM AUTHOR]

The utilisation of light to achieve precise manipulation and control over the structure and function of supramolecular assemblies has emerged as a highly promising approach in the development of complex, configurable, or multifunctional systems and nanoscopic machine‐like entities. In this minireview, we highlight recent examples of self‐assembled and covalently bound cages and macrocycles with a focus on the external and internal functionalisation of a structure with a photoswitchable unit or the embedment of a photoswitch into the framework of a structure. Functionalising the interior or exterior of a supramolecular cage or macrocycle with a photoresponsive group enables control over different properties, such as guest binding or assembly in the solid‐state, while the overall shape of the assembly often undergoes no significant change. By directly integrating a photoswitchable unit into the framework of a supramolecular structure, the isomerisation can either induce a geometry change, the disassembly, or the disassembly and reassembly of the structure. Historical and recent examples covered in this review are based on azobenzene, diarylethene, stilbene photoswitches, or alkene motors that were incorporated into macrocycles and cages constructed by metal‐organic, dynamic covalent, or covalent bonds. [ABSTRACT FROM AUTHOR]

Herein, we report a tri‐component photochromic molecular cocktail that can be used to encrypt and decrypt information. The time‐dependent fluorescent response of this cocktail is highly non‐linear with respect to the set of inputs used (concentrations of the three photochromic components, excitation‐ and emission wavelengths), a property required for the generation of so‐called encryption keys. The all‐optical system can generate more than 80 million unique fluorescence responses by applying different input combinations and is operated using a conventional fluorimeter. [ABSTRACT FROM AUTHOR]

Non‐equilibrium chemical systems underpin multiple domains of contemporary interest, including supramolecular chemistry, molecular machines, systems chemistry, prebiotic chemistry, and energy transduction. Experimental chemists are now pioneering the realization of artificial systems that can harvest energy away from equilibrium. In this tutorial Review, we provide an overview of artificial molecular ratchets: the chemical mechanisms enabling energy absorption from the environment. By focusing on the mechanism type—rather than the application domain or energy source—we offer a unifying picture of seemingly disparate phenomena, which we hope will foster progress in this fascinating domain of science. [ABSTRACT FROM AUTHOR]

Acyl hydrazones are a class of synthetically important organic compounds that are recurrently in high demand for synthesis and use in various fields of chemistry and biology. We report the first Co(II) catalyzed one‐component one‐pot sustainable synthesis of acyl hydrazones only from acyl hydrazides under mild reaction conditions. Traditional and contemporary methodologies use two components (usually acyl hydrazides and aldehydes/ketones/alcohols/styrene) as the coupling partners. Our protocol, on the other hand, involves the in situ generation of aldehyde intermediate (detected by gas chromatography) from the acyl hydrazide, which then undergoes condensation with another molecule of the same acyl hydrazide in the same pot to yield acyl hydrazones in presence of mild base K2CO3 and low‐cost Co(OAc)2 ⋅ 4H2O as catalyst. This method shows good functional group tolerance with good to excellent yield of products. Furthermore, some of the resulting acyl hydrazones have been used as synthetic precursors and explored in various post‐synthetic modifications to afford N‐heterocyclic compounds. Furthermore, photoswitchable properties of few synthesized acyl hydrazones are also explored using their E/Z isomerization around the C=N bond, as realized by high‐pressure liquid chromatography (HPLC) and UV‐vis spectroscopic studies. [ABSTRACT FROM AUTHOR]

Synthetic supramolecular ion transporters find applications as potential therapeutics and as tools for engineering functional membranes. Stimuli‐responsive systems enable external control over transport, which is necessary for targeted activation. The Minireview provides an overview of current approaches to developing stimuli‐responsive ion transport systems, including channels and mobile carriers, that can be controlled using photo or redox inputs. [ABSTRACT FROM AUTHOR]

Aromatic units tethered with an azo (−N=N−) functionality comprise a unique class of compounds, known as molecular photoswitches, exhibiting a reversible transformation between their E‐ and Z‐isomers in response to photo‐irradiation. Photoswitches have been explored extensively in the recent past to prepare dynamic self‐assembled materials, optoelectronic devices, responsive biomaterials, and more. Most of such materials involve azobenzenes as the molecular photoswitch and to date, SciFinder lists more than 7000 articles and 1000 patents. Subsequently, a great deal of effort has been invested to improve the photo‐isomerization efficiency and related mesoscopic properties of azobenzenes. Recently, azoheteroarenes and cyclic azobenzenes, such as arylazopyrazoles, arylazoisoxazoles, arylazopyridines, and diazocines, have emerged as second generation molecular photoswitches beyond conventional azobenzenes. These photoswitches offer distinct photoswitching behavior and responsive properties which make them highly promising candidates for multifaceted applications ranging from photoresponsive materials to photopharmacophores. In this minireview, we introduce the structural refinement and photoresponsive properties of azoheteroarenes and diazocines and summarize the state‐of‐the‐art on utilizing these photoswitches as responsive building blocks in supramolecular assembly, material science and photopharmacology, highlighting their versatile photochemical behavior, enhanced functionality, and latest applications. [ABSTRACT FROM AUTHOR]

Photoswitches are molecular systems that are chemically transformed subsequent to interaction with light and they find potential application in many new technologies. The design and discovery of photoswitch candidates require intricate molecular engineering of a range of properties to optimize a candidate to a specific applications, a task which can be tackled efficiently using quantum chemical screening procedures. In this paper, we perform a large scale screening of approximately half a million bicyclic diene photoswitches in the context of molecular solar thermal energy storage using ab initio quantum chemical methods. We further device an efficient strategy for scoring the systems based on their predicted solar energy conversion efficiency and elucidate potential pitfalls of this approach. Our search through the chemical space of bicyclic dienes reveals systems with unprecedented solar energy conversion efficiencies and storage densities that show promising design guidelines for next generation molecular solar thermal energy storage systems. [ABSTRACT FROM AUTHOR]

Donor-acceptor Stenhouse adducts (DASAs) are visible-light-responsive photoswitches with a variety of emerging applications in photoresponsive materials. Their two-step modular synthesis, centered on the nucleophilic ring opening of an activated furan, makes DASAs readily accessible. However, the use of less reactive donors or acceptors renders the process slow and low yielding, which has limited their development. We demonstrate here that 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) promotes the ring-opening reaction and stabilizes the open isomer, allowing greatly reduced reaction times and increased yields for known derivatives. In addition, it provides access to previously unattainable DASA-based photoswitches and DASA-polymer conjugates. The role of HFIP and the photochromic properties of a set of new DASAs is probed using a combination of 1 H NMR and UV/Vis spectroscopy. The use of sterically hindered, electron-poor amines enabled the dark equilibrium to be decoupled from closed-isomer half-lives for the first time.

The advances made in the field of stimuli‐responsive catalysis during the last five years with a focus on the novel recently‐emerged directions and applications have been surveyed. Metal‐free catalysts and organometallic complexes, as well as biomimetic systems and extended structures, which display switchable catalytic activity for a variety of organic transformations, are discussed. Light‐activated systems comprised of photochromic molecules capable of modulating reaction rate, yield, or enantioselectivity based on geometric and electronic changes associated with photoisomerization are the focus of the detailed discussion. Alternative stimuli, including pH and temperature, which could be applied either alone or in combination with light, are also addressed. Recent advances clearly demonstrate that the capability to finely tune catalyst behavior via an external stimulus is a powerful tool that could alter the landscape of sustainable chemistry. [ABSTRACT FROM AUTHOR]

Compounds that disrupt microtubule dynamics, such as colchicine, paclitaxel, or Vinca alkaloids, have been broadly used in biological studies and have found application in clinical anticancer medications. However, their main disadvantage is the lack of specificity towards cancerous cells, leading to severe side effects. In this paper, we report the first synthesis of 12 new visible light photoswitchable colchicine-based microtubule inhibitors AzoCols. Among the obtained compounds, two photoswitches showed light-dependent cytotoxicity in cancerous cell lines (HCT116 and MCF-7). The most promising compound displayed a nearly twofold increase in potency. Moreover, dissimilar inhibition of purified tubulin polymerisation in cell-free assay and light-dependent disruption of microtubule organisation visualised by immunofluorescence imaging sheds light on the mechanism of action as microtubule photoswitchable destabilisers. The presented results provide a foundation towards the synthesis and development of a novel class of photoswitchable colchicine-based microtubule polymerisation inhibitors. [ABSTRACT FROM AUTHOR]

Optogenetics is a new approach for controlling neural circuits with numerous applications in both basic and clinical science. In retinal degenerative diseases, the photoreceptors die, but inner retinal cells remain largely intact. By expressing light sensitive proteins in the remaining cells, optogenetics has the potential to offer a novel approach to restoring vision. In the past several years, optogenetics has advanced into an early clinical stage, and promising results have been reported. At the current stage, there is an urgent need to develop hardware and software for clinical training, testing, and rehabilitation in optogenetic therapy, which is beyond the capability of existing ophthalmic equipment. In this paper, we present an engineering platform consisting of hardware and software utilities, which allow clinicians to interactively work with patients to explore and assess their vision in optogenetic treatment, providing the basis for prosthetic design, customization, and prescription. This approach is also applicable to other therapies that utilize light activation of neurons, such as photoswitches.Clinical and Translational Impact Statement–The engineering platform allows clinicians to conduct training, testing, and rehabilitation in optogenetic gene therapy for retinal degenerative diseases, providing the basis for prosthetic design, customization, and prescription.

We report the design, synthesis, characterization, and photochemistry of three photoresponsive azoheteroarene‐based neutral N‐donor ligands. Furthermore, those bidentate and tridentate ligands have been coordinated with Cu(I) and Cu(II) metal ions to form seven complexes exhibiting different geometries and nuclearities. Detailed studies of the electronic properties, photoswitching, and thermal reverse isomerization behavior of the photoswitched states of the free ligands and their metal complexes in different solvents are presented. [ABSTRACT FROM AUTHOR]

The optical modulation of fluorescence characteristics in molecular aggregates, which mainly involves diverse molecular stacking and the consequent intermolecular interactions, remains a significant challenge for potential applications in optical anticounterfeiting, data storage, and imaging. Here we successfully realize in situ fluorescence switching in molecular aggregates of thianaphthene‐dioxide derivatives by topological [2+2] photocycloaddition, which represents a promising way to regulate the molecular stacking and alter photophysical processes. Notably, 2‐(3,5‐bis‐trifluoromethylphenyl)benzo[b]thiophene‐dioxide (BTO‐TF) in both crystal and powder forms exhibits a unique switching from an initial nonfluorescent state to a highly fluorescent state (ΦPL=0.46) upon UV irradiation, because of the destruction of the [2+2] cycloaddition process by volume expansion of the photodimer. Furthermore, we demonstrate such a [2+2] photocycloaddition can occur when 2‐(4‐carboxypheny)benzo[b]thiophene‐dioxide (BTO‐OH) is doped within selective polymer matrixes, and can be utilized for the visualization of macrophase separation in polymer blends. [ABSTRACT FROM AUTHOR]

A chiral molecular plier's design, synthesis, characterisation and operations are presented. The molecular plier encompasses three units: a BINOL unit which acts as a pivot as well as a chiral inducer, an azobenzene unit, which acts as a photo‐switchable component and two zinc porphyrin, acting as a reporter. E to Z isomerisation persuaded by irradiating with 370 nm light alters the dihedral angle of the pivot BINOL unit, which adjusts the distance between two porphyrin units. The plier can be switched to its initial state by exposure to 456 nm light or heating at 50 °C. NMR, CD and molecular modelling supported the reversible switching and change in dihedral angle and distance between reporter moiety, which was further exploited for binding with several ditopic guests. The longest guest was found to form the strongest complex, R,R‐isomer formed a stronger complex than S,S‐isomer, Z‐isomer of the plier formed stronger complex than the E‐isomer with the guest. Moreover, complexation also increased the E‐to‐Z switching efficiency and decreased the thermal back isomerisation of the azobenzene unit. [ABSTRACT FROM AUTHOR]

Diarylethene‐based photoswitches have become very popular over the last few decades for potential applications in chemistry, materials science, and biotechnology due to their unique physical and chemical properties. We report the isomeric separation of a diarylethene‐based photoswitchable compound using high‐performance liquid chromatography. The separated isomers were characterized by ultraviolet‐visible spectroscopy and mass spectrometry confirmed the isomeric nature of the compounds. The isomers were purified by preparative high‐performance liquid chromatography, providing fractionated samples to study the isomers individually. A total amount of 13 mg of an isomer of interest was fractionated from a solution of 0.4 mg/ml of the isomeric mixture. Because the preparative high‐performance liquid chromatographic method required large quantities of solvent, we explored the use of supercritical fluid chromatography as an alternative separation mode which, to the best of our knowledge, is the first time this technique is used to separate diarylethene‐based photoswitchable compounds. Supercritical fluid chromatography provided faster analysis times while maintaining sufficient baseline resolution for the separated compounds and consuming less organic solvent in the mobile phase compared to high‐performance liquid chromatography. It is proposed that the supercritical fluid chromatographic method be upscaled and used in future fractionation of the diarylethene isomeric compounds, becoming a more environmentally benign approach for compound purification. [ABSTRACT FROM AUTHOR]

Logic‐in‐memory devices are a promising and powerful approach to realize data processing and storage driven by electrical bias. Here, an innovative strategy is reported to achieve the multistage photomodulation of 2D logic‐in‐memory devices, which is realized by controlling the photoisomerization of donor–acceptor Stenhouse adducts (DASAs) on the surface of graphene. Alkyl chains with various carbon spacer lengths (n = 1, 5, 11, and 17) are introduced onto DASAs to optimize the organic–inorganic interfaces: 1) Prolonging the carbon spacers weakens the intermolecular aggregation and promotes isomerization in the solid state. 2) Too long alkyl chains induce crystallization on the surface and hinder the photoisomerization. Density functional theory calculation indicates that the photoisomerization of DASAs on the graphene surface is thermodynamically promoted by increasing the carbon spacer lengths. The 2D logic‐in‐memory devices are fabricated by assembling DASAs onto the surface. Green light irradiation increases the drain–source current (Ids) of the devices, while heat triggers a reversed transfer. The multistage photomodulation is achieved by well‐controlling the irradiation time and intensity. The strategy based on the dynamic control of 2D electronics by light integrates molecular programmability into the next generation of nanoelectronics. [ABSTRACT FROM AUTHOR]

Liquid crystalline‐based actuators containing azobenzene photoswitches have been used to demonstrate light‐responsive motion in soft actuator systems. Understanding the mechanical performance of these light‐responsive actuators as a function of the polymer chemistry as well as the nature and concentration of the photoswitches is crucial for developing advanced applications. A systematic study is presented here that clarifies the role of azobenzene photoswitches and the liquid crystalline networks in generating the desired photomechanical performance. Through measurement of photo stimulated mechanical behavior, in particular generated force and strain, a generalized set of guidelines concerning the appropriate subset of polymer chemistry and photoswitches required to achieve the desired performance for actuator design is derived. [ABSTRACT FROM AUTHOR]

Despite education campaigns linking sun overexposure and skin cancer, it remains one of the leading preventable cancer diagnoses. Skin cancer risk is correlated with overexposure to UV light in sunlight and can be prevented by avoiding exposure. While sun protection can be achieved using sunscreen and clothing, people must be made aware of their risk to facilitate behavior change. Herein, new rewearable UV sensors which overcome the single‐use limitations of other products are presented. These sensors utilize diarylethene photoswitches, which develop a colored appearance upon exposure to UV and are reset to colorless by green light (<10 min). These photoswitches are incorporated into a range of materials, enabling the use of advanced manufacturing to develop highly desirable consumer products. 3D stereolithographic printing is used to prototype sensors, with complex geometries and appealing aesthetics, that can be worn by users. The UV sensitivity of these devices is tuned by incorporating chromophores, meeting the needs of diverse skin types. The colorimetric response allows for direct visual feedback to the user, or quantification using photography, allowing for dosimetry of UV exposure. These new reusable devices aim to reduce people's exposure to UV, while reducing the waste generated by single‐use devices. [ABSTRACT FROM AUTHOR]