Molecular Photoswitch Research Articles

Mechanochromic Displays Based on Photoswitchable Cholesteric Liquid Crystal Elastomers.

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.

A Halogen‐Bonded Fluorescent Molecular Photoswitch: Transition from 3D Cubic Lattice to 1D Helical Superstructure for Polarization Inversion of Circularly Polarized Luminescence

AbstractThe fabrication of materials that can switch between circularly polarized luminescence (CPL) signals is both essential and challenging. Here, two new halogen‐bonded fluorescent molecular photoswitches, namely, HB‐switch 1 and HB‐switch 2, containing α‐cyano‐substituted diarylethene compounds with different end groups were developed. Upon exposure to specific UV or visible light wavelengths, they exhibited controllable and reversible Z/E photoisomerization. When these switches were integrated into blue‐phase liquid crystals (BPLCs), the temperature range of BP significantly expanded. Notably, the BP system incorporating HB‐switch 1 exclusively achieved reversible polarization inversion of CPL signals under irradiation with specific UV/Visible light and during cooling/heating. The photo/thermal dual‐response behavior of the CPL signals can be attributed to the phase transition from a high‐symmetry 3D BP Icubic lattice to a low‐symmetry 1D helical superstructure induced by the Z/E photoisomerization of HB‐switch 1 and temperature changes. This study underscores the significance of employing halogen‐bond assembly strategies to design materials with switchable CPL signals, opening new possibilities for CPL‐active systems.

A Halogen-Bonded Fluorescent Molecular Photoswitch: Transition from 3D Cubic Lattice to 1D Helical Superstructure for Polarization Inversion of Circularly Polarized Luminescence.

The fabrication of materials that can switch between circularly polarized luminescence (CPL) signals is both essential and challenging. Here, two new halogen-bonded fluorescent molecular photoswitches, namely, HB-switch 1 and HB-switch 2, containing α-cyano-substituted diarylethene compounds with different end groups were developed. Upon exposure to specific UV or visible light wavelengths, they exhibited controllable and reversible Z/E photoisomerization. When these switches were integrated into blue-phase liquid crystals (BPLCs), the temperature range of BP significantly expanded. Notably, the BP system incorporating HB-switch 1 exclusively achieved reversible polarization inversion of CPL signals under irradiation with specific UV/Visible light and during cooling/heating. The photo/thermal dual-response behavior of the CPL signals can be attributed to the phase transition from a high-symmetry 3D BP Icubic lattice to a low-symmetry 1D helical superstructure induced by the Z/E photoisomerization of HB-switch 1 and temperature changes. This study underscores the significance of employing halogen-bond assembly strategies to design materials with switchable CPL signals, opening new possibilities for CPL-active systems.

Norbornadiene-Quadricyclane Photoswitches with Enhanced Solar Spectrum Match.

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 %.

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.

Stereoselective Synthesis of Azobenzene-Based Glycomacrocycles

AbstractCarbohydrate-based macrocyclic compounds are of particular interest because of their multifunctionality, their unique structural and physicochemical properties as well as their potential applications in chemistry, biology, and drug discovery. Introducing a molecular photoswitch into the skeleton of glycomacrocycles makes possible the reversible control of properties of the resulting photoswitchable glycomacrocycles by light illumination. Therefore, development of stereoselective synthesis of this class of glycomacrocycles is of great interest. Two new azobenzene-based glycomacrocycles have been synthesized through an intramolecular glycosylation approach. Excellent 1,2-cis stereoselectivity has been achieved for the mannosylation.

ANTICANCER IMMUNOGENIC POTENTIAL OF ONCOLYTIC PEPTIDES: RECENT ADVANCES AND NEW PROSPECTS

Oncolytic peptides are derived from natural host defense peptides/antimicrobial peptides produced in a wide variety of life forms. Over the past two decades, they have attracted much attention in both basic research and clinical applications. Oncolytic peptides were expected to act primarily on tumor cells and also trigger the immunogenic cell death. Their ability in the tumor microenvironment remodeling and potentiating the anticancer immunity has long been ignored. Despite the promising results, clinical application of oncolytic peptides is still hindered by their unsatisfactory bioactivity and toxicity to normal cells. To ensure safer therapy, various approaches are being developed. The idea of the Ukrainian research group was to equip peptide molecules with a "molecular photoswitch" — a diarylethene fragment capable of photoisomerization, allowing for the localized photoactivation of peptides within tumors reducing side effects. Such oncolytic peptides that may induce the membrane lysis-mediated cancer cell death and subsequent anticancer immune responses in combination with the low toxicity to normal cells have provided a new paradigm for cancer therapy. This review gives an overview of the broad effects and perspectives of oncolytic peptides in anticancer immunity highlighting the potential issues related to the use of oncolytic peptides in cancer immunotherapy. We summarize the current status of research on peptide-based tumor immunotherapy in combination with other therapies including immune checkpoint inhibitors, chemotherapy, and targeted therapy.

Fluorescence Switching and Photoisomerization of a Spiropyran Molecular Photoswitch through Confined Spaces Regulation in Crystals.

Spiropyran (SP) and its derivatives are highly attractive owing to their distinctive merits in high contrast and fast response read-out systems. However, the realization of photoswitching properties of SP is hindered in the aggregate state, particularly in crystals owing to the dense packing of molecules leading to insufficient study of the relationship between the molecular structure/stacking mode and photoswitching behavior. Herein, we report three SP derivatives: different flexible chains (carboxyl group for SP-0 and ester group for SP-1) are attached to the indoline moiety, while the ester group is attached to the chromene moiety for SP-2. SP-1 exhibits fluorescent photoswitching properties in crystals due to the weak intermolecular interactions resulting in enough free space for the photoisomerization. The presence of hydrogen bonds in SP-0 enhances the molecular interactions to restrict the photoisomerization, and the ester group of SP-2 impacts the thermodynamic properties, thereby limiting the realization of photoswitching of SP-2.

Optical properties of a tunable microcavity/microsphere polymeric composite

The combination of a microcavity and a microsphere has been proposed in this work to manipulate light in terms of emission wavelength and propagation direction. A microcavity with a layer of molecular photoswitch between two one-dimensional photonic crystals of polyvinyl carbazole and cellulose acetate has been designed. To tune the microcavity, the molecular photoswitch has been excited taking into account its cyclization upon irradiation at 313[Formula: see text]nm and its cycloreversion at 450[Formula: see text]nm. In this way, the emission peak of the microcavity switches from 508.5[Formula: see text]nm to 525[Formula: see text]nm. A polystyrene microsphere with a radius of 1[Formula: see text][Formula: see text]m is placed near the microcavity. With the detector at an angle of 8°, the emission at 525[Formula: see text]nm is 1.73 times higher with respect to the emission at 508.5[Formula: see text]nm, while at 10.8°, the emission at 508.5[Formula: see text]nm is 1.45 times higher with respect to the emission at 525[Formula: see text]nm. The value of these findings is that they offer the experimentalists a ready means to compare the optical data of these types of composites with theory.

Ultrafast electronic relaxation pathways of the molecular photoswitch quadricyclane

The light-induced ultrafast switching between molecular isomers norbornadiene and quadricyclane can reversibly store and release a substantial amount of chemical energy. Prior work observed signatures of ultrafast molecular dynamics in both isomers upon ultraviolet excitation but could not follow the electronic relaxation all the way back to the ground state experimentally. Here we study the electronic relaxation of quadricyclane after exciting in the ultraviolet (201 nanometres) using time-resolved gas-phase extreme ultraviolet photoelectron spectroscopy combined with non-adiabatic molecular dynamics simulations. We identify two competing pathways by which electronically excited quadricyclane molecules relax to the electronic ground state. The fast pathway (<100 femtoseconds) is distinguished by effective coupling to valence electronic states, while the slow pathway involves initial motions across Rydberg states and takes several hundred femtoseconds. Both pathways facilitate interconversion between the two isomers, albeit on different timescales, and we predict that the branching ratio of norbornadiene/quadricyclane products immediately after returning to the electronic ground state is approximately 3:2.

Enhancing the Potential of Fused Heterocycle-Based Triarylhydrazone Photoswitches.

Invited for the cover of this issue are Marek Cigáň, Anna M. Grabarz and co-workers. The image depicts how a non-expert might imagine a "molecular photoswitch". Read the full text of the article at 10.1002/chem.202303509.

Study on photochemistry and component transport coupling processes of azobenzene molecular solar thermal system

Molecular solar thermal (MOST) system is a new technology to collect, transform and store solar energy. The mechanism of photochemical reaction and component transport of molecular photoswitches in the reactor is still unclear. In this paper, a simulated theoretical framework for energy conversion rate and energy storage efficiency of solar energy collection and conversion devices based on a molecular solar thermal system was presented. The mathematical model of the photochemical reaction studied was based on an azobenzene derivative, which acted as a molecular photoswitch that can store energy by the switch of molecular structures. The microscopic parameters of reactants were obtained by quantum mechanics calculation and applied to the macroscopic energy conversion analysis of reaction processes. The theoretical framework can predict the conversion and energy storage efficiency of photoisomerization reactions, and can be used for component transport analysis, energy conversion analysis and reaction rate contribution analysis in reactors. We focused on the influence of macroscopic factors, including the flow velocity, inlet reactants concentration and reactor size on the photoisomerization energy storage process. The results of the theoretical analysis were in good agreement with those of existing laboratory equipment. The relative error of the conversion rate is only 0.71% in the photostable state, and the maximum relative error of the conversion rate is 10.99% in the whole process. In addition, in the photochemical reaction, we introduced the concept of absorbance field for the absorbance attenuation caused by the absorption of photons in the medium, so that the local material conversion, absorbance and energy conversion of this type of photochemical reaction can be more clearly understood. This simulated theoretical framework allows the study of molecules in a macroscopic setting, thereby establishing a link between practical engineering and basic chemistry, and providing guidance for the design of molecular solar thermal systems in the future.

Phenolylazoindole scaffold for facilely synthesized and bis-functional photoswitches combining controllable fluorescence and antifungal properties using theoretical methods.

Functionalization is a major challenge for the application of photoswitches. With the aim to develop novel bis-functional azo photoswitches with stationary photophysical properties, a series of phenolylazoindole derivatives were designed, synthesized, and characterized via NMR spectroscopy studies and high-resolution mass spectrometry (HRMS). Herein, UV/Vis and 1H NMR spectra revealed that the photostationary state (PSS) proportions for PSScis and PSStrans were 76-80% and 68-81%, respectively. Furthermore, the thermal half-lives (t1/2) of compounds A2-A4 and B2 ranged from 0.9 to 5.3 h, affected by the diverse substituents at the R1 and R2 positions. The results indicated that azo photoswitches based on the phenolylazoindole scaffold had stationary photophysical properties and wouldn't be excessively affected by modifying the functional groups. Compounds A4 and B2, which were modified with an aryl group, also exhibited fluorescence emission properties (the quantum yields of A4 and B2 were 2.32% and 13.34%) through the modification of the flexible conjugated structure (benzene) at the R2 position. Significantly, compound C1 was obtained via modification with a pharmacophore in order to acquire antifungal activities against three plant fungi, Rhizoctonia solani (R. solani), Botrytis cinerea (B. cinerea), and Fusarium graminearum (F. graminearum). Strikingly, the inhibitory activity of the cis-isomer of compound C1towards R. solani (53.3%) was significantly better than that of the trans-isomer (34.2%) at 50 μg mL-1. In order to further reveal the antifungal mechanism, molecular docking simulations demonstrated that compound C1 effectively integrates into the cavity of succinate dehydrogenase (SDH); the optically controlled cis-isomer showed a lower binding energy with SDH than that of the trans-isomer. This research confirmed that phenolylazoindole photoswitches can be appropriately applied as molecular regulatory devices and functional photoswitch molecules via bis-functionalization.

Highly reversible photomodulated hydrosoluble stiff-stilbene supramolecular luminophor induced by cucurbituril

A photochromic molecular rotor based on stiff-stilbene (SSB-FMR) was handily prepared through coupled reaction, and further self-assembled with cucurbit[8]uril (CB[8]) to form a 2:2 quaternary supramolecular complex (SSB-FMR/CB[8]). Significantly, the intervention of CB[8] on SSB-FMR achieved dual functions that assembly-induced emission enhancement and assembly-induced improvement of photoisomerized performance (especially reversibility) of stiff-stilbene molecular photoswitch. The supramolecular strategy further facilitated the assembly as a photoresponsive fluorescence switch with outstanding fatigue resistance, which was expediently applied in high-security-level QR code anti-counterfeiting and controllable lysosome targeted imaging. The study unprecedentedly provides a supramolecular method for highly efficiently improving photoisomerized performance especially reversibility of molecular photoswitches based on stiff-stilbene, and is of vital significance for the construction of intelligent materials with excellent capability.

EqPhotochemistry of a water-soluble coumarin-based photoswitch

A novel water-soluble stilbene-type molecular photoswitch (CP) has been synthesized by attaching an N-methylpyridinium unit to 7-diethylamino-4-methylcoumarin (coumarin 1) via an ethylene bridge. The photoisomerization cycle of CP and the spectroscopic properties of the two isomers were studied in acetonitrile and in water. In both solvents, the illumination of trans-CP with green light leads to a photostationary state (PSS) with 90% cis isomer and irradiating then this PSS mixture with near UV light, the trans isomer is almost fully recovered. In water, the quantum yield for the trans-cis photoisomerization is 0.042, for the cis-trans photoisomerization it is 0.23. In acetonitrile, the photoisomerization quantum yields are even higher, the respective values are 0.12 and 0.56. The trans isomer of CP is fluorescent with red emission and it has a large Stokes shift, whereas the cis isomer is non-fluorescent. The two isomers are thermally stable at room temperature. The efficient photoisomerization of CP in both direction, the thermal stability of both isomeric forms and the distinct fluorescence of the trans isomer suggest that some water-soluble coumarin-based photoswitches may be promising candidates for applications in fluorescence imaging of biological samples.

The Growing Field of Photoswitchable Macrocycles: A Promising Way to Tune Various Properties with Light

AbstractThanks to supramolecular interactions of macrocyclic compounds with their guest ions or molecules, macrocycles have found wide applications in molecular and chiral recognition, separation, transportation, molecular machines, and so on. Photoswitchable macrocycles are especially appealing and attracting more and more interest because the embedded molecular photoswitch enables dynamic control of molecular shape, conformation, and different properties by light, a non‐invasive, remote and highly tunable stimulus. With available photochromic compounds, various photoswitchable macrocycles have been developed. In this review paper, we describe the recently reported photoswitchable macrocyclic compounds, with a focus on the control of the macrocyclic structure, dynamic, photo or thermal isomerization, as well as their applications on encapsulation and release of ionic or aromatic species, on the reversible modulation of chemical, biological, electronic, fluorescent and chiroptical properties by light.

Synthesis and cis-trans kinetics of an azobenzene-based molecular switch for light-responsive silica surfaces

Light-responsive materials design is an attractive research field that stimulates demand for the synthesis of novel molecular photoswitches. The novel photoswitches should be capable of being attached to a desired surface in order to provide it with light-responsive properties. The switchback to its ground state is expected to be gradual, with the possibility of acceleration. This study presents a comprehensive description of a chemical route to a molecular photoswitch based on an azobenzene derivative with a trifluoromethoxy group and a long alkyl chain. The photoswitch is capable of modifying submicrometer silica particles and silicon wafers as models of curved and flat surfaces, respectively. The thermal relaxation times of the synthesized azobenzene were studied in three different solvents: ethanol, chloroform, and toluene. The results reveal a significantly delayed relaxation process lasting for several days. This observation is found to be related to the polarity of the solvents used. To characterize the extensive thermal relaxation process, a methodology including the use of white-light pulses to accelerate cis-trans isomerization is suggested. The white light spectrum used in pulses affects thermal relaxation but does not alter the relaxation time extrapolated to zero. The density of the photoswitch molecules attached to particles varies from 0.7 to 1.7 molecules/nm2 as the initial amount of azobenzene in the reaction increases. Surface-attached photoswitches demonstrate reversible cis-trans isomerization behavior when exposed to UV and white light irradiation. A 14° contact angle change is observed when flat surfaces modified with photoswitches are irradiated with UV light.

Azoheteroarene and Diazocine Molecular Photoswitches: Self-Assembly, Responsive Materials and Photopharmacology.

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.

Azoheteroarene und Diazocine als Molekulare Photoschalter: Selbstassemblierung, Responsive Materialien und Photopharmakologie

AbstractAromatische Einheiten, die mit einer Azofunktionalität (−N=N−) verknüpft sind, bilden eine einzigartige Klasse von Verbindungen, bekannt als molekulare Photoschalter, die bei Bestrahlung eine reversible Umwandlung zwischen ihren E‐ und Z‐Isomeren zeigen. Photoschalter wurden in näherer Vergangenheit umfassend untersucht, um dynamische, selbstassemblierende Materialien, optoelektronische Geräte, steuerbare Biomaterialien und vieles mehr, herzustellen. Die meisten dieser Materialien beinhalten Azobenzole als molekulare Photoschalter. Hierfür zeigt SciFinder bereits mehr als 7000 Artikel und 1000 Patente. Dementsprechend wurde viel Aufwand investiert, um die Effizienz der Photoisomerisierung und die damit verbundenen mesoskopischen Eigenschaften von Azobenzolen zu verbessern. Seit kurzer Zeit haben Azoheteroarene und zyklische Azobenzole wie Arylazopyrazole, Arylazoisoxazole, Arylazopyridine und Diazocine als Photoschalter der zweiten Generation an Bedeutung gewonnen. Diese Photoschalter bieten einzigartiges Schaltverhalten und responsive Eigenschaften, die sie zu vielversprechenden Kandidaten für die Entwicklung von photoresponsiven Materialien bis hin zu Photopharmakophoren machen. In diesem Kurzaufsatz stellen wir die strukturellen Unterschiede und photoresponsiven Eigenschaften von Azohezeroarenen und Diazocinen vor und fassen den aktuellen Stand der Anwendung dieser Photoschalter als responsive Bausteine in der supramolekularen Assemblierung, Materialwissenschaften und Photopharmakologie zusammen. Dabei soll ihr vielseitiges photochemisches Verhalten, ihre verbesserten Funktionalitäten und die neusten Anwendungen hervorgehoben werden.

Selective control of donor-acceptor Stenhouse adduct populations with non-selective stimuli

Selective control of donor-acceptor Stenhouse adduct populations with non-selective stimuli