Sterically Hindered Stiff-Stilbene Photoswitch Offers Large Motions, 90% Two-Way Photoisomerization, and High Thermal Stability

Control of Bilayer Transport through a Photoswitchable Membrane-Stiffening Agent

The mobility of proteins in the bilayer membrane is affected by (local) changes in lipid environment, which is important to their biological functioning. Artificial molecular systems that-to some extent-imitate tasks of membrane-embedded proteins are increasingly developed, however, they are usually controlled through responsive units in their core structure. Here we present an alternative approach based on an amphiphilic stiff-stilbene derivative that enables control of membrane fluidity by light. The fluidity increase upon E-to-Z isomerization is shown to enhance the activity of known synthetic anion transporters as a result of a higher mobility. The photoisomerization process is studied by UV/Vis and 1H NMR spectroscopy in solution and in POPC vesicles, where the light-induced changes in fluidity and hence, activity of anion transporters, are monitored by fluorescence spectroscopy. Dynamic light-scattering (DLS) and cryo-EM studies show that vesicle integrity is not impaired by photoswitching. Our work introduces a versatile approach to control solute transport by carrier molecules. Moreover, the photocontrol over membrane fluidity and, with that, mobility could eventually be used for directed motion, which we expect to be key in achieving active transport in the future.

Synthesis of V-shaped Thiophene Based Rotor-Stilbene: Substituent Dependent Aggregation and Photophysical Properties

Thiophene core V-shaped rotor-stilbene derivatives have been synthesized utilizing two-fold Heck coupling reaction. These compounds are blue emitters with moderate quantum yield in dilute solution. Rotor nature of the synthesized stilbenes supports aggregation induced emission (AIE) behaviour and they show substituent dependent emission behavior in aggregate state. In presence of donating groups (e.g., tert-butyl, methoxy, diphenylamine group) in stilbenes, they exhibit AIE property. But with the introduction of electron withdrawing group (nitro group), they shows aggregation caused quenching (ACQ) behavior. Different types of nano-aggregates formation is observed in aggregated state, which was confirmed by dynamic light scattering (DLS) and scanning electron microscopy (SEM) studies. The details photophysical (absorption, fluorescence, and lifetime), electrochemical property (cyclic voltammetry) and thermal stability have been investigated. Optimized structure, energy and electronic distribution of molecular orbitals have been studied by theoretical calculation.

Reversible Isomerization of Stiff-Stilbene by an Oriented External Electric Field

Understanding and effectively controlling molecular conformational changes are essential for developing responsive and dynamic molecular systems. Here, we report that an oriented external electric field (OEEF) is an effective catalyst for the cis-trans isomerization of stiff-stilbene, a key component of overcrowded alkene-based rotary motors. This reversible isomerization occurs under ambient conditions, is free from side reactions, and has been verified using ultraperformance liquid chromatography and UV-vis absorption spectroscopy. Low electric field promotes cis-to-trans conversion, and high electric field enables the reverse trans-to-cis process, demonstrating the precise reaction control through electric field manipulation. Density functional theory calculations reveal the mechanism of the electric-field-catalyzed cis-trans carbon-carbon double bond isomerization. Our findings provide a novel perspective on constructing OEEF-catalyzed, reversible molecular systems and pave the way for fully electrically driven artificial molecular machines.

Main-chain stiff-stilbene photoswitches in solution, in bulk, and at surfaces

Molecular photoswitches have been incorporated into polymer backbones to control the macromolecular conformations by structural changes of the main-chain photoswitches. However, previous photoswitches installed in the main chains are thermolabile, which precludes deep understanding, precise regulation, and practical applications of the macromolecular conformational changes. Herein, we focus on sterically hindered stiff stilbene (HSS), an emerging photoswitch offering large structural changes in isomerization between the thermally bistable E and Z isomers, and disclose the chemistry of main-chain HSS photoswitches in solution, in bulk, and at thin film surfaces. We synthesize and investigate three types of linear polymers with different chemical linkages between HSS repeating units, polyurethane, polyester, and polyene. The polymer conformations in solution, i.e., hydrodynamic volume, are reversibly photocontrollable in a precise manner by the E/Z ratio. Furthermore, the nanoscopic conformational transformations are amplified to macroscopic photoswitching of the solution transmittance and the surface wettability synergistically with changes between interchain and intrachain hydrogen bonding in the polyurethanes. Additionally, the Z-to-E photoisomerization yields in the glassy state are above 70%, comparable to those in solution, and extraordinarily high despite the restricted molecular mobility. The findings of this study will pave the way for practical and unconventional applications of smart polymer systems based on photoswitches.

All-visible-light-driven stiff-stilbene photoswitches

Molecular photoswitches are potent tools to construct dynamic functional systems and responsive materials that can be controlled in a non-invasive manner. As P-type photoswitches, stiff-stilbenes attract increasing interest, owing to their superiority in quantum yield, significant geometric differences between isomers, excellent thermostability and robust switching behavior. Nevertheless, the UV-light-triggered photoisomerization of stiff-stilbenes has been a main drawback for decades as UV light is potentially harmful and has low penetration depth. Here, we provided a series of para-formylated stiff-stilbenes by Rieche ortho-formylation to achieve all-visible-light-responsiveness. Additional phenolic groups provide access to late-stage chemical modification facilitating design of molecules responsive to visible light. Remarkably, the photoisomerization of aldehyde-appended stiff-stilbenes could be fully manipulated using visible light, accompanied by a high photostationary state (PSS) distribution. These features render them excellent candidates for future visible-light-controllable smart materials and dynamic systems.

Thermally Stable Photomechanical Molecular Hinge: Sterically Hindered Stiff-Stilbene Photoswitch Mechanically Isomerizes

Molecular photoswitches are extensively used as molecular machines because of the small structures, simple motions, and advantages of light including high spatiotemporal resolution. Applications of photoswitches depend on the mechanical responses, in other words, whether they can generate motions against mechanical forces as actuators or can be activated and controlled by mechanical forces as mechanophores. Sterically hindered stiff stilbene (HSS) is a promising photoswitch offering large hinge-like motions in the E/Z isomerization, high thermal stability of the Z isomer, which is relatively unstable compared to the E isomer, with a half-life of ca. 1000 years at room temperature, and near-quantitative two-way photoisomerization. However, its mechanical response is entirely unexplored. Here, we elucidate the mechanochemical reactivity of HSS by incorporating one Z or E isomer into the center of polymer chains, ultrasonicating the polymer solutions, and stretching the polymer films to apply elongational forces to the embedded HSS. The present study demonstrated that HSS mechanically isomerizes only in the Z to E direction and reversibly isomerizes in combination with UV light, i.e., works as a photomechanical hinge. The photomechanically inducible but thermally irreversible hinge-like motions render HSS unique and promise unconventional applications differently from existing photoswitches, mechanophores, and hinges.

2,3-Diarylmaleate salts as a versatile class of diarylethenes with a full spectrum of photoactivity in water

There is incessant interest in the transfer of common chemical processes from organic solvents to water, which is vital for the development of bioinspired and green chemical technologies. Diarylethenes feature a rich photochemistry, including both irreversible and reversible reactions that are in demand in organic synthesis, materials chemistry, and photopharmacology. Herein, we introduce the first versatile class of diarylethenes, namely, potassium 2,3-diarylmaleates (DAMs), that show excellent solubility in water. DAMs obtained from highly available precursors feature a full spectrum of photoactivity in water and undergo irreversible reactions (oxidative cyclization or rearrangement) or reversible photocyclization (switching), depending on their structure. This finding paves a way towards wider application of diarylethenes in photopharmacology and bioinspired technologies that require aqueous media for photochemical reactions.

Photoswitchable Bis(amidopyrroles): Modulating Anion Transport Activity Independent of Binding Affinity

Toward photocontrol of anion transport across the bilayer membrane, stiff-stilbene, which has dimethyl substituents in the five-membered rings, is functionalized with amidopyrrole units. UV-vis and 1H NMR studies show high photostability and photoconversion yields. Where the photoaddressable (E)- and (Z)-isomers exhibit comparable binding affinities, as determined by 1H NMR titrations, fluorescence-based transport assays reveal significantly higher transport activity for the (Z)-isomers. Changing the binding affinity is thus not a necessity for modulating transport. Additionally, transport can be triggered in situ by light.