Sensitive Assays by Nucleophile-Induced Rearrangement of Photoactivated Diarylethenes

Upon light-induced isomerization, diarylethenes (DAEs) equipped with reactive aldehyde moieties rearrange selectively in the presence of amines, accompanied by decoloration. In a comprehensive study, the probe structure was optimized with regard to its inherent reactivity in the nucleophile-triggered rearrangement reaction. Detailed structure−reactivity relationships could be derived, in particular with regard to the type of integrated (het)aryl moieties as well as the location of the formyl residue, and the probes’ intrinsic reactivity with primary and secondary amines was optimized. Utilizing an ancillary base, the initially formed rearrangement product can engage in a subsequent catalytic cycle, leading to an amplified decoloration process. This additional catalytic pathway allows us to enhance the sensitivity of our method and successfully discriminate between amines and thiols. Moreover, probes that exhibit strong analyte-induced fluorescence modulation have been designed to further decrease the detection limit by using a more sensitive read-out. The optimized DAE probes are promising molecular components for future programmable sensing materials and devices.Peer Reviewe

Mechanistic Insights into the Triplet Sensitized Photochromism of Diarylethenes

Operating photoswitchable molecules repetitively and reliably is crucial for most of their applications, in particular in (opto)electronic devices, and related to reversibility and fatigue resistance, which both critically depend on the photoisomerization mechanism defined by the substitution pattern. Two diarylethene photoswitches bearing biacetyl triplet sensitizers either at the periphery or at the core were investigated using both stationary as well as transient UV/Vis absorption spectroscopy ranging from the femtosecond to the microsecond time scale. The diarylethene with two biacetyl moieties at the periphery is switching predominantly from the triplet excited state, giving rise to an enhanced fatigue resistance. In contrast, the diarylethene bearing one diketone at the photoreactive inner carbon atom cyclizes from the singlet excited state and shows significantly higher quantum yields for both cyclization and cycloreversion.Peer Reviewe

Switching Diarylethenes Reliably in Both Directions with Visible Light

A diarylethene photoswitch was covalently connected to two small triplet sensitizer moieties in a conjugated and nonconjugated fashion and the photochromic performance of the resulting compounds was investigated. In comparison with the parent diarylethene (without sensitizers) and one featuring saturated linkages, the conjugated photoswitch offers superior fatigue resistance upon visible-light excitation due to effective triplet energy transfer from the biacetyl termini to the diarylethene core. Our design makes it possible to switch diarylethenes with visible light in both directions in a highly efficient and robust fashion based on extending π-conjugation and by-product-free ring-closure via the triplet manifold.Peer Reviewe

Multistable Conventional Azobenzene Liquid Crystal Actuators Using Only Visible Light: The Decisive Role of Small Amounts of Unpolymerized Monomers

Azobenzene liquid crystal polymers offer the potential to fabricate autonomously operated actuators remotely controlled by light. Usually, in fully polymerized actuators, only three different states can be obtained: the initial state, the metastable light-actuated state, and the recovered state, where the first and last states are identical and stable. Here, we show that conventional azobenzene liquid crystal polymers that retain a small amount of unpolymerized monomers can exhibit multistable deformation states after manual bending and upon irradiation. This nonbonded fraction of monomers migrates under the influence of local stress gradients, such as those resulting from bending, enabling the actuator to adapt its shape to counteract the stresses induced manually or upon irradiation, resulting in stable recovery states that differ from the initial shape. Oscillatory movement of the azobenzenes and photosoftening facilitate monomer migration and thus allow multiple stable shapes using only lower-energy blue and green lights. Such materials have the potential for biomedical and microfluidic applications where light-induced, multistable states are desired and harmful UV-light needs to be avoided

Stimuli-responsive materials: A smart way to study dynamic cell responses

Cells in the body reside within the extracellular matrix (ECM), a three-dimensional environment that not only provides structural support for the cells, but also influences cellular processes, like migration and differentiation. The ECM and the cells continuously engage in a complex and highly dynamic interplay, shaping both the matrix as well as the cellular outcome. To study these dynamic, bidirectional interactions in a systematic manner, the ability to dynamically control cellular environments is highly desirable. Stimuli-responsive materials are a class of materials that have been engineered to respond to external cues, e.g., light, electricity, or magnetic field, and therefore hold fascinating potentials as an ideal experimental platform to introduce changing spatiotemporal signals to cells. Here, we review the state of the art in stimuli-responsive materials and their design strategies, with an emphasis on the dynamic introduction of physical and mechanical cues. The effects of such dynamic stimuli on the responses of living cells are examined on three different levels: cellular phenotypes, intracellular and cytoskeletal changes, and nuclear and epigenetic effects. Finally, we discuss the current challenges and limitations as well as the potential outlooks in exploiting stimuli-responsive biomaterials

Sensitive assays by nucleophile-induced rearrangement of photoactivated diarylethenes

Upon light-induced isomerization, diarylethenes (DAEs) equipped with reactive aldehyde moieties rearrange selectively in the presence of amines, accompanied by decoloration. In a comprehensive study, the probe structure was optimized with regard to its inherent reactivity in the nucleophile-triggered rearrangement reaction. Detailed structure-reactivity relationships could be derived, in particular with regard to the type of integrated (het)aryl moieties as well as the location of the formyl residue, and the probes' intrinsic reactivity with primary and secondary amines was optimized. Utilizing an ancillary base, the initially formed rearrangement product can engage in a subsequent catalytic cycle, leading to an amplified decoloration process. This additional catalytic pathway allows us to enhance the sensitivity of our method and successfully discriminate between amines and thiols. Moreover, probes that exhibit strong analyte-induced fluorescence modulation have been designed to further decrease the detection limit by using a more sensitive read-out. The optimized DAE probes are promising molecular components for future programmable sensing materials and devices

Molecular switches in light-responsive liquid-crystalline polymer actuators

The incorporation of photoswitches and photothermal dyes into liquid-crystal polymers (LCPs) enables various light-addressable shape changes. The anisotropic structure of LCPs allows for a conversion of molecular into macroscopic motion. Precise control of intensity and spatial resolution offers a large toolkit in fabrication, product design, sensors, or medical protheses. Lifting objects by light-responsive actuators in a non-destructive way renders the use of cable connections redundant. Whereas photothermal dyes show a fast and reversible response, the great advantage of using photoswitches in photoactuators becomes substantive when thermally bistable deformations, underwater applications, or deformation programming are required.</p

Multistable Conventional Azobenzene Liquid Crystal Actuators Using Only Visible Light: The Decisive Role of Small Amounts of Unpolymerized Monomers

Azobenzene liquid crystal polymers offer the potential to fabricate autonomously operated actuators remotely controlled by light. Usually, in fully polymerized actuators, only three different states can be obtained: the initial state, the metastable light-actuated state, and the recovered state, where the first and last states are identical and stable. Here, we show that conventional azobenzene liquid crystal polymers that retain a small amount of unpolymerized monomers can exhibit multistable deformation states after manual bending and upon irradiation. This nonbonded fraction of monomers migrates under the influence of local stress gradients, such as those resulting from bending, enabling the actuator to adapt its shape to counteract the stresses induced manually or upon irradiation, resulting in stable recovery states that differ from the initial shape. Oscillatory movement of the azobenzenes and photosoftening facilitate monomer migration and thus allow multiple stable shapes using only lower-energy blue and green lights. Such materials have the potential for biomedical and microfluidic applications where light-induced, multistable states are desired and harmful UV-light needs to be avoided

Multistable Conventional Azobenzene Liquid Crystal Actuators Using Only Visible Light: The Decisive Role of Small Amounts of Unpolymerized Monomers

Azobenzene liquid crystal polymers offer the potential to fabricate autonomously operated actuators remotely controlled by light. Usually, in fully polymerized actuators, only three different states can be obtained: the initial state, the metastable light-actuated state, and the recovered state, where the first and last states are identical and stable. Here, we show that conventional azobenzene liquid crystal polymers that retain a small amount of unpolymerized monomers can exhibit multistable deformation states after manual bending and upon irradiation. This nonbonded fraction of monomers migrates under the influence of local stress gradients, such as those resulting from bending, enabling the actuator to adapt its shape to counteract the stresses induced manually or upon irradiation, resulting in stable recovery states that differ from the initial shape. Oscillatory movement of the azobenzenes and photosoftening facilitate monomer migration and thus allow multiple stable shapes using only lower-energy blue and green lights. Such materials have the potential for biomedical and microfluidic applications where light-induced, multistable states are desired and harmful UV-light needs to be avoided

Epitaxial growth of light-responsive azobenzene molecular crystal actuators on oriented polyethylene films

We report on the epitaxial growth of photoresponsive alkyl-substituted azobenzene fibres on top of uniaxially oriented polyethylene (PE) films. In these fibres, the alkyl chains are oriented parallel with regard to the drawing direction of PE, whereas the azobenzene moieties pack into a roughly 60° angle. The bilayer films act as a light responsive actuator generating an actuation stress of about 3 MPa