Transient activation of biochemical reactions by visible light and subsequent return to the inactive state in the absence of light is an essential feature of the biochemical processes in photoreceptor cells. To mimic such light-responsiveness with artificial nanosystems, polymersome nanoreactors were developed that can be switched on by visible light and self-revert fast in the dark at room temperature to their inactive state. Donor-acceptor Stenhouse adducts (DASAs), with their ability to isomerize upon irradiation with visible light, were employed to change the permeability of polymersome membranes by switching polarity from a nonpolar triene-enol form to a cyclopentenone with increased polarity. To this end, amphiphilic block copolymers containing poly(pentafluorophenyl methacrylate) in their hydrophobic block were synthesized by reversible addition-fragmentation chain-transfer (RAFT) radical polymerization and functionalized either with a DASA that is based on Meldrum's acid or with a novel fast-switching pyrazolone-based DASA. These polymers were self-assembled into vesicles. Release of hydrophilic payload could be triggered by light and stopped as soon as the light was turned off. The encapsulation of enzymes yielded photoresponsive nanoreactors that catalyzed reactions only if they were irradiated with light. A mixture of polymersome nanoreactors, one that switches in green light, the other switching in red light, permitted specific control of the individual reactions of a reaction cascade in one pot by irradiation with varied wavelengths, thus enabling light-controlled wavelength-selective catalysis. The DASA-based nanoreactors demonstrate the potential of DASAs to switch permeability of membranes and could find application to switch reactions on and off, on demand, e.g., in microfluidics or in drug delivery.

A modular synthesis of Donor−Acceptor Stenhouse Adduct (DASA) polymer conjugates is described. Pentafluorophenyl-ester chemistry is employed to incorporate aromatic amines into acrylate and methacrylate copolymers, which are subsequently coupled with activated furans to generate polymers bearing a range of DASA units in a modular manner. The effect of polymer glass transition temperature on switching kinetics is studied, showing dramatic rate enhancements in going from a glassy to a rubbery matrix. Moreover, tuning the DASA absorption profile allows for selective switching, as demonstrated by ternary photopatterning, with potential applications in rewriteable data storage.

From particles to fibers: Nanofibers with different morphologies and periodicities can be fabricated by supraparticular assembly of magnetic spherical nanoparticles. A linear sintering process is used to merge the assembled colloids together. The structure of the obtained fibers is controlled by the process parameters and the morphology of the spherical colloidal building blocks.

Donor-acceptor Stenhouse adducts (DASAs) are visible-light-responsive photoswitches with avariety of emerging applications in photoresponsive materials.T heir 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,a llowing greatly reduced reaction times and increased yields for knownderivatives.Inaddition, it provides access to previously unattainable DASA-based photoswitches and DASA-polymer conjugates.T he role of HFIP and the photochromic properties of as et of new DASAs is probed using ac ombination of 1 HNMR and UV/Vis spectroscopy. The use of sterically hindered, electron-poor amines enabled the dark equilibrium to be decoupled from closed-isomer halflives for the first time.

when a light stimulus is applied, enabling their remote control with high spatial and temporal precision. [1][2][3] The controlled change of properties upon light irradiation has been exploited for a broad range of applications ranging from photochromic ophthalmic lenses to optical switches, phase shifters, sensors, drug delivery, and actuators for soft robotics. [4][5][6][7][8] Most established systems, however, require UV light, which provides a very limited penetration depth into many materials or into skin, and is often detrimental to their structure. [9] These limitations have boosted the search for visible light-responsive photoswitches. One of the most remarkable developments in this field was the discovery of donor-acceptor Stenhouse adducts (DASAs), a new class of visible light-responsive photoswitches with negative photochromism. [10][11][12] With the rapidly increasing knowledge on their structure-property relationships and their subsequent optimization, 2nd and 3rd generation DASAs have overcome initial limitations, providing now access to the whole range of the visible spectrum with excellent photoswitching properties both in solution and in polymer matrices. [13][14][15] In materials science, DASAs have already been employed in multiple applications Molecular photoswitches that can reversibly change color upon irradiation are promising materials for applications in molecular actuation and photoresponsive materials. However, the fabrication of photochromic devices is limited to conventional approaches such as mold casting and spin-coating, which cannot fabricate complex structures. Reported here is the first photoresist for direct laser writing of photochromic 3D micro-objects via twophoton polymerization. The integration of photochromism into thiol-ene photo-clickable resins enables rapid two-photon laser processing of highly complex microstructures and facile postmodification using a series of donoracceptor Stenhouse adduct (DASA) photoswitches with different excitation wavelengths. The versatility of thiol-ene photo-click reactions allows finetuning of the network structure and physical properties as well as the type and concentration of DASA. When exposed to visible light, these microstructures exhibit excellent photoresponsiveness and undergo reversible colorchanging via photoisomerization. It is demonstrated that the fluorescence variations of DASAs can be used as a reporter of photoswitching and thermal recovery, allowing the reading of DASA-containing sub-micrometric structures in 3D. This work delivers a new approach for custom microfabrication of 3D photochromic objects with molecularly engineered color and responsiveness.

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A versatile strategy for the fabrication of functional and nanostructured poly(N-alkyl acrylamide)-based amphiphilic polymer conetworks (APCNs) from hydrophobic precursor networks is presented. The active ester monomer pentafluorophenyl acrylate (PFPA) acts as a general hydrophobic masking group for N-alkyl acrylamides, by providing both miscibility with hydrophobic macromonomer crosslinkers and activating the acrylate for amidation reactions. Thereby, hydrophobic precursor networks can be transformed into a multitude of different poly(N-alkyl acrylamide)-l-PDMS APCNs. The resulting optically transparent APCNs possess nanophase-separated morphologies with domains sizes in the nanometer range. Variation of the amide type results in different types of APCNs, despite them being derived from the same precursor network and having identical network structures. Accordingly, the properties of these APCNs can be tailored according to the desired application by simple variation of the amide functionality. Furthermore, the combination of PFPA with another hydrophobically masked monomer allows for the fabrication of APCNs with small yet precisely defined amounts of functional amide units in the hydrophilic phase. A controlled functionalization of APCNs with pendant groups such as pH-responsive imidazole, fluorescent dyes, and biotin for specific protein binding is achieved, greatly expanding the functionality of the APCNs. Such functionalized APCNs could find application as stimuli-responsive drug delivery membranes, smart hydrogels, biosensors, or as matrices for biocatalysis.

ratiometric pH detection. Typically, ratiometric pH detection requires the combination of one pH-sensitive and one pH-insensitive fluorescent dye. [3] Pyranine, in contrast, allows ratiometric detection of pH from the comparison of one emission intensity at two different excitation wavelengths (406 and 460 nm). [6] This dual excitation-single emission property minimizes the impact of variations in fluorophore concentration, photobleaching, and instrumentation. The pH sensitivity of pyranine arises from its phenol group with a pK a of 7.3 that allows the determination of pH values ranging from ≈5 to ≈9, adequate for biologically or biomedically oriented applications. [7,8] Accordingly, pyranine has been employed to measure intracellular pH, [2,9,10] track protein structural transitions, [9][10][11][12] for metal ion-sensing, [13] and for the development of environmental sensors. [14][15][16] The monitoring of chronic wounds via pH-sensitive wound pads is a relevant application, in particular, due to the similar relevant pH range. [17,18] The low price of pyranine compared to other fluorescent dyes is especially attractive for commercial applications, even allowing its use in fluorescent text markers. However, due to the difficulty of covalent conjugation, with few exceptions, [19][20][21][22] most pyranine sensors are based on non-covalent integration. [15,[23][24][25][26] Here, the dye's high water solubility and lack of functional groups besides three sulfonic acids groups can lead to severe limitation in terms of leaching. Recently, we demonstrated that the coupling of pyranine with benzalkonium chloride into a water-insoluble ion pair can solve this problem for a range of pH values. [27] Loading of the ion pair onto a porous support allowed the fabrication of a sensor for wound pH. Still, at higher pH the ion pair separates and pyranine can leach out. Therefore, a stable covalent conjugation with an adequate host matrix would be preferable.Amphiphilic polymer conetworks (APCNs) represent a class of materials with great potential as matrices for sensor applications. [28][29][30][31] APCNs combine a hydrophilic and a hydrophobic polymer in one network with a nanophase-separated morphology. The synergistic combination of both polymers and the unique structural features of APCNs result in a set of favorable properties that includes, amongst others, optical transparency, mechanical stability, and amphiphilic swelling, resulting in permeability to aqueous solutes and compounds dissolved in organic solvents. Moreover, APCN can be permeable pH SensorsThe authors declare no conflict of interest.