Photo- and halochromism of spiropyran-based main-chain polymers

Advanced functional polymeric materials based on spiropyrans (SPs) feature multi-stimuli responsive characteristics, such as a change in color with exposure to light (photochromism) or acids (halochromism). The inclusion of stimuli-responsive molecules in general – and SPs in particular – as main-chain repeating units is a scarcely explored macromolecular architecture compared to side chain responsive polymers. Herein, we establish the effects of substitution patterns on SPs within a homopolymer main-chain synthesized via head-to-tail Acyclic Diene METathesis (ADMET) polymerization. We unambiguously demonstrate that varying the location of the ester group (–OCOR) on the chromophore, which is essential to incorporate the SPs in the polymer backbone, determines the photo- and halochromism of the resulting polymers. While one polymer shows effective photochromism and resistance towards acids, the opposite – weak photochromism and effective response to acid – is observed for an isomeric polymer, simply by changing the position of the ester-linker relative to the benzopyran oxygen on the chromene unit. Our strategy represents a simple approach to manipulate the stimuli-response of main-chain SP bearing polymers and highlights the critical importance of isomeric molecular constitution on main-chain stimuli-sensitive polymers as emerging materials

Deconstructing 3D Structured Materials by Modern Ultramicrotomy for Multimodal Imaging and Volume Analysis across Length Scales

Based on the rapid advances in additive manufacturing, micro-patterned heterostructures of soft materials have become available that need to be characterized down to the nanoscale. Advanced function-structure relationships are designed by direct 3D structuring of the object and – in the future – fine control over material functionality in 3D will produce complex functional objects. To control their design, fabrication and final structure, morphological and spectroscopical imaging in 3D at nanometer resolution are critically required. With examples of carbon-based objects, it is demonstrated how serial ultramicrotomy, that is, cutting a large number of successive ultrathin sections, can be utilized to gain access to the interior of 3D objects. Array tomography, hierarchical imaging and correlative light and electron microscopy can bridge length scales over several orders of magnitude and provide multimodal information of the sample\u27s inner structure. Morphology data derived from scanning electron microscopy are correlated with spectroscopy in analytical transmission electron microscopy and probe microscopy at nanometer resolution, using TEM-electron energy loss spectroscopy and infrared-scanning-near-field microscopy. The correlation of different imaging modalities and spectroscopy of carbon-based materials in 3D provides a powerful toolbox of complementary techniques for understanding emerging functions from nanoscopic structuring

Direct Visualization of Homogeneous Chemical Distribution in Functional Polyradical Microspheres

It is demonstrated that the postfunctionalization of solid polymeric microspheres can generate fully and throughout functionalized materials, contrary to the expectation that core–shell structures are generated. The full functionalization is illustrated on the example of photochemically generated microspheres, which are subsequently transformed into polyradical systems. Given the all-organic nature of the functionalized microspheres, characterization methods with high analytical sensitivity and spatial resolution are pioneered by directly visualizing the inner chemical distribution of the postfunctionalized microspheres based on characteristic electron energy loss signals in transmission electron microscopy (TEM). Specifically, ultrasonic ultramicrotomy is combined successfully with electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI) during TEM. These findings open a key avenue for analyzing all-organic low-contrast soft-matter material structures, while the specifically investigated system concomitantly holds promise as an all-radical solid-state functional material.</p

Molecular Photoswitching of Main-Chain α-Bisimines in Solid-State Polymers

Photoisomerization of chromophores usually shows significantly less efficiency in solid polymers than in solution as strong intermolecular interactions lock their conformation. Herein, we establish the impact of macromolecular architecture on the isomerization efficiency of main-chain-incorporated chromophores (i.e., α-bisimine) in both solution and the solid state. We demonstrate that branched architectures deliver the highest isomerization efficiency for the main-chain chromophore in the solid state─remarkably as high as 70% compared to solution. The macromolecular design principles established herein for efficient solid-state photoisomerization can serve as a blueprint for enhancing the solid-state isomerization efficiency for other polymer systems, such as those based on azobenzenes.</p

Wavelength-resolved near infra-red light induced free-radical polymerization

Initiating polymerization processes at long wavelengths, ideally in the near-infrared (NIR) range, is critical to enable applications where shorter wavelengths may be harmful and where high penetration depths may be required. While we have recently demonstrated that gold nanorods (AuNR) function as effective photothermal converters at 800 nm to initiate free radical polymerizations, a careful wavelength-by-wavelength assessment (photochemical action plot analysis) of their effectiveness is outstanding. Herein, we provide a full NIR action plot from 620 to 950 nm, probing the wavelength-by-wavelength monomer to polymer conversion with an identical number of photons at each wavelength. While the vast majority of action plots show a red-shift relative to the absorption spectrum, we herein observe a pronounced blue-shift for the most effective conversion.</p

Deconstructing 3D Structured Materials by Modern Ultramicrotomy for Multimodal Imaging and Volume Analysis across Length Scales

Based on the rapid advances in additive manufacturing, micro-patterned heterostructures of soft materials have become available that need to be characterized down to the nanoscale. Advanced function-structure relationships are designed by direct 3D structuring of the object and – in the future – fine control over material functionality in 3D will produce complex functional objects. To control their design, fabrication and final structure, morphological and spectroscopical imaging in 3D at nanometer resolution are critically required. With examples of carbon-based objects, it is demonstrated how serial ultramicrotomy, that is, cutting a large number of successive ultrathin sections, can be utilized to gain access to the interior of 3D objects. Array tomography, hierarchical imaging and correlative light and electron microscopy can bridge length scales over several orders of magnitude and provide multimodal information of the sample's inner structure. Morphology data derived from scanning electron microscopy are correlated with spectroscopy in analytical transmission electron microscopy and probe microscopy at nanometer resolution, using TEM-electron energy loss spectroscopy and infrared-scanning-near-field microscopy. The correlation of different imaging modalities and spectroscopy of carbon-based materials in 3D provides a powerful toolbox of complementary techniques for understanding emerging functions from nanoscopic structuring.</p