Linda Zedler

Self‐Healing Polymer Coatings Based on Crosslinked Metallosupramolecular Copolymers

Self-healing coating based on metallopolymers are prepared and fully characterized. Iron bisterpyridine complexes are incorporated into a polymer network based on methacrylates, resulting in self-healing properties of these materials. Moreover, the influence of the comonomers on the thermal properties is studied in detail.

Self-healing mechanism of metallopolymers investigated by QM/MM simulations and Raman spectroscopy

The thermally induced self-healing mechanisms in metallopolymers based on bisterpyridine complexes of iron(II) sulfate and cadmium(II) bromide, respectively, were studied by means of combined quantum mechanical/molecular mechanical (QM/MM) simulations and Raman spectroscopy. Two possible healing schemes, one based on a decomplexation of the cross-linking complexes and a second one relying on the dissociation of ionic clusters, have been addressed. Temperature-dependent Raman spectroscopy displayed bathochromic shifts of the Raman intensity pattern upon heating. QM/MM simulations on the polymer models assign these alterations to a partial decomplexation of the metal terpyridine complexes, i.e. signals originating from free terpyridine ligands increase upon heating. Thus, a healing mechanisms based on partial decomplexation of the cross-linking complexes is suggested. The possibility that the dissociation of ionic clusters, which are assumed to be present in this class of self-healing polymers, is also responsible for the self-healing process was investigated as well. However, such calculations on model clusters revealed relatively strong binding of the clusters, which renders reversible cluster breaking and reformation upon temperature cycling in the range up to 100 °C unlikely.

Resonance-Raman spectro-electrochemistry of intermediates in molecular artificial photosynthesis of bimetallic complexes

The sequential order of photoinduced charge transfer processes and accompanying structure changes were analyzed by UV-vis and resonance-Raman spectroscopy of intermediates of a Ru(ii) based photocatalytic hydrogen evolving system obtained by electrochemical reduction.

Disruption-free imaging by Raman spectroscopy reveals a chemical sphere with antifouling metabolites around macroalgae

Investigations of the surface chemistry of marine organisms are essential to understand their chemically mediated interactions with fouling organisms. In this context, the concentration of natural products in the immediate vicinity of algal surfaces, as well as their biological activity, are of particular importance. However, due to lack of appropriate methods, the distribution of compounds within the chemical sphere around marine algae is unknown. This study demonstrates the suitability of confocal resonance Raman microspectroscopy for the determination of metabolites around algal surfaces with a micrometer resolution. The spatial distribution of carotenoids in the diffusion boundary layer of the brown alga Fucus vesiculosus and the green alga Ulva sp. was determined using the disruption-free optical method. A gradient of carotenoids was determined within 0 to 150 μm from the surface of thealgae, thereby demonstrating the release of the non-polar metabolites involved in antifouling processes. Thedifferences in the carotenoid composition of the brown and green algae were reflected in the spectra. Resonance Raman microspectroscopy also allowed visualization of the lateral distribution of fucoxanthin on the algal surface and localization of concentration maxima within a 50 × 50 μm2 area. The results from this work show clearly that established dipping techniques suitable for the extraction of the diffusion boundary layer of macroalgae only provide an average of the local strongly variable concentrations of metabolites on algal surfaces.

Trapped in Imidazole: How to Accumulate Multiple Photoelectrons on a Black‐Absorbing Ruthenium Complex

Ruthenium dyes incorporating a 4H-imidazole chromophore as a ligand exhibit a spectrally broad absorption in the UV/Vis region. Furthermore, they show the ability to store two electrons within the 4H-imidazole ligand. These features render them promising molecular systems, for example, as inter- or intramolecular electron relays. To optimize the structures with respect to their electron-storage capability, it is crucial to understand the impact of structural changes accompanying photoinduced charge transfer in the electronic intermediates of multistep electron-transfer processes. The photophysical properties of these (reactive) intermediates might impact the function of the molecular systems quite substantially. However, the spectroscopic study of short-lived intermediates in stepwise multielectron-transfer processes is experimentally challenging. To this end, this contribution reports on the electrochemical generation of anions identical to intermediate structures and their spectroscopic characterization by in situ resonance Raman and UV/Vis spectroelectrochemistry and computational methods. Thereby, an efficient two-electron pathway to the 4H-imidazole electron-accepting ligand is identified.

Spectroelectrochemical Investigation of the One-Electron Reduction of Nonplanar Nickel(II) Porphyrins.

The electrochemical reduction of a series of nickel porphyrins with an increasing number of substituents was investigated in acetonitrile. A one-electron reduction of [5,15-bis(1-ethylpropyl)porphyrinato]nickel(II) leads to π-anion radicals and to efficient formation of phlorin anions, presumably by disproportionation and subsequent protonation of the doubly reduced species. The phlorin anion was identified by using cyclic voltammetry and UV/Vis and resonance Raman spectroelectrochemistry, complemented by quantum-chemical calculations to assign the spectral signatures. The theoretical analysis of the potential-energy landscape of the singly reduced species suggests a thermally activated intersystem crossing that populates the quartet state and thus lowers the energy barrier towards disproportionation channels. Structure-reactivity correlations are investigated by considering different substitution patterns of the investigated nickel(II) porphyrin cores, that is, for the porphyrin with additional β-aryl ([5,15-bis(1-ethylpropyl)-2,8,12,18-tetra(p-tolyl)porphyrinato]nickel(II)) and meso-alkyl substitution ([5,10,15,20-tetrakis(1-ethylpropyl)porphyrinato]nickel(II)), no phlorin anion formation was observed under electrochemical conditions. This observation is correlated either to kinetic inhibition of the disproportionation reaction or to lower reactivity of the subsequently formed doubly reduced species towards protonation.