University of Siegen
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Publication Access status: Open Access , Remote control of the synthesis of a [2]rotaxane and its shuttling via metal-ion translocation(2019); ; Remote control in an eight-component network commanded both the synthesis and shuttling of a [2]rotaxane via metal-ion translocation, the latter being easily monitored by distinct colorimetric and fluorimetric signals. Addition of zinc(II) ions to the red colored copper-ion relay station rapidly liberated copper(I) ions and afforded the corresponding zinc complex that was visualized by a bright sky blue fluorescence at 460 nm. In a mixture of all eight components of the network, the liberated copper(I) ions were translocated to a macrocycle that catalyzed formation of a rotaxane by a double-click reaction of acetylenic and diazide compounds. The shuttling frequency in the copper-loaded [2]rotaxane was determined to k298=30 kHz (ΔH≠=62.3±0.6 kJ mol−1, ΔS≠=50.1±5.1 J mol−1 K−1, ΔG≠298=47.4 kJ mol−1). Removal of zinc(II) ions from the mixture reversed the system back generating the metal-free rotaxane. Further alternate addition and removal of Zn2+ reversibly controlled the shuttling mode of the rotaxane in this eight-component network where the ion translocation status was monitored by the naked eye.Source Type:Article1 7 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Mapping the broadband circular dichroism of copolymer films with supramolecular chirality in time and spaceMeasurements of the electronic circular dichroism (CD) are highly sensitive to the absolute configuration and conformation of chiral molecules and supramolecular assemblies and have therefore found widespread application in the chemical and biological sciences. Here, we demonstrate an approach to simultaneously follow changes in the CD and absorption response of photoexcited systems over the ultraviolet−visible spectral range with 100 fs time resolution. We apply the concept to chiral polyfluorene copolymer thin films and track their electronic relaxation in detail. The transient CD signal stems from the supramolecular response of the system and provides information regarding the recovery of the electronic ground state. This allows for a quantification of singlet−singlet annihilation and charge-pair formation processes. Spatial mapping of chiral domains on femtosecond time scales with a resolution of 50 μm and diffraction-limited steady-state imaging of the circular dichroism and the circularly polarised luminescence (CPL) of the films is demonstrated.Source Type:Article3 9 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , One-dimensional suboxide TiO2 nanotubes for electrodics applicationsThis mini-review summarizes the recent research on the applications of anodic one-dimensional suboxide titania nanostructures with enhanced electrodics properties by introducing atomic-scale defects into the titania systems. Due to the unique semiconductive properties of TiO2 nanostructures, so far, the main focus of research has been on photocatalytic applications of this semiconductor. The limited conductivity of pristine anodized titania restrains the application of one-dimensional (1D) nanostructured TiO2 as an electrode. However, recently published works present that suboxide TiO2 nanotubes, due to the enhanced conductivity, are promising electrodes for electrochemical applications. In this mini-review, we highlight the unique advantages of defective TiO2-x nanotubes as an electrode and address the recent electrodics applications of 1D anodic TiO2 nanotubes.Source Type:Article1 14 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , The mechanism of the first hydration-dehydration cycle of pure α- and β-CaSO4•0.5H2OThe objective of this research was to understand the dehydration mechanism of technical dihydrate and the variation of the physical properties of β-hemihydrate after the first hydration-dehydration process. In this study, the recycling mechanism of different hemihydrate types as raw material was investigated. The influence of the first hydration-dehydration process on the hydration rate, microstructure, and mechanical properties of recycled hemihydrate were characterized by differential calorimetric analysis (DCA), calcium ion-selective electrode (Ca2+-ISE), conductivity, particle size distribution (PSD), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The results showed that the formed hemihydrate after the first hydration-dehydration process differs in its properties than the unrecycled hemihydrate in some characteristics such as the morphological structure, number of surface, and side defects due to the grinding process after the first hydration step. In addition to the grinding step, the calcination process was responsible for increasing the number of defects on the crystal surface, which leads to a change in setting time and the microstructure of the recycled hemihydrate. Therefore, after the 1st reaction cycle of β-HH, the compressive strength decreases due to a decrease in the hemihydrate crystal size, an increase in the surface area, and an increase in the amount of water required to perform the hydration reaction. The obtained hemihydrate after the first hydration-dehydration process was in β form due to the applied calcination process after the first cycle.Source Type:Article7 15
