We have investigated the structural, magnetic, and electronic properties of nonstoichiometric iron oxide nanocrystals prepared by decomposition of iron(II) and iron(0) precursors in the presence of ...organic solvents and capping groups. The highly uniform, crystalline, and monodisperse nanocrystals that were produced enabled a full structural and compositional survey by electron microscopy and X-ray diffraction. The complex and metastable behavior of nonstoichiometric iron oxide (wüstite) at the nanoscale was studied by a combination of Mössbauer spectroscopy and magnetic characterization. Deposition from hydrocarbon solvents with subsequent self-assembly of iron oxide nanocrystals into superlattices allowed the preparation of continuous thin films suitable for electronic transport measurements.
The surface of highly monodisperse nanocrystals of iron oxide (γ-Fe2O3) prepared via a non-hydrolytic controlled oxidation route were investigated using pyrene carboxylic acid and related derivatives ...(an ester and an alcohol) as spectroscopic probes of the nanocrystal surface.
Around 100 porphyrin units have been selectively linked at C(6)−O to a cellulose (Avicel®). The properties of the metal‐free and zincated porphyrin‐celluloses 2 and Zn‐2 have been determined by ...optical and electrochemical methods. Circular dichroism indicates a helical arrangement of the porphyrin units and reveals intra‐chain coupling reminiscent, in the broadest sense, of strands of nucleic acids. Cyclic voltammetry and spectroelectrochemistry have been used to characterize the radical ions and dianions. The electrochromism of the oxidation of cellulose 2 to porphyrin radical cations of 2 has been employed for both molecular switching and the transduction of an electrochemical input into chiroptical signal expression.
Die regioselektive Synthese (Ausgangsmaterial: Avicel®) liefert farbstoffmodifizierte Cellulose, derivatisiert mit etwa hundert Porphyrineinheiten pro Cellulosestrang. Die Porphyrin‐Cellulose und Zink‐Porphyrin‐Cellulose Konjugate werden mit optischen, elektrochemischen und spektroelektrochemischen Methoden untersucht. Der Circulardichroismus belegt intramolekulares „Exciton Coupling“. Eine linksgängige helikale Anordnung der Chromogene wird aus dem Vorzeichen abgeleitet. Durch in‐situ‐Circulardichroismus‐Spektroelektrochemie wird gezeigt, dass Porphyrin‐Cellulose 2 geeignet ist, elektrochemische Signaleingabe in chiroptische Signalausgabe zu wandeln.
Around one‐hundred porphyrins have been regioselectively attached at C(6)−O of a cellulose composed of about two‐hundred glucose units (see scheme). Circular dichroism indicated a helical architecture of the porphyrin subunits and revealed both intra‐chain (tetrahydrofuran) and inter‐chain (methanol) interactions. Electrochromism generated by oxidation was utilized for molecular switching and enabled the transduction of an electrochemical input into a chiroptical on/off signal expression.
Regioselective synthesis using protecting‐group strategy yields azulene‐cellulose conjugates 6‐(azulene‐2‐carboxylate)‐2,3‐di‐O‐methyl cellulose AzC‐1, 6‐(4‐azulene‐1‐yl‐benzoate)‐2,3‐di‐O‐methyl ...cellulose AzC‐2, and 6‐(azulene‐1‐carboxylate)‐2,3‐di‐O‐methyl cellulose AzC‐3. The spectral and electrochemical properties were investigated and compared with the azulene alkylesters 1 b, 2 b, and 3 b. The relative fluorescence quantum yield of methyl 2‐azulenecarboxylate 1b exceeds that of azulene cellulose AzC‐1 by an order of magnitude. Cellulose derivative AzC‐3 exhibits weak dual emission around 400 nm and 520 nm at room temperature. The circular dichroism (CD) of AzC‐1, AzC‐2, and AzC‐3 are reported. Intensity and feature of the CD signals depend on the degree of substitution (DS) as shown by AzC‐1. The CD‐split signals at 280 nm (3A1 transition of azulene) are likely to result from interacting azulene groups. A regular (helical) structure of the cellulose backbone is postulated, leading to the (M)‐configuration of the spatial azulene units. Unlike esters 2 b and 3 b azulene appended celluloses AzC‐1 and AzC‐2 electropolymerize under potentiodynamic conditions. Chemically modified electrodes are formed. Dotation sates were characterized by UV‐Vis‐NIR‐spectroelectrochemistry. Azulene appended celluloses are suitable for making conducting electrodes with chiral coating materials.
