The optical absorption spectra of trivalent thulium in single crystals of YVO, and YPO, were measured in the range from 5000 to 29000 cm-1 including the Zeeman effect at 85,4.2, and2K. Furthermorethe fluorescence spectruminYV0,between 19OOO and 25000 cm-1 was investigated. Some special features of the spectra can be explained by the assumption that in several cases the crystal field eigenfunctions consist essentially of one free ion yy J M . From the splitting of Tms+ in YV0,values for the crystal field parameters were determined.Es wurden die Absorptionsspektren des dreiwertigen Thuliums in YV0,-und YP0,-Einkristallen im Bereich von 5000 bis 29000 cm-1 einschlieBlich des Zeemen-Effekts bei 85, 4,2 und 2 K gemessen. AuBerdem wurde das Fluoreszenzspektrum in YVO, zwischen 19OOO und 25000 cm-l aufgenommen. Einige Besonderheiten der Spektren lassen sich mit der Annahme erkliiren, daB in mehreren Fiillen die Kristallfeldzustiinde iiberwiegend ein einziges py J M enthalten. Aus der Aufspaltung der Terme des TmS+ in YVO, wurden Werte fiir die Kristallfeldparameter bestimmt.
We were previously able to demonstrate that mesogens self‐assembled from small molecules, more specifically 1,3,5‐benzene‐tricarboxamides (BTAs), are capable of forming lyotropic liquid crystalline phases in chloroform and CCl4, which are suitable for use as alignment media for small organic molecules. In this context, however, it became quickly apparent that one major limitation of such systems arises from the disruption of the self‐assembly process by certain analytes. Here, we present a modified version of our original BTA‐monomers, containing an additional l‐valine moiety. Through this modification, the number of available hydrogen‐bond acceptors/donators per monomer is doubled, resulting in vastly increased stability. The new system thus obtained exhibits anisotropic properties at much lower concentrations of BTA and allows for the determination of residual dipolar couplings for previously incompatible analytes like isopinocampheol (IPC). Interestingly, the BTA system exhibits the properties of an organogel rather than of a liquid crystal. This is thus the first report of the use of an organogel‐like alignment medium.
NMR techniques incorporating pure shift methods to improve signal resolution have recently attracted much attention, owing to their potential use in studies of increasingly complex molecular systems. Extraction of frequencies from these simplified spectra enables easier structure determination, but only a few of the methods presented provide structural parameters derived from signal integral measurements. In particular, for quantification of the nuclear Overhauser effect (NOE) it is highly desirable to utilize pure shift techniques where signal overlap normally prevents accurate signal integration, to enable measurement of a larger number of interatomic distances. However, robust methods for the measurement of interatomic distances using the recently developed pure shift techniques have not been reported to date. In this work we discuss some of the factors determining the accuracy of measurements of signal integrals in interferogram-based Zangger-Sterk (ZS) pure shift NMR experiments. The ZS broadband homodecoupling technique is used in different experiments designed for quantitative NOE determination from pure shift spectra. It is shown that the techniques studied can be used for quantitative extraction of NOE-derived distance restraints, as exemplified for the test case of strychnine.
A supramolecular, lyotropic liquid crystalline alignment medium based on an azobenzene‐containing 1,3,5‐benzenetricarboxamide (BTA) building block is described and investigated. As we demonstrate, this water‐based system is suitable for the investigation of various water‐soluble analytes and allows for a scaling of alignment strength through variation of temperature. Additionally, alignment is shown to reversibly collapse above a certain temperature, yielding an isotropic solution. This collapse allows for isotropic reference measurements, which are typically needed in addition to those in an anisotropic environment, to be performed using the same sample just by varying the temperature. The medium described thus provides easy access to anisotropic NMR observables and simplifies structure elucidation techniques based thereon.
New supramolecular lyotropic liquid crystals (LLC) based on 1,3,5‐benzenetricarboxamides (BTAs) with n‐alkylaniline sidechains are described. Using NMR spectroscopy, we investigate the effects of different chain lengths along the homologous series and of non‐BTA additives on liquid crystalline behaviour. From this, we attempt to answer two questions: First, how aliphatic chain length and the addition of further aromatic rings affect the self‐assembly process in general and compared to previously reported systems with purely aliphatic sidechains. Second, whether these modifications are suitable to increases the resulting LLC phases’ resilience against disrupting effects of further, non‐BTA additives.
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