Mesogens that vary in shape anisometry have been investigated by 13C solid-state NMR in the liquid crystalline phase to inspect the conformations. The molecules examined comprise of (i) rod-like mesogen with three-phenyl ring core and terminal hexyloxy chains, (ii) three-ring core linked to the fourth phenyl ring via a spacer, and (iii) trimesic acid connected to three side arms core units through a spacer. The order parameter (Szz) values for the phenyl rings of the rod-like mesogen are 0.65-0.68, while the mesogen with a three-ring core linked to a phenyl ring via spacer showed dissimilarity. Consequently, for the core unit's phenyl rings, Szz is ~ 0.70, and the terminal phenyl ring showed a low value of 0.12. For the trimesic acid based mesogen, the Szz value for the side arm phenyl rings is ~ 0.53, and for the central phenyl ring, a very low value of 0.11 is witnessed. By considering the ordering of the rod-like mesogen as a yardstick and employing the ratios of Szz values of the phenyl rings, the average conformations of other mesogens are arrived. Accordingly, for the trimesic acid based mesogen, a tripod-like conformation instead of l shape is proposed in the liquid crystalline phase.

Local pro-aromaticity in acene thioamides chromophores is conducive to triplet photochemistry. However, additional aromatic sextet(s) on the π-core of these chromophores would affect their photostability and photochemistry.

Abstract

Poly-aromatic systems that contain quinodimethyl (QDM) units are appealing for several photonic and spintronic applications owing to the unique electronic structure, aromaticity, and spin state(s) of the QDM ring. Herein, we report the synthesis and characterization of novel QDM-based chromophores 1–3, which exhibit unique photo-excited behavior and aromaticity. Extending the aromatic core with a biphenyl/phenanthryl- and a pyrrolo-fragment led to reducing the optoelectronic bandgap and modulating the photophysics QDM 1–3. Yet, QDM 2 and 3 suffer from “aromaticity imbalance” and become relatively unstable compared to the parent compound QDM 1. Further assessment of local aromaticity using computational tools revealed that the pseudo-quinoidal ring B is the main driving force allowing to easily populate the excited triplet state of these chromophores. The present study provides complementary guidelines for designing novel non-classical poly-aromatic systems.

The adsorption and thermal stability of bromine on Rh(111) is investigated by synchrotron radiation-based XPS, LEED and DFT. Depending on the coverage, four different superstructures are observed. At low coverages, bromine occupies fcc hollow sites while, at higher coverages, a compression of the overlayer leads to bridge-bound bromine atoms. Br/Rh(111) shows a high thermal stability, which implies strong covalent bonding.

Abstract

This study addresses a fundamental question in surface science: the adsorption of halogens on metal surfaces. Using synchrotron radiation-based high-resolution X-ray photoelectron spectroscopy (XPS), temperature-programmed XPS, low-energy electron diffraction (LEED) and density functional theory (DFT) calculations, we investigated the adsorption and thermal stability of bromine on Rh(111) in detail. The adsorption of elemental bromine on Rh(111) at 170 K was followed in situ by XPS in the Br 3d region, revealing two individual, coverage-dependent species, which we assign to fcc hollow- and bridge-bound atomic bromine. In addition, we find a significant shift in binding energy upon increasing coverage due to adsorbate-adsorbate interactions. Subsequent heating shows a high thermal stability of bromine on Rh(111) up to above 1000 K, indicating strong covalent bonding. To complement the XPS data, LEED was used to study the long-range order of bromine on Rh(111): we observe a (√3×√3)R30° structure for low coverages (≤0.33 ML) and a star-shaped compression structure for higher coverages (0.33–0.43 ML). Combining LEED and DFT calculations, we were able to visualize bromine adsorption on Rh(111) in real space for varying coverages.

Fluorinated organic molecules can be used as thermosensors for MR-based temperature determination. Thirteen fluorinated organic substrates were investigated with regard to the temperature sensitivity of their ¹⁹F MR signal(s) in aqueous solution. Such molecules can be used as thermosensors for MR-based temperature determination, for example, in medical applications such as hyper- or hypothermia.

Abstract

The interest in fluorinated substances has increased significantly in recent decades due to their diverse properties and possible uses. An important analytical method in this context is NMR spectroscopy, which provides information on the structure as well as on intermolecular interactions or generally on changes in the environment of the nucleus under consideration. A physical quantity that is of great importance in most studies is temperature. However, this is not always easy, e. g. in shielded systems or within an organism. However, the application potential in chemical reactors or in medical diagnosis and therapy is very high and for this reason 13 fluorinated organic compound were chosen for a first ¹⁹F NMR signal temperature sensitivity examination for determination of local temperatures in solution. Polyfluorinated molecules with separate ¹⁹F MR signals are particularly suitable for temperature determination. Those can be serve as internal error-correcting thermometers without the need of a reference substance. Under these conditions, a ¹⁹F MR signal shift of up to 0.03 ppm/K was detectable. Fluorine position and chemical environment were very important for the temperature sensitivity.