Helical Molecular Springs under High Pressure

Although the unique structure of helicenes resembles molecular springs, the effects of pressure on their extension–contraction cycles have rarely been explored. Herein, we investigated the fluorescence of two π-extended [n]helicenes with different helical lengths n, here named [7] and [9], under high pressure in a diamond anvil cell. Based on experimental results and theoretical calculations, the mechanical and fluorescent properties of the molecular springs were found to be influenced not only by the intermolecular packing, but also by the intramolecular π-π interactions between their overlapping helixes. As a more rigid molecular spring, [9] exhibited a more sensitive response of its fluorescence to hydrostatic pressure than [7]. Our results provide new insights into structure-property relationships under high-pressure conditions and verify the potential of helicenes as molecular springs for future applications in molecular machines.

Superconductivity above 200K Observed in Superhydrides of Calcium

Searching for superconductivity with Tc near room temperature is of great interest both for fundamental science & potential applications. Here we report the experimental discovery of superconductivity with maximum critical temperature(Tc) above 210 K in calcium superhydrides, the third type hydride experimentally showing superconductivity above 200K in addition to sulfur hydride & rare earth hydride system. The materials are synthesized at the synergetic conditions of 160~190 GPa and ~2000K using diamond anvil cell combined with in-situ laser heating technique. The superconductivity was studied through in situ high pressure resistance measurements in applied magnetic field for the sample quenched from high temperature while maintained at the synthesized pressure. The upper critical field was estimated to be ~268T while the GL coherent length is ~11 Å. The in situ x ray diffractions with synchrotron suggest that the synthesized calcium hydrides are primarily composed of CaH6 while there also exist other calcium hydrids with different hydrogen.

Use of a miniature diamond-anvil cell in a joint X-ray and neutron high-pressure study on copper sulfate pentahydrate

Single-crystal X-ray and neutron diffraction data are usually collected using separate samples. This is a disadvantage when the sample is studied at high pressure because it is very difficult to achieve exactly the same pressure in two separate experiments, especially if the neutron data are collected using Laue methods where precise absolute values of the unit-cell dimensions cannot be measured to check how close the pressures are. In this study, diffraction data have been collected under the same conditions on the same sample of copper(II) sulfate pentahydrate, using a conventional laboratory diffractometer and source for the X-ray measurements and the Koala single-crystal Laue diffractometer at the ANSTO facility for the neutron measurements. The sample, of dimensions 0.40 × 0.22 × 0.20 mm3 and held at a pressure of 0.71 GPa, was contained in a miniature Merrill–Bassett diamond-anvil cell. The highly penetrating diffracted neutron beams passing through the metal body of the miniature cell as well as through the diamonds yielded data suitable for structure refinement, and compensated for the low completeness of the X-ray measurements, which was only 24% on account of the triclinic symmetry of the sample and the shading of reciprocal space by the cell. The two data-sets were combined in a single `XN' structure refinement in which all atoms, including H atoms, were refined with anisotropic displacement parameters. The precision of the structural parameters was improved by a factor of up to 50% in the XN refinement compared with refinements using the X-ray or neutron data separately.