Design and synthesis of new carbon allotropes have always been important topics in condensed matter physics and materials science. Here we report a new carbon allotrope, formed from cold-compressed ${\mathrm{C}}_{70}$ peapods, which most likely can be identified with a fully $s{p}^3$-bonded monoclinic structure, here named $V$ carbon, predicted from our simulation. The simulated x-ray diffraction pattern, near $K$-edge spectroscopy, and phonon spectrum agree well with our experimental data. Theoretical calculations reveal that $V$ carbon has a Vickers hardness of 90 GPa and a bulk modulus $\sim 400\mathrm{GPa}$, which well explains the “ring crack” left on the diamond anvils by the transformed phase in our experiments. The $V$ carbon is thermodynamically stable over a wide pressure range up to 100 GPa, suggesting that once $V$ carbon forms, it is stable and can be recovered to ambient conditions. A transition pathway from peapod to $V$ carbon has also been suggested. These findings suggest a new strategy for creating new $s{p}^3$-hybridized carbon structures by using fullerene@nanotubes carbon precursor containing odd-numbered rings in the structures.

Two new propeller-shaped benzothiazole–enamide boron difluoride complexes exhibiting piezochromic luminescence upon mechanical grinding or hydrostatic compression were prepared. The two analogues displayed the red shift in luminescence under high pressure, while compound 2 with ICT effects showed a more sensitive piezochromic response at low pressure (<1.5 GPa). The different piezochromic luminescence behaviors of these compounds were investigated.

Developing a universal strategy to design piezochromic luminescent materials with desirable properties remains challenging. Here, we report that insertion of a non-emissive molecule into a donor (perylene) and acceptor (1,2,4,5-tetracyanobezene) binary cocrystal can realize fine manipulation of intermolecular interactions between perylene and 1,2,4,5-tetracyanobezene (TCNB) for desirable piezochromic luminescent properties. A continuous pressure-induced emission enhancement up to 3 GPa and a blue shift from 655 to 619 nm have been observed in perylene-TCNB cocrystals upon THF insertion, in contrast to the red-shifted and quenched emission observed when compressing perylene-TCNB cocrystals and other cocrystals reported earlier. By combining experiment with theory, it is further revealed that the inserted non-emissive THF forms blue-shifting hydrogen bonds with neighboring TCNB molecules and promote a conformation change of perylene molecules upon compression, causing the blue-shifted and enhanced emission. This strategy remains valid when inserting other molecules as non-emissive component into perylene-TCNB cocrystals for abnormal piezochromic luminescent behaviors.

The PI-SERS signals of R6G molecules on a MoS ₂ /Au substrate are enhanced at 2.39 GPa by a two-step charge transfer process.

Graphite is known to transform into diamond under dynamic compression or under combined high pressure and high temperature, either by a concerted mechanism or by a nucleation mechanism. However, these mechanisms fail to explain the recently reported discovery of diamond formation during ambient temperature compression combined with shear stress. Here we report a new transition pathway for graphite to diamond under compression combined with shear, based on results from both theoretical simulations and advanced experiments. In contrast to the known model for thermally activated diamond formation under pressure, the shear-induced diamond formation takes place during the decompression process via structural transitions. At a high pressure with large shear, graphite transforms into ultrastrong $s{p}^3$ phases whose structures depend on the degree of shear stress. These metastable $s{p}^3$ phases transform into either diamond or graphite upon decompression. Our results explain several recent experimental observations of low-temperature diamond formation. They also emphasize the importance of shear stress for diamond formation, providing new insight into the graphite-diamond transformation mechanism.