Many novel phenomena that emerge at extreme conditions are fundamentally chemical processes; reflecting how chemical bonds break and form, how atoms and molecules organize over short- and long-range spatial extents, and how kinetics and thermodynamics govern materials stability. Many unsaturated chemical bonds in simple molecules, including two most stable C≡O and N≡N triple bonds, become unstable at high pressures of 10-100 GPa and convert to fully saturated, single bonded “polymeric” solids in three-dimensional network structures.

Examples are numerous including recent discoveries of low-Z extended phases of simple molecular solids such as N₂, CO₂, CO, and H₂S at high pressures. These covalently bonded extended framework solids exhibit unusual properties such as high energy density, extreme hardness, second harmonic generation, colossal Raman cross section, and the record high T_c superconductivity, hinting its potential for technology uses. However, these materials transform back to their molecular states upon the release of pressure, thus losing the novel properties. As a result, only a few systems have been recovered to date, limiting the materials within a realm of fundamental scientific discoveries. Therefore, an exciting new research area has emerged on understanding and, ultimately, controlling the stability, bonding, structure, and properties of low-Z extended solids in various novel framework structures.

The development of low-Z extended solids amenable to ambient stabilization poses great scientific and technological challenges. Those challenges primarily stem from the formidable transition pressures and high-energy states, which make them metastable at low pressures. A logical way to overcome these challenges is to use low-Z solid mixtures, where the internal chemical pressure can lower the transition pressure and strong hetero-nuclear chemical bonding replaces the dangling bonds enhancing the stability of extended network structures at ambient conditions. In this paper, we will describe our recent efforts to develop dense carbon-organic framework (deCOF) structures amenable to stabilization at or near ambient conditions, utilizing the concepts of solid mixtures and kinetic controlled processes at high pressures, and discuss about the basic principle of pressure-induced chemistry (or barochemistry) such as carbon Redox processes that can occur in deep Earth’s interiors and thus have strong implication of deep carbon cycle.