Rational Approaches toward the Design and Synthesis of Carbon Nanothreads

Carbon-based materials─often with superlative electronic, mechanical, chemical, and thermal properties─are often categorized by dimensionality and hybridization. Most of these categories are produced in high-temperature conditions that afford equilibrium-dictated structures, but limit their diversity. In contrast, an emerging class of one-dimensional (1D) carbon materials, coined nanothreads, are accessible through kinetically controlled solid-state reactions of small multiply unsaturated molecules. While abundant in molecular organic synthesis, exerting kinetic control over reactivity is a revolutionary approach to access dense carbon networks. Owing to their internal diamond-like core, these materials are calculated to span a wide range of mechanical and optical properties, with the introduction of functional groups and/or heteroatoms leading to tailorable band gaps and the potential to access electronic states that are not featured in traditional polymers or nanomaterials. Accessing these properties requires the ability to precisely control solid-state molecular reaction pathways, chemical connectivity, and heteroatom/functional group density. Carbon nanothreads are often synthesized through the pressure-induced polymerization of aromatic molecules (e.g., benzene, pyridine, and thiophene) upon compression to 23–40 GPa. While the high pressures required to achieve these crystalline materials often preclude making synthetically viable quantities of product, the use of lessened aromatic reactants, along with light and/or heat, enables more mild reaction pressures. Success to date in forming nanothreads from diverse reactants suggests that physical organic principles govern the reaction, along with topochemical relationships, enabling the emergence of a new field of carbon chemistry that combines the control of organic chemistry with the range of physical properties only possible in extended periodic solids.