Double-core nanothread formation from α-furil via a pressure-induced planarization pathway.

The packing and geometry of compressed small molecule precursors largely dictate the kinetically controlled formation processes of carbon nanothread materials. Structural ordering and chemical homogeneity of nanothread products may deteriorate through competing reaction pathways, and molecular phase transitions can disrupt precursor stacking geometries. Here, we report the formation of well-ordered, double-core nanothreads from compressed α-furil via a unique polymorphic transition pathway that serves to facilitate a pressure-induced reaction. At ∼1.6 GPa, α-furil transforms to the photoactive trans-planar conformation, which was previously theorized but not observed. Crystalline packing of the trans-planar structure provides closely overlapping molecular stacks that result in topochemical-like Diels-Alder cycloaddition reactions between furan rings upon further compression. The controlled reaction pathways on both sides of the molecule produce two linked "cores" of chemically homogenous nanothreads, and successive nucleophilic addition reactions crosslink a large fraction of the diketone bridges between monomers.