Evidence for Orientational Order in Nanothreads Derived from Thiophene

Nanothreads
are one-dimensional sp3 hydrocarbons that
pack within pseudohexagonal crystalline lattices. They are believed
to lack long-range order along the thread axis and also lack interthread
registry. Here we investigate the phase behavior of thiophene up to
35 GPa and establish a pressure-induced phase transition sequence
that mirrors previous observations in low-temperature studies. Slow
compression to 35 GPa results in the formation of a recoverable saturated
product with a 2D monoclinic diffraction pattern along (0001) that
agrees closely with atomistic simulations for single crystals of thiophene-derived
nanothreads. Paradoxically, this lower-symmetry packing signals a
higher degree of structural order since it must arise from constituents
with a consistent azimuthal orientation about their shared axis. The
simplicity of thiophene reaction pathways (with only four carbon atoms
per ring) apparently yields the first nanothreads with orientational
order, a striking outcome considering that a single point defect in
a 1D system can disrupt long-range structural order.