Distance-Selected Topochemical Dehydro-Diels–Alder Reaction of 1,4-Diphenylbutadiyne toward Crystalline Graphitic Nanoribbons

Solid-state topochemical polymerization
(SSTP) is a promising method
to construct functional crystalline polymeric materials, but in contrast
to various reactions that happen in solution, only very limited types
of SSTP reactions are reported. Diels–Alder (DA) and dehydro-DA
(DDA) reactions are textbook reactions for preparing six-membered
rings in solution but are scarcely seen in solid-state synthesis.
Here, using multiple cutting-edge techniques, we demonstrate that
the solid 1,4-diphenylbutadiyne (DPB) undergoes a DDA reaction under
10–20 GPa with the phenyl as the dienophile. The crystal structure
at the critical pressure shows that this reaction is “distance-selected”.
The distance of 3.2 Å between the phenyl and the phenylethynyl
facilitates the DDA reaction, while the distances for other DDA and
1,4-addition reactions are too large to allow the bonding. The obtained
products are crystalline armchair graphitic nanoribbons, and hence
our studies open a new route to construct the crystalline carbon materials
with atomic-scale control.