Topochemical Polymerization of Phenylacetylene Macrocycles under Pressure

Self-assembly
of organic macrocycles has been exploited as a preliminary
step in the synthesis of soluble and tailorable carbon-based nanostructures.
Functionalized nanotubes have been prepared using, as core building
blocks, nearly planar ring structures containing several alkyne units,
exploiting the geometry achieved in the spontaneous preassembling
step driven by π interaction. Covalent cross-linking between
these units was achieved by thermal or photochemical activation with
UV light. Here, we apply a moderate pressure in a sapphire anvil cell
(1.0 GPa) to facilitate the preassembling and induce the cross-linking
under pressure either with visible light, absorbed by two-photon absorption,
or thermally. We observe a high yield of enhanced quality cross-linked
nanotubes in a sample, showing, at ambient pressure, only side-chain
decomposition. These results show that moderate pressures, easily
achievable in large volume cells, are able to selectively favor topochemical
reactions in such complex organic systems.