Free-Standing, Single-Monomer-Thick Two-Dimensional
Polymers through Covalent Self-Assembly in Solution
- Publication date
- Publisher
Abstract
The design and synthesis of two-dimensional
(2D) polymers is a
challenging task, hitherto achieved in solution only through the aid
of a solid surface “template” or preorganization of
the building blocks in a 2D confined space. We present a novel approach
for synthesizing free-standing, covalently bonded, single-monomer-thick
2D polymers in solution without any preorganization of building blocks
on solid surfaces or interfaces by employing shape-directed covalent
self-assembly of rigid, disk-shaped building blocks having laterally
predisposed reactive groups on their periphery. We demonstrate our
strategy through a thiol–ene “click” reaction
between (allyloxy)<sub>12</sub>CB[6], a cucurbit[6]uril (CB[6]) derivative
with 12 laterally predisposed reactive alkene groups, and 1,2-ethanedithiol
to synthesize a robust and readily transferable 2D polymer. We can
take advantage of the high binding affinity of fully protonated spermine
(positive charges on both ends) to CB[6] to keep each individual polymer
sheet separated from one another by electrostatic repulsion during
synthesis, obtaining, for the first-time ever, a single-monomer-thick
2D polymer in solution. The arrangement of CB[6] repeating units in
the resulting 2D polymer has been characterized using gold nanoparticle
labeling and scanning transmission electron microscopy. Furthermore,
we have confirmed the generality of our synthetic approach by applying
it to different monomers to generate 2D polymers. Novel 2D polymers,
such as our CB[6] derived polymer, may be useful in selective transport,
controlled drug delivery, and chemical sensing and may even serve
as well-defined 2D scaffolds for ordered functionalization and platforms
for bottom-up 3D construction