Toward a Single-Layer Two-Dimensional Honeycomb Supramolecular Organic Framework in Water

The
self-assembly of well-defined 2D supramolecular polymers in solution
has been a challenge in supramolecular chemistry. We have designed
and synthesized a rigid stacking-forbidden 1,3,5-triphenyl­benzene
compound that bears three 4,4′-bipyridin-1-ium (BP) units on
the peripheral benzene rings. Three hydrophilic bis­(2-hydroxy­ethyl)­carbamoyl
groups are introduced to the central benzene ring to suppress 1D stacking
of the triangular backbone and to ensure solubility in water. Mixing
the triangular preorganized molecule with cucurbit[8]­uril (CB[8])
in a 2:3 molar ratio in water leads to the formation of the first
solution-phase single-layer 2D supramolecular organic framework, which
is stabilized by the strong complexation of CB[8] with two BP units
of adjacent molecules. The periodic honeycomb 2D framework has been
characterized by various 1H NMR spectroscopy, dynamic light
scattering, X-ray diffraction and scattering, scanning probe and electron
microscope techniques and by comparing with the self-assembled structures
of the control systems.