Folding-Generated Molecular Tubes Containing One-Dimensional Water Chains

A series
of indolo­carbazole–pyridine (IP) oligomers
were prepared that fold into helical conformations, and their folding
features in solution and in the solid state were revealed. Helical
folding of these IP foldamers is induced by dipolar interactions through
the ethynyl bond and π-stacking between two repeating units.
Upon helical folding, 1H NMR signals of aromatic protons
were significantly shifted upfield by Δδ = 0.5–2.2
ppm. In addition, hypochromic shifts and fluorescence quenching were
observed in the absorption and emission spectra. X-ray crystal structures
clearly demonstrated that IP foldamers folded to helical structures
with cylindrical internal cavities wherein 3 or 5 water molecules
were occupied by hydrogen-bonding interactions in a 1-D array, reminiscent
of transmembrane water channels, called aquaporins.