Structure of a Supramolecular Water Copolymer

The use of water as a solvent to facilitate supramolecular polymerization is well documented, however, it is rare that water acts as a monomer that undergoes polymerization. We report the copolymerization of water with a saddle-shaped porphyrinoid macrocycle, carpyridine, which allows for linearly stacked, eclipsed columns within formed 2D nanosheets. Self-assembling carpyridine monomers from solutions with different extents of wetness allow for the formation of nanosheets on surface that appear identical by microscopy. Structural analysis through electron diffrac-tion reveals fundamental changes in the local organization. Under dry conditions, carpyridine stacks are formed through π–π interactions between curved surfaces whereas in solutions containing greater quantities of water, a hy-drogen-bonded water-to-carpyridine-core network is propagated throughout perfectly linear columns. The observed wet phase can be interconverted to a dry one through vapor annealing, indicating an accessible energy surface of polymorphism.