Trimorphism of a binary cocrystal system with hydrogen-bonded zig-zag, double helix and quadruple helix structures

Helices are present in the most important biomolecules (i.e., RNA, DNA). Helices are formed in biology and the laboratory using subunits with information encoded based on molecular recognition. The production of abiotic helical structures is an ongoing goal in synthetic and materials chemistry and has involved the development of organic and metal-organic materials that rely on complementarity of noncovalent forces (e.g. hydrogen bonds, coordination bonds) for helix formation. Herein, we describe a series of supramolecular isomers of three hydrogen-bonded organic cocrystals involving components that self-assemble and show progression at the structural level from a zig-zag chain to a double helix and to a quadruple helix. The isomers constitute a form of trimorphism involving a binary cocrystal system and we show that the polymeric structures can be interconverted through solvent-mediated phase transformations. We demonstrate the cocrystal involving the double helix to possess components that undergo an intermolecular [2 + 2] photodimerization in the crystalline state.