Development of a robust supramolecular method to prepare well-defined nanofibrils from conjugated molecules

In order to produce materials with tailored structures and functions via supramolecular self-assembly of molecular precursors in a predictable fashion, it is necessary to develop 'supramolecular methods' based on structurally simple 'supramolecular synthons'. Thus, the formation of one-dimensional aggregates from pi-conjugated molecules requires a combination of non-covalent interactions that efficiently suppresses lateral aggregation, promotes one-dimensional aggregation, and is also compatible with a productive pi-pi overlap of the constituent molecules. In the present work, we demonstrate that oligopeptide-polymer derivatives comprising a flexible polymer segment terminally attached to a beta-sheet-forming oligopeptide segment are structurally simple substituents that perfectly fulfill these requirements. We synthesized a matrix of diacetylene model compounds that carried oligopeptide-polymer substituents with varying degrees of polymerization of the attached polymers and different length oligopeptide segments. We combined solution-phase IR spectroscopy, AFM imaging and the topochemical diacetylene polymerization as a highly sensitive probe for the molecular arrangement and the degree of order inside aggregates obtained in organic solvents. The thus determined molecular parameters for the reliable formation of well-defined nanoscopic fibrillar structures with uniform diameters, and defined helical 'core-shell' morphologies were then successfully transferred to analogous perylene bisimide and quaterthiophene derivatives, demonstrating the versatility and robustness of the chosen molecular design.