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

Abstract

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 π-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 π–π overlap of the constituent molecules. In the present work, we demonstrate that oligopeptide–polymer derivatives comprising a flexible polymer segment terminally attached to a β-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.