Introduction of Curvature in Amphipathic Oligothiophenes for Defined Aggregate Formation

In this study the possibility to control the size and shape of self-assembled structures through the local curvature of their molecular building blocks has been investigated. To this end a series of amphipathic conjugated oligothiophenes with a well-defined curvature of their backbone has been designed and synthesized. The molecular (local) curvature of these oligothiophenes resulted from a preference for cis instead of trans conformations at specific positions along the oligothiophene backbone, which can be controlled by the sequence of hydrophilic and hydrophobic groups, while their ratio was kept constant. The self-assembly of ter-, sexi-, and dodecathiophenes appeared to be a low-cooperative process, involving the formation of premicellar aggregates at sub-millimolar concentrations, which at concentrations in the millimolar regime transformed into micelles and cylindrical micelles. The aggregates display fine structures with dimensions reminiscent of the thiophene molecules. The structure- morphology relationship of the ter- and sexithiophenes could be described by conventional packing theory. However, with the dodecathiophene, the backbone curvature governed the formation of cylindrical aggregates with a well-defined diameter. These results demonstrate that it is possible to control the aggregation morphology of simple amphipathic oligothiophenes by implementation of an additional structural motif namely, the curvature.