A Tale of Three Hydrophobicities: Impact of Constitutional Isomerism on Nanostructure Evolution and Electronic Communication in π-Conjugated Peptides

In this work, we examine the electronic and morphological consequences of constitutional isomerism in tri- and tetrablock biohybrid self-assembling molecules that display three regimes of “hydrophobic” composition. A solubilizing hydrophilic peptide head group is attached covalently to a π-conjugated oligothiophene unit that undergoes π–π stacking interactions and introduces a unique quadrupolar character, a hydrophobic peptide segment that encourages hydrogen bonding, and in some cases, a terminal n -alkyl tail that further triggers hydrophobic collapse. We examine constitutional isomerism by swapping the presentation of these disparate hydrophobic blocks in these complex π-conjugated peptides. We found that constitutional isomerism in molecules containing two peptide segments and the π-conjugated oligomer greatly impacts solubility, nanostructure lateral bundling, and the mode of molecular packing that ultimately dictates electronic communication among the π-conjugated units. Furthermore, we found that this effect is not diluted by the addition of an n -alkyl tail that also provides access to a range of nanoarchitectures from spheres to elongated micellar structures, rods, and ribbons.