Hierarchical Self-Assembly of Semiconductor Functionalized Peptide α-Helices and Optoelectronic Properties

To determine the ability of semiconductors templated by alpha-helical polypeptides to form higher order structures and the charge carrier properties of the supramolecular assemblies, L-lysine was functionalized with a sexithiophene organic semiconductor unit via iterative Suzuki coupling and the click reaction. The resultant amino acid was incorporated into a homopolypeptide by ring-opening polymerization of an amino acid N-carboxyanhydride. Spectroscopic investigation of the polypeptide revealed that it adopted an alpha-helical secondary structure in organic solvents that underwent hierarchical self-assembly to form higher order structures. In cyclohexane, the polymer formed organogels at 2% (w/v). Organic photovoltaic and organic field effect transistor devices were fabricated by deposition of the PCBM blended active layer from chlorobenzene at concentrations shown to induce self-assembly of the polymer. Compared with control compounds, these devices showed significantly greater hole mobility, short circuit current, and efficiency. This work establishes the potential of this previously unreported bioinspired motif to increase device performance.