Supramolecular Polymorphism: Tunable Electronic Interactions within π-Conjugated Peptide Nanostructures Dictated by Primary Amino Acid Sequence

We present a systematic study of the photophysical properties of one-dimensional electronically delocalized nanostructures assembled from pi-conjugated subunits embedded within oligopeptide backbones. The nature of the excited states within these nanostructures is studied as a function of primary amino acid sequence utilizing steady-state and time-resolved spectroscopies, and their atomistic structure is probed by molecular simulation. Variations introduced into the amino acid side chains at specific residue locations along the molecular peptide backbone lead to pronounced changes in the observed photophysical behavior of the fibrillar structures (spanning H-like excitonic coupling and disordered excimeric coupling) that arise from subtle changes in the pi-stacking within them. These results indicate that residue modification-in terms of relative size, solvation properties, and with respect to the distance from the central pi-electron core-enables the ability to tune chromophore packing and the resulting photophysics of supramolecular assemblies of pi-conjugated bioelectronic materials in a rational and systematic manner.