Steric and Hydrophobic Control Over Sequence-Defined Peptide Templates to Modulate the Properties of Polydiacetylene Nanomaterials

Precision control over molecular structure-function correlations in adaptive conjugated polymers such as polydiacetylene (PDA) is rarely demonstrated in completely aqueous environments due to solvent incompatibility, yet critical for realizing their biomedical applications. For PDAs, the chromogenic transitions that are key to their stimuli-responsiveness depend on the conformation and electronic structure of the π-conjugated backbone, which can be influenced by the nature of flanking, solubilizing groups that guide the topochemical polymerization of PDAs. Here, we investigate the dependence of amphiphilic polydiacetylene properties based on the characteristic contributions of amino acids that comprise the peptide segments serving as a biomimetic template for diacetylene polymerization in water. While sequence engineering has long been used as an effective approach to tune the function of peptide- or protein-based materials, it remains elusive how the interplay between steric effects and hydrophobicity at the residue level can impact the assembly behavior and the bulk properties of the resulting materials from hierarchically ordered 1-D nanostructures. We leverage the strict geometric requirements needed to topochemically polymerize diacetylenes bearing hexameric peptide moieties to systematically probe the impact of molecular volume and polarity changes brought by dipeptide substitution domains to the assembly behavior, photophysics, electrical properties, and biocompatibility of peptide-PDA assemblies. From a series of peptide-diacetylene monomers with systematically varied sequence, we show that steric contributions predominate the resulting photophysical properties, but the trends in the formation of higher order assemblies comprising the film bioscaffolds are distinct from the trends in PDA electronic structure changes driven by the peptide templates due to the combined impact of sterics and hydrophobicity. This work demonstrates how sequence-tunable, biomimetic interactions can be used as a synthetic handle to rationally tune PDA properties across length scales.