Kinetic Insights into the Supramolecular Polymerization of Perylenediimide-Appended Dipeptides

This study describes the synthesis of two amphiphilic perylenediimide (PDI)-based systems, each incorporating lateral non-polar side chains and dipeptide units: (L)-Ala-Gly (PDI 1) or Gly-(L)-Ala (PDI 2). These amphiphilic dipeptide-functionalized systems enable the investigation of their self-assembly behavior in both apolar (MCH) and aqueous environments. The incorporation of dipeptides facilitates the formation of metastable monomeric species, M*, which have been examined through experimental and theoretical approaches. Spectroscopic analysis reveals that these monomeric species adopt various configurations stabilized by intramolecular hydrogen bonding, forming pseudocycles of varying sizes. DFT calculations suggest that the metastable monomers and their unbonded forms possess similar stabilities, allowing them to coexist in solution. Interestingly, unlike other amino acid-based scaffolds, the presence of these metastable species does not lead to pathway complexity. Instead, a single H-type aggregate species emerges, driven by π-stacking of the PDI cores and intermolecular hydrogen bonding between the dipeptide amide groups. Variable-temperature UV-vis studies in apolar MCH show that the supramolecular polymerization of these PDIs proceeds via an isodesmic or weakly cooperative mechanism, resulting in fibrillar supramolecular polymers. Similar results are observed in aqueous media, where the assembly also forms H-type aggregates without evidence of pathway complexity.