Chiral effects in peptide-substituted perylene imide nanofibres

Abstract

A series of peptide-functionalised perylene imide molecules was studied to examine the effect of peptide chirality on the self-assembly of the perylene imides core into nanofibres. Peptide stereogenic positions, stereochemical configurations, amphiphilic substitution and perylene core modification were spectroscopically evaluated with respect to chiral assembly. For dipeptide molecules, stereocenters in peptide residue positions proximal to the perylene core (1–5 units) were found to impart helical chirality to the perylene core, while stereocenters in more distal residue positions did not exert a chiral influence. Diastereomers involving stereocenter inversions within the proximal residues consequently manifested spectroscopically as pseudo-enantiomers. Increased side-chain steric demand in the proximal positions gave similar chiral influence but exhibited diminished Cotton effect intensity with additional longer wavelength features attributed to interchain excimers. Replacing one of the two peptide substituents with an alkyl chain to create strongly amphiphilic perylene bisimides disrupted chiral self-assembly. On the other hand, amphiphilic structures achieved through the modification of the perylene imide core with a bisester moiety prompted strongly exciton-coupled, solvent-responsive self-assembly into long, chiral nanofilaments.