Controlled Aggregation of Peptide Substituted Perylene-Bisimides
In recent years there has been an intersection of supramolecular chemistry and materials science, with a particular focus on the controlled self-assembly of functional building blocks. The impetus for assembly of organised architectures is a requirement due to organic electronic device performance being sensitive to the geometric configuration of adjacent molecular semiconductors, interacting by means of overlapping π-orbitals to create electronic conduction. Inspired by the formation of elegant supramolecular structures in nature, this work employs perylene bisimides coupled to synthetic peptides which are able to control the assembly of chromophores in solution. Through examining the perturbations of optical absorption and fluorescence spectroscopic signatures, the presence of aggregates, and also the geometric configurations of adjacent chromophores are determined. By exploring these features as a function of peptide design, pH, solvent composition, and ionic strength, it is demonstrated that aggregation is strongly induced by the peptide and the aromatic core, with significant dependence on the electrostatic repulsion between peptide segments. By manipulating solvent compositions, we demonstrate the ability to induce controlled reorganisation of aggregates through the introduction of charge onto the peptide sequence in high water concentration solution. Furthermore, application of the exciton model to absorption spectra establishes the tuneability of aggregates by specific ion binding between neighbouring peptides. Our results demonstrate the capability of peptide sequences to drive aggregation of molecular semiconductor building blocks; moreover, the peptides allow fine tuning of the electronic overlap between neighbouring building blocks. The proof of concept paves the way for further investigation into utilising this assembly control for device fabrication, in particular, we see this work being applicable to biosensor devices.