Thermodynamic factors impacting the peptide-driven self-assembly of perylene diimide nanofibers.

Synthetic peptides offer enormous potential to encode the assembly of molecular electronic components, provided that the complex range of interactions is distilled into simple design rules. Here, we report a spectroscopic investigation of aggregation in an extensive series of peptide-perylene diiimide conjugates designed to interrogate the effect of structural variations. By fitting different contributions to temperature dependent optical absorption spectra, we quantify both the thermodynamics and the nature of aggregation for peptides by incrementally varying hydrophobicity, charge density, length, as well as asymmetric substitution with a hexyl chain, and stereocenter inversion. We find that coarse effects like hydrophobicity and hexyl substitution have the greatest impact on aggregation thermodynamics, which are separated into enthalpic and entropic contributions. Moreover, significant peptide packing effects are resolved via stereocenter inversion studies, particularly when examining the nature of aggregates formed and the coupling between π electronic orbitals. Our results develop a quantitative framework for establishing structure-function relationships that will underpin the design of self-assembling peptide electronic materials.

Cation-induced pi-stacking.

The design and synthesis of a new dipyridyl ligand with appended phenanthryl moieties is described. On addition of increments of silver(I) trifluoromethanesulfonate to a solution of the ligand, the phenanthryl protons shift upfield in the (1)H NMR spectrum, suggesting that the phenanthrenes pi-stack on coordination of silver(I). In accord with this, the oxidation potential decreased from 1.74 to 1.55 V on complexation of silver(I). The pi-stacking was confirmed with the single-crystal X-ray structure of a palladium(II) coordination complex.