Photocurrent generation through peptide-based self-assembled monolayers on a gold surface: antenna and junction effects

The photocurrent generation properties of mono- and bi-component peptide-based self-assembled monolayers (SAMs) immobilized on a gold surface were studied by electrochemical and spectroscopic techniques. The peptides investigated comprised almost exclusively C-tetrasubstituted -amino acids. These non-coded residues, because of their unique conformational properties, forced the peptide backbone to attain a helical conformation, as confirmed by X-ray crystal structure and CD determinations in solution. The peptide helical structure promoted the formation of a stable SAM on the gold surface, characterized by an electric macrodipole directed from the C(δ−) to the N(δ+) terminus, that remarkably affected the electron transfer (ET) process through the peptide chain. The peptides investigated were derivatized with chromophores strongly absorbing in the UV region to enhance the efficiency of the photocurrent generation (antenna effect). The influence of the nature of the peptide–gold interface on the ET process (junction effect) was analyzed by comparing the photocurrent generation process in peptide SAMs immobilized on a gold surface through AuS linkages with that in a bi-component SAM embedding a photoactive peptide into the linked palisade formed by disulfide-functionalized peptides.