pH-controlled switching of photocurrent direction by self-assembled monolayer of helical peptides.

A novel molecular system, where the photocurrent direction can be reversibly switched by changing the pH of the solution, was prepared on gold from helical peptides carrying a photosensitizer and a carboxyl group at the terminal. Upon photoexcitation of the photosensitizer in an aqueous solution containing an electron donor and acceptor at pH 10, the monolayer generated an anodic photocurrent due to enhancement of the dipole moment by a carboxylate anion, while it generated an opposite cathodic photocurrent at pH 3.4