Photocurrent Generation from Ru(bpy)₃²⁺ Immobilized on Phospholipid/Alkanethiol Hybrid Bilayers

A new photocurrent-generation system based on Ru(bpy)3(2+) (bpy=2,2'-bipyridine) tethered on phospholipid/alkanethiol hybrid bilayers in aqueous media is reported. The construction of such a system is straightforward. First, a self-assembled monolayer (SAM) of alkanethiol is formed on gold, and separately, liposomes containing Ru(bpy)3(2+)-conjugated dioleoylphosphoethanolamine (DOPE) are prepared by extrusion. Subsequent exposure of the Ru(bpy)3(2+)-containing liposome solution to the preformed SAM induces the addition of a monolayer of phospholipids on top of the SAM and thereby the immobilization of a Ru(bpy)3(2+) layer on the gold electrode. Either anodic or cathodic photocurrent generation can be obtained, when ascorbate (anodic) or methyl violgen/oxygen (cathodic) is used as a sacrificial electron donor/acceptor, respectively. Light conversion quantum efficiencies of 0.84% (anodic) and 0.21% (cathodic) were obtained under blue light (lambda=470+/-20 nm) irradiation. The photocurrent-generation and electron-transfer mechanisms of this new system as well as its potential usefulness in fundamental photoconversion studies are discussed.