Generation of photocurrents by bis-aniline-cross-linked Pt nanoparticle/photosystem I composites on electrodes.

Pt nanocrystals are implanted into photosystem I (PSI) by a photochemical reaction. The PSI with the associated Pt nanoclusters was modified with thioaniline and electropolymerized with thioaniline-functionalized Pt nanoparticles (NPs) to yield a bis-aniline-cross-linked PSI/Pt NPs composite. The alignment of the PSI with respect to the Pt NPs leads to effective charge separation and to generation of a photocurrent, ϕ (λ = 420 nm) = 2.6%, IPCE ∼ 0.35%. The bis-aniline units cross-linking the PSI/Pt NPs composite exhibit quasireversible redox features (E(0)' = 0.05 V vs Ag/AgCl, at pH = 7.4). Biasing the electrode potential, E > 0.1 V vs SCE, results in the formation of the oxidized quinoid bis-aniline state that acts as an electron acceptor. At this applied potential, the bridges mediate the electron transfer to the electrode, resulting in a ∼10-fold higher photocurrent, as compared to the system that includes the reduced bis-aniline bridging units. Furthermore, the ferredoxin (Fd) electron relay was modified with thioaniline units and incorporated into the PSI/Pt NP composite during the electropolymerization process. The Fd bound to the matrix mediates the electron transfer toward the electrode and facilitates charge separation that results in enhanced generation of the photocurrent, ϕ (λ = 420 nm) = 3.8%, IPCE ∼ 0.5%.