Structural characterization and photoelectrochemical properties of the self-assembled monolayers of Tris(2′2′-bipyridine)ruthenium(II)-viologen linked compounds formed on the gold surface

Steady-state spectroscopic studies oftris(2,2'-bipyridine)ruthenium(II)-viologen ( Ru-2=' V-2=') linked thiol derivatives with different spacer-chain lengths (denoted as RuCn VCmS, where (n, m) = (11, 2), (7, 6), (7, 2), and (3, 6)) and different number ratios of Ru2+:V2+ = 1:2, Ru(C7VC6S), have been carried out, together with the corresponding reference compounds without Ru2+ or V2+. Absorption and cyclic voltalnmetric (CV) measurements indicated no appreciable electronic interactions between the two chromophores (Ru2+ and V2-) in the ground state. While luminescence spectral measurements revealed the occurrence of efficient photoinduced electron transfer from the photoexcited Ru2(-) (*Ru2+) to V2+. The electron transfer efficiency was also better for the 1:2 complex as compared with the corresponding 1:1 complex. Self-assembled monolayers (SAMs) of these compounds were fabricated on a gold electrode. XPS and ("V measurements revealed immobilization of the compounds on the gold surface via gold-sulfur bonding. In the presence of triethanolamine, all modified electrodes with the Ru2+-V2+ linked compounds showed clear anodic photocurrents. The presence of the V2+ moiety was crucial for obtaining; larger photocurrents A shorter spacer-chain length between the V2- moiety and the terminal thiol group (m = 2) afforded a larger photocurrent, while a moderate spacer-chain length between the Ru2+ and the V2+ moieties way also a key for obtaining a larger photocurrent. A possible mechanism for photocurrent generation is discussed.