Photoinduced Electron Transfer Dynamics of Cyclometalated Ruthenium (II)–Naphthalenediimide Dyad at NiO Photocathode

Abstract

Both forward and backward electron transfer kinetics at the sensitizer/NiO interface is critical for p-type dye-sensitized photocathodic device. In this article, we report the photoinduced electron transfer kinetics of a Ru(II) chromophore–acceptor dyad sensitized NiO photocathode. The dyad (O26) is based on a cyclometalated Ru(N∧C∧N)(N∧N∧N) (Ru[II]) chromophore and a naphthalenediimide (NDI) acceptor, where N∧C∧N represents 2,2′-(4,6-dimethyl-phenylene)-bispyridine and N∧N∧N represents 2,2′,6′,6″-terpyridine ligand. When the dyad is dissolved in a CH3CN solution, electron transfer to form the Ru(III)–NDI– occurs with a rate constant kf = 1.1 × 1010 s–1 (τf = 91 ps), and electron–hole pair recombines to regenerate ground state with a rate constant kb = 4.1 × 109 s–1 (τb = 241 ps). When the dyad is adsorbed on a NiO film by covalent attachment through the carboxylic acid group, hole injection takes place first within our instrument response time (∼180 fs) followed by the subsequent electron shift onto the ...