Kinetic salt effects in the quenching of the excited state of the tris(2,2′‐bipyridine)ruthenium(II) complex by 2‐methylanthraquinone

Abstract

AbstractIn the title system, quenching rate constants kq were determined as a function of c(Et4NClO4), c(NaClO4), and c(LiClO4) in acetonitrile solution. A general and a specific salt effect on kq can be distinguished. The 2‐methylanthraquinone radical anion produced by the photoinduced electron transfer forms strong associates with Na+ and even stronger ones with Li+, the formation constants of these complexes being determined from electrochemical measurements. Transient absorption spectra of the methylanthraquinone radical anion and of its associates with Na+ and Li+ are presented. The rate constant of the electron transfer step could be determined in selected systems and effΔG° values of the electron transfer step were developed. Apparent activation parameters ΔH≠, ΔS≠, and ΔG≠ were determined from the kq data. The negative values of ΔH≠ can be rationalized by the mechanism of the photoinduced electron transfer reaction. The back electron transfer in the successor complex to the ground state molecules shows Marcus‐inverted behaviour.