Acetonitrile effects on quenching and photosensitized charge separation using partially quaternized poly(1-vinylimidazole)-bound ruthenium(II) complexes

Abstract

The acetonitrile effects on the quenching and photosensitized charge separation using two partially quaternized poly(1-vinylimidazole)-bound ruthenium(II) complexes, RuQPIm-19 and RuQPIm-44, wherein the numbers represent the degree of quaternization in molar percentage, have been investigated. The systems consist of RuQPIm-19 and RuQPIm-44 as photosensitizers, 1,1′-dimethyl-4,4′-bipyridinium (MV2+) and 1,1′-didodecyl-4,4′-bipyridinium (C12V2+) dications as electron acceptors (quenchers), and triethanolamine (TEOA) as a sacrificial electron donor. The photosensitized charge separation reaction proceeds through two processes, an interactive process and a direct process, i.e., the viologen is undergoing an interaction with these polymers and no interaction, respectively. The charge separation through the interactive process is less effective than that through the direct process, because the reaction through the interactive process is effective for both the forward and the back reactions. With the addition of acetonitrile, the rates of viologen radical formation decrease for RuQPIm-19 and RuQPIm-44, while the quenching efficiency decreases for RuQPIm-19 and increases for RuQPIm-44. In MV2+, the acetonitrile effect contributes to the interactive and direct processes for RuQPIm-19, while it contributes to only the direct process for RuQPIm-44, particularly the forward reaction for RuQPIm-19 and the back reaction for RuQPIm-44. In C12V2+, the interactive process through which the C12V2+ increases, leading to a decrease in the rates for viologen radical formation. Furthermore, these results indicate that the conformational changes in these polymers play an important role in the charge separation reactions.