Solvent effects on quenching of partially quaternized poly(1-vinylimidazole)-bound ruthenium(II) complexes with viologens

Abstract

Two partially quaternized poly(1-vinylimidazole)-bound ruthenium(II) complexes (RuQPIm), in which bis(2,2′-bipyridine)ruthenium(II) complexes are coordinated to the imidazolyl residues on partially quaternized poly(1-vinylimidazole) and the degree of quaternization is 19 (RuQPIm-19) and 44 (RuQPIm-44) molar percentage, have been prepared. The solvent effect on quenching of RuQPIm with alkylviologens have been investigated in methanol and methanol–NMF (NMF, N-methylformamide). This system consists of RuQPIm-19 and RuQPIm-44 as photosensitizers, and 1,1′-dimethyl-4,4′-bipyridinium dication (MV 2+) and 1,1′-didodecyl-4,4′-bipyridinium dication (C 12V 2+) as quenchers. In MV 2+, with addition of NMF, the Stern–Volmer plot changed from an upward deviating curve to a straight line for RuQPIm-19, while they gave all straight lines for RuQPIm-44. The quenching efficiency decreased with increasing NMF content, and, at high NMF content, became almost the same for both systems. These results indicated that the reaction mechanism of quenching was varied by NMF for RuQPIm-19, but not for RuQPIm-44. In C 12V 2+, the Stern–Volmer plots gave the upward deviating curves regardless of NMF for RuQPIm-19, and they changed from upward to downward deviating curves with addition of NMF for RuQPIm-44. Furthermore, the quenching efficiency decreased up to NMF content of ca. 20%, and then increased above it. The facts suggested that the quenching reaction was affected by not only π–π interaction and van der Waals one but also shrinking of polymer domain.