Enhancement of quenching of polymer-bound ruthenium(II) complexes with MV2+ using l-tyrosine esters

Abstract

Abstract The effects of l -tyrosine esters with hexyl (C6Tyr), octyl (C8Tyr) and dodecyl (C12Tyr) groups on quenching of partially quaternized poly(1-vinylimidazole)-bound ruthenium(II) complexes (RuQPIm-19 and RuQPIm-44: the numbers represent the degree of quaternization in molar percentage) with a 1,1′-dimethyl-4,4′-bipyridinium dication (MV2+) have been investigated in methanol. The quenching efficiency was increased by the addition of l -tyrosine esters, and increased with decreasing the length of the alkyl groups in the l -tyrosine esters for RuQPIm-19 and RuQPIm-44. The Stern–Volmer plots for RuQPIm-19 significantly changed from an upward deviating curve to a downward deviating curve for C6Tyr, a straight line for C8Tyr, and a downward deviating curve for C12Tyr. For RuQPIm-44, the Stern–Volmer plots gave downward deviating curves for all l -tyrosine esters. These facts indicated that the reaction mechanism of quenching was varied by the addition of l -tyrosine esters. Furthermore, viscosity studies showed that the RuQPIm-19 shrank on addition of MV2+ and l -tyrosine esters, but not RuQPIm-44, and that the l -tyrosine esters interacted with these polymers through van der Waals interaction. Consequently, it was suggested that the l -tyrosine esters mediated the quenching reaction.