Kinetics of quenching of polymer-bound ruthenium (II) complexes with MV 2+ containing l-tyrosine esters

Abstract

The effects of l-tyrosine esters with hexyl (C 6Tyr), octyl (C 8Tyr) and dodecyl (C 12Tyr) 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 the 1,1′-dimethyl-4,4′-bipyridinium dication (methylviologen: MV 2+) have been kinetically investigated in methanol. In the absence of l-tyrosine esters, the Stern–Volmer plots for RuQPIm-19 and RuQPIm-44 showed an upward deviating curve and a straight line, respectively. This result indicated that the quenching mechanism depended significantly on the degree of quaternization. The computed curve fitting to the observed Stern–Volmer plots showed that the quenching reaction proceeded through only a static quenching process for RuQPIm-19 and through only a dynamic quenching process for RuQPIm-44. In the presence of l-tyrosine esters, the Stern–Volmer plots for quenching of RuQPIm-44 showed downward deviating curves, indicating that these quenching reactions proceeded through both dynamic quenching and static quenching processes. This was supported by the fact that the curve fitting according to the theoretical equation reported as a combination of dynamic and static quenching models agreed well with the observed Stern–Volmer plots. On the other hand, although the quenching reactions for RuQPIm-19 systems also proceeded through mediated and non-mediated processes, both were static quenching processes; namely, the quenching reactions proceeded through two different static quenching mechanisms. A new Stern–Volmer plot for the systems was proposed and the kinetic parameters were estimated. Furthermore, it was found that the quenching rate constants for the mediated processes were faster than those for the dynamic quenching process in the RuQPIm-44 and the statically non-mediated process in the RuQPIm-19.