Mediated effects of l-tyrosine esters on quenching of ruthenium(II) complex-containing polymers with C 12V 2+

Abstract

The effects of l-tyrosine esters with hexyl (C 6Tyr), octyl (C 8Tyr) and dodecyl (C 12Tyr) groups on the 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′-didodecyl-4,4′-bipyridinium dication (C 12V 2+) have been investigated in methanol. Viscosity studies revealed that the conformation of these polymers varied because of the addition of C 12V 2+ and l-tyrosine esters; the RuQPIm-19 shrank and the RuQPIm-44 bridged through the C 12V 2+ species. In quenching studies, the quenching efficiencies were increased by the addition of l-tyrosine esters in the order of C 12Tyr<C 8Tyr<C 6Tyr for RuQPIm-19 and C 12Tyr<C 6Tyr<C 8Tyr for RuQPIm-44. Stern–Volmer plots significantly changed to downward deviating curves, indicating that the reaction mechanism of the quenching varied because of the addition of l-tyrosine esters. These results suggest that the quenching reaction takes place through the l-tyrosine esters; namely, it is mediated by the l-tyrosine esters. The quenching reaction could proceed through two processes: an interactive process and a mediated process. In particular, the mediated process is the most important; namely, the Stern–Volmer plot and quenching efficiency are affected by a contribution of the mediated process to the quenching reaction. Furthermore, the effect of the l-tyrosine esters on the quenching was significant for the RuQPIm-44 system. This is attributed to the fact that the conformation of these polymers differs; shrinking for RuQPIm-19 and bridging for RuQPIm-44. The steric hindrance for access of the aromatic segment in the l-tyrosine esters is smaller for the bridging RuQPIm-44 than for the shrinking RuQPIm-19.