Quenching kinetics of partially quaternized poly(1-vinylimidazole)-bound ruthenium(II) complexes with C12V2+ mediated by L-tyrosine esters

Abstract

The quenching kinetics of the 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 1,1′-didodecyl-4,4′-bipyridinium (C₁₂V²⁺) in the presence of the L-tyrosine esters with hexyl (C₆Tyr), octyl (C₈Tyr) and dodecyl (C₁₂Tyr) groups has been investigated in methanol. A modified Stern–Volmer equation for the quenching reaction mediated by the L-tyrosine esters is proposed. In the absence of the L-tyrosine esters, the quenching reactions for the RuQPIm-19 and RuQPIm-44 systems take place through a static quenching process induced by a van der Waals interaction between the alkyl side chains on the polymers and C₁₂V²⁺. In the presence of the L-tyrosine esters, the quenching reaction only takes place through a static process mediated by the L-tyrosine esters, and the kinetic parameters were calculated from the computed curve fitting using the modified Stern–Volmer equation. The second-order quenching constants, given by the product of the equilibrium constant and the first-order quenching constant, decrease for RuQPIm-19 and increase for RuQPIm-44 with increasing length of the alkyl group in the L-tyrosine esters. These results are attributed to the fact that the kinetic parameters are affected by the conformation of these polymers; RuQPIm-19 shrinks and RuQPIm-44 is partially bridged by addition of C₁₂V²⁺ and the L-tyrosine esters.