%0 Journal Article %A Bronner, Catherine %A Wenger, Oliver S. %D 2015 %T Kinetic Isotope Effects in Reductive Excited-State Quenching of Ru(2,2′-bipyrazine)32+ by Phenols %U https://acs.figshare.com/articles/journal_contribution/Kinetic_Isotope_Effects_in_Reductive_Excited_State_Quenching_of_Ru_2_2_bipyrazine_sub_3_sub_sup_2_sup_by_Phenols/2017806 %R 10.1021/jz201494n.s001 %2 https://ndownloader.figshare.com/files/3589080 %K PhenolsElectron transfer %K Possible PCET reaction mechanisms %K Br %K emission quenching %K KIE %K OCH %K Kinetic Isotope Effects %K phenol molecules %K phenolic proton %K CH %K CN %K nitrogen atom %K isotope effects %K CPET %X Electron transfer (ET) from phenol molecules to a photoexcited ruthenium­(II) complex was investigated as a function of the para-substituent (R = OCH3, CH3, H, Cl, Br, CN) attached to the phenols. For phenols with electron-donating substituents (R = OCH3, CH3), the rate-determining excited-state deactivation process is ordinary ET. For all other phenols, significant kinetic isotope effects (KIEs) (ranging from 2.91 ± 0.18 for R = Br to 10.18 ± 0.64 for R = CN) are associated with emission quenching, and this is taken as indirect evidence for transfer of a phenolic proton to a peripheral nitrogen atom of a 2,2′-bipyrazine ligand in the course of an overall proton-coupled electron transfer (PCET) reaction. Possible PCET reaction mechanisms for the various phenol/ruthenium couples are discussed. While 4-cyanophenol likely reacts via concerted proton–electron transfer (CPET), a stepwise proton transfer–electron transfer mechanism cannot be excluded in the case of the phenols with R = Br, Cl, and H. %I ACS Publications