CONCERTED BOND FORMATION WITH ELECTRON TRANSFER TO RUTHENIUM POLYPYRIDYL EXCITED STATES

Iodide;Ruthenium polypyridyl;concerted mechanism;excited states;Chemistry

Ward, William MauriceMeyer, Gerald J. ;

Johns Hopkins University

关键词: Iodide;    Ruthenium polypyridyl;    concerted mechanism;    excited states;    Chemistry;   

Others  :  https://jscholarship.library.jhu.edu/bitstream/handle/1774.2/37954/WARD-DISSERTATION-2014.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: JOHNS HOPKINS DSpace Repository

【 摘 要 】

Electronic excited states possess an empty electron orbital at a lower energy than the ground state compound and therefore may participate in redox reactions that are energetically unfavorable for the ground state compound. These photo-initiated one-electron redox reactions often result in unstable compounds that undergo subsequent bond breakage or bond formation through a stepwise mechanism. However, some reactions that are energetically favorable overall are hindered due to a high energy product of the initial electron transfer step. In these cases, a concerted mechanism, where bond breakage or formation is coincident with electron transfer, may provide an alternative low-energy pathway for the reaction to follow. In the case of bond formation, ion-pairing in a low-dielectric solvent enables the simultaneous encounter between the two reactants and the photo-oxidant. Several ruthenium and osmium polypyridyl compounds were studied as excited-state photo-oxidants for halide ions. Reactions fell into one of three zones depending on the reduction potentials of both the halide and the excited-state compound. Combinations of transition metal compounds and halides in Zone 1 were known to proceed through the stepwise mechanism and suspected to also proceed through the concerted mechanism in a low-dielectric solvent. Combinations in Zone 2 were found to react only through the Concerted mechanism. Time-resolved spectroscopy indicated the simultaneous disappearance of reactants and appearance of products. In Zone 3 both mechanisms were energetically unfavorable and the photophysical effects of ion-pairing were studied that were otherwise masked by redox chemistry.