A time-resolved study of electron transfer mechanisms: Beyond outer-sphere electron transfer
Of the primary objectives of our research has been to understand some of the fundamental mechanistic issues underlying electron transfer reactions. We have designed molecular systems to provide information on several aspects of charge transfer reactions, including the role of protons in long-distance electron transfer, bimolecular donor-acceptor pair reactivity at high driving forces, and excited state multielectron transformations. In our systems a photon can initiate the reaction by placing the molecules in an excited electronic state, which permits the reactant and product concentrations to be monitored as a function of time. These dynamic measurements are conducted by exciting the molecules with a short light pulse, and following the progress of the reaction by optical methods, such as transient absorption spectroscopy and emission lifetime. Electron transfer reactions through a proton interface have been conducted by the design of hydrogen-bonded donor-acceptor pairs, where the donor, a carboxylic acid derivative of a Zn-substituted porphyrin, transfer an electron to several aromatic acceptors from its excited state. The charge separation and subsequent charge recombination rates have been determined utilizing picosecond transient absorption spectroscopy, for protiated and deuterated donors and acceptors. A slight attenuation in the rates is observed. The transient absorption technique has also been utilized to characterize the excited states that lead to two-electron reactivity in quadrupoly-bonded inorganic complexes of the type M{sub 2}Cl{sub 4}(L){sub n}, where M = molybdenum or tungsten and L = monodentate or bidentate phosphine ligands. It was observed that the reactions do not proceed directly from an excited electronic state, but from a conformationally-distorted intermediate formed following light excitation. The distorted intermediate is believed to possess favorable characteristics that permit the observed two-electron oxidative-addition reactions.
- Research Organization:
- Michigan State Univ., East Lansing, MI (United States)
- OSTI ID:
- 111308
- Resource Relation:
- Other Information: TH: Thesis (Ph.D.); PBD: 1992
- Country of Publication:
- United States
- Language:
- English
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