Gating reversible multielectron transfer reaction in porphyrins and metalloporphyrins

ORGN 290

Haoran Sun1, Valeriy V. Smirnov1, Andrew P. Nelson1, Justin C. Biffinger, justin.biffinger@nrl.navy.mil2, and Stephen G. DiMagno1. (1) Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588-0304, (2) Alternative Energy Section, Code 6113, U.S. Naval Research Laboratory, 4555 Overlook Ave., SW, Washington, DC 20375-5342
Porphyrins have been employed as critical components in applications ranging from photovoltaic devices to multielectron transfer catalysis. Modulation of electron transfer parameters through molecular design and medium effects is a key to tune the porphyrin function in such applications. Following on studies in which we have demonstrated modulation of electron transfer rate constants in cobalt porphyrins, here we show that the electron transfer numbers in porphyrins can be selected by control of ion-pairing, axial ligation and electronic effects. Beta-fluorinated porphyrin free bases show two-electron oxidation in presence of strongly coordinating anions, but one-electron oxidation is observed in the presence of weakly coordinating anions. Coordination by neutral axial ligands controls two-electron oxidation in rhodium thiaporphyrins. Quantitative electrochemical studies, digital simulation, together with DFT theoretical calculation point out that electronic effects, ion-pairing and axial ligation lead to the potential inversion in porphyrins, which is a key to gating multielectron transfer reactions.
 

Materials, Devices, and Switches
8:00 AM-11:40 AM, Monday, 14 March 2005 Convention Center -- Room 9, Oral

Division of Organic Chemistry

The 229th ACS National Meeting, in San Diego, CA, March 13-17, 2005