The new theory of electron transfer. Thermodynamic potential profiles in the inverted and superverted regions
journal contributionposted on 10.01.2008 by Stephen Fletcher
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In a previous paper (S Fletcher, J Solid State Electrochem 11:965 (2007)) a non- Marcus theory of electron transfer was developed, with results applicable to the normal region of thermodynamic driving forces. In the present paper the theory is extended to highly exergonic reactions (the inverted region) and to highly endergonic reactions (the superverted region). The results are presented mathematically, and in the form of Gibbs energy profiles plotted against a charge fluctuation reaction coordinate. The new theory utilizes the concept of donor and acceptor “supermolecules”, which consist of conventional donor and acceptor species plus their associated ionic atmospheres. The key findings are as follows. (1) In the inverted region, donor supermolecules are positively charged both before and after the electron transfer event. (2) In the normal region, donor supermolecules change polarity from negative to positive during the electron transfer event. (3) In the superverted region, donor supermolecules are negatively charged both before and after the electron transfer event. This overall pattern of events makes it possible for polar solvents to catalyse electron transfer in the inverted and superverted regions. Because this new effect is predicted only by the present theory, and not by the Marcus theory, it provides a clear means of distinguishing between them.