Charge separation/recombination reactions in non-polar fluids: a molecular description

Abstract

The activation energy for intramolecular electron transfer in non-polar fluids is derived in analytical form by expressing it through the chemical potential of solvation of a dipole of complex dipole moment μ. The reorganization energy of the non-polar liquid manifests itself as a nonlinear liquid response beginning with terms ∝ μ⁴ upwards in the expansion of the chemical potential over the solute dipole moment. The reorganization energy is represented as the sum of two terms arising from liquid polarization and density reorganization, with the latter component being of much greater importance. It is suggested that electron transfer in non-polar solvents is promoted by fluctuations of the number of molecules in the first coordination sphere of the donor-acceptor complex. Since the molecular polarizability is temperature independent, the reorganization energy is inversely proportional to temperature. This fact can lead to a maximum in the temperature dependence of electron transfer rates, and hence to negative activation enthalpies. Comparisons of theoretical predictions are made with experimental thermochromic shifts of charge recombination optical bands.

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Roland Schmid

On leave from the Institute of General and Inorganic Chemistry of the National Ukrainian Academy of Sciences, 32–34 Pr. Palladina, 252142, Kiev, Ukraine.