Relationship between Electron Affinity and Half-Wave Reduction Potential: A Theoretical Study on Cyclic Electron-Acceptor Compounds.

Herein we present a high-level ab initio protocol to compute accurate electron affinities and half-wave reduction potentials applied to a series of electron-acceptor compounds with potential interest in organic electronics and redox flow batteries. The comprehensive comparison between the theoretical and experimental electron affinities not only proves the reliability of the theoretical G3(MP2) approach employed but also calls into question certain experimental measurements needed to be revised. By using the thermodynamic cycle for the one-electron attachment reaction A + e- => A, theoretical estimates for the first half-wave reduction potential have been computed along the series of electron-acceptor systems investigated with maximum deviations from experiment of only 0.2 V. The precise inspection of the contributing terms into the half-wave reduction potential shows that the difference in the free energy of solvation between the neutral and the anion species (Gsolv) plays a crucial role for accurately estimating the electron-acceptor properties in solution, and thus it cannot be considered constant even in a family of related compounds. This term, which allows explaining the lack of correlation occasionally obtained between electron affinities and reduction potentials, is rationalized by the (de)localization of the additional electron involved in the reduction process along the -conjugated chemical structure.