Unraveling the Coulombic Forces in Electronically Decoupled Bichromophoric Systems during Two Successive Electron Transfers

5 years ago

Unraveling the Coulombic Forces in Electronically Decoupled Bichromophoric Systems during Two Successive Electron Transfers

Rajendra Rathore, Denan Wang, Shriya H. Wadumethrige, Maxim V. Ivanov

Coulombic forces are vital in modulating the electron transfer dynamics in both synthetic and biological polychromophoric assemblies, yet quantitative studies of the impact of such forces are rare, as it is difficult to disentangle electrostatic forces from simple electronic coupling. To address this problem, the impact of Coulombic interactions in the successive removal of two electrons from a model set of spirobifluorenes, where the interchromophoric electronic coupling is nonexistent, is quantitatively assessed. By systematically varying the separation of the bifluorene moieties using model compounds, ion pairing, and solvation, these interactions, with energies up to about 0.4 V, are absent at distances greater than about 9 Å. These findings can be (quantitatively) applied for the design of polychromophoric assemblies, whereby the redox properties of donors and/or acceptors can be tuned by judicious positioning of the charged groups to control the electron-transfer dynamics. Coulombic forces quantified: Placing a charged (cationic) group next to an electron donor at a distance of 4.6 Å increases its oxidation potential by ∼0.4 V due to electrostatic repulsion, which becomes negligible (e.g., at ∼8.9 Å) with increasing distance.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201702211