Modulating Electron Sharing in Ion-π-Receptors via Substitution and External Electric Field: A Route toward Bond Strengthening.

Substituted coronenes, a family of ion-π receptors whose ion-affinities can be explained exclusively neither via ion-quadrupole nor induction/polarization mechanisms, are studied. The best descriptors of ion-affinity among these species are those characterizing charge-transfer between ions and the π-systems, e.g. vertical ionization potential, electron affinity, and the relative energies of charge-transfer excited-states (CTESs). The variation of the electric multipole moments, polarizability, binding energy, and relative energy of CTESs in the presence of an external electric field (EEF) is evaluated. The results indicate that the EEF has a negligible effect on the polarizability and quadrupole moment of the systems. However, it significantly affects the binding energies, CTES energies, and the dipole moments of the receptors. Contrary to the changes in the dipole moment, the variation pattern of the binding energy is more consistent with the pattern observed for the CTES energy changes. Finally, by analyzing the exchange-correlation component of the binding energy we demonstrate that the increased binding energy, i.e. bond strengthening, originates from enhanced electron sharing and multicenter covalency between the ions and the π-systems as a result of the state-mixing between the ground-state and the CTESs. According to our findings, we hypothesize that the electron sharing and in extreme cases the multicenter covalency are the main driving forces for complexation of ions with extended π-receptors such as carbon nanostructures.