Counterion and solvent perturbations to the electronic structure of substituted pyrylium cations: A CNDO/S study

Abstract

The combined effects of solvation and specific counterion pairing schemes on the electronic structure of a series of closed‐shell substituted pyrylium cations are examined within the context of semiempirical molecular orbital theory. Bonding characteristics are elucidated through a comparison of free‐cation, cation/anion (supermolecule), and empirically d r e s s e dsupermolecule models. The d r e s s e d models are constructed by introducing electrostatic interaction terms as perturbations to the electronic structure of the appropriate supermolecule to account for solvent screening of localized charge centers. The d r e s s e d models are shown to exhibit shifts in the transition energies of hypothetical free‐cation models which produce excitation spectra in excellent correspondence with experiment.Electrochemical properties are also discussed in terms of counterion and solvent perturbations to the electronic structure of the free cation.