DFT Calculations and Spectral Measurements of Charge-Transfer Complexes Formed by Aromatic Amines and Nitrogen Heterocycles with Tetracyanoethylene and Chloranil

Abstract

Charge-transfer (CT) spectra of the π−π complexes formed by several aromatic amines and nitrogen heterocycles [acting as donors (Ds)] with acceptor A [A = tetracyanoethylene (TCNE), chloranil (CA)] were measured in acetonitrile. Density functional theory (DFT) calculations were then carried out in solvent to determine the probable geometric structures of the complexes that are responsible for the absorption bands. Three aspects of the intermolecular association were investigated: the D−A separations and relative orientations of the D and A, the D−A binding energies, and the excitation energies of transitions from the HOMO of D to the LUMO of A. On the basis of the calculated results, which are in good agreement with experiment, the nature and origins of the CT spectra of the various molecular complexes are clarified.