THEORETICAL-STUDY OF THE CHARGE-TRANSFER SPECTRUM OF THE INDENE TETRACYANOETHYLENE ELECTRON-DONOR ACCEPTOR COMPLEX

The ground-state intermolecular potential energy surface for the indene-tetracyanoethylene electron donor-acceptor (EDA) complex was calculated, for three of the six intermolecular degrees of freedom, using semiempirical quantum mechanical techniques. The electronic absorption spectra (frequencies and intensities) were calculated at selected points on this surface. For all geometries, two low-lying charge-transfer transitions were found, having mostly the character HOMO (indene) → LUMO (TCNE) and HOMO-1 (indene) → LUMO (TCNE). Using a quasiclassical approach, the line shape of the charge-transfer spectrum was calculated from the vertical energies and oscillator strengths obtained at a large number (206) of intermolecular geometries. The results show that the two charge-transfer bands in the experimental indene-TCNE spectrum are not associated with distinct intermolecular conformations of the complex. © 1990 American Chemical Society.