Correlation of Charge-Transfer Energies of Tetracyanoethylene-Donor Complexes with Ionization Energies of Donor Molecules

Empirical correlations between the charge-transfer energies (hvCT) of donor-tetracyanoethylene (TCNE) complexes and the ionization energies (ID) of the donor molecules using linear equations of the form have been used for more than three decades to interpret CT spectra and to estimate molecular ionization energies. Although many different values of parameters a and b have been derived for small population samples of TCNE complexes with related donors (Table 1), no values have been published for a comprehensive sample population. In view of the general usefulness of relations such as Eq. (1), an exhaustive and critical survey of CT energies and corresponding photoelectron ionization energies is reported (Table 2), and the parameters for a general correlation equation as well as specific correlation equations for 13 chemical subgroups are evaluated (Table 3).