Bound-Excited Electronic States of the Anion of 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane

Abstract

The doublet anionic states of TCNQ-F4 (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) have been studied at the Hartree−Fock and the Møller−Plesset (MP) perturbation theory levels (up to fourth order) with aug(sp)-pVDZ basis sets. Our results indicate that TCNQ-F4 forms a stable anion of B2g symmetry whose vertical electron attachment energy is 2.893 eV (at the MP4 level). In addition, we found two valence excited electronic states (22B3u and 12Ag) of the anion that are stable vertically with respect to the neutral parent. The electronic stability of the third excited state (a core-excited 12B3u state) needs to be further investigated. We conclude that the neutral TCNQ-F4 at its equilibrium D2h geometry may attach an excess electron to form any of these four states (i.e., 12B2g, 12B3u, 22B3u, and 12Ag) and the corresponding MP4 vertical attachment energies (VAE) are 2.893, 0.822, 0.244, and 0.072 eV, respectively. However, due to second-order Jahn−Teller distortion, only the ground anionic state (12B2g) possesses a minimum at D2h symmetry. For the two valence excited states (22B3u and 12Ag), negative curvatures cause out-of-plane deformations that lead to (i) an increase of the energy of the latter (12Ag) state and (ii) achieving a minimum-energy structure of C2 symmetry for the former where this state becomes a doublet A state and its vertical electronic stability increases to 2.721 eV.