Excited electronic states of the anion of 7,7,8,8-tetracyanoquinodimethane (TCNQ)

The doublet and quarter anionic states of TCNQ have been studied at the configuration interaction (CI/PM3) level. Our results support an experimental claim from the Brauman group that not only the ground anionic state but also some excited states of TCNQ(-) are electronically stable. The core excited 1(2)B(3u) state is separated from the ground B-2(2g) anionic state by only 1.2 eV at the CI/PM3 level. Two externally excited (2)A(u) and 2(2)B(3u) anionic states are separated by ca. 2.3 eV from the ground B-2(2g) state and are close in energy to the ground electronic state of the neutral TCNQ. In addition, two quartet anionic states B-4(2g) and B-4(1g) are found to be electronically stable with respect to the lowest triplet B-3(1u) State of the neutral. All these anionic states have minima at D-2h geometries. Our results suggest that the 1(2)B(3u) <-- B-2(2g) and 2(2)B(3u) <-- B-2(2g) transitions contribute to the electronic absorption and electron photodetachment spectra of TCNQ(-). This conclusion is based on calculated values of electronic transition energies, oscillator strengths, and excess electron binding energies. (C) 2000 Elsevier Science B.V. All rights reserved.