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 con figuration interaction (CI/PM3) level. Our results support an experimental claim from the Brauman group that not only the ground anionic state but als o some excited states of TCNQ(-) are electronically stable. The core excite d 1(2)B(3u) state is separated from the ground B-2(2g) anionic state by onl y 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 an d are close in energy to the ground electronic state of the neutral TCNQ. I n 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 t he neutral. All these anionic states have minima at D-2h geometries. Our re sults suggest that the 1(2)B(3u) <-- B-2(2g) and 2(2)B(3u) <-- B-2(2g) tran sitions contribute to the electronic absorption and electron photodetachmen t spectra of TCNQ(-). This conclusion is based on calculated values of elec tronic transition energies, oscillator strengths, and excess electron bindi ng energies. (C) 2000 Elsevier Science B.V. All rights reserved.