Electronic excitations in doubly charged TCNQ dimers, trimers and tetramers

Abstract

Abstract CNDO MO calculations followed by CI treatment including singly and doubly excited configurations have been carried out for doubly charged TCNQ dimers, trimers and tetramers, (TCNQ) n 2− , n = 2, 3 and 4, in the eclipsed, ring-external-bond and ring-ring geometry. Two basis sets were used for the CI calculations. The first one, containing the highest occupied and the lowest ( n − 1) virtual orbitals, {1 × ( n − 1)}, describes the charge-transfer excitations only. The second one, {( n + 1)×(3 n − 1)}, includes local excitations in addition. The extent of the CI space has been designed such that the CI eigenvalue problem corresponds to a Hubbard-type hamiltonian with one or four orbitals per site. The results show that an ( n + 1)×(3 n − 1) Cl procedure should be used to obtain satisfactory agreement with optical spectra of TCNQ salts measured both in solution and in the solid phase.