DV-X α calculation of electron energy-loss near edge-structures of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F 4TCNQ)

Abstract

The first principle molecular orbital (MO) calculations, focusing on the carbon K-edge fine structures, were performed for 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F 4TCNQ) and 7,7,8,8-tetracyanoquinodimethane (TCNQ). Electron energy-loss spectra (EELS) of F 4TCNQ were measured and analyzed through the calculation. In the discrete variational-Xα (DV-Xα) method, site-excited transition state configurations were assumed to take account of core-hole effects and, consequently, were examined in three parts: (1) partial density of states (PDOS) of unoccupied 2p orbitals; (2) inner 1s orbitals (energy-recalibrated PDOS); and (3) photo-absorption cross-section (PACS) considering the transition matrix. In F 4TCNQ, the inner 1s energy level of the quinoid-ring carbon combined to fluorine shifts deeper in energy, resulting in a high-energy shift of the π ∗ peaks in the calculation. The calculation also shows the fluorination effect on the quinoid-ring carbons appearing in the higher σ ∗ energy region. In the low energy region, the calculations accurately reproduced the core-excited spectra in both F 4TCNQ and TCNQ and succeeded in assigning each component appearing in the spectra.