Theoretical Study of the Electronic Excited States of Tetracyanoethylene and Its Radical Anion

Abstract

The low-lying electronic states of tetracyanoethylene (TCNE) and its radical anion were studied using multiconfigurational second-order perturbation theory (CASPT2) and extended atomic natural orbital (ANO) basis sets. The results obtained yield a full interpretation of the electronic absorption spectra, explain the spectral changes undergone upon reduction, give support to the occurrence of a bound excited state for the anionic species, and provide valuable information for the rationalization of the experimental data obtained with electron transmission spectroscopy.

Beyond theGWapproximation: A second-order screened exchange correction

“…4 we present several GW spectra for TCNE in comparison to the experimental photoemission data 65 . The vertical EA (vEA) values of 3.05 eV obtained from CCSD(T) 67 and 2.91 eV from the complete active space method with a secondorder perturbation (CASPT2) 68 , as well as the experimental adiabatic EA value (3.16) are indicated by vertical dashed lines. We observe that all GW meth- Moreover, we note that the improved description of G 0 W 0 +SOSEX for the unoccupied states does not deteriorate the occupied states.…”

Near-edge x-ray absorption studies of Na-doped tetracyanoethylene films: A model system for theV(TCNE)xroom-temperature molecular magnet

“…The molecular structure of TCNE and TCNE − , 19 as well as the vertical excitation energies of TCNE and TCNE − for low energy transition ͑Ͻ10 eV͒, 20,21 have been studied theoretically. For TCNE, the lowest singlet excited state involves promotion from the highest occupied molecular orbital ͑HOMO͒ into the lowest unoccupied molecular orbital ͑LUMO͒.…”

“…For TCNE, the lowest singlet excited state involves promotion from the highest occupied molecular orbital ͑HOMO͒ into the lowest unoccupied molecular orbital ͑LUMO͒. 20,21 The TCNE is reduced into its anion TCNE − , the former LUMO becomes singly occupied forming a socalled singly occupied molecular orbital ͑SOMO͒. 11,19,21 This affects the excitation energies and for TCNE − the lowest energy excitation is formed by promotion of an electron from the previous HOMO into the singly occupied molecular orbital.…”

“…20,21 The TCNE is reduced into its anion TCNE − , the former LUMO becomes singly occupied forming a socalled singly occupied molecular orbital ͑SOMO͒. 11,19,21 This affects the excitation energies and for TCNE − the lowest energy excitation is formed by promotion of an electron from the previous HOMO into the singly occupied molecular orbital. 21 In this paper, we present a combination of experimental and theoretical results that give information about the unoccupied levels in TCNE and at which part of the molecule they are localized.…”

“…11,19,21 This affects the excitation energies and for TCNE − the lowest energy excitation is formed by promotion of an electron from the previous HOMO into the singly occupied molecular orbital. 21 In this paper, we present a combination of experimental and theoretical results that give information about the unoccupied levels in TCNE and at which part of the molecule they are localized. Sodium-doped thin films of TCNE have been prepared and characterized with PES, near edge x-ray absorption fine structure ͑NEXAFS͒ and theoretical calculations.…”