Synchrotron-radiation photoemission study of in-situ synthesized DCNQI( N, N′-dicyanoquinonediimine)-Cu salts

Abstract

A photoemission study using synchrotron radiation of in-situ synthesized organic conductors (DMe-DCNQI) 2Cu and (MeBr-DCNQI) 2Cu is reported, where DMe-DCNQI and MeBr-DCNQI are dimethyl- N, N′-dicyanoquinonediimine and methyl, bromine- N, N′-dicyanoquinonediimine, respectively. The photon energy dependence of the valence band spectra is used to characterize the origin of the observed features. In both salts, the Cu 3 d derived states are situated at 3.5–4 eV binding energy, while the C and N 2 pσ states appear around 7.5 eV. The Br 4 p states are found around 5 eV in (MeBr-DCNQI) 2Cu. The states near the Fermi level have substantial C and N 2 pπ character consistent with extended Hückel molecular orbital calculations. The absence of a resonance at the Cu 3 p threshold suggests a small contribution of Cu 2+ configuration in DCNQI-Cu salts.