Magnetic and Electric Properties of Organic Conductors Probed by 13C-NMR Using Selective-Site Substituted Molecules

Quasi-One and quasi-two dimensional organic conductors consisting of TTF derivatives such as BEDT-TTF (bis-(ethylene-dithio)-tetra-thia-fulvalene) and TMTCF (C = S; TMTTF: tetra-methyl-tetra-thia-fulvalene, C = Se; TMTSF: tetra-methyl-tetraselena-fulvalene) have been well investigated in condensed matter physics because of interest in the emerging electric and magnetic properties, such as the spin density wave, charge order, superconductivity, anti-ferromagnetism, and so on. To probe the electronic state, nuclear magnetic resonance (NMR) is one of the most powerful tools as the microscopic magnetometer. A number of 13 C-NMR studies have been performed of the double-site central 13 C= 13 C bond substituted molecules. However, problems with the coupled spin system of 13 C= 13 C complicated the interpretation for observations on NMR. Therefore, single-site 13 C-enriched molecules are desired. We summarize the problem of Pake doublet and the preparation of the single-site 13 C-susbstituted BEDT-TTF and TMTCF molecules. We also demonstrate the superiority of 13 C-NMR of the single-site 13 C-susbstituted molecule utilizing the hyperfine coupling tensor.