Microscopic evidence of a metallic state in the one-pot organic conductor ammonium tetrathiapentalene carboxylate

¹H NMR (nuclear magnetic resonance) and high-field ESR (electron spin resonance) measurements were carried out for self-doped organic conductors in the ammonium tetrathiapentalene carboxylate (TTPCOO)₂[(NH₄¹⁺)_1-x(NH₃⁰)_x ] system. While the pristine TTPCOOH molecule is closed-shell, self-doped carriers are generated by substitution of the carboxyl proton by (NH₃⁰) and (NH₄¹⁺), which can be regarded as a charge reservoir. The π-extended system TTPCOO has a uniaxial g -tensor, indicating a 2D isotropic structure such as a herring-bone-like or parallel cross donor arrangement. The NMR-relaxation rate indicated the Korringa relation in the temperature dependence, and the ESR linewidth followed the Elliot mechanism. Both of these observations provide supporting evidence for a stable metallic state. In this paper, we introduce self-doped organic conductors as a branch of materials design, and emphasize that advanced magnetic resonance measurements are powerful tools for developing functional materials.