Morphology-Retained Conversion of Neutral to Mixed Valence Tetrathiafulvalene Crystals through a Spontaneous Redox Reaction

Solid-state conversion by the spontaneous redox reaction between tetrathiafulvalene (TTF) and ferric ion is employed to obtain morphology-retained TTF mixed valence (MV) salt crystals. Radical species are formed first at the surface of TTF crystals and then inside of the crystals by diffused ferric ions as revealed by the time-dependent UV–vis absorption and electron spin resonance (ESR) spectroscopy studies. The resulting TTF MV salt crystals exhibit 6 orders of magnitude higher electrical conductivity than the original neutral TTF crystals. By taking advantage of solid-state conversion, TTF neutral-MV heterostructures were demonstrated by selectively contacting TTF crystals to ferric ion solution, and they were applied to self-contact devices, which showed higher conductivity values than the silver paste devices.