Protonic defect induced carrier doping in TTFCOO-NH4+: Tunable doping level by solvent

The origin of carrier doping in TTFCOO-NH4+ has been verified to include protonic defect in salt bridge by means of X-ray photoelectron spectroscopy (XPS), for the first time. The emergence of spin in TTFCOO-NH4+ is tunable over quite a wide range (9-33%) only by selecting a suitable solvent for the salt crystallization. The spin concentration of the solvent-dependent salts weakly correlates with intensity of optical absorption in near-infrared region, values of g-tensor and dc conductivity at rt. The solvents determining doping level of the salt are classified into three categories by self-dissociation ability (pK(SH)) of solvent, which likely controls inclusion of protonic defect in the salts. (C) 2012 Elsevier B.V. All rights reserved.