No abstract

High‐quality polycrystalline polyacenes (PLAs) of anthracene (AN), tetracene (TN), and pentacene (PN) doped with potassium in the 1:1 and 1:2 stoichiometries are prepared and their physical properties are systematically studied by magnetic measurements. The magnetic susceptibilities as a function of temperature for Kx(PLAs) are interpreted in the framework of a band‐filling model. Clear evidence for the occurrence of charge transfer from K to the organic semiconductors is provided. K1(AN) prepared by a solid‐state diffusion process exhibits a pronounced magnetic hump at 140 K, which is associated with antiferromagnetic interactions ascribed to the on‐site Coulomb repulsion in a Mott insulating state, whereas both K1(TN) and K1(PN) show a conventional Curie–Weiss behavior at low temperatures. We successfully demonstrate the tuning of the electronic states of PLA‐type semiconductors in bulk. Comments are given about the possibility of metallic states in potassium‐doped PLAs, which have recently been reported for other polycyclic aromatic hydrocarbons.

High quality bulk samples of anthracene (AN) doped with potassium (K) in 1 : 1 and 2 : 1 stoichiometries were successfully prepared by a method involving a room temperature solid-state mechanical diffusion process prior to intercalation reactions during heat treatment, and their physical properties were studied using both magnetic and optical measurements. The transfer of almost one electron from K to AN in K1(AN) was confirmed by SQUID and ESR measurements. A pronounced magnetic hump centered at 150 K associated with antiferromagnetic interactions was observed, which can most likely be interpreted in terms of on-site Coulomb repulsions of the Mott insulating states. Optical spectra of K1(AN) clearly showed the insulating states, as well as the electron occupation of the LUMO-derived band of AN. Our results demonstrated tuning of the ground state of a typical bulk hydrocarbon by alkali metal intercalation.

The thermodynaqmics for intercalation of phenanthrene (PHN) with Ba, for which superconductivity has been reported, is studied in comparison with its isomer of a linear aromatic hydrocarbon of anthracene (AN). Contrary to previous reports by other authors, the important observation that Ba is intercalated into neither PHN nor AN without affecting their molecular structures is unambiguously made by differential scanning calorimetry measurements and annealing time dependences observed by powder x-ray diffraction (XRD) measurements. The reactions of Ba and PHN at elevated temperatures lead this system to molecular decomposition instead of intercalation, resulting in the BaC 2 carbide or amorphous carbon formation, which is clearly supported by XRD and Raman spectroscopy. The phenomena of metallicity and superconductivity in PHN intercalated with alkaline-earth metals (Ba or Sr) should be reconsidered.