Solid-state synthesis of highly conducting polyphenylene from crystalline oligomers

Abstract

Paraphenylene oligomers (biphenyl, p‐terphenyl, p‐quaterphenyl, p‐quinquephenyl, p‐sexiphenyl) form electrically conducting complexes with AsF₅. Prolonged exposure to AsF₅ causes a polymerization of these p‐phenylene oligomers to give highly conducting charge‐transfer complexes of poly(p‐phenylene). Conductivities as high as 50 S/cm have been measured. Powders, thin films, and single crystals of p‐phenylene oligomers have been reacted with AsF₅. The undoped oligomers and the doped, compensated, and annealed products have been investigated by means of x‐ray diffraction, and UV‐visible and IR transmission spectroscopy. The x‐ray diffraction studies give evidence for a change in lattice spacings to those characteristic of the crystalline polymer. The spectroscopic measurements during AsF₅ doping reveal shifts in absorption bands in the UV and the IR to those characteristic of poly(p‐phenylene). Paraoligophenylenes have also been reacted with elemental potassium in THF solution with trace amounts of naphthalene. Highly conducting complexes were formed (0.5 S/cm for sexiphenyl) but there is no evidence for further polymerization.