Structural Characterization of Quaterphenyl Cation Radical:  X-ray Crystallographic Evidence of Quinoidal Charge Delocalization in Poly-<i>p</i>-phenylene Cation Radicals

Abstract

Quaterphenyl derivative (QP) containing tert -butyl solubilizing groups at the terminal positions yields a stable cation radical salt that was isolated, and its structure was established by X-ray crystallography. The crystal structure of neutral QP and its cation radical (QP + • SbCl 6 - ) provides unequivocal evidence for the quinoidal stabilization of the cationic charge or polaron by smoothing out the torsional motion of the interconnected p -phenylene rings. Such an observation of stabilization of the cationic charge in a poly- p -phenylene (PPP) derivative forms the basis for the noted high conductivities in PPP oligomers in their doped state.