Direct observation of charge-inducedπ-electronic structural changes in a conjugated polymer

Ultraviolet photoelectron spectroscopy (UPS) has been used to observe changes in the {π}-band structure in poly(3-hexylthiphene) induced by doping using NOPF₆. The charge-induced movement of the Fermi energy and a finite density of electronic states at the Fermi energy in the most highly doped (saturated) material are seen unambiguously with UPS for the first time in a conjugated polymer. The results imply the existence of a new, recently predicted theoretically, but hitherto unobserved, polaron-lattice state of this conjugated polymer at the saturation-doping level.