Intramolecular band mapping of poly(p-phenylene) via UV photoelectron spectroscopy of finite polyphenyls

Ultraviolet photoelectron spectra were measured of solid sexiphenyl with synchrotron radiation and of gaseous polyphenyls from biphenyl to sexiphenyl with a Hel light source. The similarity of the spectrum of the solid with the XPS spectrum of poly(p-phenylene) (PPP) shows the usefulness of sexiphenyl as a model compound of PPP. Examination of the fine structure observed in the low binding-energy region clearly shows how the electronic structure of the p-phenylenes evolves from that of benzene including the effects of deeper levels and of the non-planarity of the molecular geometry. The experimental E = E(k) energy band-dispersion relation of a PPP chain can be deduced by giving each energy level of the oligomers an appropriate k value. An extrapolation for the total bandwidth and the threshold photoemission energy of solid PPP yields 3.9₅ and 5.6₅ eV. respectively.