The interaction of rubidium atoms with a model molecule for polyacetylene: a photoelectron spectroscopy investigation

The interaction of rubidium, a first group metal, with (alpha,omega-diphenyltetradecaheptaene) (DP7), a diphenylpolyene having seven double bonds in the polyene chain, has been studied by means of X-ray and UV photoelectron spectroscopy. DP7 can be considered as a model molecule for polyacetylene since the frontier pi-orbitals are mainly localized on the polyene part of the molecule. The experimental data are interpreted with the help of related experimental data from sodium-doping of DP7 and quantum chemical calculations. The interaction with rubidium results in n-type doping of the DP7, i.e., an electron-transfer process from the metal to the pi-conjugated system occurs. The doping process affects mainly the polyene part of the molecule, and new electronic states are created in the previously forbidden energy gap. At low doping levels, it appears that one new broad peak is developed in the band gap and, most important, a finite density of states at the Fermi energy can be detected. Upon further doping, there is a slight shift of the single peak, and a second peak is formed. The evolution of the new doping-induced states can be explained in terms of a transition from a polaron-like situation to a soliton-antisoliton pair formation.