Site-specific electronic structure of an oligo-ethylenedioxythiophene derivative probed by resonant photoemission

A combination of conventional and resonant photoemission spectroscopy, x-ray absorption spectroscopy and ground-state quantum-chemical calculations has been used to study the valence electronic structure of a phenyl-capped 3,4-ethylenedioxythiophene oligomer, in polycrystalline thin films. The photon energy-dependent intensities of specific resonant decay channels are interpreted in terms of the spatial overlap of the excitation site and the ground-state molecular orbital involved in the decay. By making use of chemical shifts, excitations on different atomic sites are distinguished. It is demonstrated that site-specific information on the electronic structure of relatively large and complex organic systems may be obtained experimentally from non-radiative resonant decay spectra. In addition, these spectra provide relevant insight into the interpretation of near-edge x-ray absorption fine structure spectra.