High-resolution electron energy loss spectroscopy studies on the electronic structure of quinquethiophene (5T) and sexithiophene (6T) films

Abstract

High-resolution electron energy loss spectroscopy (HREELS) and optical absorption spectra were recorded for 5- and 6-thiophene films. These compounds are characterized by a large excitonic band of u symmetry. Optical transitions are only allowed to the high-energy edge (top) of this band. Due to different selection rules, HREELS spectra reveal transitions to the low-energy edge (bottom) of the exciton band, and allow a precise determination of the excitonic gap. Furthermore, a second threshold above 3 eV is tentatively assigned to the electronic gap.