Plasmon excitation in a set of linear polycyclic aromatic hydrocarbons

Time-dependent density functional theory has been used to investigate the plasmon excitation processes in a set of linear polycyclic aromatic hydrocarbons. Along the direction parallel to the linear polycyclic aromatic plane, there are two main plasmon bands, one around 3.9 eV and the other around 16 eV. In the low-energy resonance region with the increase of the side length of the linear polycyclic aromatic hydrocarbons, the absorption peaks of the system are respectively blue-shifted and red-shifted along different excitation directions. Moreover, in the low-energy resonance region, compared with the pentacene, the photo absorption strength line of a chlorinated pentacene is red-shifted and greatly broadens. When the chlorine atoms at the two ends of the pentacene, it makes greatly influence to plasmon excitation of a chlorinated pentacene. In the low-energy resonance region, plasmon excitation in linear polycyclic aromatic hydrocarbons is similar to that in grapheme quantum dot. (authors)