Use of surface plasmons for manipulation of organic molecule quasiparticles and optical properties

Our recently proposed theoretical formulation based on Bethe-Salpeter G0W0 methodology is applied here to explore the quasiparticle and optical spectra of anthracene (C14H10) placed close to a metallic surface. Special attention is paid to explore how the energy shift and decay width of the low-lying anthracene bright excitons p, α and β depend on the type of the adjacent surface (described by the Wigner Seits radius rs) and the separation from the surface. It is shown that p and α excitons weakly interact with surface excitations, but for rs 3 the intensive β exciton hybridizes with surface plasmon considerably, resulting in its splitting into two optically active modes. The β exciton decays extraordinarily fast (Γ 200 meV) to the electron-hole excitations in the metallic surface even for non-contact separations (z0 12 a.u.). For rs > 5 the β exciton becomes infinitely sharp (Γ 0) and no longer interacts with the surface plasmon. Moreover, it is shown that HOMO and LUMO states near a metallic surface behave as statically screened rigid orbitals, with the result that the simple image theory arguments are sufficient to explain the HOMO-LUMO gap shift. Finally, it is demonstrated that the HOMO-LUMO gap shift dominantly depends on the position of the effective image plane zim of the adjacent surface.