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

Abstract

Our recently proposed theoretical formulation based on Bethe–Salpeter G(0)W(0) methodology is applied here to explore the quasiparticle and optical spectra of anthracene (C(14)H10) 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 r(s)) and the separation from the surface. It is shown that p and α excitons weakly interact with surface excitations, but for r(s) ≈ 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 (z(0) ≈ 12 a.u.). For r(s) > 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 z(im) of the adjacent surface.

Prediction of Strong Transversal s(TE) Exciton–Polaritons in C60 Thin Crystalline Films

“…When the molecule is deposited at the Al 2 O 3 surface, the excitation band barely changes at all, due to the well-known cancellation effect: the substrate weakens the interaction between the excited electron and the hole, which reduces the exciton binding energy and, therefore, cancels the gap reduction. This phenomenon was studied in detail in references [62,66,84]. Since the influence of the dielectric surface on the molecular optical conductivity is weak, we shall further approximate σx i (ω) ≈ σx (ω), where σx (ω) is the optical conductivity in the self-standing molecular single layer, i.e., for z 0 → ∞.…”