Recently, much attention has been paid to an interesting subject, i.e., the interactions between surface plasmon polaritons(SPPs) and molecules. The interactions between SPPs and molecules often appear in two opposite cases,namely weak and strong coupling. When the interaction is weak, the absorption maximum simply coincides with the electronic transition energy of the molecule. In the weak coupling regime, the wave functions of the molecule and the SPP modes are considered to be unperturbed, only leading t...