  In the paper, we considered a molecular structure that consists of a
molecular chain and an additional molecule ("donor"/"acceptor") that can inject
(or remove) single excitation (vibron, electron, e.t.c.) onto the molecular
chain. We assumed that the excitation forms a self-trapped state due to the
interaction with mechanical oscillations of chain structure elements. We
analyzed the energy spectra of the excitation and showed that its state (when
it migrates to the molecular chain) has the properties of the non-adiabatic
polaron state. The conditions under which the excitation can migrate from one
subsystem to another were considered. It was shown that the presence of a
"donor" molecule cannot significantly change the properties of the excitation
located on the molecular chain. At the same time, the molecular chain can
affect the position of the energy level of the excitation localized on the
"donor" subsystem. Indirectly, this can influence the process of excitation
migration from one subsystem to another one. The influence of basic energy
parameters of the system and the environment temperature on this process are
discussed. The entire system was assumed to be in thermal equilibrium with the
environment.
