  The theoretical studies of light absorption and scattering spectra of the
plexcitonic two-layer triangular nanoprisms and three-layer nanospheres are
reported. The optical properties of such metal-organic core--shell and
core--double-shell nanostructures were previously explained within the
framework of pure isotropic models for describing their outer excitonic shell.
In this work, we show that the anisotropy of the excitonic shell permittivity
can drastically affect the optical spectra of such hybrid nanostructures. This
fact is confirmed by directly comparing our theory with some available
experimental data, which cannot be treated using conventional isotropic shell
models. We have analyzed the influence of the shell anisotropy on the optical
spectra and proposed a type of hybrid nanostructure that seems most convenient
for experimental observation of the effects associated with the anisotropy of
the excitonic shell. A strong dependence of the anisotropic properties of the
J-aggregate shell on the material of the intermediate spacer layer is
demonstrated. This allows proposing a new way to effectively control the
optical properties of metal-organic nanostructures by selecting the spacer
material. Our results extend the understanding of physical effects in optics of
plexcitonic nanostructures to more complex systems with the anisotropic and
multi-excitonic properties of their molecular aggregate shell.
