  Strong coupling between light and molecular matter is currently attracting
interest both in chemistry and physics, in the fast-growing field of molecular
polaritonics. The large near-field enhancement of the electric field of
plasmonic surfaces and their high tunability make arrays of metallic
nanoparticles an interesting platform to achieve and control strong coupling.
Two dimensional plasmonic arrays with several nanoparticles per unit cell and
crystalline symmetries can host topological edge and corner states. Here we
explore the coupling of molecular materials to these edge states using a
coupled-dipole framework including long-range interactions. We study both the
weak and strong coupling regimes and demonstrate that coupling to topological
edge states can be employed to enhance highly-directional long-range energy
transfer between molecules.
