  Plasmonic nanocavities form very robust sub-nanometer gaps between
nanometallic structures and confine light in deep subwavelength volumes to
enable unprecedented control on light-matter interactions. However, spherical
nanoparticles acquire various polyhedral shapes during their synthesis, which
has defining impact on controlling many light-matter interactions, such as
photocatalytic reactions. Here, we focus on nanocavities made of three
polyhedral nanoparticles (cuboctahedron, rhombicuboctahedron, decahedron) that
commonly occur during the synthesis of spherical nanoparticles. Their photonic
modes have a very intricate and rich optical behaviour, both in the near- and
far-field. Through a recombination technique, we obtain the total far-field
produced by a molecule placed within these nanocavities, to reveal how energy
couples in and out of the system. This work paves the way towards understanding
and controlling light-matter interactions, such as photocatalytic reactions and
non-linear vibrational pumping, in such extreme environments.
