  Metallic nanostructures are able to concentrate light into volumes far below
the diffraction limit. Here we show, by accurate scattering calculations, that
nanostructures obtained from thin films of J-aggregate dyes, concentrate the
electromagnetic field at optical frequencies. Moreover, in contrast to metal
nanoparticles, these molecular aggregates display highly attractive nonlinear
optical properties that can be exploited for the realization of ultracompact
devices for switching light by light on the nanoscale without the need of
additional nonlinear materials. These results open new perspectives in
plasmonic based nanophotonics.
