Shape Dependency of the Plasmon-Exciton Interaction at the Nanoscale: Interplay between the Plasmon Local Density of States and the Plasmon Decay Rate

Unravelling how various physical parameters influence the strength of plasmon-exciton coupling is crucial for the successful realization of the exciting potential applications of plexcitonic nanostructures. Here, in this paper, using single-particle-level spectroscopy, we demonstrate how nanostructures' shapes and morphologies affect the plasmon-exciton interaction. We studied cyanine dye J-aggregate hybrids of four nanostructures of different shapes and morphologies: nanorod, concave nanocube, nanostar, and truncated trigonal bipyramid. The localized surface plasmon resonances of each of these particles are chosen to be identical and at the same time resonant with the J-band of our cyanine dye to make sure that any indirect effect of particle size and shape through plasmon frequency does not arise. Working with these different shapes allows us to observe the effect of variation in the plasmon local density of states, plasmon damping, exciton number densities at hot-spots, and how the interplay of these factors finally affect plasmon-exciton coupling at the nanoscale. We find that the shape and morphology of a plasmonic nanoparticle influence not only the Rabi splitting energies and the transparency dip depth but also the plexciton dynamics.