Spontaneous
emission of quantum emitters can be enhanced by increasing
the local density of optical states, whereas engineering dipole–dipole
interactions requires modifying the two-point spectral density function.
Here, we experimentally demonstrate long-range dipole–dipole
interactions (DDIs) mediated by surface lattice resonances in a plasmonic
nanoparticle lattice. Using angle-resolved spectral measurements and
fluorescence lifetime studies, we show that unique nanophotonic modes
mediate long-range DDI between donor and acceptor molecules. We observe
significant and persistent DDI strengths for a range of densities
that map to ∼800 nm mean nearest-neighbor separation distance
between donor and acceptor dipoles, a factor of ∼100 larger
than free space. Our results pave the way to engineer and control
long-range DDIs between an ensemble of emitters at room temperature.