  Dipole-coupled subwavelength quantum emitter arrays respond cooperatively to
external light fields as they may host collective delocalized excitations (a
form of excitons) with super- or subradiant character. Deeply subwavelength
separations typically occur in molecular ensembles, where in addition to
photon-electron interactions, electron-vibron couplings and vibrational
relaxation processes play an important role. We provide analytical and
numerical results on the modification of super- and subradiance in molecular
rings of dipoles including excitations of the vibrational degrees of freedom.
While vibrations are typically considered detrimental to coherent dynamics, we
show that molecular dimers or rings can be operated as platforms for the
preparation of long-lived dark superposition states aided by vibrational
relaxation. In closed ring configurations, we extend previous predictions for
the generation of coherent light from ideal quantum emitters to molecular
emitters, quantifying the role of vibronic coupling onto the output intensity
and coherence.
