  Rapid and repeated photon cycling has enabled precision metrology and the
development of quantum information systems using a variety of atoms and simple
molecules. Extending optical cycling to structurally complex molecules would
provide new capabilities in these areas, as well as in ultracold chemistry.
Increased molecular complexity, however, makes realizing closed optical
transitions more difficult. Building on the already established strong optical
cycling of diatomic, linear triatomic, and symmetric top molecules, recent
theoretical and experimental work has indicated that cycling will be extendable
to phenol containing molecules, as well as other asymmetric species. The
paradigm for these systems is the use of an optical cycling center bonded to a
molecular ligand. Theory has suggested that cycling may be extended to even
larger ligands, like naphthalene, pyrene and coronene. Here, we study the
optical excitation and vibrational branching of the molecules CaO-2-naphthyl,
SrO-2-naphthyl and CaO-1-naphthyl and find only weak decay to excited
vibrational states, indicating a promising path to full quantum control and
laser cooling of large arene-based molecules.
