  Designing closed, laser-induced optical cycling transitions in trapped atoms
or molecules is useful for quantum information processing, precision
measurement, and quantum sensing. Larger molecules that feature such closed
transitions are particularly desirable, as they extend the scope of
applicability of such systems. The search for molecules with robust optically
cycling centers has been a challenge, and requires design principles beyond
trial-and-error. Here, two design principles are proposed for the particular
architecture of M-O-R, where M is an alkaline earth metal radical, and R is a
ligand: 1) Fairly large saturated hydrocarbons can serve as ligands, R, due to
a substantial HOMO-LUMO gap that encloses the cycling transition, so long as
the R group is rigid. 2) Electron-withdrawing groups, via induction, can
enhance Franck-Condon factors (FCFs) of the optical cycling transition, as long
as they do not disturb the locally linear structure in the M-O-R motif. With
these tools in mind, larger molecules can be trapped and used as optical
cycling centers, sometimes with higher FCFs than smaller molecules.
