  Optical cycling transitions and direct laser cooling have recently been
demonstrated for a number of alkaline-earth dimers and trimer molecules. This
is made possible by diagonal Franck-Condon factors between the vibrational
modes of the optical transition. Achieving a similar degree of cooling to
micro-Kelvin equivalent kinetic energy for larger polyatomic molecules,
however, remains challenging. Since polyatomic molecules are characterized by
multiple degrees of freedom and have a correspondingly more complex structure,
it is far from obvious whether there exist polyatomic molecules that can
repeatedly scatter photons. Here, we propose chemical substitution approaches
to engineer large polyatomic molecules with optical cycling centers (OCCs)
containing alkaline-earth oxide dimers or acetylenic alkaline-earth trimers
(i.e. M--C$\equiv$C) connected to CH$_n$ chains or fullerenes. To validate the
OCC-character of the selected molecules we performed electronic structure
calculations of the equilibrium configuration of both ground and excited
potential energy surfaces, evaluated their vibrational and bending modes, and
corresponding Franck-Condon factors for all but the most complex molecules. For
fullerenes, we have shown that OCCs based on M--C$\equiv$C can perform better
than those based on alkaline-earth oxide dimers.
  In addition, for heavier polyatomic molecules it might be advantageous to
attach two OCCs, thereby potentially doubling the photon scattering rate and
thus speeding up cooling rates.
