  A search for long-lived particles decaying to photons and weakly interacting
particles, using proton-proton collision data at $\sqrt{s} =$ 13 TeV collected
by the CMS experiment in 2016-2017 is presented. The data set corresponds to an
integrated luminosity of 77.4 fb$^{-1}$. Results are interpreted in the context
of supersymmetry with gauge-mediated supersymmetry breaking, where the
neutralino is long-lived and decays to a photon and a gravitino. Limits are
presented as a function of the neutralino proper decay length and mass. For
neutralino proper decay lengths of 0.1, 1, 10, and 100 m, masses up to 320,
525, 360, and 215 GeV are excluded at 95% confidence level, respectively. We
extend the previous best limits in the neutralino proper decay length by up to
one order of magnitude, and in the neutralino mass by up to 100 GeV.
