Disclosed is a curable sealant composition including: (i) a thiol-terminated prepolymer and/or monomers thereof, wherein the thiol-terminated prepolymer is a polythioether or a polysulfide; (ii) an “ene” crosslinker having a molecular weight of about 100 to about 5000; and (iii) a pH indicator molecule including a quantum dot functionalized with a pH-responsive ligand. Methods for determining a sufficient cure state of a composition by combining the thiol-terminated prepolymer and/or monomers thereof and the “ene” crosslinker with a pH indicator molecule, including a quantum dot functionalized with a pH-responsive ligand, and (ii) then subjecting a resultant mixture of (i) to curing conditions until the mixture changes its color are also disclosed.