Two structurally related macrocyclic amines with naphthalene groups are shown to act as fluorescent dosimeters for reactive chloroalkanes, including the common industrial solvent dichloromethane. The macrocyclic structures contain two NH residues which greatly accelerate N-alkylation by activating the chloride leaving group. The chemical reaction increases fluorescence intensity by promoting excimer emission and attenuating the quenching induced by photoinduced electron transfer (PET).