Studies on the Transition Metal Ion Induced Fluorescence Enhancement of 1,8‐Naphthalimide Derivatives†

Abstract Two fluorosensor systems have been designed and synthesized with their photophysical properties and fluorescence responses toward the transition metal ions studied. The fluorosensor was composed of 1,8‐naphthalimide and 4‐chloro‐1,8‐naphthalimide as fluorophore respectively, an amino moiety as the receptor and a hydrocarbon chain as the spacer to link the fluorophore and receptor. Fluorescence intensity of these systems is very weak due to the process of the efficient intramolecular photoinduced electron transfer (PET) in the absence of metal ions. Titration of the transition metal ions can switch on the fluorescence immediately. The intensity of released fluorescence is even higher than the expected from the consideration of the PET in these systems. It may be rationalized that the receptor bound to transition metal ions and the solvation of the fluorophore by the water molecules from the hydrated transition metal salts, may significantly cause fluorescence enhancement.