Novel 4-(2,2,6,6-tetramethylpiperidin-4-ylamino)-1,8-naphthalimide based yellow-green emitting fluorescence sensors for transition metal ions and protons

Two novel yellow-green emitting 1,8-naphthalimides, containing a 4-amino-2,2,6,6-tetramethylpiperidinyl moiety, were configured as “fluorophore–spacer–receptor” systems. The photophysical characteristics of the dyes were investigated in both DMF and water/DMF (4:1, v/v) solutions. The ability of the new compounds to detect cations was evaluated by means of the changes in their fluorescence intensity imparted by the presence of transition metal ions (Cu2+, Pb2+, Zn2+, Ni2+) and protons. The presence of metal ions and protons was found to disallow photoinduced electron transfer resulting in enhanced fluorescence intensity. The results clearly show that only Cu2+ ions and protons were effectively detected, indicating the potential of the novel compounds as highly efficient “off–on” switchers for Cu2+ ions and protons.