Novel blue emitting tetra- and pentamethylpiperidin-4-yloxy-1,8-naphthalimides as photoinduced electron transfer based sensors for transition metal ions and protons

Two novel blue emitting 1,8-naphthalimides ( 1 and 2 ), containing 2,2,6,6-tetramethylpiperidin-4-yloxy moieties, and newly synthesized under phase transfer catalysis conditions 4-(1,2,2,6,6-pentamethylpiperidin-4-yloxy)-1,8-naphthalimide 7 , were configured as “fluorophore–spacer–receptor” systems. Basic photophysical characteristics of the novel fluorescent brighteners were investigated in both DMF and water/DMF (4:1, v/v) solution. Their ability to detect cations was evaluated in the presence of transition metal ions (Cu 2+ , Pb 2+ , Zn 2+ , Ni 2+ , Co 2+ ) and protons. The presence of metal ions and protons was found to disallow a photoinduced electron transfer leading to an enhancement in the fluorophore emission intensity. The results clearly showed a good sensor activity towards transition metal ions and protons, especially of compound 7 , containing tertiary amine receptor. This indicates the potential of the novel compounds as highly efficient “ off – on ” pH switchers and fluorescent detectors for metal ions.