Synthesis and sensor activity of photostable blue emitting 1,8-naphthalimides containing s-triazine UV absorber and HALS fragments

Two novel highly photostable blue emitting 1,8-naphthalimides, containing active fragments of both a hindered amine radical scavenger (HALS) and an s-triazine UV absorber were synthesized for the first time. They showed substantially higher photostability in respect to other similar fluorescent brighteners, not containing either UV absorber or HALS component in their molecules. Novel compounds were also configured as “fluorophore–spacer–receptor” systems based on photoinduced electron transfer by incorporation a cation receptor at the C-4 position of the 1,8-naphthalimide fluorophore. The ability of the new compounds to detect cations was evaluated by the changes in their fluorescence intensity in the presence of metal ions and protons. The presence of metal ions and protons was found to disallow a photoinduced electron transfer leading to an enhancement in the 1,8-naphthalimide fluorescence intensity. The results obtained indicate the potential of the novel compounds as highly photostable and efficient “off–on” pH switchers and fluorescent detectors for metal ions with pronounced selectivity towards Zn2+ and Cu2+ ions.