A Terpyridine Based 1,2,3-Triazol-1,4-diyl-Fluoroionophore-A Fluorometric Study Towards 3d Metal Ions in Acetonitrile

In this paper, we report on the sensing role of the 1,2,3-triazol unit in a 1,4-diyl arrangement in a fully π-conjugated fluorescent probe 1 (cf. Scheme 1) towards the fluorometric detection of 3d metal ions. The 1,2,3-triazol-1,4-diyl-fluoroionophore 1 was designed in a donor(D)-acceptor(A) arrangement with a 1,2,3-triazol unit as a π-linker between a terpyridine (A) ionophore and a diethylaminocoumarin (D) fluorophore to study the fluorescence behavior towards the divalent 3d metal ions Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺. This fluoroionophore 1 is based on an intramolecular charge transfer (ICT) and shows a moderate quantum yield (φ_f) of 0.508 in acetonitrile. A modulation of the ICT process in 1 through Fe²⁺, Co²⁺, Cu²⁺, Ni²⁺ and Zn²⁺ leads to a small red shift of the lowest energetically lying absorption UV/Vis absorption band and to a very strong 3d metal ion induced fluorescence quenching. It should be considered, that the installation of a 1,2,3-triazole unit as a fully π-linker in ICT probes originates no ratiometric fluorescence response towards Fe²⁺, Co²⁺, Cu²⁺, Ni²⁺ and Zn²⁺.