Nickel(ii) and iron(iii) selective off-on-type fluorescence probes based on perylene tetracarboxylic diimide

Abstract

Two novel “turn-on” fluorescent probes with perylene tetracarboxylic diimide (PDI) as the fluorophore and two different di-(2-picolyl)-amine (DPA) groups as the metal ion receptor (PDI-1 and PDI-2) were successfully synthesized with satisfactory yields. PDI-1 exhibited high selectivity toward Ni²⁺ in the presence of various other metal cations including Zn²⁺, Cd²⁺ and Cu²⁺ which were expected to interfere significantly. A 1 : 2 stoichiometry was found for the complex formed by PDI-1 and Ni²⁺ by a Job's plot and by non-linear least square fitting of the fluorescence titration curves. By introducing an extra diamino ethylene group between DPA and the phenyl bridge, the receptor was modified and the high selectivity of the sensor toward Ni²⁺ shifted to Fe³⁺. The enhancement factor of the fluorescence response of PDI-2 to Fe³⁺ was as high as 138. The binding behavior of the receptors in these two compounds is affected significantly by the PDI fluorophores. Most interestingly, both Ni²⁺ and Fe³⁺ are paramagnetic metal ions, which are known as fluorescence quenchers and are rarely targeted with “turn-on” fluorescence probes. This result suggests that PDIs are favorable fluorophores for a “turn-on” fluorescence probe for paramagnetic transition metal ions because of their high oxidation potential.