Europium(III) Macrocyclic Chelates Appended with Tyrosine-based Chromophores and Di-(2-picolyl)amine-based Receptors: Turn-On Luminescent Chemosensors Selective to Zinc(II) Ions.

Zinc ions play an important role in many biological processes in the human body. To selectively detect Zn2+ , two EuDO3A-based complexes (DO3A=1,4,7,10-tetraazacyclododecane-1,4,7-tricarboxylic acid) appended with tyrosine as a chromophore and di-(2-picolyl)amine (DPA) as the Zn2+ recognition moiety were developed as suitable luminescent sensors. Their luminescence intensity is affected by the photoinduced electron transfer mechanism. Upon addition of Zn2+ , both probes display an up to sevenfold enhancement in Eu3+ emission. Competition experiments demonstrated their specificity toward Zn2+ over other metal ions, while also revealing the nonspecificity of the derivatives lacking the DPA-moiety, thus confirming the essential role of the DPA for the recognition of Zn2+ . The induced emission changes of Eu3+ allow for precise quantitative analysis of Zn2+ , establishing these lanthanide-based complexes as viable chemosensors for biological applications.