Bimodal Magneto‐Luminescent Response of Lanthanide Metallopolymers for Distinguishing of Phosphates in Aqueous Solutions

Abstract

Linear N‐substituted polyacrylamides bearing tricarboxylic moieties pendant to the backbone are synthesized, and coordinative binding approach is developed to convert them into Gd3+/Eu3+‐metallopolymers. Inner‐sphere coordination of the lanthanide ions with the pendant chelating moieties, together with their outer‐sphere stabilization by the randomly coiled backbone, are the reasons for peculiar water proton relaxation and luminescence properties of the metallopolymers obtained. Indeed, for Gd3+‐metallopolymer, the values of longitudinal and transverse relaxivity (r1 and r2) are 50 and 60 mm−1·s−1, respectively, while for the Eu3+‐counterpart, Eu3+‐centered luminescence is significantly raised compared to Eu3+ aquaions. Coil‐like conformation of the metallopolymer molecules undergoes a swelling at pH values above 5.0 as evidenced by transmission electron microscopy TEM and dynamic light scattering (DLS) data, which is followed by the changes in the Eu3+‐centered luminescence and r1(2)‐values of Gd3+/Eu3+‐metallopolymers. The phosphates additives (adenosine monophosphoric acid (AMP), adenosine diphosphoric acid (ADP), HPO42− and adenosine triphosphoric acid (ATP) induce well detectable changes in both water proton relaxation and luminescence of Gd3+/Eu3+‐metallopolymers. The luminescent changes distinguish AMP from the other phosphates, while the changes in water proton relaxation are greater for HPO42− and ATP compared to AMP and ADP. This study explains this by interplay of the effects associated with the formation of ternary phosphate‐lanthanide‐polymer complexes and stripping of lanthanide ions from the polymer molecules.