Binding of europium complex to polymerizable macrocyclic molecules and its optical properties

Abstract

Study on the incorporation of trivalent europium (Eu3+) complex into polymerizable macrocylic molecules, namely calixarene and calixresorcinarene derivatives, has been carried out. Broadening of hypersensitive luminescence peak was observed in solution and polymer containing a compound of europium complex and calixresorcinarene monomer, which is ascribed to ligand field splitting due to anisotropic local field at the Eu3+ ion site. From 1H NMR spectroscopy, it is found that the chemical shift originated from the moiety at the upper rim of calixresorcinarene is remarkably downfield shifted. Pseudocontact shift analysis suggests that binding between Eu3+ ion and calixresorcinarene monomer is formed at the Eu3+ second coordination sphere. These experimental results show that the binding does not alter nephelauxetic effect of the Eu3+ first coordination shell, but only slightly change coordination structure and symmetry. Nevertheless, the binding results in longer luminescence lifetime in comparison to the case of pure europium complex indicating significant reduction of non-radiative decay.