New advances in the synthesis of tripyridinophane macrocycles suitable to enhance the luminescence of Ln(III) ions in aqueous solution

Abstract

A series of four new 18-membered hexaaza macrocyclic ligands bearing three endocyclic pyridine units and acetate or methylenephosphonate pendant arms has been prepared. The new synthetic procedure is based on the use of amine and diamine precursors incorporating masked carboxylate or phosphonate functions and on an efficient sodium template effect which controls the crucial macrocyclization step (yields of macrocyclization reactions: 62–88%). This procedure appears as a suitable alternative compared to the classical Richman-Atkins methodology generally used for the preparation of this class of macrocycles. As demonstrated with the EuIII and TbIII complexes derived from two ligands, these tripyridinophane chelators form luminescent and stable mononuclear LnIII complexes in aqueous solution at physiological pH. In such a medium, TbIII complexes exhibit a brightness of 1700 (λexc = 279 nm) and 3000 (λexc = 268 nm) M−1 cm−1.