New 2,6-Bis(5-phenyloxazolyl)pyridine Ligands for Luminescent LnIII Complexes

Lanthanide (Ln(III)) luminescent complexes have been attracting a lot of interest for technological applications and molecular imaging. The luminescence of Ln(III)) ions is weak and depends on the use of light absorbing coordination ligands which sensitizes the lanthanide ion. [1,2] A large variety of coordination ligands has been screened such as dipicolinates, oligopyridines, cyclen and crown ether derivatives, porphyrins, cryptands or calixarenes. [1]

In our research group we have developed an expeditious methodology to prepare bis(oxazolyl)pyridine ligands for LnIII from threonine and 2,6-pyridinedicarbonyl dichloride.[2] In this work, two new pyridine-bis-oxazolyl ligands with an aromatic ring in position 5 of the oxazole ring (Figure 1) were prepared from phenylserine and 2,6-pyridinedicarbonyl dichloride. The photophysical properties of compounds 1 and 2 were studied in acetonitrile and in Tris-HCl buffer (0.1 M, pH 7.1). These compounds were used for complexation with Eu(III) and/or Tb(III) ions, and the photophysical properties of the complexes studied. Luminescence titrations with anhydrous EuCl₃ and TbCl₃ allowed the determination of the stoichiometry of the complexes and of the stability constants.

[1] A. Bettencourt-Dias, P. S. Barber, S. Bauer, J. Am. Chem. Soc., 2012, 134, 6987

[2] G. Pereira, M.F. Ferreira, E.M.S. Castanheira, J.A. Martins, P.M.T. Ferreira, Eur. J. Org. Chem. 2012, 3905