Structural and Spectroscopic Properties of New Chiral Quinoline-based Ln(III) Complexes

The synthesis, the structural characterization and the luminescence spectroscopy of new Ln(III) nitrate complexes (Ln = La, Eu, Gd, Tb and Lu) with the quinoline-based N, N’-bis(2-quinolylmethylidene)- 1,2-(R,R+S,S)-cyclohexanediamine, L1 and N, N’-bis(2-quinolylmethyl)- 1,2-(R,R+S,S)-cyclohexanediamine, L2 are presented. All the L1Ln(NO3)3 complexes and L2Ln(NO3)3 with Ln= La, Eu and Tb are isostructural. Metal ions such as La(III), Gd(III) and Lu(III) are able to promote intra-ligand (IL) fluorescence from L1 and L2. Gd(III) and Lu(III) in addition, are also able to stimulate IL phosphorescence at room temperature from the L2 ligand, by means of “paramagnetic effect” and/or “heavy-atom effect”. Both ligands are able to sensitize the typical f-f Eu(III) luminescence and only L2 the one of Tb(III) (green emission). The Eu(III) emission features for both complexes [L1Eu(NO3)3 and L2Eu(NO3)3] are in agreement with their structural properties. All the complexes under investigation reveal promising application in the field of luminescent devices and biomedicine. In particular, excitation at 360 nm, in the case of L1-based complexes, enable the use of glass optics and minimize interfering excitation by chromophores in biological media.