Structural and Photophysical Properties of Tb3+ - Complexes With Tetra-1,3-Diketone Derivatives Based on Calix[4]arene and Tetrathiacalix[4]arene Platforms

Calix[4]arenes and tetrathiacalix[4]arenes are well known as a convenient macromolecules for creating ligands that can provide stable coordination of transition metal ions, particularly lanthanides, and sensitize their luminescence. The present work highlights the key aspects of the influence of calix[4]arene and tetrathiacalix[4]arene scaffolds on the structural and photophysical properties of Tb3+ complexes with tetra-1,3-diketone derivatives of the macrocycles in DMF solutions. The equil forms of Tb3+ complexes with unsubstituted and functionalized by acetylacetonyl groups at the upper rim of calix[4]arenes and thiacalix[4]arenes are revealed from UV-, NMR and luminescence spectroscopy data. In alkaline DMF solutions, the ligands form predominantly 1:1 complexes with Tb3+ ions. However, the replacement of a calix[4]arene-scaffold by a thiacalix[4]arenescaffold in the tetra-1,3-diketone derivatives shifts the equilibrium forms of Tb3+ complexes from monomeric to the dimeric ones. The difference in the complexes composition can be due to the more efficient complexation ability of the lower rim of thiacalix[4]arenes compared to their classical counterparts. The quantitative analysis of the photophysical parameters in correlation with the structural features of the complexes highlights the specific inner-sphere environment of Tb3+ ions in the dimeric complexes with the thiacalix[4]arene derivatives as a reason for greater sensitization of Tb3+-centered luminescence by these macrocycles. The obtained data revealed that the calix[4]arene and thiacalix[4]arene macrocyclic platforms using allows to control the structural and photophysical properties of Tb3+ complexes of ligands, containing 1,3-diketone functional groups.