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The present work for the first time reports an application of the thiacalix[4]arene scaffold for the preparation of Tb3+ complexes possessing high thermal luminescence sensitivity in the physiological temperature range of 20–50 °C. Non-substituted thiacalix[4]arenes form luminescent complexes with Tb3+ ions, but they do not reveal any meaningful thermal sensitivity. To solve this problem, an upper-rim bromination of thiacalix[4]arenes, as well as distal bromination along with the embedding of two 1,3-diketone substituents are proposed as new simple synthetic approaches to enhance the thermal luminescence sensitivity of the Tb3+ complexes. A combination of mass spectrometry, NMR, UV-Vis and luminescence spectroscopy with quantum chemical calculations reveals a dimeric structure of the complexes formed by thiacalix[4]arenes with Tb3+ ions in DMF solutions. The steady-state luminescence of the Tb3+ complexes has demonstrated more than one order higher thermal sensitivity for the complexes of bromo-substituted ligands in comparison with the non-substituted thiacalix[4]arenes. The reasons for such behavior are discussed. The results highlight new opportunities for the thiacalix[4]arene platform for controlling ligand-to-metal energy transfer in terbium complexes and tuning their thermo-responsive luminescence properties. [ABSTRACT FROM AUTHOR]

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 equilibrium 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, MALDI TOF mass spectroscopy, quantum-chemical calculations at the DFT level 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]arene-scaffold in the tetra-1,3-diketone derivatives shifts the equilibrium forms of Tb3+ complexes from monomeric to the dimeric ones. DFT calculations in combination with experimental data reveal the most reliable structures of complexes. 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. [ABSTRACT FROM AUTHOR]