Search

The present work introduces the series of thiacalix[4]arenes (H4L) bearing different upper-rim substituents (R = H, Br, NO2) for rational design of ligands providing an antenna-effect on the NIR Yb3+-centered luminescence of their Yb3+ complexes. The unusual inclusive self-assembly of H3L− (Br) through Br...π interactions is revealed through single-crystal XRD analysis. Thermodynamically favorable formation of dimeric complexes [2Yb3+:2HL3−] leads to efficient sensitizing of the Yb3+ luminescence for H4L (Br, NO2), while poor sensitizing is observed for ligand H4L (H). X-ray analysis of the single crystal separated from the basified DMF solutions of YbCl3 and H4L(NO2) has revealed the transformation of the dimeric complexes into [4Yb3+:2L4−] ones with a cubane-like cluster structure. The luminescence characteristics of the complexes in the solutions reveal the peculiar antenna effect of H4L(R = NO2), where the triplet level at 567 nm (17,637 cm−1) arisen from ILCT provides efficient sensitizing of the Yb3+ luminescence. [ABSTRACT FROM AUTHOR]

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]

A novel temperature probe with −1.0% K−1 mean relative and −5.4 μs K−1 mean absolute sensitivity of the luminescence decay time in the range of 270–370 K is presented. The probe is a 20 μm thick vitrified film (sandwiched between two quartz plates) fabricated from an amorphous powder of an anisometric europium(III) β-diketonate complex through a melt-processing technique. It is established that the film exhibits bright Eu3+ ion luminescence with the most intense peak at 611 nm caused by efficient ligand-to-metal energy transfer. The observed thermal luminescence sensitivity we associate with a well-known non-radiative relaxation mechanism of the Eu3+ ions through the low-lying ligand-to-metal charge transfer state. The experiments also showed that (i) the luminescence of the film is insensitive to oxygen, (ii) the film is completely resistant to UV-vis light, (iii) there is full reversibility of the temperature dependent luminescence decay time, and (iv) the strong luminescence of the film can be efficiently excited by irradiation in the wavelength range of 280–425 nm (including inexpensive and portable blue-violet light sources). The listed facts allow us to consider the film as a promising probe for reusable luminescent thermometers, suitable for long-term temperature monitoring. [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]

A novel temperature-sensitive luminescent material was fabricated from a powder of a mesogenic terbium(iii) β-diketonate complex, [Tb(CPDK3–7)3phen] (CPDK3–7 = 1-(4-(4-propylcyclohexyl)phenyl)decane-1,3-dione, phen = 1,10-phenanthroline) by a melt-processing technique. The material is a 20 μm thick vitrified film sandwiched between two quartz plates. The film effectively absorbs light in the wavelength range of 280–405 nm and exhibits a green narrow-band luminescence of Tb3+ ions due to efficient ligand-to-metal energy transfer. The average luminescence decay time varies reversibly with temperature from 373 μs at 143 K to 33 μs at 253 K having the mean absolute sensitivity of −3.3 μs K−1. The simplicity in design, the high optical transmittance (around 90%) in the visible wavelength region of 450–800 nm, the insensitivity to atmospheric oxygen and the complete resistance to UV light provide technological and operational advantages of the proposed material. The findings demonstrated that the material is promising as a sensing element for luminescent thermometers suitable for long-term temperature monitoring in the range of 143–253 K. [ABSTRACT FROM AUTHOR]

New bis-1,3-diketone derivatives of calix[4]arene (3–5) have been synthesized with good yields by the addition of a sodium salt of acetylacetone, 1-benzoylacetone and dibenzoylmethane to 5,17-bis-(bromomethyl)-25,26,27,28-tetrahydroxycalix[4]arenes. The structural properties of the obtained compounds and their complexes have been established by means of IR, UV-Vis, NMR spectroscopy and quantum-chemical calculations. The complex ability of bis-1,3-diketones towards Al3+, Ni2+, Cu2+ and lanthanide ions (Nd3+, Eu3+, Tb3+) has been investigated by using a liquid–liquid extraction method. The UV-Vis data indicate thermodynamically favorable 1 : 1 complex formation of the ligands with Tb3+ in alkaline DMF, although the time required for the equilibration reveals the difference between calix[4]arenes bearing acetylaceton-, benzoylaceton- and dibenzoylmethane-substituents. The steric hindrance effect on keto–enol transformation is the reason for the difference. The ligand-centered emissions of Gd3+ complexes with benzoylaceton- and acetylaceton-substituted calix[4]arenes reveal them both as more convenient antennae for red and infra-red than for green lanthanide luminescence. Indeed, the benzoylaceton-substituted counterpart sensitizes Yb3+-centered luminescence to a good extent. Nevertheless, the luminescence of Tb3+ is sensitized by the acetylaceton-substituted counterpart to a better extent than that of Yb3+, while only poor red Eu3+ emission is observed under sensitization by both the ligands. [ABSTRACT FROM AUTHOR]

This is the first report on the synthesis and characterization of tetra-1,3-diketone derivatives of tetrthia- and calix[4]arenes substituted by acetylacetonyl or dipivaloylmethanyl moieties at the upper rim and bearing hydroxyl groups at the lower rim as ligands for Tb 3+ complexes. The spatial structure and tautomeric content for the synthesized ligands have been determined by means of X-ray, IR and NMR spectroscopy. Comparison of the sensitizing properties of tetrathiacalix[4]arenes and their calix[4]arene analogues on the Tb 3+ -centered luminescence in DMF solutions has been performed. A substantial enhancement of the luminescent properties of Tb 3+ - complexes with tetra-1,3-diketone ligands promoted by the tetrathiacalix[4]arene scaffold was established. [ABSTRACT FROM AUTHOR]