AUTHOR=Félix Gautier , Kulakova Alena N. , Sene Saad , Khrustalev Victor N. , Hernández-Rodríguez Miguel A. , Shubina Elena S. , Pelluau Tristan , Carlos Luís D. , Guari Yannick , Carneiro Neto Albano N. , Bilyachenko Alexey N. , Larionova Joulia 

TITLE=Luminescent Ln3+-based silsesquioxanes with a β-diketonate antenna ligand: toward the design of efficient temperature sensors

JOURNAL=Frontiers in Chemistry

VOLUME=12

YEAR=2024

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2024.1379587

DOI=10.3389/fchem.2024.1379587

ISSN=2296-2646

ABSTRACT=<p>We report the synthesis and single-crystal X-ray diffraction, magnetic, and luminescence measurements of a novel family of luminescent cage-like tetranuclear silsesquioxanes (PhSiO<sub>1.5</sub>)<sub>8</sub>(LnO<sub>1.5</sub>)<sub>4</sub>(O)(C<sub>5</sub>H<sub>8</sub>O<sub>2</sub>)<sub>6</sub>(EtOH)<sub>2</sub>(CH<sub>3</sub>CN)<sub>2</sub>⋅2CH<sub>3</sub>CN (where Ln = Tb, <bold>1</bold>; Tb/Eu, <bold>2</bold>; and Gd, <bold>3</bold>), featuring seven-coordinated lanthanide ions arranged in a one-capped trigonal prism geometry. Compounds <bold>1</bold> and <bold>2</bold> exhibit characteristic Tb<sup>3+</sup> and Tb<sup>3+</sup>/Eu<sup>3+</sup>-related emissions, respectively, sensitized by the chelating antenna acetylacetonate (acac) ligands upon excitation in the UV and visible spectral regions. Compound <bold>3</bold> is used to assess the energies of the triplet states of the <italic>acac</italic> ligand. For compound <bold>1</bold>, theoretical calculations on the intramolecular energy transfer and multiphonon rates indicate a thermal balance between the <sup>5</sup>D<sub>4</sub> Stark components, while the mixed Tb<sup>3+</sup>/Eu<sup>3+</sup> analog <bold>2</bold>, with a Tb:Eu ratio of 3:1, showcases intra-cluster Tb<sup>3+</sup>-to-Eu<sup>3+</sup> energy transfer, calculated theoretically as a function of temperature. By utilizing the intensity ratio between the <sup>5</sup>D<sub>4</sub>→<sup>7</sup>F<sub>5</sub> (Tb<sup>3+</sup>) and <sup>5</sup>D<sub>0</sub>→<sup>7</sup>F<sub>2</sub> (Eu<sup>3+</sup>) transitions in the range 11–373 K, we demonstrate the realization of a ratiometric luminescent thermometer with compound <bold>2</bold>, operating in the range 11–373 K with a maximum relative sensitivity of 2.0% K<sup>−1</sup> at 373 K. These findings highlight the potential of cage-like silsesquioxanes as versatile materials for optical sensing-enabled applications.</p>