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

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

doi:10.3389/fchem.2024.1379587

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

Front Chem. 2024 Apr 3:12:1379587. doi: 10.3389/fchem.2024.1379587. eCollection 2024.

Authors

Affiliations

¹ CNRS, ENSCM, University Montpellier, Montpellier, France.
² Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Moscow, Russia.
³ Peoples' Friendship University of Russia (RUDN University), Moscow, Russia.
⁴ Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, Russia.
⁵ Phantom-g, Physics Department and CICECO-Aveiro Institute of Materials, University of Aveiro, Aveiro, Portugal.
⁶ Departamento de Física, Universidad de La Laguna San Cristóbal de La Laguna, Santa Cruz de Tenerife, Spain.

Abstract

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_1.5)₈(LnO_1.5)₄(O)(C₅H₈O₂)₆(EtOH)₂(CH₃CN)₂⋅2CH₃CN (where Ln = Tb, 1; Tb/Eu, 2; and Gd, 3), featuring seven-coordinated lanthanide ions arranged in a one-capped trigonal prism geometry. Compounds 1 and 2 exhibit characteristic Tb³⁺ and Tb³⁺/Eu³⁺-related emissions, respectively, sensitized by the chelating antenna acetylacetonate (acac) ligands upon excitation in the UV and visible spectral regions. Compound 3 is used to assess the energies of the triplet states of the acac ligand. For compound 1, theoretical calculations on the intramolecular energy transfer and multiphonon rates indicate a thermal balance between the ⁵D₄ Stark components, while the mixed Tb³⁺/Eu³⁺ analog 2, with a Tb:Eu ratio of 3:1, showcases intra-cluster Tb³⁺-to-Eu³⁺ energy transfer, calculated theoretically as a function of temperature. By utilizing the intensity ratio between the ⁵D₄→⁷F₅ (Tb³⁺) and ⁵D₀→⁷F₂ (Eu³⁺) transitions in the range 11-373 K, we demonstrate the realization of a ratiometric luminescent thermometer with compound 2, operating in the range 11-373 K with a maximum relative sensitivity of 2.0% K^-1 at 373 K. These findings highlight the potential of cage-like silsesquioxanes as versatile materials for optical sensing-enabled applications.

Keywords: energy transfer; lanthanides; luminescence; magnetism; silsesquioxanes; thermometry.

Grants and funding

The author(s) declare that financial support was received for the research, authorship, and/or publication of this article. This work was financially supported by the Russian Science Foundation (project No. 22-13-00250, synthetic and luminescent studies), the University of Montpellier and CNRS, and the project PRC2287 Premium 2019–2021. Elemental analysis data were collected using the equipment of the Center for Molecular Composition Studies of INEOS RAS with support from the Ministry of Science and Higher Education of the Russian Federation. JL acknowledges the Vernadsky program of the Embassy of France in the Russian Federation (2019–2021). This project was developed within the scope of the national program ANR (Project Hotspot), France. MAHR acknowledges the Beatriz Galindo Fellowship (BG22/00061). This work was also developed within the scope of the projects CICECO, Aveiro Institute of Materials, UIDB/50011/2020, UIDP/50011/2020, and LA/P/0006/2020 financed by Portuguese funds through the FCT/MCTES (PIDDAC).