Luminescent Lanthanide Metal–Organic Frameworks for Temperature Sensing in Two Distinct Temperature Regions

Abstract

High Resolution Image Download MS PowerPoint Slide Luminescent ratiometric temperature sensors based on lanthanide(III) (Ln 3+ ) metal–organic frameworks (LnMOFs) have emerged as promising materials in nanothermometry due to their hybrid nature and unique photophysical and structural properties. These include high chromophore density and well-defined, robust crystalline structures enabling efficient energy transfer and high luminescence performance in various external conditions such as alternating temperatures. However, current LnMOF-based nanothermometers often require high loadings of emissive centers leading to concentration quenching and limited sensitivity and typically operate in a single-temperature region. In this work, we present a new series of LnMOFs based on the ligand 1,4-benzenedicarboxylic acid (H 2 BDC) and its 2-amino derivative (H 2 ABDC), with the general formula [La 1– x Ln x (BDC) 1– y (ABDC) y Cl(DMF)] (Ln = Eu, Tb, Sm, Dy; DMF = N, N -dimethylformamide; x = 0–0.5, y = 0–1). Photophysical studies revealed that (i) the MOF scaffolds can efficiently sensitize the visible-emitting Ln 3+ ions leading to quantum yields of up to 81%; (ii) mixed-ligand LnMOFs exhibit ligand-centered fluorescence lifetimes of 0.11–9 ns and exceptionally long phosphorescence lifetimes of 0.33 s. Additionally, we demonstrated the remarkable potential of mixed-metal-mixed-ligand LnMOFs, containing very low loadings of emissive components (up to 10 mol %), to function as ratiometric luminescence thermometers (RLTs) across a wide temperature range, including cryogenic (10–110 K) and ambient (70–330 K) temperatures. These LnMOFs exhibit relative sensitivities ( S rel ) of up to 11.1% K –1 in the cryogenic range and 2.2% K –1 at higher temperatures, comparable to the highest values reported in the literature.

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