Lanthanide Luminescence Thermometry and Slow Magnetic Relaxation in 3-D Polycyanidometallate-Based Materials

Abstract

Two three-dimensional (3-D) polycyanidometallate-based luminescent thermometers with the general formula {Ln4Co4(CN)24(4-benpyo)17(H2O)·7H2O} n Ln = (Dy­(III)­(1), Eu­(III)­(2)), based on the red-emissive diamagnetic linker [Co­(CN)6]3– and the bulky pyridine derivative that possesses the N-oxide moiety, 4-benzyloxy-pyridine N-oxide (benpyo), were prepared for the first time. The structure of compound 1 has been determined by single-crystal X-ray crystallography while the purity and structure of 2 have been confirmed by CHN, Fourier transform infrared spectroscopy (FT-IR), and powder X-ray diffraction (PXRD) analysis. Magnetic AC susceptibility measurements at zero field show no single-molecule magnet (SMM) behavior indicating fast relaxation operating in 1. Upon application of an optimal field of 2 kOe, the SMM character of compound 1 is revealed while the τ­(Τ) can be reproduced solely considering the Raman process τ–1 = CT n with C = 7.0901(3) s–1 K–n and n = 3.58(1), indicating that a high density of low-lying states and optical as well as acoustic phonons play a major role in the relaxation mechanism. Micron-sized superconducting quantum interference device (μ-SQUID) loops show a very narrow opening in agreement with the AC susceptibility studies and complete active space self-consistent field (CASSCF) calculations. The interaction operating between the Dy­(III) ions was quantified from CASSCF calculations. Good agreement is found by fitting the experimental DC χM Τ(Τ) and M(H), employing the Lines model, with J Lines = −0.087 cm–1 (−0.125 K). The excitation spectra of compound 2 are used for temperature sensing in the 25–325 nm range with a maximum relative thermal sensitivity, S r = 0.6% K–1 at 325 K, whereas compound 1 operates as a luminescent thermometer based on its emission features in the temperature range of 16–350 K with S r ≈ 2.3% K–1 at 240 K.

Toward Magneto‐Optical Cryogenic Thermometers with High Sensitivity: A Magnetic Circular Dichroism Based Thermometric Approach

“…In recent years, luminescence thermometry has been successfully demonstrated as a highly sensitive remote technique to probe temperature [1–3] . Several concepts have been employed to target different probing strategies, such as band‐shift, [7–9] lifetime, [10–12] energy‐transfer‐based ratiometric thermometry, [13–25] and single‐band, [26–38] each approach having its own advantages/disadvantages. In the presented context, bifunctional compounds acting as Single‐Molecule Magnet (SMM) and Stark‐sublevel ratiometric luminescent thermometers have been demonstrated as potential candidates for magnetic memory storage devices with real‐time temperature sensing [26–38] …”

“…Nevertheless, despite the demonstrated success of different approaches, implementing luminescence thermometry at very low temperatures (<10 K) remains a difficult task. Most temperature‐dependent processes that favor temperature‐related spectral changes, such as energy‐transfer (ET), hot bands population, and quenching pathways, are inefficient at such low temperatures [20–38] . Another potential limitation in luminescence thermometry with molecular complexes is the choice of ligands with adequate energy‐level position to promote an effective ET to the metal center and act as an efficient luminescent material.…”

“…[4][5][6] In recent years, luminescence thermometry has been successfully demonstrated as a highly sensitive remote technique to probe temperature. [1][2][3] Several concepts have been employed to target different probing strategies, such as band-shift, [7][8][9] lifetime, [10][11][12] energy-transfer-based ratiometric thermometry, [13][14][15][16][17][18][19][20][21][22][23][24][25] and single-band, [26][27][28][29][30][31][32][33][34][35][36][37][38] each approach having its own advantages/disadvantages. In the presented context, bifunctional compounds acting as Single-Molecule Magnet (SMM) and Stark-sublevel ratiometric luminescent thermometers have been demonstrated as potential candidates for magnetic memory storage devices with real-time temperature sensing.…”

Multifunctionality of luminescent molecular nanomagnets based on lanthanide complexes

“…For these candidates, optical thermometry was achieved, by us and other groups, by tracing the temperature variation of the detailed emission pattern where thermal depopulation of the m J levels, including those responsible for the strongly temperature-dependent hot bands, is observed. 83,198,[247][248][249][250] In our work, we searched for non-trivial approaches to achieve optical thermometry in Ln-SMMs constructed using cyanido metalloligands. We obtained dinuclear molecules, {[Ho III…”

“…For these candidates, optical thermometry was achieved, by us and other groups, by tracing the temperature variation of the detailed emission pattern where thermal depopulation of the m J levels, including those responsible for the strongly temperature-dependent hot bands, is observed. 83,198,247–250…”