Impacts of β-Diketonate Terminal Ligands on Slow Magnetic Relaxation and Luminescence Thermometry in Dinuclear DyIII Single-Molecule Magnets Leveraging Subtle Local Coordination Modifications to Refine the Slow Relaxation of Magnetization and Enhance Luminescence Thermometry in Dinuclear DyIII Single-Molecule Magnets

Abstract

Lanthanide-based Single-Molecule Magnets (SMMs) with opto-magnetic properties provide a means to understand intrinsic energy levels of 4f ions and their influence on optical and magnetic behaviour. Fundamental understanding of their luminescent and slow relaxation of the magnetzation behaviour is critical for targetting and designing SMMs with multifunctionalities. Herein, we seek to investigate the role of DyIII coordination environment and fine electronic structure on the slow magnetic relaxation and luminescent thermometry. Our findings are illustrated through two distinct DyIII complexes, [Dy2bpm(hexd)6] (1) and [Dy2bpm(hpd)6] (2), (bpm = 2,20-bipyrimidine, hexd = 2,4-hexanedione, hpd = 3,5-Heptanedione), by comparing their features with a family of DyIII dinuclear species bridged by bpm. These findings highlight that the hexd- and hpd- ligand yields similar effective barrier to the reversal of magnetization (280 – 290 K). The values are among the highest for dinuclear DyIII complexes bridged by bpm, due to the low distortion of the DyIII coordination polyhedra and the long Dy–N equatorial bonds. Furthermore, the luminescence performance is affected by the triplet state energy of the terminal ligand, influencing ligand-to-DyIII energy transfer. The hpd- ligand's higher T1 state energy leads to poor ligand-to-DyIII energy transfer, limiting the use of 2 for luminescence thermometry. Conversely, this issue is absent in 1, which offers a relative thermal sensitivity of 0.1 to 0.7% K-1 (10 to 60 K) with a temperature uncertainty below 1 K. These findings contribute to our understanding of lanthanide-based SMMs and facilitate the design of multifunctional materials with tailored magnetic and luminescent properties for molecular electronics and beyond.