Triplet‐State Position and Crystal‐Field Tuning in Opto‐Magnetic Lanthanide Complexes: Two Sides of the Same Coin

• Published in: Chemistry : a European journal 2019-11, Vol.25 (64), p.14625-14637
• Main Authors: Gálico, Diogo A., Marin, Riccardo, Brunet, Gabriel, Errulat, Dylan, Hemmer, Eva, Sigoli, Fernando A., Moilanen, Jani O., Murugesu, Muralee
• Format: Article
• Language: English
• Subjects: Atomic energy levels; Chemistry; lanthanides; Ligands; Liquid nitrogen; Luminescence; luminescence thermometry; Magnetic properties; Magnetism; Magnets; opto-magnetic properties; photoluminescence; single-molecule magnets; Spatial discrimination; Spatial resolution; Spintronics; Temperature; Terbium; Thermometers; Triplet state
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201902837

Lanthanide‐complex‐based luminescence thermometry and single‐molecule magnetism are two effervescent fields of research, owing to the great promise they hold from an application standpoint. The high thermal sensitivity achievable, their contactless nature, along with sub‐micrometric spatial resolution make these luminescent thermometers appealing for accurate temperature probing in miniaturised electronics. To that end, single‐molecule magnets (SMMs) are expected to revolutionise the field of spintronics, thanks to the improvements made in terms of their working temperature—now surpassing that of liquid nitrogen—and manipulation of their spin state. Hence, the combination of such opto‐magnetic properties in a single molecule is desirable in the aim of overcoming, among others, addressability issues. Yet, improvements must be made through design strategies for the realisation of the aforementioned goal. Moving forward from these considerations, we present a thorough investigation of the effect that changes in the ligand scaffold of a family of terbium complexes have on their performance as luminescent thermometers and SMMs. In particular, an increased number of electron‐withdrawing groups yields modifications of the metal coordination environment and a lowering of the triplet state of the ligands. These effects are tightly intertwined, thus, resulting in concomitant variations of the SMM and the luminescence thermometry behaviour of the complexes. Supported by ab initio calculations, we can rationally interpret the observed trends and provide solid foundations for the development of opto‐magnetic lanthanide complexes. Intertwined effects: Triplet‐state position and metal coordination environment synergistically determine the properties of opto‐magnetic lanthanide complexes. Both features are governed by the nature of the ligands. The introduction of electron‐withdrawing groups in the ligand scaffold impacts the performance of the complexes in terms of photoluminescence quantum yield, luminescence thermometry, and single‐molecule magnet behaviour.