Abstracts

The application of lanthanide(3+) (Ln) ions for optical thermometry gained enormous attention in the last decade due to the possibility of temperature sensing via the emission signal originating from their f-f electronic transitions located in the wide vis-to-NIR window (C. D. S. Brites et al. Adv. Opt. Mater. 2019, 7, 1801239). Strong and tunable temperature-variable emission characteristics enable the contactless use of such thermometers in various aspects of industry and medicine. On the other hand, the development of Ln(III)-based single-molecule magnets (SMMs), i.e., magnetic entities showing a magnetic hysteresis loop at the level of a single paramagnetic center or single molecule, makes them promising in future high-performance data storage tools, quantum computing, and spintronic devices (D. N. Woodruff et al. Chem. Rev. 2013, 113, 5510). The conjunction of SMM behavior and optical thermometry based on Ln(III) complexes emerged a few years ago, as a method to develop future SMM-based technology with a self-monitoring temperature mechanism (R. Marin et al. Angew. Chem. Int. Ed. 2021, 60, 1728). This aim stems from the large sensitivity of SMM performance, such as the blocking temperature and the related magnetic relaxation times, on the temperature of the system. Up to now, different Ln(3+) ions have been tested in this aspect, starting from Dy(3+), the best-performing center for the construction of SMMs, and Yb(3+), well-known for its efficient near-infrared-centered f-f emission. In this field, we focused on the development of luminescent SMMs built of less common lanthanide centers, such as Ho(III) and Tb(III). Both of them show prominent SMM performance if only employed in the crystal field of proper symmetry. On the other hand, the Tb(III) is recognized for its use in luminescent thermometers when combined with Eu(3+) ions; however, its application for a single-center thermometry is quite limited, while Ho(III)-based systems show rather small potential as efficient solid-state luminophores. As the result of proper design, we discovered unique strategies to generate high-performance optical thermometers based on SMMs for those centers, which include luminescence re-absorption effect for Ho(III) complexes diluted in a luminescent matrix (J. Wang, J. J. Zakrzewski, et al. Chem. Sci. 2021, 12, 730), and generation of high-symmetry Tb(III) centers by the desolvation of a rigid Tb^III–[Co^III(CN)₆]^3– inorganic framework (J. Wang, J. J. Zakrzewski, et al. Angew. Chem. Int. Ed. 2023, 62, e202306372).