An air-stable high-performance single-molecule magnet operating as a luminescent thermometer below its blocking temperature

Abstract

The field of molecule magnets has advanced significantly in recent years. Yet, key challenges persist for their practical applications, such as achieving higher blocking temperatures and maintaining precise temperature control in air-stable magnets. This work addresses aspects related to both challenges. Thus, it presents the air-stable hexagonal bipyramidal compound {[Dy(LN6en)(OSiPh3)2](BPh4)}·1.5CH2Cl2 (1·1.5CH2Cl2) and its diluted analogue {[Dy0.1Y0.9(LN6en)(OSiPh3)2](BPh4)}·1.5CH2Cl2 (1@Y·1.5CH2Cl2). Their high axiality, achieved by reducing equatorial charge, enables magnetic behaviour with energy barriers higher than 1500 K and blocking temperatures based on hysteresis (TBH) of 12 and 40 K, respectively. Hence, 1@Y·1.5CH2Cl2 is the SMM with the highest TBH reported among air-stable uncapsulated molecule magnets. Besides, both complexes show temperature-dependent luminescence. Remarkably, 1@Y·1.5CH2Cl2 stands out as the pioneering example of a bifunctional molecule magnet and luminescent thermometer with both functionalities active below its T_B^H. This breakthrough makes it possible to monitor the temperature of a molecule in the range where it exhibits remanent magnetization for the first time. Moreover, this molecular material presents by far the best magnetic characteristics (Ueff and TBH) of any SMM luminescent thermometer reported to date. Experimental magnetic and luminescent data are analysed using theoretical calculations. Notably, luminescence is interpreted via coupled cluster methods, offering a more sophisticated alternative to the traditional time-dependent DFT approach.