Single‐molecule magnets (SMMs) are at the forefront of new technological advances in quantum information processing and spintronics. Despite the recent impressive breakthroughs in extending the magnetic blocking temperatures beyond liquid‐nitrogen temperatures, significant challenges await in terms of integrating and addressing such compounds in devices. With this ultimate goal in mind, the design of multifunctional SMMs not only allows to imbue molecules of interest with specific properties that would allow for in situ monitoring of the SMM operation in real time, but can also provide critical insights into our understanding of the magnetic behaviour. In this Review, we highlight how magnetism and luminescence can be harmoniously combined within single molecules to achieve these objectives. The key design principles to attain the simultaneous combination of photoluminescence and slow relaxation of the magnetization are discussed, along with an outlook on how such molecules could be beneficial for emerging next‐generation spintronics devices.

The development and integration of Single-Molecule Magnets (SMMs) into molecular electronic devices continue to be an exciting challenge. In such potential devices, heat generation due to the electric current is a critical issue that has to be considered upon device fabrication. To read out accurately the temperature at the submicrometer spatial range, new multifunctional SMMs need to be developed. Herein, we present the first self-calibrated molecular thermometer with SMM properties, which provides an elegant avenue to address these issues. The employment of 2,2′-bipyrimidine and 1,1,1-trifluoroacetylacetonate ligands results in a dinuclear compound, [Dy 2 (bpm)(tfaa) 6 ], which exhibits slow relaxation of the magnetization along with remarkable photoluminescent properties. This combination allows the gaining of fundamental insight in the electronic properties of the compound and investigation of optomagnetic cross-effects (Zeeman effect). Importantly, spectral variations stemming from two distinct thermal-dependent mechanisms taking place at the molecular level are used to perform luminescence thermometry over the 5–398 K temperature range. Overall, these properties make the proposed system a unique molecular luminescent thermometer bearing SMM properties, which preserves its temperature self-monitoring capability even under applied magnetic fields.

A combined experimental and theoretical approach reveals the intricacies related to an YbIII complex, which functions dually as a SMM and a luminescent thermometer.

The spectrally narrow, long-lived luminescence of lanthanide ions makes optical nanomaterials based on these elements uniquely attractive from both a fundamental and applicative standpoint. A highly coveted class of such nanomaterials is represented by colloidal lanthanide-doped semiconductor nanocrystals (LnSNCs). Therein, upon proper design, the poor light absorption intrinsically featured by lanthanides is compensated by the semiconductor moiety, which harvests the optical energy and funnel it to the luminescent metal center. Although a great deal of experimental effort has been invested to produce efficient nanomaterials of that sort, relatively modest results have been obtained thus far. As of late, halide perovskite nanocrystals have surged as materials of choice for doping lanthanides, but they have non-negligible shortcomings in terms of chemical stability, toxicity, and light absorption range. The limited gamut of currently available colloidal LnSNCs is unfortunate, given the tremendous technological impact that these nanomaterials could have in fields like biomedicine and optoelectronics. In this Review, we provide an overview of the field of colloidal LnSNCs, while distilling the lessons learnt in terms of material design. The result is a compendium of key aspects to consider when devising and synthesizing this class of nanomaterials, with a keen eye on the foreseeable technological scenarios where they are poised to become front runners.* In their book "Understanding Chemistry", Pimentel and Sprately commented how "Lanthanum has only one important oxidation state in aqueous solution, the +3 state. With few exceptions, this tells the whole boring story about the other 14 Lanthanides". Scheme 1. Aspects discussed in this Review about colloidal Ln 3+ -doped semiconductor nanocrystals (LnSNCs). * In 1798, B. M. Tassaert reported the first coordination compound of cobalt and ammonia without, however, fully understanding the material. Passing through S. M. Jörgensen's chain theory to explain metal complexes, it was only in 1893 that A. Werner finally realized the existence of a principal (oxidation state) and auxiliary (coordination number) for the metal in that "odd" class of complex compounds (as Tassaert first referred to them).* This last statement is only partially true. There are slight changes in the position of the 4f-4f emission lines of Ln 3+ depending on the coordination environment of the ion. The extent of such shifts is of up to a few hundred wavenumbers at most and they occur because of the so-called nephelauxetic effect, where changes in the bond length between Ln 3+ and the surrounding anions result in variation of 4f electronic distribution. * A Lewis acid is a species that accepts lone electron pairs from a donor species (Lewis bases). The less (more) the Lewis acid is polarizable, the harder (softer) its acid character is, according to the hard soft acids bases (HSAB) theory. This acidity can be regarded as a measure of how "thirsty" for electrons a species is.* Preliminary information a...

In the context of light-mediated tumor treatment, the application of ultraviolet (UV) radiation can initiate drug release and photodynamic therapy. However, its limited penetration depth in tissues impedes the subcutaneous applicability of such radiation. On the contrary, near-infrared (NIR) light is not energetic enough to initiate secondary photochemical processes, but can pierce tissues at a significantly greater depth. Upconverting nanoparticles (UCNPs) unify the advantages of both extremes of the optical spectrum, they can be excited by NIR irradiation and emit UV light through the process of upconversion, effective NIR-to-UV generation being attained with UCNPs as large as 100 nm. However, in anticipation of biomedical applications, the size of UCNPs must be greatly minimized to favor their cellular internalization; yet straightforward size reduction negatively affects the NIR-to-UV upconversion efficiency. Herein, we propose a two-step strategy to obtain small yet bright lithium-based UCNPs. First, we synthesized UCNPs as small as 5 nm by controlling the relative amount of coordinating ligands, namely oleylamine (OM) and oleic acid (OA). Although these UCNPs were chemically unstable, particle coarsening via an annealing process in the presence of fresh OA yielded structurally stable and highly monodisperse sub-10 nm crystals. Second, we grew a shell with controlled thickness on these stabilized cores of UCNPs, improving the NIR-to-UV upconversion by orders of magnitude. Particularly in the case of LiYbF:Tm/LiYF UCNPs, their NIR-to-UV upconversion surpassed the gold standard 90 nm-sized LiYF:Tm, Yb UCNPs. All in all, these UCNPs show great potential within the biomedical framework as they successfully combine the requirements of small size, deep tissue NIR penetration and bright UV emission.