Due to their reduced dimensionality, 2D materials show intriguing optical properties and strong light matter interaction. In particular group VI transition metal dichalcogenides (TMDs) have been extensively studied and proof of principle optical applications demonstrated. Most studies to date focus on individual mono-or bilayered micromechanically-exfoliated samples which often display significant variations between flakes. In this work, we study size-dependent optical properties of four group VI TMD materials; WS2; MoS2; WSe2 and MoSe2, each consisting of ensembles of nanosheets suspended in the liquid environment. Samples were produced by liquid phase exfoliation and size-selected using cascade centrifugation with size and layer number distributions quantified by statistical atomic force microscopy. Differences in lateral size and layer number are 2 reflected in systematic changes in the optical extinction and absorbance spectra, which we exploit to establish quantitative spectroscopic metrics to facilitate measurement of nanosheet dimensions for each of the four materials. The lowest energy resonance, referred to as Aexciton, is analyzed in more detail. In all cases, an exponential red-shift with increasing layer number is observed. Our experimental data, backed up with first principle calculations, reveals that the magnitude of the shift is dependent on the molecular mass of the central metal atom (W, Mo), while the rate at which the peak shifts from monolayer to bulk depends on the band gap of the semiconductor.

While Mn II complexes meet increasing interest in biomedical applications, ligands are lacking that enable high Mn II complex stability and selectivity vs. Zn II , the most relevant biological competitor. We report here two new bispidine derivatives, which provide rigid and large coordination cavities that perfectly match the size of Mn II , yielding eight-coordinate Mn II complexes with record stabilities. In contrast, the smaller Zn II ion cannot accommodate all ligand donors, resulting in highly strained and less stable six-coordinate complexes. Combined theoretical and experimental data (X-ray crystallography, potentiometry, relaxometry and 1 H NMR spectroscopy) demonstrate unprecedented selectivity for Mn II vs. Zn II (K MnL / K ZnL of 10 8 -10 10 ), in sharp contrast to the usual Irving-Williams behavior, and record Mn II complex stabilities and inertness with logK MnL close to 25.

As an essential metal ion and an efficient relaxation agent, Mn2+ holds a great promise to replace Gd3+ in magnetic resonance imaging (MRI) contrast agent applications, if its stable and inert complexation can be achieved. Toward this goal, four pyridine and one carboxylate pendants have been introduced in coordinating positions on the bispidine platform to yield ligand L3. Thanks to its rigid and preorganized structure and perfect size match for Mn2+, L3 provides remarkably high thermodynamic stability (log K MnL = 19.47), selectivity over the major biological competitor Zn2+ (log(K MnL/K ZnL) = 4.4), and kinetic inertness. Solid-state X-ray data show that [MnL3(MeOH)](OTf)2 has an unusual eight-coordinate structure with a coordinated solvent molecule, in contrast to the six-coordinate structure of [ZnL3](OTf), underlining that the coordination cavity is perfectly adapted for Mn2+, while it is too large for Zn2+. In aqueous solution, 17O NMR data evidence one inner sphere water and dissociatively activated water exchange (k ex 298 = 13.5 × 107 s–1) for MnL3. Its water proton relaxivity (r 1 = 4.44 mM–1 s–1 at 25 °C, 20 MHz) is about 30% higher than values for typical monohydrated Mn2+ complexes, which is related to its larger molecular size; its relaxation efficiency is similar to that of clinically used Gd3+-based agents. In vivo MRI experiments realized in control mice at 0.02 mmol/kg injected dose indicate good signal enhancement in the kidneys and fast renal clearance. Taken together, MnL3 is the first chelate that combines such excellent stability, selectivity, inertness and relaxation properties, all of primary importance for MRI use.

We report a nonadentate bispidine (3,7-diazabicyclo[3.3.1]nonane) that unveils the potential to bind theranostically relevant radionuclides, including indium-111, lutetium-177, and actinium-225 under mild labeling conditions. This radiopharmaceutical candidate allows the simultaneous application of imaging and treatment (radionuclide theranostics) without changing the type of the bioconjugate; that is, it allows the strong binding to an imaging and a therapeutic radionuclide by the same chelator. Since sophisticated coordination chemistry is required to achieve high thermodynamic and kinetic stability (inertness), it is not surprising that only a few chelators have been reported that are able to strongly bind several radionuclides to a satisfactory extent. Bispidine-derived ligands have proven to be ideal for di- and trivalent metal ions with generally fast complexation kinetics and high in vitro and in vivo stabilities. The presented (radio)complexes are formed under mild conditions (pH 6, <40 °C) and exhibit thermodynamic stability and inertness in human serum comparable to the corresponding DOTA complexes. The bispidine-based complexing agent was conjugated to a peptide, targeting somatostatin type 2 receptors (SSTR2), overexpressed on neuroendocrine tumors. The 177Lu- and 225Ac-labeled conjugates were investigated, considering their binding to two different SSTR2-positive cell lines, including the human pancreatic carcinoid tumor (BON-SSTR2+) and the murine pheochromocytoma cell line (MPC). The biodistribution and accumulation pattern in MPC tumor-bearing mice was also evaluated. The LuIII and AcIII complexes studied show how ligand structures can be optimized in general by extending the denticity and varying the donor set in order to allow for fast complex formation and medically relevant inertness.

Eu III , Tb III , Gd III and Yb III complexes of the nonadentate bispidine derivative L 2 (bispidine = 3,7-diazabicyclo [3.3.1]nonane) were successfully synthesized and their emission properties studied. The X-ray crystallography reveals full encapsulation by the nonadentate ligand L 2 that enforces to all Ln III cations a common highly symmetrical capped square antiprismatic (CSAPR) coordination geometry (pseudo C 4v symmetry). The well-resolved identical emission spectra in solid state and in solution confirm equal structures in both media. As therefore expected, this results in long-lived excited states and high emission quantum yields ([Eu III L 2 ] + , H 2 O, 298 K, τ = 1.51 ms, ϕ = 0.35; [Tb III L 2 ] + , H 2 O, 298 K, τ = 1.95 ms, ϕ = 0.68). Together with the very high kinetic and thermodynamic stabilities, these complexes are a possible basis for interesting biological probes.