Herein, we report a comprehensive coordination study of the previously reported ligands cyclam, CB-cyclam TMC, DMC, CB-DMC, and of their C-functional analogues, cyclam-E, CB-cyclam-E, TMC-E, DMC-E and CB-DMC-E. This group of ligands includes cyclam, cross-bridged cyclams, their di-or tetramethylated derivatives and the analogues bearing an additional hydroxyethyl group on one β-N position of the ring. These Cu(II) and Zn(II) complexes of these macrocycles have been highlighted previously for the biological interest, but the details of their structures in the solid state and in solution remained largely unexplored. In particular, we analyzed the impact that adding non-coordinating Nmethyl and C-hydroxyethyl functionalities has in the structures of the complexes. All the Cu(II) and Zn(II) complexes were synthetized and investigated using single crystal X-ray diffraction and NMR, electronic absorption and EPR spectroscopies, along with DFT studies. Dissociation kinetics experiments in acidic conditions and an electrochemical study were also performed. A special attention was paid to analyze the different configurations present in solution and in the solid state, as well as the impact of the Cappended hydroxyethyl group on the coordination behavior. Various ratios of the trans-I, trans-III, and cis-V configurations have been observed depending on the degree of N-methylation and the presence of the ethylene cross-bridge.

We report a macrocyclic ligand (H 3 L 6 ) based on a 3,6,10,13-tetraaza-1,8(2,6)-dipyridinacyclotetradecaphane platform containing three acetate pendant arms and a benzyl group attached to the fourth nitrogen atom of the macrocycle. The X-ray structures of the Y L 6 and Tb L 6 complexes reveal nine coordination of the ligand to the metal ions through the six nitrogen atoms of the macrocycle and three oxygen atoms of the carboxylate pendants. A combination of NMR spectroscopic studies ( 1 H, 13 C, and 89 Y) and DFT calculations indicated that the structure of the Y L 6 complex in the solid state is maintained in an aqueous solution. The detailed study of the emission spectra of the Eu L 6 and Tb L 6 complexes revealed Ln 3+ -centered emission with quantum yields of 7.0 and 60%, respectively. Emission lifetime measurements indicate that the ligand offers good protection of the metal ions from surrounding water molecules, preventing the coordination of water molecules. The Y L 6 complex is remarkably inert with respect to complex dissociation, with a lifetime of 1.7 h in 1 M HCl. On the other hand, complex formation is fast (∼1 min at pH 5.4, 2 × 10 –5 M). Studies using the 90 Y-nuclide confirmed fast radiolabeling since [ 90 Y]Y L 6 is nearly quantitatively formed (radiochemical yield (RCY) > 95) in a short time over a broad range of pH values from ca. 2.4 to 9.0. Challenging experiments in the presence of excess ethylenediaminetetraacetic acid (EDTA) and in human serum revealed good stability of the [ 90 Y]Y L 6 complex. All of these experiments combined suggest the potential application of H 3 L 6 derivatives as Y-based radiopharmaceuticals.

We report a detailed investigation of the potential as magnetic resonance imaging (MRI) contrast agents of Fe(III) complexes with H4EDTA derivatives containing different spacers: trans-cyclohexane-1,2-diamine (t H4CDTA), cis-cyclohexane-1,2-diamine (c H4CDTA),...

anti-Stokes emission, UC is a process of choice for bio-analytical applications, removing spurious signals originating from autofluorescence of the samples and light scattering. Consequently, UC has found many applications such as in microscopy and photodynamic therapy, [2] remote cellular activation, [3] or bioassays. [4,5] However, these processes are typically observed in solid-state materials [6] or nanoparticles, [7] but a seminal example of energy transfer UC (ETU) at the molecular scale was reported by Piguet and co-workers in 2011, which consisted of a triply stranded Cr III -Er III -Cr III helicate. [8,9] In the subsequent years this has been expanded to encompass a range of discrete upconverting systems, operating by excited state absorption (ESA), [10][11][12] energy transfer UC, or cooperative sensitizaton (CS). [15][16][17][18] At the molecular scale, much attention must be paid to minimize quenching due to the increased prevalence of nonradiative de-excitation processes from molecules in solution, primarily through OH, NH, and CH oscillators in the first or second coordination sphere. [20][21][22] This is achieved by using sterically encumbering ligand systems, [23] deuteration of the ligand scaffold, [16] or using perdeuterated solvents. [16,24,25] One key impediment in the development of new molecular UC devices is the typical requirement to prepare heterometallic polyads, as is the case with CS systems comprising two or more Yb III sensitizers around Tb III or Ru II acceptors (Figure 1a). [17,26] This approach, despite its effectiveness, is onerous due to the similar chemical reactivity between lanthanides, [27,28] as is the case for mixed Yb/Tb systems, which constrains the synthetic accessibility. [15,16] Inspired by the pioneering work by Auzel [29] on solid-state materials, [30,31] we reported the first example of solution-state molecular cooperative luminescence (CL) using a Yb 9 cluster. [32] This entails double excitation of two proximate Yb III ions at 980 nm which produces emission from a virtual excited state at 503 nm via a two-photon process (Figure 1b). While it is a key tenet of UC processes that the efficiency of UC is improved using more donor ions, there also remains the possibility of concentration quenching, which has been observed in nanoparticles. [33,34] Furthermore, the two-photon power dependence of the UC observed in homo-nonanuclear Yb 9 clusters supports the accepted mechanism of the requirement of only two proximate Yb III ions. Conclusive confirmation of this dinuclear mechanism can only occur through removal of the extraneous Yb III donors to its fundamental form in a dimeric Yb 2 system (lex parsimoniae). This strategy is not feasible in either Two homometallic ytterbium dimers are prepared and their solution-state photoluminescence and upconversion properties are investigated. Both complexes exhibit two-photon cooperative luminescence upconversion in the visible region (λ em ≈ 510 nm) upon excitation into the near-infrared Yb 2 F 5/2 ← 2 F 7/2 absorption band at 98...

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