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1. Luminescent lanthanide complexes with a pyridine-bis(carboxamide)-bithiophene sensitizer showing wavelength-dependent singlet oxygen generation

   https://doi.org/10.1039/d0dt01034k  

   Johnson, Katherine R.; Vittardi, Sebastian B.; Gracia-Nava, Manuel A.; Rack, Jeffrey J.; de Bettencourt-Dias, Ana (May 2020, Dalton Transactions)

   A new pyridine-bis(carboxamide)-based ligand with a bithiophene pendant, 2Tcbx, was synthesized. Its lanthanide ion (Ln III ) complexes, [Ln(2Tcbx) 2 ] 3+ , were isolated and their photophysical properties were explored. Upon excitation at 360 nm, these complexes display emission in the near-infrared (NIR) with efficiencies of 0.69% for Ln III = Yb III , 0.20% for Ln III = Nd III , and 0.01% for Ln III = Er III , respectively. Concurrent 1 O 2 formation was seen for all complexes, with efficiencies of 19% for the Yb III complex, 25% for the Nd III complex, and 9% for the Er III complex. When exciting at a longer wavelength, 435 nm, only Ln III emission was observed and larger efficiencies of Ln III -centered emission were obtained. The lack of 1 O 2 generation indicates that energy pathways involving different ligand conformations, which were investigated by transient absorption spectroscopy, are involved in the sensitization process, and enable the wavelength-dependent generation of 1 O 2 . 

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2. Accessing lanthanide-based, in situ illuminated optical turn-on probes by modulation of the antenna triplet state energy

   https://doi.org/10.1039/d1sc02148f  

   Cosby, Alexia G.; Woods, Joshua J.; Nawrocki, Patrick; Sørensen, Thomas J.; Wilson, Justin J.; Boros, Eszter (July 2021, Chemical Science)

   Luminescent lanthanides possess ideal properties for biological imaging, including long luminescent lifetimes and emission within the optical window. Here, we report a novel approach to responsive luminescent Tb( iii ) probes that involves direct modulation of the antenna excited triplet state energy. If the triplet energy lies too close to the 5 D 4 Tb( iii ) excited state (20 500 cm −1 ), energy transfer to 5 D 4 competes with back energy transfer processes and limits lanthanide-based emission. To validate this approach, a series of pyridyl-functionalized, macrocyclic lanthanide complexes were designed, and the corresponding lowest energy triplet states were calculated using density functional theory (DFT). Subsequently, three novel constructs L3 (nitro-pyridyl), L4 (amino-pyridyl) and L5 (fluoro-pyridyl) were synthesized. Photophysical characterization of the corresponding Gd( iii ) complexes revealed antenna triplet energies between 25 800 and 30 400 cm −1 and a 500-fold increase in quantum yield upon conversion of Tb( L3 ) to Tb( L4 ) using the biologically relevant analyte H 2 S. The corresponding turn-on reaction can be monitored using conventional, small-animal optical imaging equipment in presence of a Cherenkov radiation emitting isotope as an in situ excitation source, demonstrating that antenna triplet state energy modulation represents a viable approach to biocompatible, Tb-based optical turn-on probes. 

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3. New up-conversion luminescence in molecular cyano-substituted naphthylsalophen lanthanide( iii ) complexes

   https://doi.org/10.1039/D0CC08128K  

   Monteiro, Jorge H.; Hiti, Ethan A.; Hardy, Emily E.; Wilkinson, Grant R.; Gorden, John D.; Gorden, Anne E.; de Bettencourt-Dias, Ana (March 2021, Chemical Communications)

   null (Ed.)

   A new naphthylsalophen and its 3 : 2 ligand-to-lanthanide sandwich-type complexes were isolated. When excited at 380 nm, the complexes display the characteristic metal-centred emission for Nd III , Er III and Yb III . Upon 980 nm excitation, in mixed lanthanide and the Er complexes, Er-centred upconversion emission at 543 and 656 nm is observed, with power densities as low as 2.18 W cm −2 . 

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4. Solution structure of a europium–nicotianamine complex supports that phytosiderophores bind lanthanides

   https://doi.org/10.1039/D0CP06150F  

   Kaliakin, Danil S.; Sobrinho, Josiane A.; Monteiro, Jorge H.; de Bettencourt-Dias, Ana; Cantu, David C. (February 2021, Physical Chemistry Chemical Physics)

   null (Ed.)

   We report the solution structure of a europium-nicotianamine complex predicted from ab initio molecular dynamics simulations with density functional theory. Emission and excitation spectroscopy show that the Eu 3+ coordination environment changes in the presence of nicotianamine, suggesting complex formation, such as what is seen for the Eu 3+ –nicotianamine complex structure predicted from computation. We modeled Eu 3+ –ligand complexes with explicit water molecules in periodic boxes, effectively simulating the solution phase. Our simulations consider possible chemical events ( e.g. coordination bond formation, protonation state changes, charge transfers), as well as ligand flexibility and solvent rearrangements. Our computational approach correctly predicts the solution structure of a Eu 3+ –ethylenediaminetetraacetic acid complex within 0.05 Å of experimentally measured values, backing the fidelity of the predicted solution structure of the Eu 3+ –nicotianamine complex. Emission and excitation spectroscopy measurements were also performed on the well-known Eu 3+ –ethylenediaminetetraacetic acid complex to validate our experimental methods. The electronic structure of the Eu 3+ –nicotianamine complex is analyzed to describe the complexes in greater detail. Nicotianamine is a metabolic precursor of, and structurally very similar to, phytosiderophores, which are responsible for the uptake of metals in plants. Although knowledge that nicotianamine binds europium does not determine how plants uptake rare earths from the environment, it strongly supports that phytosiderophores bind lanthanides. 

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5. Chemical design of electronic and magnetic energy scales of tetravalent praseodymium materials

   https://doi.org/10.1038/s41467-023-38431-7  

   Ramanathan, Arun; Kaplan, Jensen; Sergentu, Dumitru-Claudiu; Branson, Jacob A.; Ozerov, Mykhaylo; Kolesnikov, Alexander I.; Minasian, Stefan G.; Autschbach, Jochen; Freeland, John W.; Jiang, Zhigang; et al (December 2023, Nature Communications)

   Abstract Lanthanides in the trivalent oxidation state are typically described using an ionic picture that leads to localized magnetic moments. The hierarchical energy scales associated with trivalent lanthanides produce desirable properties for e.g., molecular magnetism, quantum materials, and quantum transduction. Here, we show that this traditional ionic paradigm breaks down for praseodymium in the tetravalent oxidation state. Synthetic, spectroscopic, and theoretical tools deployed on several solid-state Pr 4+ -oxides uncover the unusual participation of 4 f orbitals in bonding and the anomalous hybridization of the 4 f 1 configuration with ligand valence electrons, analogous to transition metals. The competition between crystal-field and spin-orbit-coupling interactions fundamentally transforms the spin-orbital magnetism of Pr 4+ , which departs from the J eff  = 1/2 limit and resembles that of high-valent actinides. Our results show that Pr 4+ ions are in a class on their own, where the hierarchy of single-ion energy scales can be tailored to explore new correlated phenomena in quantum materials. 

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