We report the synthesis and full characterization of a family of phosphorus-containing polymethine cyanines (phospha-cyanines). The compounds are easily prepared in two steps, starting from readily ...available phosphanes. The impact of the P-substituents and the counterions on the structural and optical properties is investigated through a joint experimental/theoretical approach. Based on the study of the single-crystal X-ray diffraction structures, all phospha-cyanines present a bond length alternation close to zero, independently of the substituents and counterions, which indicates an ideal polymethine state. All these compounds display the typical cyanine-like UV–vis absorption with an intense and sharp transition with a vibronic shoulder despite possessing a reverse electronic configuration compared to “classical” cyanines. Time-dependent density-functional theory calculations allowed us to fully rationalize the optical properties (absorption/emission wavelengths, luminescence quantum yields). Interestingly, due to the tetrahedral shape of the P atom, the optical properties are independent of the counterion, which is in marked contrast with N-analogues, which enables predictive engineering of the phospha-cyanines regardless of the medium in which they are used.
A field-induced chiral Yb
Single-Molecule Magnet (SMM) displayed an unprecedented near-infrared circularly polarized luminescence (NIR-CPL) in the solid-state. The bridging ...bis(1,10-phenantro5,6b)tetrathiafulvalene triad (L) allowed an efficient sensitization of the NIR
F
→
F
emission while the NIR-CPL is associated to the f-f transitions of the Yb
ion bearing chiral β-diketonate derived-camphorate ancillary ligands.
A family of four mononuclear DyIII complexes of the guanidine-based ligand L L = tris(2-hydroxybenzylidene)triaminoguanidine with formulas DyLCl2(DMF)2·DMF·CH3OH (1), DyL2(CH3OH)2Br·H2O·3CH3OH (2), ...DyL2(H2O)2SCN·3H2O·CH3OH (3) and DyL2(CH3OH)2SCN·CH3CN·CH3OH (4) were successfully prepared by varying reaction conditions. Complex 1 is seven-coordinate, with three N2O from ligand L along with two equatorially trapped DMF molecules and two axial Cl- anions, adopting pentagonal bipyramidal D5h symmetry. Complexes 2-4 have somewhat similar structures with six donor N4O2 sites from two ligands and two O from corresponding solvent molecules, featuring a N4O4 octa-coordinate environment with triangular dodecahedron D2d symmetry. Magnetic investigations indicated that complex 1 did not demonstrate single-molecule magnetic behavior, while complexes 2-4 were single-ion magnets (SIMs) under zero applied DC field with the effective energy barriers (Ueff) of 207.3 (2), 222.5 (3) and 311.7 K (4), respectively. The different types of coordinated solvent molecules and counter anions caused changes in intermolecular interactions and coordination geometries that severely affected their magnetic dynamics. The magnetic behaviors of these complexes were investigated through complete-active space self-consistent field (CASSCF) calculations with the inclusion of spin-orbit effects. Calculations revealed that the measured differences in magnetic behaviors originated mainly from intermolecular and crystal-packing effects as isolated complexes 1-4 have almost identical electronic and magnetic properties.
Molecular materials that possess a toroidal moment associated to a non-magnetic ground state are known as single-molecule toroics (SMTs) and are usually planar molecules. Herein, we report a Dy
...cubane, namely Dy
(Bppd)
(μ
-OH)
(Pa)
(H
O)
⋅0.333 H
O (where BppdH=1,3-Bis(pyridin-4-yl)propane-1,3-dione and PaH=2-Picolinic acid) for which magnetometry measurements and state-of-art ab initio calculations highlight SMT behavior in a tridimensional structure (3D-SMT). The in-depth theoretical analysis on the resulting low-lying energy states, along with their variation in function of the magnetic exchange pathways, allows further light to be shed on the description of single-molecule toroics and identify the coupling scheme that better reproduces the observed data.
A series of europium and terbium complexes based on a functionalized triazacyclononane carboxylate or phosphinate macrocyclic ligand is described. The influence of the anionic group, that is, ...carboxylate, methylphosphinate, or phenylphosphinate, on the photophysical properties was studied and rationalized on the basis of DFT calculated structures. The nature, number, and position of electron‐donating or electron‐withdrawing aryl substituents were varied systematically within the same phenylethynyl scaffold in order to optimize the brightness of the corresponding europium complexes and investigate their two‐photon absorption properties. Finally, the europium complexes were examined in cell‐imaging applications, and selected terbium complexes were studied as potential oxygen sensors.
Ultrabright! A series of EuIII and TbIII triazacyclononane carboxylate and phosphinate complexes was prepared. The nature of the antenna was systematically investigated to optimize the brightness and determine the two‐photon absorption properties. Finally, the Eu complexes were examined in cell‐imaging applications, and selected terbium compounds were studied as potential oxygen sensors (see figure).
Lanthanide Single-Molecule Magnets (SMMs) fascinate the scientific community due to their plethora of potential applications ranging from data storage to spintronic devices and quantum computing. ...This review article proposes a comprehensive description of the influence of the nuclear spin,
i.e.
hyperfine interaction, on the magnetic properties of lanthanide SMMs and on quantum information processing of qudit. This influence is analysed for non-Kramers and Kramers lanthanide SMMs as well as for the electronic distribution of the electron in 4f orbitals
i.e.
oblate and prolate ions. Then the role of magnetic interactions in isotopically enriched polynuclear Dy(
iii
) SMMs is discussed. Finally the possible effect of superhyperfine interaction due to the nuclear spin of elements originating from the surrounding of the lanthanide centre is analyzed. The effect of nuclear spin on the dynamics of the lanthanide SMMs is demonstrated using different techniques such as magnetometry, muon spectroscopy (μ-SR), and Mössbauer and Resonance Vibrational Spectroscopies.
Isotopic enrichment in lanthanide compounds is a powerful tool to enhance our knowledge and the performance of single-molecule magnets and Qudit behaviors for potential applications in high density data storage and quantum information processing.
The physicochemical properties of cationic dioxa (1), azaoxa (2), and diaza (3) 6helicenes demonstrate a much higher chemical stability of the diaza adduct 3 (pKR+=20.4, Ered1/2
=−0.72 V) compared to ...its azaoxa 2 (pKR+=15.2, Ered1/2
=−0.45 V) and dioxa 1 (pKR+=8.8, Ered1/2
=−0.12 V) analogues. The fluorescence of these cationic chromophores is established, and ranges from the orange to the far‐red regions. From 1 to 3, a bathochromic shift of the lowest energy transitions (up to 614 nm in acetonitrile) and an enhancement of the fluorescence quantum yields and lifetimes (up to 31 % and 9.8 ns, respectively, at 658 nm) are observed. The triplet quantum yields and circularly polarized luminescence are also reported. Finally, fine tuning of the optical properties of the diaza 6helicene core is achieved through selective and orthogonal post‐functionalization reactions (12 examples, compounds 4–15). The electronic absorption is modulated from the orange to the far‐red spectral range (560–731 nm), and fluorescence is observed from 591 to 755 nm with enhanced quantum efficiency up to 70 % (619 nm). The influence of the peripheral auxochrome substituents is rationalized by first‐principles calculations.
In rainbows: The physicochemical properties of cationic dioxa, azaoxa, and diaza 6helicenes demonstrate remarkably high chemical stabilities, fluorescence from orange to the far‐red regions with non‐negligible quantum yields and lifetimes, and circularly polarized luminescence in the same ranges. Selective post‐functionalization of the diaza 6helicene introduces peripheral auxochrome substituents, the influence of which on the optical properties of the compounds was rationalized by first‐principles calculations (see figure).
The synthesis of molecules featuring different properties is a perpetual challenge for the chemists’ community. The coexistence and even more the synergy of those properties open new perspectives in ...the field of molecular devices and molecular electronics. In that sense, coordination chemistry contributed to the development of new functional molecules through, for instance, single-molecule magnets (SMMs) and light emitting molecules with potential applications in high capacity data storage and OLEDs, respectively. The appealing combination of both electronic properties into one single object may offer the possibility to have magnetized luminescent entities at nanometric scale. To that end, lanthanides seem to be one of the key ingredients since their peculiar electronic structures endow them with specific magnetic and luminescence properties. Indeed, lanthanides cover a wide range of emission wavelengths, from infrared to UV, which add up to a large variety of magnetic behaviors, from the fully isotropic spin (e.g., GdIII) to highly anisotropic magnetic moments (e.g., DyIII). In lanthanide complexes, ligands play a fundamental role because on one hand they govern the orientation of the magnetic moment of anisotropic lanthanides and on the other hand they can sensitize efficiently the luminescence. The design of appropriate organic ligands to elaborate such chemical objects with the desired property appears to be essential but remains a perpetual challenge. In this Account, we describe the design of lanthanide-based complexes that emit light, behave as SMMs, or combine both properties. We have paid peculiar attention to the design of ligands based on the tetrathiafulvalene (TTF) moiety. TTF and its derivatives are well-known chemical entities, stable at different oxidation states, and employed mainly in the synthesis of molecular conductors and superconductors. In addition to their redox properties, TTF-based derivatives act as organic chromophores for the sensitization of visible and near-infrared (NIR) luminescence of lanthanides. The mechanism of sensitization involves either antenna effect (energy transfer from the excited state) or photoinduced electron transfer. TTF-based ligands act also as structural agents in the conception of SMM in crystals. Such objects are obtained with the highly anisotropic DyIII ion in crystalline phase as well as in frozen solution with magnetic memory at helium-4 temperature (4 K). We highlight the influence of the magnetic dilution (both in amorphous solution and in diamagnetic crystalline matrix) and, particular case of dysprosium based SMMs, the effect of metal-centered isotope enrichment on the SMM properties. Our aim is not only to realize functional molecules but to rationalize both luminescence and magnetic properties on the basis of the structure of the molecules. These two properties are intimately intricate and governed by the electronic structure, which can be calculated and interpreted using modern quantum chemistry tools.
A family of europium (III) complexes based on a polydentate ligand functionalized by charge‐transfer antennae presents remarkable one‐ and two‐photon photophysical proper‐ties in water or buffer. A ...detailed analysis of their emission properties suggests that the wrapping of the ligand around the central rare‐earth ion results in an overall Cs symmetry in agreement with the theoretical simulation and that about 65–70 % of the emission intensity is concentrated in the hypersensitive 5D0→7F2 transition at 615 nm. Their brightness is excellent, in the range of the best lanthanide bioprobes making them very attractive for bio‐imaging experiments.
A family of europium (III) complexes based on a polydentate ligand functionalized by charge‐transfer antennae presents remarkable one‐ and two‐photon photophysical properties in water and an excellent brightness suitable for bio‐imaging applications.
Lanthanide ions when complexed by polyamino-polycarboxylate chelators form a class of compounds of paramount importance in several research and technological areas, particularly in the fields of ...magnetic resonance and molecular magnetism. Indeed, the gadolinium derivative is one of the most employed contrast agents for magnetic resonance imaging while the dysprosium one belongs to a new generation of contrast agents for T
2
-weighted MRI. In molecular magnetism, Single Molecule Magnets (SMMs) containing lanthanide ions have become readily popular in the chemistry and physics communities since record energy barriers to the reversal of magnetization were reported. The success of lanthanide complexes lies in their large anisotropy due to the contribution of the unquenched orbital angular momentum. However, only a few efforts have been made so far to understand how the f-orbitals can be influenced by the surrounding ligands. The outcomes have been rationalized using mere electrostatic perturbation models. In the archetype compound Na{Dy(DOTA) (H
2
O)}·4H
2
O (Na{DyDOTA}·4H
2
O) an unexpected easy axis of magnetization perpendicular to the pseudo-tetragonal axis of the molecule was found. Interestingly, a dependency of the orientation of the principal magnetization axis on the simple rotation of the coordinating apical water molecule (AWM) - highly relevant for MRI contrast - around the Dy-O
AWM
bond was predicted by
ab initio
calculations, too. However, such a behaviour has been contested in a subsequent paper justifying their conclusions on pure electrostatic assumptions. In this paper, we want to shed some light on the nature of the subtle effects induced by the water molecule on the magnetic properties of the DyDOTA archetype complex. Therefore, we have critically reviewed the structural models already published in the literature along with new ones, showing how the easy axis orientation can dangerously depend on the chosen model. The different computed behaviors of the orientation of the easy axis of magnetization have been rationalized as a function of the energy gap between the ground and the first excited doublet. Magneto-structural correlations together with a mapping of the electrostatic potential generated by the ligands around the Dy(
iii
) ion through a multipolar expansion have also been used to evidence and quantify the covalent contribution of the AWM orbitals.
The unexpected covalent contribution in the DOTADy-OH
2
bond revealed by
ab initio
calculations of the easy axis of magnetization through simple H
2
O rotations.
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