Toward Programmed Molecular Lanthanide Probes and Sensors

The peculiar spectroscopic properties of the lanthanide metal ions (4f-block, Lnlll), and particularly Eulll and Tblll, make them suitable for the design of chemical luminescent probes and analytical sensors when Lnlll is introduced into organized molecular architectures possessing controlled and protected coordination sites. The tridentate receptors 2,6-bis(1-alkylbenzimidazol-2-yl)pyridine (Li, i=2-7) play a crucial role since they react with Ln3+ to give mononuclear building blocks [Ln(Li)3]3+ where the metal ion is protected by the wrapping of the aromatic ligands. In these ultraviolet to visible light-converting devices (Ln=Eu, Tb), the size of the internal cavity is controlled by the three closely packed strands which produce i) a promising discrimination between Lnlll according to their sizes and ii) efficient light-harvesting resulting form the strong absoprtion of ultraviolet light by the ligands. These building blocks have been introduced into more sophisticated homodinuclear triple-helical complexes [Ln2(L8)3]6+ and statistical mixtures containing the heterodinuclear directional visible to visible light-converting device [EuTb(L8)3]6+. Improved molecular programming results form the use of acyclic segmental ligand possessing different binding units coded for one particular ion. The segmental ligands Li (i=9,10) discriminate Fell and AgI to give the heterodinuclear double helicate [FeAg(L10)2]3+ and the heterotrinuclear organometallic [2]-catenate [FeAg2(L9)2]4+ where each metal ion occupies a coordination site satisfying its stereochemical requirements. The receptor L11 recognizes 3d- and 4f-block metal ions to give the heterodinuclear d-f-triple-helical complexes [LnZn(L11)3]5+ where Znll occupies the pseudo-octahedral capping site and corresponds to a noncovalent tripod which properly organizes the strands for their coordination to Lnlll. In these new self-assembled lanthanide podates, predetermined structural and physical properties result form i) the judicious choice of the d-block ion associated with Lnlll and ii) the design of the tridentate unit bound to Lnlll. [LnFe(L11)3]5+ (Ln=La-Eu) display thermochromism and spin-crossover behavior while light emission can be increased by a factor 104 when going from [EuZn(L11)3]5+ to [EuZn(L12)3]5+. The design of tailored receptors for the preparation of stable lanthanide light-converting devices is discussed together with new characterization methods applied to complicated assembly processes in solution

Lanthanide Metal Ions as Cornerstones in Functional Self-Assembled Supramolecular Complexes

The peculiar spectroscopic, magnetic, and chemical properties of lanthanide ions (4f block, LnIII) are particularly attractive for the design of functional supramolecular devices if these ions can be selectively introduced into organized self-assembled architectures. The systematic investigation of a complete library of tridentate receptors leading to nine-coordinate tricapped trigonal prismatic sites upon coordination to LnIII allows the elucidation of the factors governing the structural, thermodynamic, electronic, magnetic, and spectroscopic properties of the final complexes. The simultaneous use of LnIII as cement between the molecular components of the supramolecular edifices and as functional vectors of the devices has been realized in self-assembled poly nuclear d-f and f-f complexes. Predetermined properties may result from a judicious molecular programming of the nanometric architecture leading to fascinating applications in luminescence, magnetism, template syntheses, and liquid crystals

Chiral Chromium(III) Complexes as Promising Candidates for Circularly Polarized Luminescence

This work is supported through grants from the Swiss National Science Foundation (grant 200020178758).The search for chiral chromophores with efficient circularly polarized luminescence (CPL) is an on-going hot topic in chemistry due to their potential applications in emerging fields such as spintronics and photonics. Beyond the largely exploited p-block, 4d/5d-block and f-block chiral entities, chiral chromium (III) complexes have recently attracted interest because of the abundancy of chromium in the earth’s crust, its kinetic inertness and its promising metal-centered Cr(2E) and Cr(2T1) phosphorescence. The associated spin-flip transitions could provide large dissymmetric factor (glum) and high luminescence quantum yields (ϕ) when six-membered strong-field chelate rings are coordinated to chiral six-coordinate Cr(III) centers. In this minireview, we intend to focus our attention on the state-ofthe- art for the design of pseudo-octahedral chiral mononuclear Cr(III) complexes for which chiroptical properties were investigated. The promising electronic properties of these complexes together with their low cost make these underexplored systems appealing candidates for CPL applications.Swiss National Science Foundation (SNSF) European Commission 20002017875