Self-Assembled Tetrahedral [CrL] Cage Displaying Near-Infrared Spin-Flip Photoluminescence.

The thermodynamically controlled self-assembly of bis-bidentate quaterpyridine ligand, L = 2,2':5',5″:2″,2‴-quaterpyridine, with Cr and subsequent oxidation to Cr yields the first photoluminescent tetrahedral [CrL] molecular cage. Single-crystal X-ray diffraction reveals the presence of two homochiral cages (ΛΛΛΛ and ΔΔΔΔ) in the unit cell that crystallize as a racemic mixture. Additionally, a PF anion is observed inside the cavity, in line with isostructural cages built with Ni or Fe.

Complex-as-Ligand Strategy as a Tool for the Design of a Binuclear Nonsymmetrical Chromium(III) Assembly: Near-Infrared Double Emission and Intramolecular Energy Transfer.

The chromium(III) polypyridyl complexes are appealing for their long-lived near-infrared (NIR) emission reaching the millisecond range and for the strong circularly polarized luminescence of their isolated enantiomers. However, harnessing those properties in functional polynuclear Cr devices remains mainly inaccessible because of the lack of synthetic methods for their design and functionalization. Even the preparation and investigation of most basic nonsymmetrical Cr dyads exhibiting directional intramolecular intermetallic energy transfer remain unexplored.

Luminescent polypyridyl heteroleptic Cr complexes with high quantum yields and long excited state lifetimes.

Implementing high quantum yields and long-lived excited state lifetimes within heteroleptic luminescent CrIII complexes is a keystone for the design of supramolecular energy-converting devices exploiting this cheap metal. In this contribution, we discuss the stepwise and rational optimization of these two limiting factors within a series of heteroleptic CrIII complexes.

Beyond Chiral Organic (p-Block) Chromophores for Circularly Polarized Luminescence: The Success of d-Block and f-Block Chiral Complexes.

Chiral molecules are essential for the development of advanced technological applications in spintronic and photonic. The best systems should produce large circularly polarized luminescence (CPL) as estimated by their dissymmetry factor ( ), which can reach the maximum values of -2 ≤ ≤ 2 when either pure right- or left-handed polarized light is emitted after standard excitation. For matching this requirement, theoretical considerations indicate that optical transitions with large magnetic and weak electric transition dipole moments represent the holy grail of CPL.

Dual switchable molecular tweezers incorporating anisotropic Mn-salphen complexes.

An alternative strategy for the synthesis of terpyridine based switchable molecular tweezers has been developed to incorporate anisotropic Mn(iii)-salphen complexes. The free ligand was synthesized using a building block strategy based on Sonogashira coupling reactions and was then selectively metalated with manganese in a last step. The conformation of the tweezers was switched from an open 'W' shaped form to a closed 'U' form by Zn(ii) coordination to the terpyridine unit bringing the two Mn-salphen moieties in close spatial proximity as confirmed by X-ray crystallography.

Key Strategy for the Rational Incorporation of Long-Lived NIR Emissive Cr(III) Chromophores into Polymetallic Architectures.

The CrN chromophores are particularly appealing for low-energy sensitization via energy transfer processes since they show extremely long excited state lifetimes reaching the millisecond range in the technologically crucial near-infrared domain. However, their properties were barely harnessed in multimetallic structures because of the lack of both monitoring methods and accessible synthetic pathways. We herein report a remedy to monitor and control the formation of Cr-containing assemblies in solution via the design of a CrN inert "complex-as-ligand" that can be included into polymetallic architectures.

Chiral Molecular Ruby [Cr(dqp)] with Long-Lived Circularly Polarized Luminescence.

The chiral resolution of a kinetically inert molecular ruby [Cr(dqp)] (, dqp = 2,6-di(quinolin-8-yl)pyridine) displaying strong dual light emission at room temperature has been achieved. The wrapped arrangement of the six-membered dqp chelating ligands around the Cr(III) provided nonplanar helical conformations leading to the diastereoselective assembly of chiral bis-tridentate monometallic Cr(III)-helix. The (+)-[Cr(dqp)] and -(-)-[Cr(dqp)] enantiomers could be separated and isolated by using cation-exchange chromatography and subsequent salt-metathesis with KPF.

Versatile heteroleptic bis-terdentate Cr(iii) chromophores displaying room temperature millisecond excited state lifetimes.

Substitution of Ru(ii)-based chromophores with cheaper Cr(iii)-based complexes in optically active metallo-supramolecular architectures is limited by the lack of synthetic strategies leading to heteroleptic Cr(iii)-polypyridyl complexes with long excited-state lifetimes. Herein, we report on a versatile method yielding heteroleptic bis(terdentate) Cr(iii) complexes with room temperature millisecond range excited-state lifetimes, tuneable electronic and photophysical properties and easy anchoring possibilities.

Heteroleptic Ter-Bidentate Cr(III) Complexes as Tunable Optical Sensitizers.

To exploit Cr(III) coordination complexes as sensitizers in supramolecular energy-converting devices, the latter optical relays should display long-lived excited states, broad emission bands, and tunable spatial and electronic connections to activator units. An ad-hoc versatile strategy has been therefore developed for the preparation of a family of luminescent pseudo-octahedral [CrN] chromophores made up of ter-bidentate heteroleptic [Cr(phen)(N-N'')] complexes, where phen is 1,10-phenanthroline, and N-N' stands for α,α'-diimine ligands possessing peripheral substituents compatible with both electronic tuning and structure extensions. As long as the ligand field in these [CrN] chromophores remains sufficiently strong to avoid back-intersystem crossing, photophysical studies indicate that the lifetime of the near-infrared emissive Cr(E) excited state is poorly sensitive to ligand-based electronic effects.

Synthesis and Guest Recognition of Switchable Pt-Salphen Based Molecular Tweezers.

Molecular tweezers are artificial receptors that have an open cavity generated by two recognition units pre-organized by a spacer. Switchable molecular tweezers, using a stimuli-responsive spacer, are particularly appealing as prototypes of the molecular machines that combine mechanical motion and allosteric recognition properties. In this present study, the synthesis of switchable molecular tweezers composed of a central terpyridine unit substituted in 4,4″ positions by two Pt(II)-salphen complexes is reported.

Cr as an alternative to Ru in metallo-supramolecular chemistry.

Compared to divalent ruthenium coordination complexes, which are widely exploited as parts of multi-component photonic devices, optically active trivalent chromium complexes are under-represented in multi-metallic supramolecular architectures performing energy conversion mainly because of the tricky preparation of stable heteroleptic Cr building blocks. We herein propose some improvements with the synthesis of a novel family of kinetically inert heteroleptic bis-terdentate mononuclear complexes, which can be incorporated into dinuclear rod-like dyads as a proof-of-concept. The mechanism and magnitude of intermetallic CrCr communication have been unraveled by a combination of magnetic, photophysical and thermodynamic investigations.

Six States Switching of Redox-Active Molecular Tweezers by Three Orthogonal Stimuli.

A six level molecular switch based on terpyridine(Ni-salphen) tweezers and addressable by three orthogonal stimuli (metal coordination, redox reaction, and guest binding) is reported. By a metal coordination stimulus, the tweezers can be mechanically switched from an open "W"-shaped conformation to a closed "U"-shaped form. Theses two states can each be reversibly oxidized by the redox stimulus and bind to a pyrazine guest resulting in four additional states.

Mechanical switching of magnetic interaction by tweezers-type complex.

A control of the interaction between two spin centers was achieved by using a mechanical motion in a terpy(Cu-salphen)2 complex. Upon coordination a conformation change and switching from a paramagnetic to an antiferromagnetically coupled system was observed by EPR and SQUID measurements.

Switchable platinum-based tweezers with Pt-Pt bonding and selective luminescence quenching.

Molecular tweezers incorporating peripheral platinum salphen complexes and a central chelating terpyridine group have been synthesized. The terpyridine can be switched upon metal binding between a free 'W' shaped form and a coordinated 'U' form. The crystallographic structure of the zinc-closed molecular tweezers was obtained and presented a strong π-stacking between the Pt-salphen units associated with a Pt-Pt bond.

Terpy(Pt-salphen)2 switchable luminescent molecular tweezers.

The design and synthesis of switchable molecular tweezers based on a luminescent terpy(Pt-salphen)2 (1; terpy=terpyridine) complex is reported. Upon metal coordination, the tweezers can switch from an open "W"-shaped conformation to a closed "U"-shaped form that is adapted for selective recognition of cations. Closing of the tweezers by metal coordination (M=Zn(2+), Cu(2+), Pb(2+), Fe(2+), Hg(2+)) was monitored by (1)H NMR and/or UV/Vis titrations.