Luminescent materials based on copper complexes are currently receiving increasing attention because of their rich photophysical properties, opening a wide field of applications. The copper iodide clusters formulated [CuIL] (L = ligand), are particularly relevant for the development of multifunctional materials based on their luminescence stimuli-responsive properties. In this context, controlling and modulating their photophysical properties is crucial and this can only be achieved by thorough understanding of the origin of the optical properties. We thus report here, the comparative study of a series of cubane copper iodide clusters coordinated by different phosphine ligands, with the goal of analyzing the effect of the ligands nature on the photoluminescence properties. The synthesis, structural, and photophysical characterizations along with theoretical investigations of copper iodide clusters with ligands presenting different electronic properties, are described. A method to simplify the analysis of the P solid-state NMR spectra is also reported. While clusters with electron-donating groups present classical luminescence properties, the cluster bearing strong electron-withdrawing substituents exhibits original behavior demonstrating a clear influence of the ligands properties. In particular, the electron-withdrawing character induces a decrease in energy of the unoccupied molecular orbitals, that consequently impacts the emission properties. The modification of the luminescence thermochromic properties of the clusters are supported by density functional theory (DFT) calculations. This study demonstrates that the control of the luminescence properties of these compounds can be achieved through modification of the coordinated ligands, nevertheless the role of the crystal packing should not be underestimated.
The article presents the synthesis, structure, and bonding of a series of neutral and linear sandwich compounds with the cyclononatetraenyl (Cnt) ligand and divalent lanthanides. These compounds account for the emergence of the lanthanidocene series in reference to the ferrocene and uranocene. The synthetic strategy uses the solubility difference between two conformation isomers of the ligand as well as their isomerization induced by solvent coordination, yielding to the isomorphous and isostructural, neutral and rigorously linear sandwich complexes. The molecular structures highlight a Cnt-Ln-Cnt angle at 180° and a ring size close to the Cnt-Cnt (centroid) distance. A qualitative molecular orbital diagram is provided in D 9d symmetry and DFT calculations enforce the bonding model.
Two 1,1,4,4-tetracyanobutadiene (TCBD) derivatives were prepared by reaction of tetracyanoethylene with ynamides bearing either a pyrene or a perylene unit. They display luminescence that could be detected up to 1350 nm in the solid state.
We report persistent chiral organic mono-and diradical cations based on bicarbazole molecular design with an unprecedented stability dependence on the type of chirality, namely axial versus helical. An unusual chemical stability was observed for sterically unprotected axial bicarbazole radical, in comparison with monocarbazole and helical bicarbazole ones. Such results were experimentally and theoretically investigated, revealing an inversion in energy of the singly occupied molecular orbital (SOMO) and the doubly highest occupied molecular orbital (HOMO) in both axial and helical bicarbazole monoradicals, along with a subtle difference of electronic coupling between the two carbazole units, which is modulated by their relative dihedral angle and related to the type of chirality. Such findings allowed us to explore in-depth the SOMO-HOMO inversion (SHI) in chiral radical molecular systems and provide new insights regarding its impact on the stability of organic radicals. Finally, these specific electronic properties allowed us to prepare a persistent, intrinsically chiral, diradical which notably displayed near infrared electronic circular dichroism responses up to 1100 nm and almost degenerate singlet-triplet ground states with weak antiferromagnetic interactions evaluated by magnetometry experiments.
Luminescent mechanochromic materials exhibiting reversible changes of their emissive properties in response to external mechanical forces are currently emerging as an important class of stimuli-responsive materials because of promising technological applications. Here, we report on the luminescence mechanochromic properties of a [CuI(PPh)] copper iodide cluster presenting a chair geometry, being an isomer of the most common cubane form. This molecular cluster formulated [CuI(PPh)]·2CHCl (1) exhibits a highly contrasted emission response to manual grinding, and, interestingly, the optical properties of the ground phase present striking similarities with those of the cubane isomer. In order to understand the underlying mechanism, a comparison with two related compounds has been conducted. The first one is a pseudopolymorph of 1 formulated as [CuI(PPh)]·CHCl (2), which exhibits luminescent mechanochromic properties as well. The other one is also a chair compound but with a slightly different phosphine ligand, namely, [CuI(PPhCHCOH)] (3), lacking mechanochromic properties. Structural and optical characterizations of the clusters have been analyzed in light of previous electronic structure calculations. The results suggest an unpreceded mechanochromism phenomenon based on a solid-state chair → cubane isomer conversion. This study shows that polynuclear copper iodide compounds are particularly relevant for the development of luminescent mechanochromic materials.
The unique combination of a divalent organolanthanide fragment, Cp*2Yb, with bipyrimidine (bipym) and a palladium bis-alkyl fragment, PdMe2, allows the rapid formation and stabilization of a PdIV tris-alkyl moiety after oxidative addition with MeI. The crucial role of the organolanthanide fragment is demonstrated by the substitution of bipym by the 4,5,9,10-tetraazaphenanthrene ligand, which drastically modifies the electronic structure and tunes the stability of the PdIV species.
The first molecular Tm luminescence measurements are reported along with rare magnetic, X and Q bands EPR studies. Access to simple and soluble molecular divalent lanthanide complexes is highly sought for small-molecule activation studies and organic transformations using single-electron transfer processes. However, owing to their low stability and propensity to disproportionate, these complexes are hard to synthetize and their electronic properties are therefore almost unexplored. Herein we present the synthesis of [Tm(μ-OTf) (dme) ] , a rare and simple coordination compound of divalent thulium that can be seen as a promising starting material for the synthesis of more elaborated complexes. This reactive complex was structurally characterized by X-ray diffraction analysis and its electronic structure has been compared with that of its halide cousin TmI (dme) .
In the field of stimuli-responsive luminescent materials, mechanochromic compounds exhibiting reversible emission color changes activated by mechanical stimulation, present appealing perspectives in sensor applications. The mechanochromic luminescence properties of the molecular cubane copper iodide cluster [Cu4I4(PPh2(C6H4-CH2OH))4] (1), are reported in this study. This compound can form upon melting an amorphous phase giving an unprecedented opportunity to investigate the mechanochromism phenomenon. Because the mechanically induced crystalline-toamorphous transition is only partial, the completely amorphous phase represents the ultimate state of the mechanically altered phase. Furthermore, the studied compound could form two different crystalline polymorphs namely 1•CH3CN and 1•THF, allowing establishment of straightforward structureproperties relationships. Photophysical and structural characterizations of 1 in different states were performed and the experimental data were supported by theoretical investigations. Solid-state NMR (Nuclear Magnetic Resonance) analysis permit to quantify the amorphous part in the mechanically altered phase. IR (Infra-Red) and Raman analysis enabled identification of the spectroscopic signatures of each states. DFT (density functional theory) calculations led to assignment of both the NMR characteristics and the vibrational bands. Rationalization of the photoluminescence properties was also conducted with simulation of the phosphorescence spectra allowing an accurate interpretation of the thermochromic luminescence properties of this family of compounds. The combined study of crystalline polymorphism and amorphous state permit to get deeper into the mechanochromism mechanism that implies changes of the [Cu4I4] cluster core geometry. By combining multi-stimuli responsive properties, copper iodide clusters constitute an appealing class of compounds towards original functional materials.
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