Light responsive metal-organic frameworks as controllable CO-releasing cell culture substrates

A new carbon monoxide (CO)-releasing material has been developed by embedding a manganese carbonyl complex, MnBr(bpydc)(CO)3 (bpydc = 5, 5′-dicarboxylate-2, 2′-bipyridine) into a highly robust Zr(iv)-based metal-organic framework (MOF). Efficient and controllable CO-release was achieved under exposure to low intensity visible light. Size-controllable nanocrystals of the photoactive MOF were obtained and their CO-releasing properties were correlated with their crystal sizes. The photoactive crystals were processed into cellular substrates with a biocompatible polymer matrix, and the light-induced delivery of CO and its subsequent cellular uptake were monitored using a fluorescent CO-probe. The results discussed here demonstrate a new opportunity to use MOFs as macromolecular scaffolds towards CO-releasing materials and the advantage of MOFs for high CO payloads, which is essential in future therapeutic applications

A de novo strategy for predictive crystal engineering to tune excitonic coupling

In molecular solids, the intense photoluminescence (PL) observed for solvated dye molecules is often suppressed by nonradiative decay processes introduced by excitonic coupling to adjacent chromophores. We have developed a strategy to avoid this undesirable PL quenching by optimizing the chromophore packing. We integrated the photoactive compounds into metal-organic frameworks (MOFs) and tuned the molecular alignment by introducing adjustable “steric control units” (SCUs). We determined the optimal alignment of core-substituted naphthalenediimides (cNDIs) to yield highly emissive J-aggregates by a computational analysis. Then, we created a large library of handle-equipped MOF chromophoric linkers and computationally screened for the best SCUs. A thorough photophysical characterization confirmed the formation of J-aggregates with bright green emission, with unprecedented photoluminescent quantum yields for crystalline NDI-based materials. This data demonstrates the viability of MOF-based crystal engineering approaches that can be universally applied to tailor the photophysical properties of organic semiconductor materials

Tuning Optical Properties by Controlled Aggregation: Electroluminescence Assisted by Thermally‐Activated Delayed Fluorescence from Thin Films of Crystalline Chromophores

Several photophysical properties of chromophores depend crucially on intermolecular interactions. Thermally‐activated delayed fluorescence (TADF) is often influenced by close packing of the chromophore assembly. In this context, the metal‐organic framework (MOF) approach has several advantages: it can be used to steer aggregation such that the orientation within aggregated structures can be predicted using rational approaches. We demonstrate this design concept for a DPA‐TPE (diphenylamine‐tetraphenylethylene) chromophore, which is non‐emissive in its solvated state due to vibrational quenching. Turning this DPA‐TPE into a ditopic linker allows to grow oriented MOF thin films exhibiting pronounced green electroluminescence with low onset voltages. Measurements at different temperatures clearly demonstrate the presence of TADF. Finally, we show that the layer‐by‐layer process used for MOF thin film deposition allowed to integrate the TADF‐DPA‐TPE in a functioning LED device

Synthèse de complexes luminescents de platine (II) appliquée à la construction d'édifices multichromophoriques

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Synthèse de complexes luminescents de platine (II) appliquée à la construction d'édifices multichromophoriques

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Synthèse de complexes luminescents de platine (II) appliquée à la construction d édifices multichromophoriques

Les travaux réalisés durant cette thèse s articulent autour de deux grands axes. La première partie des travaux a consisté à étudier des complexes luminescents de platine(II). Une méthodologie de synthèse reposant sur une réaction de Diels-Alder nous a permis d obtenir une série de ligands de type phényl-bipyridine diversement fonctionnalisés. Nous avons obtenu les complexes de platine(II) correspondants et avons étudié et la variation de leurs propriétés photophysiques, en fonction de la nature des groupes fonctionnels présents sur le ligand ou directement connectés au centre métallique.La seconde partie du travail s intéresse à la conception de systèmes multichromophoriques autour d une plateforme structurante. Cette dernière est constituée par un système polyaromatique plan, présentant une symétrie C3, le truxène. La dissymétrisation du truxène nous a permis d obtenir des systèmes où s agencent en périphérie du truxène des fluorophores organiques dérivés du difluoroboradiazaindacène (Bodipy®) de différents niveaux énergétiques, d une part, et des fragments polypyridiniques d osmium(II), de ruthénium(II) et de platine(II) d autre part. Les études photophysiques de ces systèmes ont permis de mettre en évidence des transferts d énergie intramoléculaires très efficaces.The first part of the thesis is focused on the synthesis and photophysical properties of luminescent platinum(II) complexes. A series of diversely functionalized phenyl-bipyridine ligands were obtained using a synthetic methodology based on a retro-Diels-Alder reaction. The corresponding orthometallated platinum(II) complexes were obtained and the variation of their photophysical properties as a function of the appended functional groups, on the ligand or directly connected to the metal center, was investigated. The second part deals with the construction of multichromophoric arrays grafted on a central polyaromatic core with a C3 symetry: truxene. A synthetic methodology based on statistical coupling reactions allowed us to obtain systems where either highly efficient organic dyes derived from difluoroboradiazaindacenes (Bodipy®) or phosphorescent osmium(II), ruthenium(II) and platinum(II) polypyridine fragments are connected to the periphery of the truxene plateform. Photophysical studies allowed us to highlight very efficient intramolecular energy transfers between the different chromophores.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Click Chemistry on NiO Photocathode to Postfunctionalize a Diketopyrrolopyrrole Sensitizer by Naphthalene Diimide Electron Acceptor

This study addresses a practical aspect of hybrid dye-sensitized photoelectrochemical cells by exploring a simple method to prepare multicomponent systems. Building on a previously reported methodology based on a copper-free click chemistry dipolar cycloaddition of azide with activated alkyne, a naphthalene diimide (NDI) derivative substituted with two propiolic esters was clicked on a NiO photocathode already coated with a diketopyrrolopyrrole (DPP) dye bearing two azido groups. A detailed photophysical study by transient absorption spectroscopy demonstrates that optical excitation of DPP dye leads to an effective electron transfer chain from the NiO valence band to the NDI passing via the DPP dye, resulting in a long-lived charge-separated state (hole in NiO/NDI radical anion) of 170 μs. The p-type dye-sensitized solar cells were also fabricated with the above molecular components and confirm the occurrence of the electron transfer as the performances of the solar cells were improved in terms of Voc and Jsc compared to the DPP dye lacking the NDI unit. The above-clicked system was also compared to a covalently linked DPP–NDI dyad, whose performances are 30% superior to the clicked system probably due to longer mean distance between the NiO surface and the NDI with the dyad. This finding paves the way for the design of multicomponent hybrid dye-sensitized photoelectrochemical cells by chemistry on the electrode

Structuring of metal–organic frameworks at the mesoscopic/macroscopic scale

International audienceThe assembly of metal ions with organic ligands through the formation of coordination bonds gives crystalline framework materials, known as metal–organic frameworks (MOFs), which recently emerged as a new class of porous materials. Besides the structural designability of MOFs at the molecular length scale, the researchers in this field very recently made important advances in creating more complex architectures at the mesoscopic/macroscopic scale, in which MOF nanocrystals are used as building units to construct higher-order superstructures. The structuring of MOFs in such a hierarchical order certainly opens a new opportunity to improve the material performance via design of the physical form rather than altering the chemical component. This review highlights these superstructures and their applications by categorizing them into four dimensionalities, zero-dimensional (0D), one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) superstructures. Because the key issue for structuring of MOFs is to spatially control the nucleation process in desired locations, this review conceptually categorizes the available synthetic methodologies from the viewpoint of the reaction system

Antenna Doping: The Key for Achieving Efficient Optical Wavelength Conversion in Crystalline Chromophoric Heterolayers

High‐yield wavelength conversion is one of the key requirements for efficient photon energy harvesting. Attempts to realize efficient conversion by simply stacking layers of chromophores have failed so far, even when using highly crystalline assemblies and employing the recently discovered long‐range (>100 nm) Förster resonance energy transfer (LR‐FRET). Optical conversion efficiency is drastically improved using chromophoric metal–organic framework heterolayers fabricated layer‐by‐layer in connection with an “antenna doping” strategy. Systematic investigations reveal that the LR‐FRET mechanism, reported previously in chromophoric aggregates, is highly anisotropic for neat materials but can be made more isotropic by employing doping strategies. Using optimized fabrication parameters and dopant concentrations, a three‐layer, two‐step cascade with an overall optical conversion efficiency of ≈75% is realized