Synthesis of an Electrodeficient Dipyridylbenzene-like Terdentate Ligand: Cyclometallating Ligand for Highly Emitting Iridium(III) and Platinum(II) Complexes

Cyclometallated iridium(III) and platinum(II) complexes are intensely used in optoelectronics for their photophysical properties and ability to convert excitons from singlet to triplet state, thus improving the device efficiency. In this contribution, we report the multi-steps synthesis of an electrodeficient dipyridylbenzene-like terdentate ligand [N^C^N], namely 2′,6′-dimethyl-2,3′:5′,2″-terpyridine (6), with 18% overall yield. Compound 6 has been employed to synthesize two phosphorescent complexes of platinum(II) and iridium(III), namely compounds 7 and 8, respectively. Both complexes have been characterized by NMR and high resolution mass spectrometry, and demonstrate high luminescence quantum yields in a deaerated solution at room temperature, with 18% and 61% for 7 and 8, respectively. If the iridium(III) complex displays similar emission properties to [Ir(dpyx)(ppy)Cl] (dpyx = 3,5-dimethyl-2,6-dipyridylbenzene and ppy = 2- phenylpyridine), the platinum(II) derivative, with λem = 470 nm, is a rare example of a fluorine atom-free blue emitting [N^C^N]PtCl complex

Ingénierie moléculaire de complexes de platine (application à la détection de cations par luminescence)

Les complexes de platine (II) cyclométallés et à ligand acétylure ont une phosphorescence intense et sensible à l environnement chimique. Leur utilisation en tant que sondes luminescentes est en accord avec le besoin actuel de nouveaux matériaux moléculaires. Nous avons choisi d incorporer sur le ligand acétylénique un récepteur apte à la coordination de cations de métaux de transition. Le choix du motif a été motivé par ses aptitudes à la fois à la coordination de cations et à modifier les propriétés luminescentes. Notre stratégie s est révélée être fructueuse avec le développement de complexes sélectifs, notamment à l ion plomb (II). La coordination du cation par le récepteur provoque des réponses très variées: exaltation de l émission, extinction de l émission, basculement phosphorescence à fluorescence. Ces processus sont explicités au cours des différents chapitres de cette thèse.Cyclometallated platinum (II) acetylide complexes are known for their strong phosphorescence which is versatile to the chemical environment. The development of such complexes is in adequacy to the current need in luminescent molecular. We have designed and synthesized Pt acetylide complexes incorporating various binding sites for transition metal cation. The choice of the receptor is based on both its fitness in the cation binding ability and in contribution to the luminescence properties of the complex. Our strategy was successful; we found series of complexes which are able to bind selectively lead cation. In addition, cation binding process gives rise to a variety of unprecedented optical responses: enhancing, quenching of the luminescence, switching from phosphorescence to fluorescence. The origin of those processes is described through the different chapters of this thesis.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

N-Heterocyclic Carbene Coinage Metal Complexes Containing Naphthalimide Chromophore: Design, Structure, and Photophysical Properties

A series of novel N-heterocyclic carbene coinage metal complexes containing a naphthalimide (NI) chromophore has been prepared and fully characterized. Two types of molecules are described those where the NI unit is directly attached to the carbene unit with the general formulae [(L1)–M–X], M = Cu, X = Cl (1a); M = Ag, X = I (1b) and M = Au, X = Cl, (1c). While in the second family, a π-extended carbene ligand precursor L2–H+I− (3) was prepared where the NI unit is distant from the imidazole unit via a phenyl-alkyne bridge. Only two N-heterocyclic carbene metal complexes were prepared [(L2)–M–Cl], M = Cu (2a) and M = Au (2c). The related silver carbene compound could not be isolated. The molecular structure of the carbene complex 1c was determined and confirmed the formation of the target compound. Interestingly, the structure shows the presence of an aurophilic interaction Au···Au at 3.407 Å between two individual molecules. The photophysical properties of the compounds were investigated in solution at room temperature. Preliminary results suggested that all compounds are luminescent and act as blue emitters (420–451 nm). These transition emissions can be attributed to the intraligand origin of the NI chromphore. Moreover, the carbene complexes featuring L2 ligand with π-extended system were found to be more luminescent

Study of a phosphorescent cationic iridium(III) complex displaying blue shift in crystals

International audienceWe report the synthesis and the characterization of a new cationic iridium(III) complex featuring two 1-(p-methoxyphenyl)-5-methoxybenzimidazole cyclometallating ligands and a dimethylbipyridine ancillary ligand. The complex has been fully characterized by 1D and 2D NMR (1H, 13C, 19F and 31P), elemental analysis and high-resolution mass spectrometry (HRMS). The photoluminescence studies performed in solution, on amorphous powder and on crystals revealed an unexpected behavior. Indeed, the emission spectra displayed in both solution (CH2Cl2) and amorphous powder samples are centered around 580 nm, whereas in crystals the emission displays a large hypsochromic shift of ~800 cm-1 (λem = 558 nm). X-ray diffraction experiments, photophysical studies and DFT calculation allow to rationalize the hypsochromic shift

Bis-Heteroleptic Cationic Iridium(III) Complexes Featuring Cyclometalating 2-Phenylbenzimidazole Ligands: A Combined Experimental and Theoretical Study

International audienceIn this report, we investigate a new family of cationic iridium(III) complexes featuring the cyclometalating ligand 2-phenylbenzimidazole and ancillary ligand 4,4′-dimethyl-2,2′-bipyridine. Our benchmark complex IrL 1 2 (L 1 = 2-phenylbenzimidazole) displays emission properties similar to those of the archetypical complex 2,2′dipyridylbis(2′,4′-phenylpyridine)iridium(III) in deaerated CH 3 CN (Φ = 0.20, λ em = 584 nm and Φ = 0.14, λ em = 585 nm, respectively) but exhibits a higher photoluminescence quantum yield in deaerated CH 2 Cl 2 (Φ = 0.32, λ em = 566 nm and Φ = 0.20, λ em = 595 nm, respectively) and especially a lower nonradiative constant (k nr = 6.6 × 10 5 s −1 vs k nr = 1.4 × 10 6 s −1 , respectively). As a primary investigation, we explored the influence of the introduction of electron-donating and electron-withdrawing groups on the benzimidazole moiety and the synergetic effect of the substitution of the cyclometalating phenyl moiety at the para position with the same substituents. The emission energy displays very good correlation with the Hammett constants of the introduced substituents as well as with ΔE redox values, which allow us to ascribe the phosphorescence of these series to emanate mainly from a mixed metal/ligand to ligand charge transfer triplet excited state (3 M/LLCT*). Two complexes (IrL 5 2 and IrL 8 2) display a switch of the lowest triplet excited state from 3 M/LLCT* to ligand centered (3 LC*), from the less polar CH 2 Cl 2 to the more polar CH 3 CN. The observed results are supported by (TD)-DFT computations considering the vibrational contributions to the electronic transitions. Chromaticity diagrams based on the maximum emission wavelength of the recorded and simulated phosphorescence spectra demonstrate the strong promise of our complexes as emitting materials, together with the very good agreement between experimental and theoretical results

Influence of bromine substitution pattern on the singlet oxygen generation efficiency of two-photon absorbing chromophores

International audienceA molecular engineering strategy based on rational variations of the bromine substitution pattern in two-photon absorbing singlet oxygen sensitizers allows studying the relations that exist between the positioning of an inter-system crossing promoter on the charge-transfer chromophore and its ability to generate singlet oxygen

The Role of Dinuclearity in Promoting Thermally Activated Delayed Fluorescence (TADF) in Cyclometallated, N^C^N-coordinated Platinum(II) Complexes

In this work we present synthesis and an in-depth photophysical analysis of a di-Pt(II) complex with a ditopic bis-N^C^N ligand. The complex exhibits a dual luminescent behaviour by emitting simultaneously delayed fluorescence and phosphorescence. By comparing with the mono-Pt(II) analogue, we demonstrate that thermally activated delayed fluorescence (TADF) is turned on in the di-Pt(II) complex due to the occurrence of three main factors which are not verified in the mono-Pt(II) analogue: a larger singlet radiative rate (krS), a smaller singlet-triplet energy gap (ΔEST) and a longer phosphorescence decay lifetime (τPH). We observe similar trends among other di-Pt(II) complexes and concluded that bimetallic structures promote conditions favourable for TADF to occur. The diplatinum(II) complex also shows a long wavelength-emissive excimer which yields near infrared electroluminescence, λel = 805 nm, in a solution-processed OLED device with EQEmax = 0.51 %. We believe this is the highest efficiency reported to date for an excimer Pt(II) emitter with λel > 800 nm in a solution-processed OLED device

Theoretical and Experimental Study on Boron β-Diketonate Complexes with Intense Two-Photon-Induced Fluorescence in Solution and in the Solid State

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Fluorescent gold nanoparticles with chain-end grafted RAFT copolymers: influence of the polymer molecular weight and type of chromophore

International audienceFluorescent gold nanoparticles (GNPs) were prepared by chain-end grafting of RAFT copolymers bearing multiple fluorophores distributed along the chain. Two different synthetic approaches in water were first studied with well-defined and biocompatible homopolymers. Both led to very stable samples and the corona thickness at the gold surface increased with the polymer molecular weight. The two-step ligand exchange approach was then selected to synthesize GNPs grafted with polymer–chromophore conjugates exhibiting different molecular weights, backbone architectures and chromophores. Again, the thickness of the organic corona increased with the polymer molecular weight but was also dependent on the conformation of the conjugate chains which depends on the nature of the chromophores. By adjusting these parameters, it was possible to control the average chromophore–gold distance which is of paramount importance for the fluorescence properties of the nanoparticles. We indeed showed that the fluorescence of the hybrid nano-objects increased with the corona thickness

Base de données des structures périglaciaires pléistocènes en France : description de la version accessible en ligne

International audienceA database of Pleistocene periglacial features in France has been compiled from a review of academic literature and reports of rescue archaeology, the analysis of aerial photographs and new field surveys. Polygons, soil stripes, ice-wedge pseudomorphs, sand wedges and composite wedge pseudomorphs are included in the database together with their geographic coordinates, geological context, description and associated references. It is hoped that this database, which aim is to be integrated in broader studies, will stimulate further work on past permafrost reconstruction and will favour greater understanding of the climatic events that lead to the formation of the periglacial features. The database is available online on the AFEQ-CNF INQUA website (https://afeqeng.hypotheses.org/487). A folder that contains photographs and sketches of the features is also available on request