Cyclometalated platinum(II) with ethynyl-linked azobenzene ligands: an original switching mode.

International audienceThe photophysical properties of 6-phenyl-2,2'-bipyridyl platinum(ii) complexes bearing different σ-alkynyl-linked azobenzene ancillary ligands were investigated. These complexes exhibited strong, broad, structureless charge-transfer bands in the visible region, which were red-shifted when the electron-donating ability of the para substituent on the azo-acetylide ligand increased. When excited at the charge-transfer absorption band, the complexes exhibited weak green emission, which was assigned to a triplet metal-to-ligand charge transfer/interligand charge transfer emission ((3)MLCT/(3)L'LCT). The presence of an amino substituent in the azobenzene moiety opened the possibility of protonation, which led to the formation of an azonium based derivative and resulted in drastic perturbations of the molecular orbitals and photophysical properties of the Pt-acetylide complex. These studies are fully supported by DFT and TD-DFT calculations

Heteroleptic diimine copper(i) complexes with large extinction coefficients: synthesis, quantum chemistry calculations and physico-chemical properties.

International audience: Using the HETPHEN approach, five new heteroleptic copper(i) complexes composed of a push-pull 4,4'-styryl-6,6'-dimethyl-2,2'-bipyridine ligand and a bulky bis[(2-diphenylphosphino)phenyl]-ether (DPEphos) or a bis2,9-mesityl phenanthroline (Mes2Phen) were prepared and characterized by electronic absorption spectroscopy, electrochemistry, and TD-DFT calculations. These complexes exhibit very intense absorption bands in the visible region with extinction coefficient in the range of 5-7 × 10(4) M(-1) cm(-1). The analysis of the position, intensity and band shape indicates a strong contribution from an intra-ligand charge-transfer transition centered on the styrylbipyridine ligand along with MLCT transitions. These new complexes experimentally demonstrate that good light harvesting properties with bis-diimine copper(i) complexes are a reality if one chooses suitable ligands in the coordination sphere. This constitutes a milestone towards using bis-diimine copper(i) complexes for solar energy conversion (artificial photosynthesis and solar cells)

Photoisomerisation in Aminoazobenzene-Substituted Ruthenium(II) Tris(bipyridine) Complexes: Influence of the Conjugation Pathway.

International audienceTransition-metal complexes containing stimuli-responsive systems are attractive for applications in optical devices, photonic memory, photosensing, as well as luminescence imaging. Amongst them, photochromic metal complexes offer the possibility of combining the specific properties of the metal centre and the optical response of the photochromic group. The synthesis, the electrochemical properties and the photophysical characterisation of a series of donor-acceptor azobenzene derivatives that possess bipyridine groups connected to a 4-dialkylaminoazobenzene moiety through various linkers are presented. DFT and TD-DFT calculations were performed to complement the experimental findings and contribute to their interpretation. The position and nature of the linker (ethynyl, triazolyl, none) were engineered and shown to induce different electronic coupling between donor and acceptor in ligands and complexes. This in turn led to strong modulations in terms of photoisomerisation of the ligands and complexes

Synthesis, photophysics and nonlinear optical properties of stilbenoid pyrimidine-based dyes bearing methylenepyran donor groups.

International audienceThe nonlinear properties and the photophysical behavior of two π-conjugated chromophores that incorporate an electron-deficient pyrimidine core (A) and γ-methylenepyrans as terminal donor (D) groups have been thoroughly investigated. Both dipolar and quadrupolar branching strategies are explored and rationalized on the basis of the Frenkel exciton model. Even though a cooperative effect is clearly observed if the dimensionality is increased, the nonlinear optical (NLO) response of this series is moderate if one considers the nature of the D/A couple and the size of the chromophores (as measured by the number of π electrons). This effect was attributed to a disruption in the electronic conjugation within the dyes' scaffold for which the geometry deviates from planarity owing to a noticeable twisting of the pyranylidene end-groups. This latter structural parameter also has a strong influence on the excited-state dynamics, which leads to a very efficient fluorescence quenching

Nonlinear optical properties of intriguing Ru σ-acetylide complexes and the use of a photocrosslinked polymer as a springboard to obtain SHG active thin films

This work reports on the design, synthesis and photo-physical properties of two ruthenium σ-alkynyl complexes. It is shown that, despite similar optical absorption features recorded in solution, the introduction of a benzaldehyde moiety leads to an improved non-linear optical (NLO) response as measured by Electric Field Induced Second Harmonic (EFISH) generation and Third Harmonic Generation (THG) at 1.907 μm, both related to the second order hyperpolarizability. These structure–property relationships are rationalized based on few state modelling. Complex 2 is subsequently processed to afford composite films that demonstrate a χ2 of 1.4 pm V−1, quite remarkable given the ease of film processing implemented in this work

Access to 3-Oxindoles from Allylic Alcohols and Indoles

International audienceThe site-selective and regioselective allylation of 2-substituted indoles was performed by using a ruthenium(IV) precatalyst containing a phosphine-sulfonate chelate. Mono-, di-, and triallylated indoles were selectively obtained depending on the reaction conditions with the formation of water as the only byproduct. The preparation of 3-oxindole derivatives was then successfully performed owing to air oxidation of the corresponding allylated indoles. Diallylated pseudoindoxyls were proven to be good synthons to perform cyclization through a ring-closing metathesis reaction to afford the corresponding tricyclic adducts. The photophysical properties of the 3-oxindoles were measured, and some of the compounds showed strong fluorescence in water

Switching of reverse charge transfers for a rational design of an OFF-ON phosphorescent chemodosimeter of cyanide anions.

International audienceA rational approach to luminescence turn-on sensing of cyanide by a dicyanovinyl-substituted acetylide Pt(II) complex, which primarily relies on the nucleophilic addition reaction of cyanide anions to the α-position of the dicyanovinyl group, is described. The strategy used for the design of this cyanide-selective sensor takes advantage of a switch of charge transfer from ML'CT to MLCT/L'LCT in this acetylide Pt(II) sensor. As a result, this chromophore that exhibits almost no basal luminescence displays observable changes in its UV-visible spectrum and acquires strong phosphorescence upon addition of cyanide anions. DFT computations reveal that the frontier molecular orbitals of the anionic system obtained after addition of CN(-) are drastically different from those of the neutral initial species. TD-DFT computations permitted a full assignment of the observed absorption bands and explained well the emissive properties of the species under consideration

Theoretical evidence of metal-induced structural distortions in a series of bipyrimidine-based ligands.

International audienceHerein, we report theoretical evidence of the geometric changes occurring upon complexation, for a series of octupolar bipyrimidine-based ligands incorporating the NPh2 terminal donor group. It is shown that ligands 1 and 2 (4,4',6,6'-tetrakis(N,N-diphenylaminostyryl)-[2,2']bipyrimidine and 4,4',6,6'-tetrakis((N,N-diphenyl)-9,9'-dioctyl-9H-fluorene-2-amine)-2,2'-bipyrimidine) exhibit a non-planar geometry with a torsion angle between both pyrimidine moieties of ∼25° and 50° respectively. 1a (complex of 1) becomes planar upon addition of ZnCl2 to the bipyrimidine moiety whereas 2a remains distorted. Furthermore, an assignment of the absorption bands for all compounds is presented

Tuning the nonlinear optical properties of BODIPYs by functionalization with dimethylaminostyryl substituents

International audienceTwo difluoroboradiazaindacene (BODIPY) scaffolds with attached dimethylaminostyryl substituents were synthesized. Guest-host polymeric films were produced by incorporating these chromophores into polymethylmethacrylate matrices. The second and third nonlinear optical properties of the resulting polymer composites were studied by means of the Maker fringe technique using a laser generating at 1064 nm with a 30 ps pulse duration. The macroscopic and microscopic nonlinearities were found to be comparatively high and dependent on the number of dimethylaminostyryl substituents attached to BODIPY core. The development of integrated optics makes such nonlinear films of particular interest, since they can be used in the creation of efficient nonlinear devices

Azobased iminopyridine ligands and their rhenium metal complexes: Syntheses, spectroscopic, trans-cis photoisomerization and theoretical studies

International audienceThe reaction of rhenium(I) pentacarbonyl chloride Re(CO)5Cl with N,N-dimethyl-4-((E)-(pyridin-2-ylmethylene) amino)phenyl) diazenyl) aniline L1 and (E)-4-((E)-(4-nitrophenyl)diazenyl)-N-(pyridin-2-ylmethylene) aniline L2 affords two rhenium metal complexes [ReL1(CO)3Cl] (ReL1) and [ReL2(CO)3Cl] (ReL2), respectively. These Re(I) complexes were characterized in detail, including their single crystal structures, absorption spectra and electronic structures using DFT calculations. Trans to cis photoisomerization of the free ligands and complexes was investigated experimentally and rationalized theoretically. Interestingly, light-induced photoisomerization of the azo fragment is observed for free ligand L1 while inhibition of this process is produced upon coordination to Re metal cation