Abderrahim Khatyr

Intramolecular Triplet Energy Transfer in Pyrene–Metal Polypyridine Dyads: A Strategy for Extending the Triplet Lifetime of the Metal Complex

Anelegantandflexiblesynthesis of pyrene-based dyads bearing ruthenium or osmium chromophoric moieties connected through a single C≡C bond or a Pt(C≡C)2 spacer is described (see picture). Photophysical properties reveal that the two Ru-based units enter into reversible triplet energy transfer with the appended pyrene. This effect is responsible for the unusual prolongation of the ruthenium triplet excited (40 and 17 μs, for pyr–Ru and pyr–Pt–Ru, respectively).

Reactivity of CuI and CuBr toward Et2S: a reinvestigation on the self-assembly of luminescent copper(I) coordination polymers.

CuI reacts with SEt(2) in hexane to afford the known strongly luminescent 1D coordination polymer [(Et(2)S)(3){Cu(4)(mu(3)-I)(4)}](n) (1). Its X-ray structure has been redetermined at 115, 235, and 275 K in order to address the behavior of the cluster-centered emission and is built upon Cu(4)(mu(3)-I)(4) cubane-like clusters as secondary building units (SBUs), which are interconnected via bridging SEt(2) ligands. However, we could not reproduce the preparation of a coordination polymer with composition [(Et(2)S)(3){Cu(4)(mu(3)-Br)(4)}](n) as reported in Inorg. Chem. 1975, 14, 1667. In contrast, the autoassembly reaction of SEt(2) with CuBr results in the formation of a novel 1D coordination polymer of composition [(Cu(3)Br(3))(SEt(2))(3)](n) (2). The crystal structure of 2 has been solved at 115, 173, 195, and 235 K. The framework of the luminescent compound 2 consists of a corrugated array with alternating Cu(mu(2)-Br)(2)Cu rhomboids, which are connected through two bridging SEt(2) ligands to a tetranuclear open-cubane Cu(4)Br(4) SBU, ligated on two external Cu atoms with one terminal SEt(2). The solid-state luminescence spectra of 1 and 2 exhibit intense halide-to-metal charge-transfer emissions centered at 565 and 550 nm, respectively, at 298 K. A correlation was also noted between the change in the full width at half-maximum of the emission band between 298 and 77 K and the relative flexibility of the bridging ligand. The emission properties of these materials are also rationalized by means of density functional theory (DFT) and time-dependent DFT calculations performed on 1.

Extending the luminescence lifetime of ruthenium(II) poly(pyridine) complexes in solution at ambient temperature

A set of ruthenium(II) poly(pyridine) complexes has been synthesized in which a central diethynylated pyrene moiety separates the 2,2′-bipyridine- and 2,2′:6′,2″-terpyridine-based terminals. The mononuclear complex, having only the 2,2′-bipyridine ligand coordinated with the metal cation, and the corresponding binuclear complex show remarkably similar luminescence properties in deoxygenated acetonitrile solution at room temperature. Two emission bands are evident in the spectrum. These bands appear to be in thermal equilibrium over the temperature range 0–60 °C but only a single emitting species is seen in a frozen glass at 77 K. The phosphorescence lifetimes are significantly longer than those associated with the parent complexes under the same experimental conditions but, unlike most other metal complex–pyrene dyads, the luminescence yield is extremely sensitive to the presence of trace amounts of molecular oxygen. The analogous compound having two ruthenium(II) tris(2,2′-bipyridine)-based terminals shows comparable behaviour. Allowing for all of the measured photophysical and electrochemical properties, it is concluded that the triplet manifold has the metal-to-ligand, charge-transfer state localised on the metal complex in equilibrium with an intramolecular charge-transfer state involving the pyrene and a coordinated poly(pyridine) group. The latter state lies at lower energy in a polar solvent and controls the photophysics. At low temperature, only the metal-to-ligand, charge-transfer triplet is observed.

Syntheses, structures, and photophysical properties of mono- and dinuclear sulfur-rich gold(I) complexes.

The dinuclear gold complexes [{Au(PPh 3)} 2(mu- dmid)] ( 1) ( dmid = 1,3-dithiole-2-one-4,5-dithiolate) and [{Au(PPh 3)} 2(mu- dddt)] ( 2) ( dddt = 5,6-dihydro-1,4-dithiine-2,3-dithiolate) were synthesized and characterized by X-ray crystallography. Both complexes exhibit intramolecular aurophilic interactions with Au...Au distances of 3.1984(10) A for 1 and 3.1295(11) A for 2. A self-assembly reaction between 4,5-bis(2-hydroxyethylthio)-1,3-dithiole-2-thione ( (HOCH 2 CH 2 ) 2 dmit) and [AuCl(tht)] affords the complex [AuCl{ (HOCH 2 CH 2 ) 2 dmit}] 2 ( 4), which possesses an antiparallel dimeric arrangement resulting from a short aurophilic contact of 3.078(6) A. This motif is extended into two dimensions due to intra- and intermolecular hydrogen bonds via the hydroxyethyl groups, giving rise to a supramolecular network. Three compounds were investigated for their rich photophysical properties at 298 and 77 K in 2-MeTHF and in the solid state; [Au 2(mu- dmid)(PPh 3) 2] ( 1), [Au 2(mu- dddt)(PPh 3) 2] ( 2), and [AuCl{( HOCH 2 CH 2 ) 2 dmit}] ( 4). 1 exhibits relatively long-lived LMCT (ligand-to-metal charge transfer) emissions at 298 K in solution (370 nm; tau e approximately 17 ns, where M is a single gold not interacting with the other gold atom; i.e., the fluxional C-SAuPPh 3 units are away from each other) and in the solid state (410 nm; tau e approximately 70 mus). At 77 K, a new emission band is observed at 685 nm (tau e = 132 mus) and assigned to a LMCT emission where M is representative for two gold atoms interacting together consistent with the presence of Au...Au contacts as found in the crystal structure. In solution at 77 K, the LMCT emission is also red-shifted to 550 nm (tau e approximately 139 mus). It is believed to be associated to a given rotamer. 2 also exhibits LMCT emissions at 380 nm at 298 K in solution and at 470 nm in the solid state. 4 exhibits X/MLCT emission (halide/metal to ligand charge transfer) where M is a dimer in the solid state with obvious Au...Au interactions, resulting in red-shifted emission band, and is a monomer in solution in the 10 (-5) M concentration (i.e., no Au...Au interactions) resulting in blue-shifted luminescence. Both fluorescence and phosphorescence are observed for 4.

A ruthenium(II) tris(2,2′-bipyridine) derivative possessing a triplet lifetime of 42 µs

Grafting an ethynylated-pyrene moiety to a Ru(II) or Os(II) polypyridine complex perturbs the photophysical properties of the metal fragment and, when the relevant energy levels are properly balanced, provides a 115-fold prolongation of the triplet lifetime.

Stepwise construction of rigid rod-like terpyridine ligands based on alternating ethynyl/phenyl modules

Abstract We report the synthesis of novel soluble ditopic terpyridine ligands bearing an alternance of acetylenic/phenyl modules (one to five) built in the centre. The protocol is based on sequential Pd-promoted cross-coupling reaction between selected mono-terpy fragments and either mono-protected 1,4-diethynyl-2,5-di(dodecyloxy)benzene or 1,4-diethynyl-2,5-di(dodecyloxy)benzene synthons. The ligand bearing a central diethynyl spacer was prepared by an oxidative self-coupling reaction promoted by copper salts and O 2 .

The photophysical properties of short, linear arrays of ruthenium(II) tris(2,2′-bipyridine) complexes

A series of linear polynuclear ruthenium(II) tris(2,2′-bipyridine) complexes has been synthesized whereby individual chromophores are separated by 1,4-diethynylenebenzene subunits bearing alkoxy groups for improved solubility. These arrays contain two, three, four or five metal centers. The compounds are reasonably soluble in polar organic solvents and they possess optical absorption spectral properties that are dominated by transitions associated with the polytopic ligand. Weak luminescence is observed for each complex in deoxy genated acetonitrile at room temperature that appears to be characteristic of emission from a metal-to-ligand charge-transfer triplet state. The emission lifetime is essentially independent of temperature, at least over a modest range. There is no indication for interaction between close-lying triplet states and no obvious sign of a low-energy τ, τ* triplet associated with the polytopic ligand. The photophysical properties suggest that the longer arrays are segmented.

Stepwise construction of pyrene bridged polytopic ligands carrying acetylenic tethers

Reliable and practical synthetic routes for the construction of polytopic bipyridine or terpyridine frameworks are presented. These ligands are prepared by sequential Pd-promoted cross-coupling reactions between selected ethynyl substituted bipyridine or terpyridine building blocks and 1,6-dibromopyrene. A convergent synthetic route for the preparation of Ru complexes bearing peripheral uncomplexed fragments has been established starting from preorganized building blocks carrying a bromide function. This protocol highlights the use of metallo-synthons in Sonogashira cross-coupling reactions and allows the synthesis of very soluble complexes.

Sequential synthesis of rigid multi-bipyridine ligands bearing diethynyl/phenyl solubilizing fragments

Abstract Reliable and practical synthetic routes for the construction of multitopic bipyridine ligands are presented. The first series contains the chelating fragments connected via an ethynyl function and the second series is built from an alternation of ethynyl/phenyl/bipyridine modules. The synthetic protocol is based on sequential Pd-promoted cross-coupling reactions between selected bis-bpy or ethynyl/phenyl/bpy intermediates of increasing size. The ligands bearing functionalized 1,4-diethynyl-2,5-di(dodecyloxy)benzene subunits are soluble in chlorinated solvents.

UV-C as a means to combat biofilm proliferation on prehistoric paintings: evidence from laboratory experiments

A laboratory investigation of UV-C effects was conducted over a 62-h period: a much higher dose than in classic UV-C treatment was applied to five pigments and two painting binders used by prehistoric humans. Colorimetric parameters were compared to a control to see if UV-C can change pigment and binder color. Infrared spectroscopy, scanning electron microscopy, inductively coupled plasma and X-ray crystallography were also carried out to confirm colorimetric measurement. In order to understand how microorganism may physically deteriorate paintings, limestone blocks were painted and monitored until their complete colonization by algae, cyanobacteria, fungi and/or mosses. The results show that UV-C has no effect on mineral compounds. Conversely, it is noteworthy that binder color changed under both UV-C light conditions as well as in visible light. Concerning painted blocks, a fast proliferation has been observed with deterioration of the paintings. These results show the high importance of treating biofilm as soon as possible. Moreover, these findings may be a promising avenue inducing cave managers to use friendly UV-C light to treat contaminated cave paintings and also in the prevention of biodeterioration by lampenflora.