Synthèse du mèthyl-1 diformyl-2,3 pyrrole,de la méthyl-1 pyrrolo[2,3-d] pyridazine et de la méthyl-1 oxo-6 (6h)cycloheptatrieno[b] pyrrole

This communication describes the synthesis of l-methyl-2,3-diformylpyrrole. This new compound is used to prepare a new heterocycle, l-methylcyclohepta[b]pyrrol-6-one and thus allows a new synthesis of l-methylpyrrolo[2,3-d]pyridazine.     

Ultrafast energy-electron transfer cascade in a multichromophoric light-harvesting molecular square

A molecular square with dimensions of about 4 nm, incorporating sixteen pyrene chromophores attached to four ditopic bay-functionalized perylene bisimide chromophores, has been synthesized by coordination to four Pt(II) phosphine corner units and fully characterized via NMR spectroscopy and ESI-FTICR mass spectrometry. Steady-state and time-resolved emission as well as femtosecond transient absorption studies reveal the presence of a highly efficient (>90%) and fast photoinduced energy transfer (k(en) approximately equal to 5.0 x 10(9) s(-1)) from the pyrene to the perylene bisimide chromophores and a very fast and efficient electron transfer (>94%, k(et) approximately equal to 5 x 10(11) up to 43 x 10(11) s(-1)). Spectrotemporal parametrization indicates upper excited-state electron-transfer processes, various energy and electron-transfer pathways, and chromophoric heterogeneity. Temperature-dependent time-resolved emission spectroscopy has shown that the acceptor emission lifetime increases with decreasing temperature from which an electron-transfer barrier is obtained. The extremely fast electron-transfer processes (substantially faster and more efficient than in the free ligand) that are normally only observed in solid materials, together with the closely packed structure of 20 chromophoric units, indicate that we can consider the molecular square as a monodisperse nanoaggregate: a molecularly defined ensemble of chromophores that partly behaves like a solid material.     

Rodlike bimetallic ruthenium and osmium complexes bridged by phenylene spacers. Synthesis, electrochemistry, and photophysics

In the search for light-addressable nanosized compounds we have synthesized 10 dinuclear homometallic trisbipyridyl complexes of linear structure with the general formula [M(bpy)3-BL-M(bpy)3]4+ [M = Ru(II) or Os(II); BL = polyphenylenes (2, 3, 4, or 5 units) or indenofluorene; bpy = 2,2'-bipyridine]. By using a "chemistry on the complex" approach, different sizes of rodlike systems have been obtained with a length of 19.8 and 32.5 A for the shortest and longest complex, respectively. For one of the ruthenium precursors, [Rubpy-ph2-Si(CH3)3][PF6]2, single crystals were obtained by recrystallization from methanol. Their photophysical and electrochemical properties are reported. All the compounds are luminescent both at room and low temperature with long excited-state lifetimes due to an extended delocalization. Nanosecond transient absorption showed that the lowest excited state involves the chelating unit attached to the bridging ligand. Electrochemical data indicated that the first reduction is at a slightly more positive potential than for the reference complexes [M(bpy)3]2+ (M = Ru, Os). This result confirms that the best acceptor is the bipyridine moiety connected to the conjugated spacers. The role of the tilt angle between the phenylene units, in the two series of complexes, for the ground and excited states is discussed.     

Ultrafast photoinduced electron transfer within a self-assembled donor-acceptor system

A photoactive supramolecular assembly that is based on the hydrogen-bonded system H1.G2, consisting of a methyl viologen-functionalized barbiturate host (H1) (1-(N-(3,5-bis[[(6-tert-butylacetylamino-2-pyridyl)amino]carbonyl])-phenylacetamide)-1'-methyl-4,4'-bipyridium) and a [Re(Br)(CO)3(barbi-bpy)] (barbi-bpy = 5-[4-(4'-methyl)-2,2'-bipyridyl]methyl-2,4,6-(1H,3H,5H)-pyrimidinetrione) complex as the guest (G2) is described. The host molecule contains a well-known electron accepting group (methyl viologen), whereas the guest system can act as an efficient electron donor in the excited state. Upon self-assembly, the resulting adduct (H1.G2) represents an interesting noncovalently linked donor-acceptor system. The H1.G2 complex has been characterized in acetonitrile-d3 using 1H NMR and diffusion-ordered NMR spectroscopy (DOSY). The photophysical properties of the components and of the assembly have been studied in dichloromethane, in which the assembly has a high binding constant (Kass > or = 2 x 10(5) M(-1)), using time-resolved fluorescence and transient absorption spectroscopy. A detailed investigation of the hydrogen-bonded complex H1.G2 revealed that, upon excitation of the rhenium compound G2, an ultrafast electron-transfer process occurs from the metal-based component to the acceptor unit. The kinetics of the forward and back electron-transfer processes have been determined.     

The correct assignment of stereochemistry in di‐μ‐dichlorido‐bis{bis[2‐(5‐benzylsulfonyl)‐3‐fluoro‐2‐(pyridin‐2‐yl)phenyl‐κ2N,C1]iridium(III)} toluene monosolvate

The title complex, [Ir₂(C₁₈H₁₃FNO₂S)₄Cl₂]·C₇H₈, was crystallized from dichloromethane solution under a toluene atmosphere. It is a dimeric complex in which each of the two Ir^III centres is octahedrally coordinated by two bridging chloride ligands and by two chelating cyclometalated 2‐(4‐benzylsulfonyl‐2‐fluorophenyl)pyridine ligands. The crystal structure analysis unequivocally establishes the trans disposition of the two cyclometalated ligands bound to each Ir^III centre, contrary to our previous hypothesis of a cis disposition. The latter was based on the ¹H NMR spectra of a series of dimeric benzylsulfonyl‐functionalized dichloride‐bridged iridium complexes, including the compound described in the present work [Ragni et al. (2009). Chem. Eur. J. 15 , 136–148]. The toluene solvent molecules, embedded in cavities in the crystal structure, are highly disordered and could not be modelled successfully; their contribution was removed from the refinement using the SQUEEZE routine in the program PLATON [Spek (2009). Acta Cryst. D 65 , 148–155].