Design of Ru(II) sensitizers endowed by three anchoring units for adsorption mode and light harvesting optimization

We report the design, synthesis and computational investigation of a class of Ru(II)-dyes based on mixed bipyridine ligands for use in dye-sensitized solar cells. These dyes are designed to preserve the optimal anchoring mode of the prototypical N719 sensitizer by three carboxylic groups, yet allowing for tunable optimization of their electronic and optical properties by selective substitution at one of the 4-4′ positions of a single bipyridine ligand with π-excessive heteroaromatic groups. We used Density Functional Theory/Time Dependent Density Functional Theory calculations to analyze the electronic structure and optical properties of the dye and to investigate the dye adsorption mode on a TiO2 nanoparticle model. Our results show that we are effectively able to introduce three carboxylic anchoring units into the dye and achieve at the same time an enhanced dye light harvesting, demonstrating the design concept. As a drawback of this type of dyes, the synthesis leads to a mixture of dye isomers, which are rather tedious to separate

Evidences for the Key Role of Hydrogen Bonds in Nucleophilic Aromatic Substitution Reactions

International audienceThe effect of hydrogen bonds on the fate of nucleophilic aromatic substitutions (SNAr) has been studied in silico using a density functional theory approach in the condensed phase. The importance of these hydrogen bonds can explain the “built-in solvation” model of Bunnett concerning intermolecular processes between halogenonitrobenzenes and amines. It is also demonstrated that it can explain experimental results for a multicomponent reaction (the Ugi–Smiles coupling), involving an intramolecular SNAr (the Smiles rearrangement) as the key step of the process. Modeling reveals that when an intramolecular hydrogen bond is present, it lowers the activation barrier of this step and enables the multicomponent reaction to proceed

pH-Sensitive Bis(2,2′:6′,2"-terpyridine)ruthenium(II) Complexes - A DFT/TDDFT Investigation of Their Spectroscopic Properties

We report a DFT/TDDFT study on the geometric, electronic and optical properties of [Ru{4'-(4-pyridyl)-2,2':6',2"-terpyridine}2]2+. Because of the presence of the basic nitrogen atom on the terminal pyridyl ligands, in solution the complex can exist in three different protonation states depending on the pH, each with markedly different photophysical properties. We investigated the effect of protonation of the terminal pyridine groups on the electronic and optical properties of this RuII complex. TDDFT calculations in vacuo and aqueous solution were performed, finding good agreement between the simulated and the experimental absorption spectra, and reproducing the experimentally observed absorption redshift upon pyridine protonation. The calculated excited-state data provide a rationale for the luminescence properties observed by varying the solution pH, in terms of the different energy separation between MLCT and MC excited states in the complexes

Direct asymmetric aldol reactions between aldehydes and ketones catalyzed by l-tryptophan in the presence of water

10.1039/b921460gOrganic and Biomolecular Chemistry861368-137

Dicationic μ-Diborolyl Arene Triple-Decker Complexes [CpCo(μ-1,3-C 3

The reaction of the bromide complexes [CpCo(μ-1,3-C3B2Me5)MBr2]2 [M = Rh (1), Ir (2); Cp = cyclopentadienyl] with AgBF4 in acetonitrile affords the tris(acetonitrile) μ-diborolyl triple-decker complexes [CpCo(μ-1,3-C3B2Me5)M(MeCN)3]2+ [Rh (3), Ir (4)]. The labile nitromethane solvates [CpCo(μ-1,3-C3B2Me5)M(MeNO2)3]2+, generated in a similar way, react with benzene and its methylated derivatives to give the arene triple-decker complexes [CpCo(μ-1,3-C3B2Me5)M(arene)]2+ [M = Rh (5), Ir (6); arene = C6H6 (a), 1,2,4,5-Me4C6H2 (b), C6Me6 (c)]. The structures of 5b(BF4)2, 5c(BF4)2, 6b(BF4)2 and 6c(BF4)2 were determined by X-ray diffraction. The electron-transfer ability of the arene complexes was ascertained by electrochemical techniques. In general, they are able to undergo two separate one-electron reductions reversibly. DFT calculations revealed structural changes caused by redox processes and satisfactorily predicted the redox potentials. The second reduction is accompanied by a η6-→-η4 hapticity change of the arene ligand. Energy decomposition analysis revealed that the Rh-benzene bond in cation 5a is weaker than in cyclopentadienyl analogues [(C5R5)Rh(C6H6)]2+; however, 5a proved to be the least reactive in benzene replacement with acetonitrile and mesitylene. The labile nitromethane solvates [CpCo(μ-1,3-C3B2Me5)M(MeNO2)3]2+ {generated from the bromide complexes [CpCo(μ-1,3-C3B2Me5)MBr2]2 (M = Rh, Ir; Cp = cyclopentadienyl) and AgBF4 in MeNO2} react with arenes to give triple-decker complexes [CpCo(μ-1,3-C3B2Me5)M(arene)]2+. X-ray diffraction, electrochemical techniques and DFT calculations were used for the characterization of the complexes obtaine