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A novel tridentate ligand featuring an acridine core and pyrazole rings, namely 2,7- di-tert-butyl-4,5-di(pyrazol-1-yl)acridine, L, was designed and used to create two ruthenium(II) complexes: [RuL2](PF6)2 and [Ru(tpy)L](PF6)2. Surprisingly, the ligand adopted different coordination modes in the complexes: facial coordination for the homoleptic complex and meridional coordination for the heteroleptic complex. The electronic absorption and electrochemical properties were evaluated. Although both complexes exhibited favorable electronic properties for luminescence, neither emitted light at room temperature nor at 77 K. This study highlights the complex interplay between ligand design, coordination mode, and luminescence in ruthenium(II) complexes. [ABSTRACT FROM AUTHOR]

Three new ruthenium(II) complexes are prepared which contain two 1,10-DMOLECULAR DYNAMICS units and a third sterically hindering chelate. These complexes are aimed at providing building blocks of future light-driven molecular machines.

[Cr(ttpy)2]3+ (ttpy = 4′-(4-methylphenyl)-2,2′:6,2′′-terpyridine) exhibits rich electrochemical and photophysical properties. Cyclic voltammetry performed in CH3CN shows in the cathodic part the presence of three one-electron reversible systems at −0.47, −0.85 and −1.35 V vs. Ag/AgNO3 10−2 M. These systems are attributed to the reduction of the terpyridine ligands with a partial delocalization of the charge on the tolyl for the last reduction event. The three different reduced species were generated by exhaustive electrolysis and characterized by EPR and UV-visible spectroscopy; DFT calculations were performed to locate the spin density of the electrons added during the reduction. Visible light irradiation of [Cr(ttpy)2]3+ induces the population of a luminescent metal-centered excited state with a lifetime of 270 ns in deoxygenated CH3CN. This excited state can be quenched by an electron transfer process with triphenylphosphine (PPh3) or triethanolamine (TEOA). Using TEOA as a sacrificial electron donor, the doubly reduced species (i.e.[Cr(ttpy)2] +) can be generated under continuous irradiation. In the presence of [Ru(bpy)3]2+ as an additional photosensitizer, the photoreduction of [Cr(ttpy)2]3+ towards [Cr(ttpy)2]+ is accelerated. The trinuclear [{RuII(bpy)2(bpy-O-tpy)}2CrIII]7+ complex ([Ru2Cr]7+) in which a CrIII-bis-terpyridine centre is covalently linked to two RuII-tris-bipyridine moieties by oxo bridges has been synthesised. Its electrochemical, photophysical and photochemical properties were investigated in deoxygenated CH3CN. Cyclic voltammetry indicates only a poor electronic communication between the different subunits, whereas luminescence experiments show a strong quenching of the RuII* excited state by an intramolecular process. Continuous irradiation of [Ru2Cr]7+ under visible conditions in the presence of TEOA leads to [Ru2Cr]4+ where three electrons are stored on the [Cr(ttpy)] subunit. [ABSTRACT FROM AUTHOR]

The article discusses the photoelectric conversion at a bipyridine ruthenium chloride-based on metallic triad grafted on a Indium tin oxide (ITO) electrode under the visible light. Topics discussed include interaction between phosphonates with ITO and terpyridine ligands; characterization of all experiments by cyclic voltammetry in acetonitrile and tetrabutylammonium perchlorate; and the redox potential throught out the procedure.

Abstract: Three new ruthenium(II) complexes which contain two 1,10-phenanthroline units and a third bis-thioether chelate have been prepared and characterized. For two complexes, the X-ray structure shows a perfect fit between the two phen ligands and the bis-thioethers, with almost perfect C 2 symmetry for the Ru(phen)2 unit and the S-containing ligand. This geometrical complementarity is also reflected by π–π stacking between the phen nuclei and the S-borne phenyl rings. In relatively harsher preparation conditions a ruthenium complex composed of one phenanthroline and two bis-thioethers is formed as a result of a scrambling reaction. When a bis-thioether chelate incorporated in a macrocycle also including a 6,6′-disubstituted-2,2′-bipyridine unit is used, 1H NMR study shows that an exo S-bonded ruthenium(II) complex is obtained. In presence of chloride anions a photosubstitution reaction of the bis-thioether chelate takes place selectively and efficiently. [Copyright &y& Elsevier]

Three new ruthenium(II) complexes have been prepared which contain two 1,10-phenanthroline units and a third sterically hindering chelate. In one case, the hindering ligand is a disubstituted 2,2'-bipyridine (bpy) attached to two very bulky manisyl groups. The two other systems are similar in terms of size of the hindering groups (anisyl substituents) located close to the central metal. The complexes investigated in the Present Report are aimed at providing building blocks of future light-driven molecular machines. The photochemical expulsion of the sterically hindering chelate has thus been studied by UV-vis spectroscopy and ¹H NMR. Surprisingly, the manisyl-containing complex turned out to be photochemically inert, indicating that a too bulky group acts as a protecting function versus decomplexation rather than as a destabilizing group. For the two other systems, a pronounced ring effect was observed: whereas the acyclic systems undergo fast photochemical expulsion of the bipy-based ligand, in the cyclic complex, the bipy-incorporating ring is decoordinated about 5 times less efficiently than the acyclic ligand of the previous case. These observations on the strong dependence of the photochemical behavior of the ruthenium(Il) complexes on their structural properties are corroborated by X-ray diffraction studies on the three compounds investigated. [ABSTRACT FROM AUTHOR]

A pyridinium substituted dithienylethene derivative was used for the first time as an efficient photoreducing agent of two different substrates. This reaction exhibits high catalytic yields due to the continuous regeneration of the initial state of the photochromic molecule., (© 2020 Wiley-VCH GmbH.)

The synthesis of two multisite ligands containing four and five 1,10-phenanthroline (phen) chelates in line, respectively, is presented. The connectors are 1,3-phenylene linkers. The two ligands were prepared following multistep procedures, the two key reactions being the Suzuki coupling reaction between aromatic nuclei and the nucleophilic addition of aryllithium derivatives onto a phen fragment. The coordination chemistry of both ligands with Li+ ions was very clean and selective, whereas their reaction with copper(I) led to intractable mixtures of insoluble complexes. The tetraphen and the pentaphen compounds afforded almost quantitatively the four- and five-lithium double-stranded helical complexes, respectively. The helical systems are probably highly wound, as indicated by NMR measurements. The pronounced strain of the 5-Li+ complex is reflected by the easy loss of a lithium cation, as shown by electrospray mass spectrometry.

A rotaxane containing a ruthenium bisphenanthroline complex, acting as an axis, and a macrocycle incorporating a 2,2'-bipyridine (bpy) unit, threaded by the axis, has been synthesized. The bisphenanthroline ligand is such that its ruthenium(II) complexes possess a clearly identified axis, making such compounds ideal components of rotaxanes constructed around an octahedral ruthenium(II) center, which serves as a template. The ring is threaded by the axial ruthenium(II) precursor complex, to afford the corresponding pseudorotaxane in moderate yield. The X-ray structure analysis of this compound reveals the threaded nature of the complex. The length of the threaded ring (35 atoms in the periphery) is too short to allow easy threading of the axis through the macrocycle. As a consequence, an isomer is also obtained for which the axial ruthenium complex is attached in an exo fashion. (1)H NMR studies have been carried out, which reveal various conformational equilibria for the pseudorotaxane. Light-induced decoordination of the bpy-containing cyclic fragment was shown to be quantitative and to lead to the free ring and the axial ruthenium(II) complex, regardless of the starting compound (pseudorotaxane or exo isomer). Finally, the real rotaxane could be prepared, although it could not be separated from its exo isomer.