Alternated bimetallic [Ru–M] (M = Fe²⁺, Zn²⁺) coordination polymers based on [Ru(bpy)₃]²⁺ units connected to bis-terpyridine ligands: synthesis, electrochemistry and photophysics in solution or in thin film on electrodes

Abstract

Two alternated bimetallic Ru-Fe and Ru-Zn coordination polymers, [{Ru II (bpy) 2 (L2)M II } n ] 4n+ (M ¼ Fe 2+ , Zn 2+ ), were synthesized using the [Ru(bpy) 2 (L2)] 2+ (bpy ¼ 2,2 0 bipyridine) complex as a building block, in which L2 is a bipyridine ligand substituted by two terpyridine sites. The [Ru(bpy) 3 ] 2+ like-subunits provide the assemblies with photoredox properties whereas the second metal allows the build-up of the polymer structure by coordination of the free terpyridine units, associated with additional redox activities. Thin robust films of these metallo supramolecular structures can be easily obtained as a coating on electrode surfaces (C, Pt, and ITO) by a simple electrochemical procedure based on an electroreductive precipitation adsorption process. The morphology of the films has been characterized by AFM. Electrochemical and photophysical properties of these coordination polymers were investigated in CH 3 CN solution as well as thin films deposited on an electrode. The Ru(II)-Zn(II) film, deposited on a transparent ITO electrode, displays luminescence properties. On the other hand, the Ru(II)-Fe(II) film exhibits electrochromic properties under continuous cycling over the Fe II /Fe III and Ru II /Ru III waves, shifting from reddish dark at the Fe(II)-Ru(II) reduced state to orange-yellow at the Fe(III)-Ru(II) state and to pale green at the more oxidized state Fe(III)-Ru(III). These oxidation processes can be also driven by visible light. Indeed, upon continuous irradiation of an CH 3 CN solution of the Ru-Fe polymer in the presence of a diazonium salt as a sacrificial electron acceptor, the fast quantitative one-electron oxidation of the Fe(II) centers followed by that of the Ru(II) ones occurs, despite the strong quenching of the luminescence of the Ru(II) moieties by the Fe(II) center. The photoinduced oxidation of the Fe(II) center is still efficient when the Ru(II)-Fe(II) polymer is electrodeposited as a thin film on ITO leading to the storage of an oxidative equivalent on an electrode. † Electronic supplementary information (ESI) available: Electrochemical behaviour of [Ru(bpy) 2 (L2)] 2+ , [{Ru II -Fe II } n ] 4n+ and [{Ru II -Zn II } n ] 4n+ ; absorption and emission of [{Ru II -Zn II } n ] 4n+ on ITO. See Scheme 1 Chemical structure of the heteroditopic ligands bearing [Ru(bpy) 3 ] 2+ like moieties we have previously developed. 26 9826 | J. Mater. Chem. C, 2014, 2, 9824-9835 This journal is Scheme 2 Chemical formation of [{Ru(bpy) 2 (L2)M} n ] 4n+ (M ¼ Fe, Zn). This journal is

Photoactive Molecular Dyads [Ru(bpy)3–M(ttpy)2]n+ on Gold (M = Co(III), Zn(II)): Characterization, Intrawire Electron Transfer, and Photoelectric Conversion

“…The M­(II)/M­(III) oxidation potentials are estimated to be −0.06 V for Au/[Co II ] 2+ , −0.07 V (Co­(II)), and 0.96 V (Ru­(II)) for Au/[Co II –Ru II ] 4+ microelectrodes. These oxidation processes appear at similar potentials to the parent complexes in solution (i.e., [Co­(ttpy) 2 ] 2+ E 1/2 = −0.06 V vs Ag/AgNO 3 and [Ru­(bpy) 2 (bpyOtpy)] 2+ E 1/2 = 1.01 V vs Ag/AgNO 3 ), showing that the ether linkage serves as an innocent bridge to connect the different components of the dyad. In the case of Au/[Zn II –Ru II ] 4+ , since Zn 2+ cannot be oxidized or easily reduced, the cyclic voltammogram shows only the redox response of the Ru­(II) subunits at around E 1/2 = 0.96 V. For all of the modified electrodes, a linear relationship between anodic peak current density J and scan rate ν at low ν values indicates that the faradic signal stems from species anchored onto the electrode.…”

“…Among the different SAMs, those incorporating ruthenium complexes derived from 2,2′-bipyridine (bpy) or 1,10-phenanthroline are of particular interest because of their unique combination of photophysical and electrochemical properties. − Aiming to reach a system that can generate a charge-separated species on surface under visible light irradiation, our group has designed a series of [Ru­(bpy) 3 ] 2+ cores bearing one or two free terpyridines. These metalloligands can be associated with first-row transition metals to prepare supramolecular photoactive polymers , in solution, or in a stepwise mode to afford inorganic dyads and triads on a transparent electrode, such as indium tin oxide (ITO). − We have notably grafted dyads and triads using a Ru­(II) metalloligand in association with Co­(III) and/or Fe­(II) as electron-acceptor or electron-donor subunits, respectively. Under visible light irradiation and in the presence of sacrificial acceptor like a diazonium salt, the Ru II –Fe II dyad on ITO behaves as a photocathode .…”

Photoinduced Charge Separation within Metallo-supramolecular Wires Built around a [Ru(bpy)3]2+–Bisterpyridine Linear Entity

“…The detected polymer length doubles that of previously reported bimetallic Ru II /Fe II polymers containing ethyl bridges at the 4,4' position of the same bipyridine. 22 This result shows that 2,5-dimethyl benzene as linkages at the 5 and 5' positions of the same bipyridine limited the formation of small cyclic oligomers and lead to the formation of more tailored 1D polymers.…”

“…21 This building block has been recently used in association with Fe(II) or Zn(II) to obtain alternated bi-metallic coordination polymer. 22 These polymers can be deposited by an electroinduced process on a substrate and exhibit luminescence and photoredox properties. Using this approach to construct an efficient charge separated metallic triad system, we designed a ruthenium based metallo-ligand in which one of the bipyridine ligands of the [Ru(bpy) 3 ] 2+ photosensitive unit is substituted at the 5 and 5' positions by two terpyridines via an ether bridge.…”

Geometrically isomeric Pt(ii)/Fe(ii)-based heterometallo-supramolecular polymers with organometallic ligands for electrochromism and the electrochemical switching of Raman scattering

“…[9][10][11] The main benefits of these metallo-supramolecular polymers over their conventional covalent counterparts originate from the presence of metallic centers, providing a wide range of properties, such as optical, electrical, redox, photochemical, magnetic, or catalytic activities. 12 Due to the large range of available organic ligands and metallic cations, metallo-supramolecular polymers offer the vast potential to develop smart materials with tunable properties. In this context, if two metal ions are introduced to a metallo-supramolecular polymer chain regularly, unique properties due to the neighboring metalmetal interactions are expected to appear in the polymer.…”