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

Abstract

We propose in this work a stepwise approach to construct photoelectrodes. This takes advantage of the self-assembly interactions between thiol with a gold surface and terpyridine ligands with first-row transition metals. Here, a [Ru(bpy)] photosensitive center bearing a free terpyridine group has been used to construct two linear dyads on gold (Au/[Zn-Ru] and Au/[Co-Ru]). The stepwise construction was characterized by electrochemistry, quartz crystal microbalance, and atomic force microscopy imaging. The results show that the dyads behave as rigid layers and are inhomogeneously distributed on the surface. The surface coverages are estimated to be in the order of 10 mol cm. The kinetics of the heterogeneous electron transfer is determined on modified gold ball microelectrodes using Laviron's formula. The oxidation rates of the terminal Ru(II) subunits are estimated to be 700 and 2300 s for Au/[Zn-Ru] and Au/[Co-Ru], respectively. In the latter case, the rate is limited by the kinetics of electron transfer between an intermediate Co(II) center and the gold surface. For Au/[Zn-Ru], the Zn-bis-terpyridine center is not involved in the electron-transfer process and the oxidation of the Ru(II) subunit occurs through a superexchange process. In the presence of a tertiary amine in solution, the electrodes at a bias of 0.12 V behave as photoanodes when subjected to visible light irradiation. The magnitude of the photocurrent is around 10 μA cm for Au/[Co-Ru] and 5 μA cm for Au/[Zn-Ru], proving the importance of an electron relay on the photon-to-current conversion. The results suggest an efficient conversion for Au/[Co-Ru], since each bound dyad, once excited, injects an electron around 10 times per second.

Crystal structure, electrochemical and spectroscopic investigation of mer-tris[2-(1H-imidazol-2-yl-κN 3)pyrimidine-κN 1]ruthenium(II) bis(hexafluoridophosphate) trihydrate

“…Since the first preparation of the tris(2,2-bipyridine) ruthenium(II) complex by Burstall (1936), its interesting electrochemical and photochemical properties have stimulated the preparation and characterization of numerous analogous ruthenium(II) complexes (Le-Quang et al, 2018;Dong et al, 2018;Linares et al, 2013). When asymmetric bidentate ligands are used to obtain homoleptic complexes, facial and meridional isomers can be obtained, depending on steric and electronic properties with important implications on chemical reactivity and spectroscopy (Metherell et al, 2014).…”

Spacer Conjugation and Surface Support Effects in Monolayer Electrochromic Materials

“…Therefore, by adjusting the ligand electronics, both electric and optic responses of the metal complex can be fine-tuned . Incorporating a [Ru­(bpy) 3 ] 2+ motif to modify indium–tin oxide (ITO) with a Co­(III)/Ru­(II)/Fe­(II) triad and irradiating the assembly at a bias of 0.12 V (to maintain a Co­(III) state, thus making it a good electron acceptor toward the excited state of [Ru­(bpy) 3 ] 2+ *), Chauvin observed the generation of an anodic photocurrent in the presence of a tertiary amine as a sacrificial electron donor . The back electron transfer within the ITO/[Co­(II)–Ru­(III)–Fe­(II)] 7+ assemblies is short-circuited either by a fast electron injection from the Co­(II) center to the ITO electrode at 0.12 V and/or by an efficient electron transfer process from the Fe­(II) subunits to the Ru­(III) center (Δ G = −200 mV).…”

“…Traditional EC materials are based on relatively thick layers of organic, − organometallic, , or inorganic − compounds or composites that change their absorbance or reflectance through an electrochemical redox process . Among others, terpyridine (tpy)-based ligands have been shown to form stable complexes with a wide range of metal ions in different oxidation states. ,,, Since the seminal works by Constable, , the synthetic methodology of tpy derivatives has been significantly improved. − In contrast to bpy-based asymmetric ligands that often form a mixture of facial and meridional isomers, tpy-containing ligands are structurally more appealing, because they form well-defined six-coordinate cationic Fe­(II), Co­(II), Ru­(II), and Os­(II) complexes where two ligating moieties are situated in an orthogonal fashion. Introducing two or more tpy moieties into one ligand leads to a range of molecules that can form metallo-supramolecular coordination polymers (MSCPs) in the presence of corresponding metal ions.…”

Optical Read‐Out of the Electrical Switching of Cobalt‐Terpyridine‐BODIPY Molecules Immobilized as Single Layer on ITO

“…One decisive advantage is the possibility to control the magnetic behavior from an electrical input with an optical output. Ultrathin films of covalently immobilized Co complexes on conductive substrates were investigated for a variety of purposes: catalysis, [9,10] electron conduction, [11] molecular transistor, [12] photoelectric conversion, [13,14] electrochromism, [15,16] switchable materials. [17][18][19] One of the bottlenecks is to reduce the delay time between applying the electrical stimulus and reading the optical response that must be intense enough.…”