A series of electrochromic metal complex nanosheets comprising 1,3,5-tris(4-(2,2':6',2″-terpyridyl)phenyl)benzene or 1,3,5-tris((2,2':6',2″-terpyridyl)ethynyl)benzene and Fe(2+) or Co(2+) was synthesized. The preparation of multilayered nanosheets was achieved by liquid/liquid interfacial synthesis using an organic ligand solution and an aqueous metal-ion solution. The resultant nanosheet had a flat, smooth morphology and was several hundreds of nanometers thick. Upon its deposition on an indium tin oxide (ITO) electrode, the nanosheet underwent a reversible and robust redox reaction (Fe(3+)/Fe(2+) or Co(2+)/Co(+)) accompanied by a distinctive color change. Electrochromism was achieved in a solidified device composed of the nanosheet, a pair of ITO electrodes, and a polymer-supported electrolyte. The combination of Fe(2+) and Co(2+) nanosheets in one device-deposited on each ITO electrode-demonstrated dual-electrochromic behavior.

No abstract

The present work reports a tripodal scaffold for bis(terpyridine)-Fe(II) oligomer wires on an Au(111) surface: the tripodal scaffold realised both orthogonality of the oligomer wires, and fast interfacial electron transfer through the oligomer wires.

Dendritic bis(terpyridine)iron(II) wires with terminal ferrocene units were synthesized on a Au(111) surface by stepwise coordination using a three-way terpyridine ligand, a ferrocene-modified terpyridine ligand, and Fe(II) ions. Potential-step chronoamperometry, which applied overpotentials to induce the redox of the terminal ferrocene, revealed an unusual electron-transport phenomenon. The current-time profile did not follow an exponential decay that is common for linear molecular wire systems. The nonexponentiality was more prominent in the forward electron-transport direction (from the terminal ferrocene to the gold electrode, oxidation) than in the reverse direction (from the gold electrode to the terminal ferrocenium, reduction). A plateau and a steep fall were observed in the former. We propose a simple electron transport mechanism based on intrawire electron hopping between two adjacent redox-active sites, and the numerical simulation thereof reproduced the series of "asymmetric" potential-step chronoamperometry results for both linear and branched bis(terpyridine)iron(II) wires.

This article completes our comprehensive understanding of the electron transport properties of our original π-conjugated redox-active molecular wires comprising Fe bridged by p-phenylene linkers (tpy=2,2':6',2''-terpyridine). The Fe(tpy)2 oligomer wires comprise three types of tpy ligands: the anchor tpy ligand (A series) makes a junction between the wire and electrode, the bridging bis-tpy ligand (L series) connects the Fe(tpy)2 units, and the terminal tpy ligand (T series) possesses a redox site as a probe for the long-range electron transport ability. Taking advantage of the precise tunability of the composition of the Fe(tpy)2 oligomer wires, thus far we investigated how A and L impacted on the electron-transport ability. The excellent long-range electron transport ability with ultrasmall attenuation constants (β(d), 0.002 Å(-1) as the minimum) depends on L significantly [Chem. Asian J. 2009, 4, 1361], whereas A is unrelated to the β(d) value, but influences the zero-distance electron-transfer rate constant, k(et)(0) [J. Am. Chem. Soc. 2010, 132, 4524]. Herein we study the influence of terminal ligand T(x) (x=1-3). β(d) is independent of T, however, T(3), with a cyclometallated Ru complex as the redox site, gives rise to a k(et)(0) value greater than T(1) and T(2) with ferrocene. This series of simple but definitive conclusions indicates that we have reached the stage of being able to precisely design molecular wires to attain desirable single-molecule electron conduction.