Surface coordination chemistry has a promising potential to construct a well-defined surface functional architectures such as metal-organic framework and 2D layered structure on surface.  In order to arrange the molecular units on the surface, surface anchors play an important role to determine the molecular orientation and the surface density of the molecules.  Here, we present the fabrication and functions of surface molecular assemblies based on photo- and redox-active metal complexes with multipod anchors.  Particularly, we discuss two topics as shown in Fig. 1; i.e, (1) dsDNA wires between two electrodes and (2) layered photoelectrochemical molecular devices with memory effect on a solid surface.¹⁾ 

1) Fabrication of DNA wires by surface immobilized DNA intercalator:¹⁾  A novel Ru complex bearing both an acridine group and anchoring phosphonate groups was immobilized on a surface in order to capture double-stranded DNAs (dsDNAs) from solution. The immobilized surface could capture DNAs; however, the optimal number of molecular density on the surface exist to obtain the extended dsDNAs on the surface. The construction of DNA nanowires on the Au/SiO2 patterned surface was accomplished by the molecular combing method of the selective immobilized Ru complex on Au electrodes. These interconnected nanowires between Au electrodes were used as a scaffold for the modification of Pd nanoparticles on the DNA.

 2) Combinatorial approach to redox-active layered Ru complexes bearing tetrapod anchors:²⁾  New tetrapod phosphonate ligand XP and its Ru/Os complexes (Figure 1) have been synthesized. Oxidation potentials of [M(XP)(BL)M(XP)](M =Ru or Os) complexes on ITO electrode showed one-step two-electron process at +0.93 V for M = Ru and +0.66 V for M = Os, respectively. Layer-by-layer growth on ITO electrode was achieved by the surface assembling of the complexes with Zr(IV) ion. By changing the arranging order of the complex units with a variety of redox potentials, the different potential sequences were formed, some of which showed a current rectifier and a memory effect upon the photoelectrochemical response.

Fig. 1. Fabrication of multilayer and nanowire from molecular units with surface anchor group on surface.

References

1. K. Kobayashi, N. Tonegawa, S. Fujii, J. Hikida, H. Nozoye, K. Tsutsui, Y. Wada, M. Chikira, and M. Haga, Langmuir, 2008, 224, 13203.

2. M. Haga, K. Kobayashi, and K. Terada, Coord. Chem. Rev., 2007, 251, 2688.

3. K. Terada, K. Kobayashi, and M. Haga, , Dalton Trans., 2008, 4846.

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1. Surface manipulation and immobilization of single DNA wire on Au surface
2. Surface Immobilization of Dinuclear Ruthenium Complexes Bearing Aqua Ligand on ITO or TiO₂ Electrode: Fabrication and Its Photoelectrochemical Properties