Stepwise coordination method

FIGURE 2. Chemical structures of the ligands and stepwise coordination methods to prepare linear and branched oligomer and polymer wires on an Au/mica or Au/ITO plate. (Reprinted with permission from Ref. 13.)... 

We describe here that the redox oligomer wires fabricated with the stepwise coordination method show characteristic electron transport behavior distinct from conventional redox polymers. Redox polymers are representative electron-conducting substances in which redox species are connected to form a polymer wire.21-25 The electron transport was treated according to the concept of redox conduction, based on the dilfusional motion of collective electron transfer pathways, composed of electron hopping terms and/or physical diffusion.17,18,26-30 In the characterization of redox conduction, the Cottrell equation can be applied to the initial current—time curve after the potential step in potential step chronoamperometry (PSCA), which causes the redox reaction of the redox polymer film ... 

While molecular assembly has proven to be effective for a photoelectric conversion system, coordination reactions are possibly a simple approach for connecting such functional molecules, as presented in the previous section. We applied the stepwise coordination method to prepare a photoelectric conversion system. Since the molecular wire exhibits redox conduction through the wire,11,13 efficient photo-electron transport through the redox sites in the wire is also expected. In this section, we demonstrate the fabrication of a photoelectric conversion system using ITO electrodes modified with M(tpy)2 (M = Co, Fe, Zn) complex wires with a terminal porphyrin moiety as a photosensitizer. The behavior of photo-electron transfer from porphyrin to ITO through the molecular wire was investigated by changing the metal element in the M(tpy)2 moieties.14... 

FIGURE 11. Chemical structure of the ligands used in this chapter, and stepwise coordination methods for the preparation of modified ITO electrodes (i) immobilization of tpy-BzA, (ii) complexation with a metal ion, and (iii) complexation with tpy-ZnTPP. (Reprinted with permission from Ref. 14.)... 

This section described the fabrication of ITO electrodes modified with porphyrin-terminated M(tpy)2 complex wires by the stepwise coordination method, and it is demonstrated that the electronic nature of the molecular wire is critical to the photoelectron transfer from the porphyrin to ITO. These results suggest that the new facile fabrication method of molecular assemblies is effective in the construction of photoelectron transfer systems. The system could be upgraded by extending the wire length, embedding the redox potential step in the wire, increasing the photoreceptors in the wire, and/or incorporating donors and acceptors. 

Figure 9.13 Stepwise coordination method to prepare metal complex molecular wire on Au.

One of the interesting things about the redox polymers is their use in the creation of the molecular electronic devices.3-5 Redox polymer films on electrodes have been fabricated using chemical modification, electrochemical polymerization, polymer coating, and so on.88 Recently, stepwise complexation methods have been employed to fabricate multiple complex layers.89,90,91 In this section, the stepwise preparation of bis(tpy)metal polymer chains by combining terpyridine (tpy) ligand self-assembled monolayer (SAM) formation and metal-tpy coordination reactions is described as an example. This method realized the formation of a desired number of polymer units and a desired sequence of Co-Fe heterometal structures in the polymer chain.92... 

PVP were calculated by computer, using the modified method of Bjenum, and the constants obtained are plotted in Fig. 9 together with those of a pyridine-Cu systemS5 In the monomeric pyridine system, the stepwise formation constant decreases with the number of coordinated ligands because the number of vacant sites on the Cu ion, or the ligand-accepting ability of the Cu ion, decreases with succes-... 

The decarboxylation reaction coordinate was then explored using the EVB methods described above, assuming, based on the results of solution simulations, that a stepwise decarboxylation-then-proton transfer mechanism (mechanism... 

Reaction of aluminum halides with acetonitrile solutions of terpy leads to the formation of [Al(terpy)Cl3] or [Al(terpy)2]Xj (X = Cl, Br, or I) (48). Spectroscopic and conductivity measurements suggest that these complexes are octahedral. Moore and co-workers have investigated the reaction of terpy with [A1(DMS0)6] (DMSO, dimethylsulfoxide) by NMR methods stepwise release of DMSO indicated sequential coordination of the pyridine rings, and it is noteworthy that the closure of the final ring is significantly slower than the other two, as predicted by our concepts of increasing strain in the chelated complex (78). 

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