Coordination complexes porphyrin polymers

This chapter describes the synthesis and properties of a number of classes of polymers containing metal coordination complexes in their structures. These polymers are prepared by polymerization reactions of metal-containing monomers and through metal coordination reactions. Schiff base-containing polymers (5) were one of the earUest classes of coordination polymers examined. Polymers incorporating macro-cycUc porphyrins and phthalocyanines (7) in their backbones and sidechains are known to exhibit interesting optical and electrical properties. The best-studied classes of metal-containing polymers contain bipyridyl and other related units coordinated to metal ions (8). 

A carbon monoxide (CO)-saturated dichloromethane solution containing the Fe(III) complex with 1-ethylimidazole was vigorously stirred with an aqueous solution of sodium dithionite under a CO atmosphere. The dichloromethane solution was evaporated to dryness, and the residue was heated to about 80 C in vacuo to remove the coordinating CO molecule from the complex. Water was added to the powdery iron-porphyrin polymer with shaking to yield a micellar solution of the iron-porphyrin polymer Structure (4). 

Cationic polymerization of alkylene oxides generally produces low molecular weight polymers, although some work [26] seems to indicate that this difficulty can be overcome by the presence of an alcohol (Fig. 1.3). Higher molecular weight polyethylene oxides can be prepared by a coordinated nucleophilic mechanism that employs such catalysts as alkoxides, oxides, carbonates, and carboxylates, or chelates of alkaline earth metals (Fig. 1.4). An aluminum-porphyrin complex is claimed to generate immortal polymers from alkylene oxides that are totally free from termination reaction [27]. 

The coordination compounds are widely used as luminescent probes for polymer-based PSP. The coordination compounds are classified into two categories. One is the transition metal polypyridyl complex. In this group, transition metals are Ru2+, Os+ and Ir3+ as shown in Fig. 10. The second group comprises the metalloporphyrins as shown in Fig. 11. Pt2+ and Pd2+ porphyrins are especially used as PSP probes. 

Elucidation of the Mn coordination sphere allows for further mechanistic insights into the Mn oxidation process specifically the electron transfer pathway from Mn11 to the acceptor (delocalized porphyrin % radical or the Fe center) may take place via the heme propionate ligand [52]. Upon further chelation a (neutral) Mnm complex may diffuse outside the enzyme and into the lignin polymer. 

In this chapter, we presented three different systems of molecular assemblies using molecular wires. The first involved the fabrication of the molecular wire system with metal complex oligomer or polymer wires composed of bis(terpyridine)metal complexes using the bottom-up method. This system showed characteristic electron transfer distinct from conventional redox polymers. The second involved the fabrication of a photoelectric conversion system using ITO electrodes modified with porphyrin-terminated bis(terpyr-idine)metal complex wires by the stepwise coordination method, which demonstrated that the electronic nature of the molecular wire is critical to the photoelectron transfer from the porphyrin to ITO. This system proposed a new, facile fabrication method of molecular assemblies effective for photoelectron transfer. The third involved the fabrication of a bioconjugated photonic system composed of molecular wires and photosystem I. The feasibility of the biophotosensor and the biophotoelectrode has been demonstrated. This system proposed that the bioconjugation and the surface bottom-up fabrication of molecular wires are useful approaches in the development of biomo-lecular devices. These three systems of molecular assemblies will provide unprecedented functional molecular devices with desired structures and electron transfer control. 

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