Type II polymers with pendant metal complexes

2 Type II polymers with pendant metal complexes Polymers containing bipyridyl and terpyridyl metal-binding sites 

Diimine-based ligands such as bipyridine have been used widely as ligands for transition metals. Their conjugated structure makes them attractive candidates for incorporation directly into a conjugated polymer backbone. In this configuration, metal centers that are coordinated by the diimine are strongly electronically coupled to the polymer. 

The bipyridyl group has been incorporated into ligands 65a and 65b (Chart 5.19) [73]. The shorter of the two oligomers, 65a, does not polymerize electrochemically however, ligand 65b does form conductive films by electropolymerization. The complex [Ru(65b)3] + electropolymerizes and forms conductive thin 

The phenanthroline-containing ligands 66a and b (Chart 5.19) have been incorporated into Cu complexes and electropolymerized [74]. The geometry at the Cu center in poly-[Cu(66a)2] and poly-[Cu(66b)2] was probed using X-ray absorption. It was shown that the Cu centers in poly-[Cu(66b)2] contribute to the conductivity of the film. Removal of the copper with cyanide causes the structure of the polymer to irreversibly collapse in poly-[Cu(66a)2], whereas the presence of the hexyl chains in poly-[Cu(66b)2] help to maintain an intact polymer structure after the removal of the metal. 

Several related polymers prepared via chemical polymerization are mentioned here as they are closely related to the systems discussed above. Polymers 69 and 70 (Chart 5.20) have been prepared via Pd-catalyzed Stille coupling [77]. The electrochemistry of these polymers both in solution and as thin films shows well-defined redox waves due to the metal and oligothiophene units. ESR reveals the presence of mobile charge carriers in the polymer and a polaronic band in the UV-Vis spectrum of the doped material correlates with the ESR results [78]. Photophysical analysis of the polymers reveals that in the case of the Ru polymers the k state is lower in energy than the MLCT band. 

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