Synthesis and Photophysical Properties of Some Conjugated Polymers Functionalized with Ruthenium Polypyridine Complexes
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ABSTRACT A series of conjugated polymers functionalized with different ruthenium polypyridine metal complexes were synthesized by the palladium catalyzed reaction. Two conjugated polymer systems have been studied: 1. poly(phenylenevinylene) with bis(2,2':6',2"-terpyridine) ruthenium (II) on the mainchain and 2. quinoxaline based polymers with tris(2,2'-bipyridine) ruthenium (II). The ruthenium polypyridine complexes exhibit a long-lived metal to ligand charge transfer excited state which can enhance the photosensitivity of the resulting polymers. Different physical properties such as the photoconductivity and charge mobility in these polymers are also studied. INTRODUCTION Organic conjugated polymers and oligomers have been used as the active semiconducting layer in various organic-based thin film devices such as solid state laser materials,' organic transistors, 2 light emitting diodes, 3 photodiodes, 4 and electrode active materials. 5 They combine the electronic and photonic properties of traditional inorganic semiconductors and the synthetic and processing advantages of organic polymers. In addition, organic materials also enjoy the advantages of ease of structural design and modification. The physical properties, solubility, and processibility can be easily "tuned" by attaching different functionalities to the polymer backbone or side chain. When conjugated polymers are coupled with transition metal complexes, they are expected to exhibit new properties because many transition metal complexes have specific catalytic, redox, and photophysical properties. A polymer-metal complex is a metal complex containing a polymer ligand which presents a remarkably specific structure in which central metal ions are surrounded by an enormous polymer chain. Based on this polymeric ligand, the polymer-metal complex shows interesting and important characteristics. Most of the studies on polymer-metal complexes are directed toward their catalytic activities not only because they are excellent models for the metalloenzymes, but also lead to the development of 6 highly efficient catalysts. Here, we report the synthesis and characterization of two series of conjugated polymers which contain polypyridine complexes. The first system is a poly(p-phenylenevinylene) (PPV) incorporating ruthenium terpyridine complexes [Ru(tpy) 2]2+ in the polymer mainchain, while the second system is quinoxaline-based poly(p-phenylene) (PPP), which contains a ruthenium bipyridine [Ru(bpy) 3] 2+ metal complex. The chemistry and photophysics of ruthenium polypyridine complexes have been studied extensively. 7 They are well known photosensitizers because of the relatively long-lived metal-ligand charge transfer (MLCT) excited states. When incorporated into conjugated polymers, the ruthenium polypyridine complexes may act as 581 Mat. Res. Soc. Symp. Proc. Vol. 488 © 1998 Materials Research Society
photosensitizers and thus enhance the photoconductivity. Moreover, the ruthenium complexes are also electrochemically active exhibiting a reversible Ru"'" redox p
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