This paper reports the synthesis and physical properties of a series of novel bipyridine-containing poly(benzobisoxazole)s and poly(benzobisthiazole)s. The polymers were synthesized by polycondensation of 2,2‘-bipyridine-5,5‘-dicarboxylic acid with diaminobenzenediols in poly(phosphoric acid). Some model compounds were also synthesized by a similar approach for comparison. The polymers exhibited extremely high thermal stabilities in air or nitrogen atmosphere. From the polarized microscopic studies, lyotropic mesophases were observed in some polymer solutions in methanesulfonic acid. The 2,2‘-bipyridyl moieties on the polymer main chain were able to form metal complexes with bis(2,2‘-bipyridyl)ruthenium(II) compounds, which was proved by different characterization methods such as electronic and luminescence spectroscopy, cyclic voltammetry, and thermal analysis. The charge carriers mobilities of the polymer metal complexes are of the order of 10-5 cm2 V-1 s-1, which are 2 orders of magnitude higher than that of the metal-free polymers. This clearly shows that the ruthenium complexes can play the role as charge carriers in the charge transport process.

Two series of polyamides and polyesters derived from 2,2′-bipyridine-5,5′-dicarboxylic acid have been synthesized. Different types of aliphatic and aromatic diamine and diol monomers with different structure were polymerized with the diacid or diacid chloride by using different polymerization methods. Most of these polymers exhibited modest thermal stabilities with decomposition temperatures in the range 320-500°C, depending on the structure of the polymer main chain. It was found that some polyamides with a rigid main chain formed a lyotropic mesophase when dissolved in concentrated sulfuric acid or HMPA-4% LiCl solvent systems. For those polyamides and polyesters with a more flexible main chain, a thermotropic liquid crystal phase was observed. If a long and flexible pendant chain was attached to the polyesters, side chain melting was observed before the onset of the crystalline-nematic transition. The 2,2′-bipyridyl moieties were able to form a complex with ruthenium. These polymer-ruthenium complexes were either synthesized by metalation of the polymers or synthesized directly from the corresponding ruthenium-containing monomer. After the formation of ruthenium complexes, they were able to enhance the photosensitivity and charge carrier mobility of the polymers. The ruthenium-containing polymers also emit red light at ca. 700 nm owing to the emission from the metal-ligand charge-transfer excited states. Some polymers with good film forming properties were fabricated into simple single-layer light-emitting devices, and red light emission was observed when the devices were subjected to forward bias.

The search for new classes of organic and metal-organic compounds for organic thin-film transistors (OTFTs) is of immense current interest due to the relatively low cost and potential applications of OTFTs in flexible large-area electronic devices such as displays [1,2] and sensors.[3±5] Indeed,OTFTs have been recently reported in the fabrication of active-matrix displays [6] and integrated circuits (ICs) for logic and memory chips. [7] Unlike their silicon-based TFTs counterparts which require expensive and complicated fabricating systems at a high temperature, [8] the deposition of organic materials on large-area substrates, including flexible polymer substrates, is much less complicated.[1]Over the last decade, much attention has been focused on the study of pentacene and its derivatives as organic semiconductors for OTFTs. This class of materials has been shown to exhibit excellent field-effect mobilities [9] and environmental stabilities.[1] Similarly, oligothiophenes, [10] poly(3-alkyl-thiophene) (P3HT), [11] and fused heterocyclic compounds [12] have been shown to possess comparable properties that are highly desirable for OTFT applications. Despite these advances, difficulties in structural modification of these literature-reported organic semiconductors remain. Current methods used to modify charge-carrier properties of the materials rely on changing the type of substitution on the materials. By introducing electron-donating (D) or electron-accepting (A) functional groups, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) levels of the materials can be fine-tuned to give either p-type or n-type organic semiconductors. In this context, it would be desirable to develop new classes of organic materials which possess extended p-conjugated electronic systems that can be easily prepared and modified and exhibit effective intermolecular interactions for charge transportation. Work in our laboratory and by others has demonstrated the potential applications of conjugated ethynylated arylacetylene materials such as arylacetylenes, [13] poly(arylene ethylene)s, [14] and metal-containing acetylide complexes. [15] These materials have received considerable attention in organic light-emitting diodes, [16] optoelectronics, [17] molecular electronics, [18] and sensors. [19] Through incorporation of different electron-donating or electron-withdrawing functional groups, the physical and electronic behavior of oligomeric arylacetylenes such as thermal stabilities, carrier transport, and structural packing properties could be readily and systematically modified for OTFT applications. Also, the p-conjugation length of the linear molecules can easily be extended by synthetically controlling the number of repeating arylacetylene moieties incorporated into the structures. For example, Wong et al. recently reported the synthesis of crystalline pyrimidine-containing arylethynyl molecules with dipole±dipole and face-to-face p±p interactions. [20] Indeed, the relative pl...

This paper reports the synthesis and physical properties of a novel aromatic polymer which contains the tridentate 2,6-bis(benzimidazol-2-yl)pyridine moiety. It was found that the polymer exhibits different luminescence properties in solution and in the solid state because of the formation of polymer aggregates. Upon doping with iodine, the electrical conductivity of the polymer film was increased to 2.4 × 10-6 S/cm. The polymer was fabricated into a single-layer light-emitting device, and yellow light emission was observed under forward bias. Besides, it is able to form complexes with ruthenium, and the resulting polymer−metal complexes exhibit different solubilities and physical properties. The ruthenium complexes strongly enhance the absorption and photosensitivity beyond 500 nm due to the presence of the metal−ligand charge-transfer transitions. As a result, a large photocurrent response was observed when the polymer was irradiated with visible light. On the other hand, there was no electroluminescence in the metal-containing polymers because of the intrinsic nonemitting properties in ruthenium terpyridine complexes.

A series of novel aromatic polyamides containing 2,2'-bipyridine moiety were synthesized by polycondensation of 2,2'-bipyridine-S,S'-dicarboxylic acid (2) with various aromatic diamines in hexamethylphosphoramide (HMPA) containing lithium chloride. The resulting polyamide solutions in 98% sulfuric acid and in HMPA-LiCI exhibited lyotropic liquid crystal phases. The phase transition behaviors were studied by polarizing microscopy and X-ray diffraction. The polyamides also formed metal complexes with cisdichlorobis(bipyridine)ruthenium dihydrate [cis-Ru(bpy),CI, -2 H,O] which was supported by changes in electronic spectra.