Ruthenium-chelating poly(heteroaryleneethynylene)s: Synthesis and properties

A series of ruthenium(II)-chelating poly(heteroaryleneethynylene)s were synthesized by the palladium-catalyzed cross-coupling polycondensation of diethynylbenzenes and dibromobipyridine-Ru(II) chelates. The grafting of different alkoxy side chains including n-butoxy, (2-ethylhexyl)oxy, and n-octadecyloxy in the diethynylbenzene compounds enhances the solubility and processability of the new polymers. The same effect is attainable by tert-butyl substituents in the 2,2'-bipyridine ligands. The UV/vis absorption showed a considerable red shift of the lambda(max) from poly bis(2,2'-bipyridine)-[2,2'-bipyridine-5,5'-diylethynylene-(2,5-dialkoxy)ethylene]ruthenium(II) bis(hexafluorophosphate)l (5) to the 4,4'-diylethynylene isomers 6, suggesting an increase in the electronic delocalization between the backbone and ruthenium(II) chelate. The polymers are good photoconducting materials (I-Ph = 3.7 x 10(-12) A at 18 000 cm(-1)), exhibiting an oxidation potential of 1.24 V vs SCE. The polymers are thermostable and exhibit a good solubility in acetone, DMF, DMSO, acetonitrile, and cyclohexanone. Last, an improved method of molecular weight determination by GPC was devised.