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 λ max from poly{bis(2,2‘-bipyridine)-[2,2‘-bipyridine-5,5‘-diylethynylene-(2,5-dialkoxy)ethylene]ruthenium(II) bis(hexafluorophosphate)} ( 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 × 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.