Synthesis of conjugated polymers with azobenzene moieties in the main chain

Poly(phenylenevinylene)-based conjugated polymers with azobenzene groups in the main chains were prepared by the Pd-catalyzed coupling polymerization of divinylarenes with dihaloarenes. The Pd-catalyzed coupling polymerization of 4,4′-divinylazobenzene with dihaloarenes such as 1,3-dibromobenzene, 1,4-dibromo-2,5-dihexylbenzene, 4,4′-dibromoazobenzene, and 4,4′-diiodoazobenzene resulted in polymers with poor solubility. In contrast, soluble polymers containing azobenzene moieties in the main chains were attainable from divinylbenzenes with 4,4′-dihaloazobenzenes if either or both of the monomers possessed hexyl groups on the aromatic rings. The number-average molecular weight of the polymer exceeded 10,000 under optimized conditions, and the polymer showed a remarkably redshifted absorption in the visible region (456 nm). 1H NMR and IR spectra supported that the polymers having only trans-geometry for the double bonds.