Synthesis and characterization of polythiophenes with liquid crystalline azobenzene as side chains

A series of azobenzene-functionalized liquid-crystalline (LC) polythiophene derivatives: poly[4-((4-(phenyl)azo)phenoxy)alkyl-3-thienylacetate] (alkyl=hexyl, octyl and undecyl) (P6EtO, P8EtO and P11EtO) were synthesized. The composition, structure and thermal property of these LC polythiophene derivatives were fully characterized, and their LC behavior and photoresponsive property were also investigated by means of POM and UV source. The results have shown that PnEtO exhibited the nematic (N) phase when the azobenzene moiety was in the trans form while no LC phase was observed when the azobenzene was in the cis form. Photoirradiation of these polymers with UV light brings about the trans-cis isomerization of the azobenzene pendants and results in disappearance of the nematic phase.