Synthesis of new Azo‐based liquid crystalline polymers and their selective sensing behaviors to alkali metal ions

Abstract

We report novel liquid crystalline (LC) polymers containing pendant azobenzene moieties with n-dodecyl substituents and ethyleneoxy spacers of different lengths and describe their selective detection behaviors to alkali metal ions. The new azopolymers produce homogenous smectic phases with a typical fan-shaped texture. UV-Vis and 1 H NMR studies confirm that the azopolymers selectively bind to Li 1 and Na 1 , but do not complex with K 1 , Ba 21 , Mg 21 , or Ca 21 . Both the ethyleneoxy spacer and azobenzene units participate in binding to Li 1 and Na 1 cations in solution. Interestingly, after formation of the complexed structure, the ratio of cis to trans con-former is considerably increased suggesting stronger interactions of the cis conformer with alkali metal ions. Irradiation of the complexed structure with 365 nm UV induces conversion of the uncomplexed trans to the cis. These findings suggest a great potential of the LC azopolymers as selective sensors or separation membranes for alkali metal ions.