Dynamic switching of linearly polarized emission in liquid-crystallinity-embedded photoresponsive conjugated polymers

Multifunctional conjugated polymers bearing fluorescent, liquid crystalline, and photoresponsive functions were synthesized by introducing the dithienylethene moieties into side chains of poly(p-phenylene-vinylene) [P1] and poly(bithienylene-phenylene) [P2]. Observation of polarizing optical microscope showed that the polymers have main-chain-type liquid crystallinity. Reversible photoisomerization of the dithienylethene moiety was observed in both solution and cast film. Drastic quenching of fluorescence occurred when the photoresponsive moiety changed from an open form to a closed one upon irradiation of ultraviolet light. The quenched fluorescence was recovered through a photoisomerization from the closed form to the open one. Macroscopically aligned P2 film, prepared by a rubbing in liquid crystalline phase, exhibited a linearly polarized fluorescence with significant anisotropy. Reversible quenching and emitting behavior in anisotropic fluorescence was well controlled by the photochemical switching.