Synthesis of laterally attached side-chain liquid crystalline poly(p-phenylene vinylene) and polyfluorene derivatives for the application of polarized electroluminescence

Two series of poly(p-phenylene vinylene) and polyfluorene derivatives (PPV1–PPV4 and PF1–PF5) containing laterally attached penta(p-phenylene) mesogenes were synthesized and characterized. These polymers show nematic liquid crystalline behavior. The optical properties of the polymers were investigated by UV–vis absorption and photoluminescence spectrometers and these polymers were fabricated to form the polarized electroluminescent devices using poly(ethylenedioxythiophene)–poly(styrene sulfonic acid) (PEDOT–PSS) as an alignment layer. In the series of poly(p-phenylene vinylene) derivatives, polymer PPV4 offered the best EL device performance. It emitted yellow light at 588 nm at 4 V. The maximum brightness was about 1337 cd/m2 at 9 V with a polarized ratio of 2.6. In another series of polyfluorene derivatives, PF4 offered the best EL device performance with the polarized ratio of 12.4 and a maximum luminescence of 1855 cd/m2. In the case of polarized white light, as a consequence of blending small amount of PF4 and PF5 with a host polymer PF2, polarized ratio of up to 10.2 and a maximum brightness of 2454 cd/m2 have been attained. The aligned films exhibited pronounced polarized ratio, implying that the polymers exhibit potential for linearly polarized LED application.