Synthesis and characterization of liquid-crystalline alternating copolymers based on fluorene and thiophene

Abstract

New alternating conjugated copolymer (PFTT) comprised of 9,9´-dioctylfluorene and thienothiophene has been synthesized by palladium-catalyzed Suzuki coupling reaction. The synthesized polymer could be well characterized by $^1H-NMR, ^13C-NMR$, and elemental analysis. Not only did it show high thermal stability, but also PFTT displayed a unique phase transition behavior between crystalline state and liquid-crystalline (LC) state. In proof of its LC property, the film of polymer showed a birefringent fluid phase as annealed above its melting temperature ($T_Cr-LC$). In addition, owing to its relatively high characteristic temperatures, the fluorene-based copolymer PFTT is expected to be used as semiconducting layers in organic field-effect transistors (OFETs). Light-emitting diode (LED) device fabricated with ITO/PEDOT/PFTT/LiF/Al configuration revealed pure green light emission with a maximum EL peak at 515 nm. Such emission corresponded to the CIE coordinates (0.29, 0.63), which close to standard green used in national television system committee (NTSC). As the controlled HOMO and LUMO energy levels conduced toward enhanced hole and electron injection, PFTT exhibited high electroluminescent performances better than the other similar copolymer (e.g, PFT2), which demonstrated the superiority of PFTT in LEDs. New alternating conjugated copolymer (PFTT) comprised of 9,9´-dioctylfluorene and thienothiophene has been synthesized by palladium-catalyzed Suzuki coupling reaction. The synthesized polymer could be well characterized by $^1H-NMR, ^13C-NMR$, and elemental analysis. Not only did it show high thermal stability, but also PFTT displayed a unique phase transition behavior between crystalline state and liquid-crystalline (LC) state. In proof of its LC property, the film of polymer showed a birefringent fluid phase as annealed above its melting temperature ($T_Cr-LC$). In addition, owing to its relatively high characteristic temperatures, the...