beta-Phase formation in poly(9,9-di-n-octylfluorene) by incorporating an ambipolar unit containing phenothiazine and 4-(dicyanomethylene)-2-methyl-6-[p-(dimethylamino)styryl]-4H-pyran

Abstract

Novel fluorene-based blue-light-emitting copolymers (F8Rs) in the beta-phase are designed and synthesized using the palladium-catalyzed Suzuki reaction. The beta-phase can be generated by introducing an ambipolar unit, that contains 10-n-hexylphenothiazine (PTZ) and 4-(dicyanomethylene)-2-methyl-6-[p-(dimethylamino)styryl]-4H-pyran (DCM) (as the donor and acceptor moieties, respectively) on a polyfluorene backbone. By comparing the absorption (peak at 437 +/- 1 nm), photoluminescence (PL) (peak at 441 +/- 1 nm), and X-ray diffraction (XRD) (peak centered around 2 theta = 7.0 degrees) characteristics of the resulting polymers (F8Rs) with those of the polyfluorene homopolymer (PFO), we found that fluorene-based copolymers with ambipolar moieties, such as PTZ and DCM, can prompt the formation of the beta-phase after spin-coating without gelling in a poor solvent, exposure to tetrahydrofuran vapor, cooling to liquid-N-2 temperature, and reheating. The PL and electroluminescence (EL) efficiencies of the copolymer F8R5 are higher than those of PFO (by factors of two and 15, respectively). The EL spectrum of the copolymer showed almost pure blue emission, with CIE (Commission Internationale de l'Eclairage) coordinates of x = 0.17 and y = 0.10.