A novel conjugated aromatic core containing direct-coupled fluorene, thiophene, and biphenyl groups via Suzuki coupling reaction was synthesized. The asymmetrical molecules contain two kinds of poly(ethylene oxide)s (PEO, M n = 750 and 2000, n = 17 and 44) on one side of the rigid cores. Asymmetrical FOC 8 PEO 17 and FOC 16 PEO 17 contain flexible PEO chains ( n = 17) displaying the smectic phases. However, FOC 8 PEO 44 and FOC 16 PEO 44 consisting of flexible PEO chains ( n = 44) exhibit two kinds of columnar phases, Col h and Col r . Besides, alkoxy groups with different lengths (−OC 8 H 17 and −OC 16 H 33 ) on both sides of the rigid cores were used as another flexible chain to form symmetrical molecules. Symmetrical FOC 8 and FOC 16 exhibit the nematic and smectic mesophases, respectively. Optical textures (POM) and XRD patterns have confirmed the structure of the mesophases and the molecular arrangements. The photophysical characteristics of all luminescent compounds were studied by photoluminescence and UV−vis absorption. In addition, a series of double-layered PLED devices with the configuration of PVK:emitters(100:8 by weight)/TPBI/MgAg/Ag were fabricated and investigated.
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Lin et al. (2006) studied this question.
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