Directed ortho metalation-boronation Suzuki-Miyaura cross coupling leading to synthesis of azafluorenol core liquid crystals
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The synthesis of chiral fluorenol crystal materials employing directed ortho metalation (DoM) combined with directed remote metalation (DreM) and Suzuki-Miyauara Coupling was previously reported by McCubbin, Snieckus and Lemieux.ref? This study reported that certain fluorenol derivatives form a chiral smectic C phase (SmC*) with a spontaneous polarization (Ps) that is amplified by intermolecular hydrogen bonding. Dilution and deuterium exchange experiments suggest that antiparallel hydrogen bonded dimer formation increases the rotational bias about the director that is thought to induce the Ps.needs definition The research reported in this thesis is concernded with an investigation on the effects of hydrogen bonds on the Ps of the liquid crystal by the variation of core structure, particularly the substitution of one aryl ring to pyridinyl ring. An efficient synthesis of liquid crystals (LC) 1.14 and 2.22 by Directed ortho Metalation-boronation, Suzuki-Miyaura Cross Coupling reaction accompanied with Directed remote metalation was achieved. Compound 1.14 was found to be not useful as a LC material because it was unstable in the air and underwent rapid oxidation to give 2.22 upon heating. Thus, this project was focused on the preliminary study on mesophase characterization of 1.14 and 2.22. The results (Table 2.3) show both 1.14 and 2.22 formed SmC phases, but only 1.14 showed smectic A (SmA) mesophase and only 2.22 showed nematic (N) mesophase cooling from isotropic liquid phase. The increase in temperature range of smectic phases for the azafluorenol 1.14 is expected because intermolecular hydrogen bonding between the hydroxyl group and aza group as shown by Figure 1.21 may play a role to stabilize the formation of smectic (Sm) phase.