Study of Hydrogen-Bonded Banana-Shaped Supramolucular Liquid Crystals
Banana-shaped (so called bent-core) liquid crystals are achiral structures with spontaneous polarization and chirality properties. In this thesis, the identifications and classifications of banana-phase types, electro-optical properties, and bent-core structural configurations were introduced. Meanwhile, the influences of H-bonded functional insertions in bent-core supramolecular materials on the mesomorphic and electro-electric properties were investigated in this doctoral dissertation as well. In chapter 2, the existence of polar switching behavior in the polar smectic (SmCP) phase of bent-core asymmetric hetero-dimers (with one H-bond) was proven to be associated by their configurations with higher dipole moments and suitable bent angles. In addition, the lack of polar switching behavior in supramolecular bent-core symmetric trimers (with two H-bonds), which exhibited the regular SmC phase with weak electrical stabilities, might be related to their conﬁgurations with smaller dipole moments. In chapter 3, the novel examples of supramolecular bent-core dimers and main-chain polymers with various siloxyl units of central linking spacer, which exhibited voltage-sensitive removable and reassemble (anti)ferroelectric polar switching behavior of spontaneous polarization, were established due to the reorganized H-bonded designs. The ferroelectricity and chirality properties could be adjusted by the controlling of siloxyl units, where the anticlinic tilt in the antiferroelectric ground state (SmCAPA) of chiral domain and anticlinic tilt in the ferroelectric ground state (SmCAPF) of racemic domain were displayed in bent-core supramolecules with less siloxyl units (di-siloxyl unit) and more siloxyl units (tri-siloxyl unit), respectively. In chapter 4, the voltage-dependent anti-ferroelectric properties of spontaneous polarization behavior in the polar smectic phase, which were displayed in H-bonded bent-core side-chain copolymers, were also reported influenced by tuning of proper intermolecular stacking in bent-core covalent- and H-bonded components. A special approach to constructing (or stabilizing) the SmCP phase was first developed by copolymerization of bent-core covalent- and H-bonded units in side-chain polymer complexes with proper molar ratios from both bent-core covalent- and H-bonded monomers without the SmCP phase. With respect to mesomorphic and electro-optical properties of the bent-core H-bonded dopant systems, more stable SmCP mesophases and low phase tansition temperatures were achieved and the mesophasic range and Ps value of H-bonded complexes could be tuned by the modulating of covalent- and H-bonded doping ratio due to the softer intermolecular arrangement of H-bonded structural dopants. The phenomena were revealable in both small molecular and small molecule/polymer dopant systems as shown in chapters 5 and 6. Overall, the details of influences by H-bonded and configuration effects in bent-core supramolecules, containing small molecules, imers, and main-chain polymers, and side-chain polymers, on the mesomorphic, molecular stacking, and electro-optical propeties were futher studied in this article.