含氫鍵之香蕉型液晶超分子之研究

Abstract

香蕉型(彎曲型)液晶是不具旋光中心結構卻具有光學活性(或稱對掌異構性質)的液晶材料，本研究著重於氫鍵超分子引入至彎曲型液晶結構時，所產生的液晶性質與光電性質的影響。分子設計上分為：含單雙氫鍵之香蕉型液晶超分子、氫鍵與共價鍵共聚之香蕉型側鏈液晶高分子、含氫鍵之香蕉型主鏈液晶雙/高分子，若又包含了混掺效應討論，總共分為五個章節(討論點)在本文中討論。 由研究結論得知，氫鍵的引入會降低垂直於分子軸向的偶極距，因此彎曲型分子引入雙氫鍵官能機時會因分子整體偶極距降低而無法得到自發極化能力。若引入單氫鍵官能基，因為不對稱結構，雖然垂直於分子軸的偶極距下降，可其他軸向的偶極會提升，所以分子整體偶極距會保有一定的向量，當分子有適當的彎曲角度、適當的硬段與軟段長度時，可以誘導出自發極化能力以及光學活性。 以氫鍵連結之香蕉型液晶雙分子與主鏈高分子是世界首例的分子設計，並且量測到自發極化能力。鐵電/反鐵電行為與消旋/對掌特性可藉由分子結構內的矽氧基團數目不同而調控，因氫鍵而對電壓敏感之特性也在此研究中觀測得到。 於側鏈型高分子而言，因為高分子結構內分子堆疊較為緊密的關係，純共價鍵之彎曲型側鏈高分子無法有效的誘導出自發極化能力，可是卻可藉由共聚氫鍵結構來調控分子間疏密的堆疊行為。在氫鍵分子較多共價鍵分子較少的情況下，彎曲型側鏈共聚高分子可以有效的誘導出自發極化能力。 混掺系統而言，可以延展與降低具極化能力的液晶相溫寬與相發生溫度，穩定自發極化能力，而溫度範圍與自發極化值也可藉由混合不同氫鍵與共價鍵彎曲型分子的比值進行調控，不論在共價/氫鍵小分子混掺系統或者共價/氫鍵高/小分子混掺系統皆有上述類似性質。 含氫鍵之香蕉型液晶超分子的液晶與光電特性皆在本文中被充分探討。

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.