系列一以具盤形向列型之hexakis(4-hexyloxyphenylethynyl)ben- zene，藉著改變其中一個側臂之烷氧鏈位置，進而限制其在液晶相時的旋轉，來了解其對降低液晶形成溫度之影響。將其中一側臂之烷氧鏈位置換成間位或鄰位，確實可使熔點分別下降107 oC至87 oC；當引入同時具有對位及間位或具鄰、間、對位烷氧鏈之側臂時，其熔點繼續小幅下降，但液晶溫度範圍則回復至與全對位化合物之72 oC。為了進一步降低熔點，於其中一側臂維持三條鏈的情況下，將另五個相同側臂的烷氧鏈置換為烷鏈後，可成功的使熔點下降至接近室溫的30 oC，且具穩定的液晶性質。 系列二希望藉由在分子側邊作取代而改變垂直分子軸方向的折射率，並利用增加分子間作用力來平衡因Y形幾何結構所導致之不穩定液晶性質。故合成以噻吩為中心分別接上一個苯基及二個炔聯苯基之Y形分子，在總鏈長為6時，其液晶溫度範圍為76 oC，熔點為64 oC，且具有穩定的液晶性質。 In the first part of this thesis, incorporation of a laterally substituted peripheral into the disc-like hexaynylbenzene to exhibit restricted rotation of the unique side-arm was performed to enhance the π-π interactions for stabilization of the ND phase. At the same time, the lateral substitution should lower the transition temperatures. Compared with the model compound, hexa(hexyloxyphenylethynyl)benzene, moving the alkoxy chains of one side-arm from para- to meta- or ortho-position significantly lowered the transition temperatures. Moreover, combining the effects caused by para-, meta-, and ortho-alkoxy chains can decrease the melting temperature was further lowered. In series 2, the synthesis and mesogenic properties of rigid y-shape molecules were explored. By introducing a biphenyl unit onto a bent thiophene-based mesogen, a rigid y-shaped molecule, 2-(4-hexyloxy- phenyl)-3,5-(4’-hydroxybiphenylethynyl)thiophene was obtained. The rigid lateral substitution did not cause the loss of liquid crystallinity and on the contrary, an enantiotropic nematic phase was achiered.
