含氟三聯苯及蒽并二噻吩液晶分子之合成及其在顯示器及有機場效電晶體之應用

Abstract

本研究共計兩個部分，第一部分為含氟三聯苯液晶分子的合成與性質鑑定。由於三聯苯液晶具有高雙折射率的特性，向來是液晶螢幕裡共熔配方中常見的材料，但是此類材料的熔點偏高，不利於商業應用。我們利用氟取代基與末端環戊烷基團修飾三聯苯液晶分子，合成了兩個系列的三聯苯化合物，以期降低其熔點與旋轉黏滯性。第一個系列液晶分子雙折射率與旋轉黏滯性表現不俗，最令人驚豔的是相當低的熔點，此系列中，最低的熔點為－13.2 oC，該化合物的液晶相溫度間寬甚至高達160 oC，其中向列型液晶相有130 oC的溫寬，涵蓋室溫範圍，這是因為末端環戊烷基團破壞了棒狀液晶分子的直線型結構，使得此系列分子的熔點大幅降低，也使得此系列分子在顯示器應用上極有發展潛力。除了正介電異方性的液晶分子，我們也合成了一系列負介電異方性的三聯苯液晶，同樣修飾上氟取代基和末端環戊烷基團，以降低熔點和旋轉黏滯性。在此，我們將2,3－鄰二氟苯導入此系列的三聯苯液晶分子，在分子長軸側邊的兩個高負電性的氟原子會使分子短軸的介電常數大於分子長軸的介電常數，而引發負介電異方性。如我們所預期，此系列分子都具有相當高的負介電異方性與相當寬的液晶溫度範圍。第二部分的研究著重在液晶分子在有機場效電晶體上的應用。有機分子在元件基板上的排列對其電荷傳導率有舉足輕重的影響，為了增加分子的排列性，我們以高秩序度液晶分子為目標，合成了一系列以彎曲型蒽并二噻吩為液晶元的液晶小分子。相較於直線型蒽并二噻吩，彎曲型蒽并二噻吩不但有合成優勢，更具有較低的最高填滿分子軌域，使得該分子不易受到氧氣侵蝕，適合應用於光電元件。如我們所預期，此系列分子具有液晶相與相當低的最高填滿分子軌域－5.5 eV。在元件方面，我們將目標放在適合商業上大面積與低成本製作元件的溶液製程，我們利用旋轉塗佈的技術以底閘極上接觸的元件結構製作元件，而此系列分子在有機場效電晶體上的表現優異，最高的電荷傳導率可達0.6 cm2/Vs。

There are two parts in this dissertation. The first one is the synthesis of fluorinated terphenyl liquid crystals. Because of its high birefringence, terphenyl liquid crystals are always important ingredients need for display eutectic mixture. Terphenyl liquid crystals, however, suffer from high melting temperature and high rotational viscosity; in order to solve the problem, we introduce lateral fluoro-substituent, and a terminal cyclopentyl group to the terphenyl core. This first series of terphenyl liquid crystals has positive dielectic anisotropy, moderate birefringence, rotational viscosity and impressive melting point. The lowest melting point of the compounds in this series reaches -13.2 oC, and the mesophase range is 160 oC which includes 130 oC nematic phase temperature range. The low melting point is attributed to the cyclopentyl end group which curves the molecular backbone. The second series is terphenyl liquid crystals with negative dielectric anisotropy. In order to enhance the dielectric constant perpendicular to the long axis of the molecule, 2,3-ortho-difluorphenyl is introduced to terphenyl mesogen. The obtained compounds in the second series possess highly negative dielectric anisotropy and wide mesophase range. The second part in this dissertation focuses on the synthesis of anthradithiophene small molecules and their application to organic field effect transistors (OFETs). Strong stacking facilitates effective carrier transport in OFETs. Therefore, we expect highly ordered mesophase liquid crystals to have ordered alignment on OFETs. Highly ordered liquid crystals can be achieved by the introduction of long conjugated molecules. Therefore, we choose angular anthraditiophene (a-ADT) as the mesogen and synthesize a series of a-ADT liquid crystals successfully. The highest carrier mobility of OFETs for this series is 0.6 cm2/Vs.