蒽并二噻吩液晶分子之合成與鑑定及其在有機場效電晶體之應用

Abstract

本研究為合成一系列彎曲型蒽并二噻吩液晶分子運用在有機場效電晶體中，彎曲型蒽并二噻吩相較於直線型具有較低的最高填滿分子軌域，能夠不受水氧干擾、穩定性比較好；具有液晶相的小分子能夠彌補分子與分子之間作用力的不足，增加分子的排列性。 本研究主要為單邊分子與雙邊分子之比較，首先以彎曲型蒽并二噻吩做為中心結構，在兩邊延伸出噻吩分子以增加整體分子的柔軟性，再加上長碳鏈增加溶解度，使元件能以溶液製程方式製作，形成雙邊分子Bis-C8T-a-ADT和Bis-C12T-a-ADT，並且運用其在液晶相能夠自組裝形成高秩序排列，在元件表現中，分別在250 oC和220 oC出現最高載子遷移率10-3 cm2/Vs。 由於雙邊分子液晶相溫度和熔點都過高，因此為了降低溫度，增加元件製程的便捷，因此同樣以彎曲型蒽并二噻吩做為中心結構，在其中一邊延伸出噻吩分子及長碳鏈形成單邊分子C12T-a-ADT，以不對稱結構降低熔點，相較於雙邊分子，不僅保有液晶相，更具有較低的最高填滿分子軌域－5.34 eV。在元件方面，採取與雙邊分子相同的元件製程方式，唯一不同的是退火溫度，最高的載子遷移率高達0.12 cm2/Vs。

This study is aimed to synthesize three liquid crystal molecules based on angular anthradithiophene (a-ADT) as core for the application in organic thin film transistors (OTFT). The a-ADT molecules have low HOMO energy level and good stability for the development of OFETs, and the liquid crystals can enhance ordered alignment on OFETs. Thiophenic-octyl group and thiophenic-dodecyl group were introduced onto the core of a-ADT on both sides to yield compounds Bis-C8T-a-ADT and Bis-C12T-a-ADT. On the other hand, thiophenic-dodecyl group was attached to the core of a-ADT on one side to yield compound C12T-a-ADT. The obtained compounds were characterized by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and X-ray diffraction to determine their mesomorphic properties. Compound Bis-C8T-a-ADT showed nematic and smectic A phases while both compounds Bis-C12T-a-ADT and C12T-a-ADT revealed smectic A phase. Their optical and electrochemical properties were measured by UV and CV instruments. All compounds showed low HOMO energy level which meant they are good stability for the development of OFETs. Compound C12T-a-ADT displayed the highest carrier mobility of 0.12 cm2/Vs.