近年來，藍相液晶相關研究在液晶界中持續發展，主要在於其可經由自組裝產生獨特的三維週期性奈米超分子結構，此結構可引致選擇性布拉格反射特性，除了擁有較窄的光子能隙外，其可外部調控性與快速反應使藍相液晶具備強大的應用潛能。因此，本論文著重以手性分子馬達材料作為有效改變藍相系統三維光子結構之高度光敏手性媒介，藉由適當控制紫外激發光與樣品溫度來控制藍相液晶晶格與反射顏色變化，讓藍相樣品之可光控反射波段涵蓋超廣波段範圍，並具備可重複可逆光控性與高度反射色飽和度。
本論文之第一部分主要探討具有不同配向(無配向及水平配向)之藍相樣品反射特性與溫度之間關係，實驗結果發現藍相反射波長隨溫度下降，有先藍移再紅移之連續變化趨勢(亦即先dλBP /dT > 0再dλBP /dT < 0)，研究證明與兩種手性材料之螺旋扭轉力與溫度之相異關係有關。第二部分為探討此兩種藍相樣品於受紫外光照射時，於非動態平衡和平衡狀態下反射特性之變化，實驗結果發現藍相反射波帶會隨紫外光照光時間與照光強度而紅移，而停止照光之後，反射波帶會回復至原位置。當紫外光照射藍相樣品時，由分子馬達之光致異構化效應主導之下，使樣品照光區之有效螺旋扭轉力下降，導致藍相晶格變大而產生反射波帶從藍光區大量紅移至近紅外光區之現象。此外，當紫外光停止照射後，由分子馬達之熱致異構化效應主導之下，樣品之有效螺旋扭轉力逐漸恢復而增強，致使藍相晶格逐漸恢復而變小，反射波段也逐漸恢復而藍移回初始的藍光區。實驗中，藍相反射顏色之可光調控範圍幾乎涵蓋整個可見光區與部分紅外光區，最大可紅移波段範圍可包含483.40 nm至864.89 nm。另外，實驗結果亦顯示紫外光照光時間過長將引致無配向與水平配向之藍相樣品因有效螺旋力過低而分別相變至膽固醇液晶之焦錐與平面結構，藉此找出本藍相樣品於可重複光控要求下之適當照光條件。第三部分為藍相樣品於動態平衡狀態下，探討紫外光照光強度與藍相反射波長及科索圖案之對應關係，實驗結果證明照光過程藍相一直維持在藍相I之結構，同時亦證明第一部分實驗中觀察到在dλBP /dT > 0與dλBP /dT < 0兩溫度區的藍相皆屬於藍相I。最後本論文量測藍相液晶樣品之可光控可逆與重複性及反射色之色度圖，其可高度光控重複性及廣大反射色域使本論文之藍相液晶系統具備強大的應用潛力，包含應用於光控液晶雷射、光控顯示器、光感測器等光電元件上。

In recent years, the unique optical properties of blue phase liquid crystals (BPLC) characterized by three-dimensional (3D) periodic nanostructures have attracted much attention among researchers investigating liquid crystals (LCs). Apart from its photonic bandgap (PBG) properties of selective Bragg reflection, the external controllability and fast response capabilities of the blue phase make it extremely attractive for various photonic applications. This research aims to study the maximization of the isomerization ability of light-responsive chiral molecular motors to effectively modulate the 3D photonic structure of the BPLC system and further modulate its PBG.
For the experiments in this study, nonaligned and parallel-aligned BPLC samples are prepared and two different working temperatures are chosen to investigate the differences of these sample conditions during ultraviolet (UV)-controlling. When the BPLC sample is irradiated with UV light, the trans-cis photoisomerization of molecular motors causes a decrease in the effective helical twisting power (HTP) in the illuminated region of the sample. This leads to an expansion of the lattices and a significant red-shift of the PBG from the blue region of visible light to the near-infrared (NIR) region. Furthermore, due to the thermal cis-trans-back isomerization of molecular motors, the effective HTP of the sample gradually recovers after the cessation of UV irradiation, resulting in the recovery of BPLC lattices and the blue-shift of PBG. In addition, the sample also exhibits stable multiple reversibility and repeatability of optical tunability under multiple UV exposures without phase transition. Prolonged UV irradiation can cause the nonaligned and parallel-aligned BPLC samples to transform into focal conic and planar structures of cholesteric liquid crystal (CLC) due to insufficient effective HTP.
This study also investigates the relationship between UV irradiation intensity, the reflection wavelength, and Kossel diagrams of the BPLC under dynamic equilibrium conditions. Experimental results confirm that the sample can maintain the BPI phase during the entire UV irradiation process. This thesis further measures the chromaticity diagram of the reflection colors of the BPLC samples during the UV-controlling. The broad reflection color gamut and excellent light-controllable characteristics of the BPLC in this study highlight its significant potential applications in the areas of light-controllable LC lasers, light-modulating displays, photodetectors, and other optoelectronic devices, to name a few.

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