膽固醇液晶具有週期性螺旋排列結構，可形成一維光子晶體，並選擇性反射與其螺旋旋性相同之圓偏振光。藉由摻入具光致異構化能力之手性分子馬達，可利用紫外光非接觸式調控其螺旋扭轉能力，進而改變本質螺距與反射波段。然而，在強配向邊界條件下，液晶盒內可容納之螺旋層數受離散整數條件限制，使光致螺距變化無法連續進行，並引發螺旋層數刷新與 Helfrich-Hurault（HH）形變。本研究探討光響應膽固醇液晶之光致結構演變，並建立自由能密度分析架構，以釐清螺旋層數刷新與HH形變之形成機制及其關聯。
本研究結合反射光譜、偏光顯微鏡與Frank-Oseen彈性理論，分析不同光照條件下膽固醇液晶之平面結構與自由能演化。首先發現，不論光致反射中心波長呈藍移或紅移，其皆呈階梯式變化，顯示系統透過離散螺旋層數跳變釋放累積之扭轉彈性能；然而，HH形變僅於藍移過程中產生，即使提高紅移速率亦未出現相同現象，顯示其形成具有明顯之藍、紅移不對稱性。其次，藉由量化HH形變生成前之平面態自由能密度，發現在固定材料組成與液晶盒厚度下，HH形變皆於自由能累積至相對較高之臨界值時發生，說明光強主要影響本質螺距之演化速率，而非直接決定形變門檻；相較之下，材料彈性常數與液晶盒厚度則直接影響形變所需之彈性能，其中降低彎曲彈性常數可降低HH形變之失穩門檻，而減少液晶盒厚度則提高其臨界自由能密度。
基於上述自由能與失穩條件，本研究進一步藉由調控材料彈性常數與液晶盒厚度降低 HH 形變門檻。在固定紫外光強驅動下，系統可於光致藍移過程中的不同螺距狀態反覆跨越HH穩門檻，形成涵蓋約690~487 nm反射中心波長之多波段二維網格結構，且網格週期隨螺距演化而改變；相較之下，未進行彈性常數調控的比較樣品，並未在如此寬廣的波長範圍內產生 HH 形變。綜合而言，本研究建立光致本質螺距演化、螺旋層數刷新與 HH形變之自由能關聯，揭示HH形變之藍、紅移不對稱性及其臨界條件，並透過材料與幾何參數調控降低失穩門檻，使二維網格結構得以於廣泛反射波段內重複生成，展現其作為多波段光學繞射元件之應用潛力。

Photoresponsive cholesteric liquid crystals (CLCs) are attractive for tunable photonic structures because their helical pitch can be controlled by light-induced changes in molecular chirality. In this study, photoisomerizable chiral molecular motors were incorporated into CLCs to investigate pitch evolution, discrete refreshing behavior, and Helfrich-Hurault (HH) deformation. Reflection spectroscopy and polarized optical microscopy showed that the reflection wavelength changed stepwise under ultraviolet (UV) irradiation because strong surface anchoring restricted the number of half-pitch layers to discrete integer values. A Frank-Oseen free-energy model was used to describe twist-energy accumulation and release during refreshing. HH deformation appeared only during photoinduced blue shifting, revealing an asymmetric instability. A modified free-energy framework was therefore proposed to describe the different energy pathways during blue and red shifts. Light intensity mainly controlled the rate of free-energy accumulation, whereas elastic constants and cell thickness determined the HH threshold. Reducing the bend elastic constant lowered the threshold, while decreasing cell thickness increased it. Repeated HH two-dimensional grid structures were achieved over a broad reflection range of approximately 690–487 nm under a single UV intensity.

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