為了探討凝膠化合物之碳鏈長度對於其於溶劑中形成凝膠能力之影響，本研究合成了 cholesteryl 2-(4-(4-dimethylamino)-azobenzene- 4’-amido) ethyl carbamate (N2) 與 cholesteryl 4-(4-(4-dimethylamino) -azobenzene- 4’-amido) butyl carbamate (N4) 兩種化合物。於小分子凝膠體設計上，除了導入膽固醇基團以增強分子間凡德瓦力以及誘導螺旋結構外，並加入偶氮苯基團以獲得光調變性與π-π stacking作用力。
從SEM與TEM觀察到化合物N4為一維纖維結構交織成的網狀結構，而N2則多為球狀團聚結構。由DSC配合POM觀察化合物N4的相轉移溫度。由分子軟體模擬軟體與XRD證明化合物於最低能量的型態因分子內氫鍵而呈彎曲摺疊狀。偶氮苯之氮上孤對電子與醯胺產生的分子間氫鍵不僅使順式較反式穩定，並且於紫外光與可見光照射下產生不可逆的光致變現象。此外該氫鍵影響分子的堆疊，N4在xylene與diphenyl ether的自組裝為短纖維結構。變溫1H-NMR與ATR結果顯示氫鍵、π-π堆疊作用力與凡德瓦爾力為形成凝膠主要的驅動力。N4於水/xylene與DMSO/hexane兩系統中皆出現選擇性凝膠化性質，具有將來相分離技術之前景。

In order to discuss the effect of gelation with various alkyl chain length, we synthesized two gelators: cholesteryl 2-(4-(4-dimethylamino)-azobenzene-4’-amido) ethyl carbamate (N2) and cholesteryl 4-(4-(4-dimethylamino)-azobenzene- 4’-amido) butyl carbamate (N4). Cholesterol group was introduced to enhance the gelation ability and its chiral center induces the asymmetric helical structure. Azobenzene with dimethyl aniline was also introduced to offer π-π stacking forces and phoisomerization property. Fibrillar structures were observed in the N4 xerogel via SEM and TEM. For N2 system, only ball cluster can be found. Phase transition temperature were measured using DSC and the phase change study was performed using POM. The morphology of N2 and N4 at lowest energy were simulated by a software. The structure is folded due to the intramolecular hydrogen bonding. The calculated molecular length is in accordance with the XRD results. It was found that cis-form of azobenzene is more stable than trans-form due to the intermolecular hydrogen bonding between the nitrogen of azobenzene and the amide groups. The irreversible photoisomerization was investigated using UV-visible spectroscopy. 1H-NMR and ATR results show that the hydrogen bonding, π-π stacking force and Van der Waals force are the driving forces forming one-dimensional structure. The selective-gelation ability is observed in water/xylene and DMSO/hexane systems, which can be applied for phase separation.

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