本研究合成具有光異構化特性之偶氮苯單體，再以原子轉移自由基聚合法製備一系列含不同偶氮苯鏈段比之雙團聯共聚物poly(ethylene glycol)methylether-block-poly(6-[4-(4'-methoxyphenyl azo)phenoxy]hexylmethacrylate) (PEG-b-PAzo)，並利用小角度中子散射觀察其在混合溶液中結構的變化。PEG-b-PAzo於中性溶劑(DMF)中為random coil結構，當選擇性溶劑(H2O)加入時則會形成具核殼之微胞結構，且隨著混合溶液中水的比例增加，核之半徑會因為水與疏水端鏈段間的界面張力而變大，殼之厚度則隨之減少。
　　PEG-b-PAzo具有偶氮苯分子之光異構化特性，經紫外光照射後會由反式異構物變為順式異構物，在照射可見光後可誘發逆反應。利用紫外光-可見光分光光譜儀分析PEG-b-PAzo於混合溶劑中之光應答行為。在中性溶劑中，偶氮苯分子聚集型態以nonassociation為主；在選擇性溶劑中則因微胞形成，其聚集型態以H-aggregate為主。偶氮苯分子之光異構化速率在選擇性溶劑中相較於其在中性溶劑中慢，這是由於微胞的形成使PAzo鏈段產生聚集，阻礙了偶氮苯分子進行光異構化之旋轉與反轉機制，導致光異構化速率下降。此外，不同偶氮苯鏈段比之團聯共聚物的光異構化表現亦不相同，高偶氮苯鏈段比之團聯共聚物較容易受到溶液的選擇性影響而改變偶氮苯分子排列型態，導致光異構化速率隨著偶氮苯鏈段比增加而變慢。
　　PEG-b-PAzo亦具有偶氮笨分子之螢光特性，PEG-b-PAzo之螢光強度會隨著溶劑選擇增加而下降，這是由於偶氮苯分子在選擇性溶劑中傾向低螢光放射強度之H-aggregate型態所致。在照射紫外光後，PEG-b-PAzo於各溶劑中之螢光放射強度皆下降，這是由於經紫外光照射後，微胞之核變大，使偶氮苯分子進行快速的非放射性鬆弛之機率增加，導致螢光強度減弱。此外，隨著溶劑極性的增加，螢光強度亦會減弱，且發生紅位移。
　　本研究亦探討鹽類對於PEG-b-PAzo之結構影響，添加KCl於含PEG-b-PAzo之混合溶液時，KCl會產生鹽析效應，將微胞周圍之溶劑抽離而使殼厚度變小；添加KSCN於含PEG-b-PAzo之混合溶液時，KSCN會產生鹽溶效應，將更多溶劑帶至微胞周圍而使殼厚度變大。同時，鹽類對微胞結構的改變也會對偶氮苯分子之光應答特性產生相對應的影響。螢光強度主要受到偶氮苯聚集型態影響，添加鹽類時，因微胞結構改變使nonassociation比例上升，使螢光強度有所增加。

In this study, we synthesized a series of poly(ethylene glycol) methylether-block-poly(6-[4-(4'-methoxyphenyl azo) hexylmethacrylate) (PEG-b-PAzo) block copolymers, and investigating the relationship the structural changes of PEG-b-PAzo and their photoresponsive properties of azobenzene mesogens. The morphology of PEG-b-PAzo in mixed dimethylformamide (DMF)/H2O solvents was characterized by using small angle neutron scattering. When PEG-b-PAzo was dissolved in a selective solvent (H2O), PEG-b-PAzo assembled into core-corona micelles, with PAzo in the micelle core. Additionally, when the amount of H2O in mixed solvents increased, the radius of core increased, whereas the thickness of the corona decreased. This confinement of azobenzene mesogens in the micelle core hindered rotation and inversion of photoisomerization, thereby the photoisomerization rate of azobenzene mesogens in selective solvents was slower than that in neutral solvents. The fluorescence intensity of PEG-b-PAzo decreased with an increase in the solvent selectivity. Such behavior was associated with the high population of low-emissive H-aggregated azobenzene mesogens in selective solvents.
We also investigated the effect of salt addition (KCl and KSCN) on the structure of PEG-b-PAzo in mixed solvents. The addition of KCl in mixed solvents caused the salting-out effect, thereby dehydrating micelles, resulting in the decrease in the corona thickness. By contrast, the addition of KSCN in mixed solvents induced the salting-in effect, which hydrated micelles, and thereby the corona thickness increased. Additionally, the structural changes of PEG-b-PAzo because of the salt addition simultaneously influenced the photoresponsive properties of azobenzene mesogens. When salt was added to the solvent, the fluorescence intensity increased, which was associated with an increase in the population of high-emissive nonassociated azobenzene mesogens.

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