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莫耳分率之雙團聯共聚物poly(tert-butyl acrylate)-block-poly(6-[4-(4'-methoxyphenylazo)phenoxy] hexylmethacrylate) (PtBA-b-PAzoMA)，並利用小角度中子散射觀察其在不同溶劑中結構的變化。PtBA-b-PAzoMA於中性溶劑中為random coil之結構，於選擇性溶劑中則是會形成微胞。
由於偶氮苯之光異構化特性，因此高分子可經由紫外光誘導其構型從穩定的反式異構物轉變為介穩的順式異構物；反之，順式異構物在可見光的照射下或是置於黑暗中會回復至反式異構物。將PtBA-b-PAzoMA溶於不同性質之溶劑(中性、選擇性、混合溶劑(DMF/hexanol))中，利用紫外光-可見光分光光譜儀分析其光異構化行為，結果顯示在選擇性溶劑中之光異構化速率相較於在中性溶劑中較慢，因為PtBA-b-PAzoMA在選擇性溶劑中會形成微胞，偶氮苯鏈段被包覆於內層，形成立體障礙，導致光異構化速率下降；在混合溶劑中，隨著hexanol含量增加，其光異構化速率亦是隨之下降。除此之外，偶氮苯鏈段的莫耳分率亦會影響偶氮苯分子於溶劑中之聚集型態及光異構化速率，當偶氮苯莫耳分率越大時，聚集型態變化為：non-association及H-aggregation比例逐漸下降，而J-aggregation比例則是逐漸增加。另外，光異構化速率則是隨著偶氮苯莫耳分率增加而下降。
本研究亦探討PtBA-b-PAzoMA在不同溶劑中之螢光特性，PtBA-b-PAzoMA在選擇性溶劑之螢光放射強度會小於中性溶劑，這是由於PtBA-b-PAzoMA在選擇性溶劑中之聚集排列傾向於無螢光放射之H-aggregation型態所造成。在照射紫外光後，PtBA-b-PAzoMA在各溶劑中之螢光放射強度皆有提升，這是由於偶氮苯順式結構有利於螢光放射的發生；另外，照射紫外光後，在選擇性溶劑中，因所含偶氮苯的順式含量少於中性溶劑，所以整體螢光放射強度提升較少。

In this study, we synthesized a series of azobenzene-containing block copolymers poly(tert-butyl acrylate)-block-poly(6-[4-(4'-methoxyphenylazo) phenoxy]hexylmethacrylate) (PtBA-b-PAzoMA) with various mole fractions of azobenzene through atom transfer radical polymerization. The morphology of PtBA-b-PAzoMA in DMF/hexanol mixed solvents was characterized by using small angle neutron scattering. In a neutral solvent (DMF), PtBA-b-PAzoMA exhibited a random coil conformation, whereas PtBA-b-PAzoMA assembled into micelles when dissolved in a selective solvent (hexanol).
When PtBA-b-PAzoMA was subjected to UV illumination, azobenzene mesogens transformed from stable trans-isomers to metastable cis-isomers and the reverse process could be initiated via visible light or in dark. We dissolved PtBA-b-PAzoMA in various solvents, including neutral solvents, selective solvents, and DMF/hexanol mixed solvents, and investigated the photoresponsive behavior of PtBA-b-PAzoMA using UV-Vis spectroscopy. The photoisomerization rate of PtBA-b-PAzoMA in a selective solvent was slower than that in a neutral solvent. This was attributed to the steric hindrance caused by the micelle formation of PtBA-b-PAzoMA with azobenzene moieties in the core of micelles in a selective solvent. When PtBA-b-PAzoMA was dissolved in DMF/hexanol mixed solvents, the photoisomerization rate decreased with an increase in the content of hexanol. The mole fraction of azobenzene moieties also affected the photoisomerization rate and aggregation state of PtBA-b-PAzoMA. With an increase in the mole fraction of azobenzene segment, the population of both non-associated and H-aggregated azobenzene mesogens decreased, whereas the population of J-aggregated mesogens increased. Furthermore, the photoisomerization rate decreased when the mole fraction of azobenzene segment was increased.
We also investigated the fluorescence behavior of PtBA-b-PAzoMA in various solvents. The intensity of the fluorescence emission of PtBA-b-PAzoMA in neutral solvents was higher than that in selective solvents, which was associated with the high population of non-emissive H-aggregated mesogens in selective solvents. The fluorescence emission was increased with UV illumination, which was originated from the formation of cis-isomers. The bent-like cis-isomers inhibited photoinduced electron transfer, thereby enhancing the fluorescence emission. By contrast, after UV illumination, the population of cis-isomers in selective solvents was less than that in neutral solvents, resulting in the less enhancement of the fluorescence emission of PtBA-b-PAzoMA in selective solvents.

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