直接芳基化聚合反應來合成水溶性高分子及其發光性質

Abstract

直接芳基化法在過渡金屬的催化下(通常為鈀金屬)可活化碳-氫鍵並直接與芳香族鹵化物進行偶合反應，此反應相較於傳統偶合反應為更符合原子經濟且環保的方法，因此近年來被廣泛應用於合成，使用鈀金屬催化的直接芳基化可能反應機構有Heck-type、芳香基親電子取代反應以及協同金屬化去質子反應(concerted metalationdeprotonation, CMD)，總體而言，結合實驗數據與理論計算，CMD為最有可能的反應機構，而文獻指出在直接芳基化法中催化劑種類、配位基功能性及溶劑極性的不同對催化結果都有十分的影響，因此最佳反應條件的選擇必須考慮到催化劑、配位基、添加劑及溶劑等因素。 水溶性共軛高分子擁有π電子共軛的主鍊，可以表現出優異的光學性質如螢光及光捕捉，因此在生物相關應用方面相當的熱門，尤其是生物感應及細胞顯影領域，然而合成水溶性共軛高分子都是使用傳統偶合反應，在水相環境中使用直接芳基化法聚合高分子的實驗還未有文獻記載，因此相當值得去嘗試其可能性。 因此，以水溶性聚芴作為目標產物，聚芴有很強的螢光能力且結構利於側鍊改質。在嘗試不同催化條件後，得到了高分子量且分散度很低的聚芴高分子也歸納出最佳反應條件。我們亦發現直接芳基化聚合法所使用的試劑對芴單體分子的1H NMR及螢光訊號有顯著的影響，其原因與其聚集行為的改變有關，此外試劑中的磷配位基會與芴單體分子或高分子上的溴化铵基團進行離子交換反應，因而增加了高分子結構變化上的可能性。

Direct arylation can carry out the coupling of C−H bond with electrophilic aryl halide with the transition metal catalytic system. In comparison to traditional cross-coupling reactions, direct arylation is considered a more atom-economy and environmental-friendly method and has been used to synthesize conjugated polymers in the recent years. Several mechanisms, such as Heck-type reaction, aromatic electrophilic substitution, and concerted metalation deprotonation (CMD) have been proposed to account for this reaction. Among all, CMD is the most likely one,as supported by numerous experimental results and theoretical calculations. The optimal reaction conditions often involve the use of catalyst, ligand, additive, and solvent. Water-soluble conjugated polymers with π-electron conjugated backbone exhibit noticeable optoelectronic properties. They have attracted much attention in bio-related applications, such as biological sensing and cell imaging. To synthesize the water-soluble conjugated polymers by direct-arylation polymerizationin aqueous media has not been reported. It is therefore intriguing to examine its possibilities. Herein, water-soluble polyfluorene is selected as the target polymer on account of its good fluorescence properties and easy structural modification. The catalytic conditions were optimized and polyfluorene with high average molar weight and narrow dispersity was obtained. During the optimization, we noticed that 1H NMR and fluorescence signals of fluorene monomer are quite sensitive to the reagents used the in the direct-arylation polymerization, which is linked with the variation of aggregation behavior in water. Moreover, the phosphine ligand could under ion-exchange reaction with the ammonia bromide functionality in both the monomer and polymer, thus increasing the diversity in the spatial structure of the polymers.