Organocatalyzed Atom Transfer Radical Polymerization Using N-Aryl Phenoxazines as Photoredox Catalysts.
Organocatalyzed Atom Transfer Radical Polymerization Using N-Aryl Phenoxazines as Photoredox Catalysts.
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DOI：
10.1021/jacs.6b08068
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发表时间：
2016-09-07
影响因子：
15
通讯作者：
Miyake GM
中科院分区：
文献类型：
--
作者：
Pearson RM;Lim CH;McCarthy BG;Musgrave CB;Miyake GM
在有机催化原子转移自由基聚合中，N-芳基吩恶嗪被合成并引入作为强还原的无金属光氧化还原催化剂，用于合成规整的聚合物。实验证实了量子化学预测，与它们的二氢吩嗪类似物一样，吩恶嗪光还原催化剂的光激发态被强烈地还原，当它们具有电荷转移特性时，它们获得了优异的性能。我们将吩恶嗪与先前报道的二氢吩嗪和吩噻嗪作为光氧化还原催化剂进行比较，以深入了解这些催化剂的性能，并建立催化剂设计的原则。一项关键发现表明，在催化循环中保持吩恶嗪催化剂的平面构象有助于合成定义明确的大分子。利用这些原理，我们实现了一种核心取代吩恶嗪作为可见光光氧化还原催化剂，其在有机催化原子转移自由基聚合中的性能优于紫外光吸收的吩恶嗪以及以前报道的有机光催化剂。使用这种催化剂，并用白光LED照射，通过实现定量引发剂效率，可以生产具有目标分子量的聚合物，其分散度从1.13到1.31。
N-Aryl phenoxazines have been synthesized and introduced as strongly reducing metal-free photoredox catalysts in organocatalyzed atom transfer radical polymerization for the synthesis of well-defined polymers. Experiments confirmed quantum chemical predictions that, like their dihydrophenazine analogs, the photoexcited states of phenoxazine photoredox catalysts are strongly reducing and achieve superior performance when they possess charge transfer character. We compare phenoxazines to previously reported dihydrophenazines and phenothiazines as photoredox catalysts to gain insight into the performance of these catalysts and establish principles for catalyst design. A key finding reveals that maintenance of a planar conformation of the phenoxazine catalyst during the catalytic cycle encourages the synthesis of well-defined macromolecules. Using these principles, we realized a core substituted phenoxazine as a visible light photoredox catalyst that performed superior to UV-absorbing phenoxazines as well as previously reported organic photocatalysts in organocatalyzed atom transfer radical polymerization. Using this catalyst and irradiating with white LEDs resulted in the production of polymers with targeted molecular weights through achieving quantitative initiator efficiencies, which possess dispersities ranging from 1.13 to 1.31.