Department of Chemistry and Biochemistry, ‡Department of Chemical and Biological Engineering, and §Materials Science and Engineering Program, University of Colorado Boulder , Boulder, Colorado 80309, United States.
J Am Chem Soc. 2016 Sep 7;138(35):11399-407. doi: 10.1021/jacs.6b08068. Epub 2016 Aug 24.
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.
已合成了 N-芳基吩嗪，并将其作为强还原的无金属光氧化还原催化剂引入到有机催化原子转移自由基聚合中，用于合成具有明确结构的聚合物。实验证实了量子化学预测，即像它们的二氢吩嗪类似物一样，吩嗪光氧化还原催化剂的光激发态是强还原剂，并且当它们具有电荷转移特性时，会表现出优异的性能。我们将吩嗪与之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原则。一个关键的发现表明，在催化循环中保持吩嗪催化剂的平面构象有助于合成具有明确结构的大分子。利用这些原则，我们实现了一种核取代的吩嗪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吸收的吩嗪以及之前报道的有机光催化剂。使用这种催化剂并通过照射白色 LED，可以定量引发剂效率实现目标分子量的聚合物的制备，其分散度范围为 1.13 至 1.31。
