Structure-Property Relationships for Tailoring Phenoxazines as Reducing Photoredox Catalysts.
Structure-Property Relationships for Tailoring Phenoxazines as Reducing Photoredox Catalysts.
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DOI：
10.1021/jacs.7b12074
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发表时间：
2018-04-18
影响因子：
15
通讯作者：
Miyake GM
中科院分区：
文献类型：
--
作者：
McCarthy BG;Pearson RM;Lim CH;Sartor SM;Damrauer NH;Miyake GM
通过使用实验和计算分析相结合的结构-性能关系的研究，已经开发了一些吩恶嗪衍生物作为可见光吸收的有机光氧化还原催化剂（PC），其激发态还原电位可与高度还原的过渡金属PC相媲美。含时密度泛函理论（TD-DFT）的N-芳基和核心改性吩恶嗪的光激发的计算建模指导的PC的设计与可见光区的吸收曲线。根据我们以前的工作与N，N-二芳基二氢吩嗪，非核心改性的N-芳基吩恶嗪在激发态的表征表明，N-芳基取代基的性质决定的PC访问电荷转移激发态的能力。然而，我们目前对核修饰的吩恶嗪的分析表明，这些分子可以进入不同类型的CT激发态，我们认为该激发态涉及核取代基作为电子受体。用给电子和吸电子取代基修饰吩恶嗪衍生物的核，用于改变三重态能量、激发态还原电位和吩恶嗪衍生物的氧化电位。在白色光照射下，利用有机催化原子转移自由基聚合（O-ATRP）合成聚甲基丙烯酸甲酯（PMMA），考察了这些分子的催化活性。所有的衍生物被确定为O-ATRP的合适的PC，如由作为单体转化率的函数的聚合物分子量的线性增长和合成具有中等至低的分散度（分散度小于或等于1.5）和引发剂效率通常大于70%的PMMA的能力在高转化率所指示的。然而，只有表现出强可见光吸收和强三重激发态还原电位的PC在整个反应过程中保持对聚合的控制。本文建立的结构-性质关系将使这些有机PC在O-ATRP和其他光氧化还原催化的小分子和聚合物合成中的应用成为可能。
Through the study of structure–property relationships using a combination of experimental and computational analyses, a number of phenoxazine derivatives have been developed as visible light absorbing, organic photoredox catalysts (PCs) with excited state reduction potentials rivaling those of highly reducing transition metal PCs. Time-dependent density functional theory (TD-DFT) computational modeling of the photoexcitation of N-aryl and core modified phenoxazines guided the design of PCs with absorption profiles in the visible regime. In accordance with our previous work with N,N-diaryl dihydrophenazines, characterization of noncore modified N-aryl phenoxazines in the excited state demonstrated that the nature of the N-aryl substituent dictates the ability of the PC to access a charge transfer excited state. However, our current analysis of core modified phenoxazines revealed that these molecules can access a different type of CT excited state which we posit involves a core substituent as the electron acceptor. Modification of the core of phenoxazine derivatives with electron-donating and electron-withdrawing substituents was used to alter triplet energies, excited state reduction potentials, and oxidation potentials of the phenoxazine derivatives. The catalytic activity of these molecules was explored using organocatalyzed atom transfer radical polymerization (O-ATRP) for the synthesis of poly(methyl methacrylate) (PMMA) using white light irradiation. All of the derivatives were determined to be suitable PCs for O-ATRP as indicated by a linear growth of polymer molecular weight as a function of monomer conversion and the ability to synthesize PMMA with moderate to low dispersity (dispersity less than or equal to 1.5) and initiator efficiencies typically greater than 70% at high conversions. However, only PCs that exhibit strong absorption of visible light and strong triplet excited state reduction potentials maintain control over the polymerization during the entire course of the reaction. The structure–property relationships established here will enable the application of these organic PCs for O-ATRP and other photoredox-catalyzed small molecule and polymer syntheses.
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