Powell Daniel, Rhodes Zayn, Zhang Xinwen, Miller Edwin J, Jonely McKenzie, Hansen Kameron R, Nwachukwu Chideraa I, Roberts Andrew G, Wang He, Noriega Rodrigo, Minteer Shelley D, Whittaker-Brooks Luisa
Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, United States.
Department of Physics, University of Miami, Coral Gables, Florida 33146, United States.
ACS Mater Au. 2022 Jul 13;2(4):482-488. doi: 10.1021/acsmaterialsau.2c00019. Epub 2022 Apr 22.
Perylene diimides (PDIs) have garnered attention as organic photocatalysts in recent years for their ability to drive challenging synthetic transformations, such as aryl halide reduction and olefin iodoperfluoroalkylation. Previous work in this area employs spectator pendant groups attached to the imide nitrogen positions of PDIs that are only added to impart solubility. In this work, we employ electron-rich ammonium iodide or ammonium hydroxide pendant groups capable of self-n-doping the PDI core to form radical anions ( ) and dianions ( ). We observe formation is favored at low concentrations where aliphatic linkers are able to freely rotate, while formation is favored at elevated concentrations likely due to Coulombic stabilization between adjacent chromophores in a similar manner to that of Kasha exciton stabilization. Cyclic voltammetric measurements are consistent with steric encumbrance increasing the Lewis basicity of anions through Coulombic destabilization. However, sterics also inhibit dianion formation by disrupting aggregation. Finally, femtosecond transient absorption measurements reveal that low wavelength excitation (400 nm) preferentially favors the excitation of to the strongly reducing doublet excited state [ ]. In contrast, higher wavelength excitation (520 nm) favors the formation of the singlet excited state []. These findings highlight the importance of dopant architecture, counterion selection, excitation wavelength, and concentration on and formation, which has substantial implications for future photocatalytic applications. We anticipate these findings will enable more efficient systems based on self-n-doped PDIs.
近年来，苝二酰亚胺（PDIs）作为有机光催化剂受到关注，因为它们能够驱动具有挑战性的合成转化反应，如芳基卤化物还原和烯烃碘全氟烷基化反应。该领域以前的工作使用连接在PDIs酰亚胺氮位置上的旁观侧基，这些侧基仅用于增加溶解度。在这项工作中，我们使用富电子的碘化铵或氢氧化铵侧基，它们能够对PDI核心进行自n-掺杂，形成自由基阴离子（ ）和二阴离子（ ）。我们观察到，在脂肪族连接基能够自由旋转的低浓度下， 的形成更有利，而在较高浓度下， 的形成更有利，这可能是由于相邻发色团之间的库仑稳定作用，类似于卡沙激子稳定作用。循环伏安测量结果表明，空间位阻通过库仑去稳定作用增加了阴离子的路易斯碱性。然而，空间位阻也会通过破坏聚集来抑制二阴离子的形成。最后，飞秒瞬态吸收测量结果表明，低波长激发（400 nm）优先有利于将 激发到强还原双重激发态[ ]*。相比之下，较高波长激发（520 nm）有利于单重激发态[]*的形成。这些发现突出了掺杂剂结构、抗衡离子选择、激发波长和浓度对 和 形成的重要性，这对未来的光催化应用具有重大意义。我们预计这些发现将使基于自n-掺杂PDIs的系统更加高效。
