Streater Daniel H, Kennehan Eric R, Wang Denan, Fiankor Christian, Chen Liangji, Yang Chongqing, Li Bo, Liu Daohua, Ibrahim Faysal, Hermans Ive, Kohlstedt Kevin L, Luo Long, Zhang Jian, Huang Jier
Department of Chemistry, Marquette University, Milwaukee, Wisconsin 53233, United States.
Magnitude Instruments, 200 Innovation Boulevard Ste. 224, State College, Pennsylvania 16803, United States.
J Am Chem Soc. 2024 Feb 21;146(7):4489-4499. doi: 10.1021/jacs.3c10627. Epub 2024 Feb 7.
Two-dimensional covalent organic frameworks (COFs) are an emerging class of photocatalytic materials for solar energy conversion. In this work, we report a pair of structurally isomeric COFs with reversed imine bond directions, which leads to drastic differences in their physical properties, photophysical behaviors, and photocatalytic CO reduction performance after incorporating a Re(bpy)(CO)Cl molecular catalyst through bipyridyl units on the COF backbone (Re-COF). Using the combination of ultrafast spectroscopy and theory, we attributed these differences to the polarized nature of the imine bond that imparts a preferential direction to intramolecular charge transfer (ICT) upon photoexcitation, where the bipyridyl unit acts as an electron acceptor in the forward imine case (f-COF) and as an electron donor in the reverse imine case (r-COF). These interactions ultimately lead the Re-f-COF isomer to function as an efficient CO reduction photocatalyst, while the Re-r-COF isomer shows minimal photocatalytic activity. These findings not only reveal the essential role linker chemistry plays in COF photophysical and photocatalytic properties but also offer a unique opportunity to design photosensitizers that can selectively direct charges.
二维共价有机框架（COFs）是一类新兴的用于太阳能转换的光催化材料。在这项工作中，我们报道了一对具有相反亚胺键方向的结构异构体COFs，通过在COF主链上的联吡啶单元引入Re(bpy)(CO)Cl分子催化剂后，它们在物理性质、光物理行为和光催化CO还原性能方面存在显著差异（Re-COF）。通过超快光谱和理论相结合的方法，我们将这些差异归因于亚胺键的极化性质，这种性质在光激发时赋予分子内电荷转移（ICT）一个优先方向，其中在正向亚胺情况（f-COF）下联吡啶单元作为电子受体，而在反向亚胺情况（r-COF）下联吡啶单元作为电子供体。这些相互作用最终导致Re-f-COF异构体作为一种高效的CO还原光催化剂发挥作用，而Re-r-COF异构体的光催化活性则极低。这些发现不仅揭示了连接体化学在COF光物理和光催化性质中所起的关键作用，还为设计能够选择性引导电荷的光敏剂提供了独特的机会。
