Chiral Covalent Organic Frameworks:Designed Synthesis,Characterization,and Application

Covalent organic frameworks(COFs)have been receiving much research interest because of their ordered channels,high surface areas and tunable functions.Construction of chiral COFs was considered as an important challenge in this research area.In this thesis,we focus on the designed synthesis,characterization,and application of chiral COFs.The main results were summarized as follows:I.Construction of crystalline COFs from chiral building blocks.By the judicious design of building blocks,two chiral 2D COFs,denoted as LZU-72 and LZU-76,were constructed directly from the chiral building blocks.LZU-72 and LZU-76 are highly crystalline,possess permanent porosities,and showed high activities as heterogeneous organocatalysts(e.r.up to 94.0:6.0).The key design is to use the rigid scaffold 4,4'-(1H-benzo[d]imidazole-4,7-diyl)dianiline(2)for attaching the chiral moieties.Given that the versatile scaffold 2 could attach different chiral moieties,various chiral COFs are expected to facilely construct via this strategy.It,therefore,paves a new way for the construction of functional COFs for high value-added applications.II.Designed synthesis of chiral 3D COFs.By using imidazole as the scaffold,a linear chiral building block was designed and synthesized.Condensation of the linear chiral building block with a tetrahedral building block yielded a chiral 3D COF(denoted as LZU-74).Circular dichroism(CD)spectra of LZU-74 indicated its enantiomeric nature.Our results demonstrate the possibility of constructing 3D COFs directly form chiral building block.III.Construction of chiral COFs for asymmetric photocatalysis.By combination of benzotriazole and chiral pyrrolidine,a chiral building block with optical activity and asymmetric catalytic activity was obtained.A photoactive COF material(denoted as LZU-78)was constructed by using the chiral building block and a structural building block.Although LZU-78 showed no photoactivity in the tested reactions up to now,LZU-78 could catalyze the asymmetric Michael addition with excellent enantioselectivity(92% ee).