Isoreticular\nSeries of Two-Dimensional Covalent Organic\nFrameworks with the kgd Topology and Controllable Micropores

Abstract

Two-dimensional\n(2D) covalent organic frameworks (COFs) possess\ndesignable pore architectures but limited framework topologies. Until\nnow, 2D COFs adopting the <b>kgd</b> topology with ordered and\nrhombic pore geometry have rarely been reported. Here, an isoreticular\nseries of 2D COFs with the <b>kgd</b> topology and controllable\npore size is synthesized by employing a <i>C</i>₆-symmetric aldehyde, <i>i.e</i>., hexa­(4-formylphenyl)­benzene\n(HFPB), and <i>C</i>₃-symmetric amines <i>i.e</i>., tris­(4-aminophenyl)­amine (TAPA), tris­(4-aminophenyl)­trazine\n(TAPT), and 1,3,5-tris­[4-amino­(1,1-biphenyl-4-yl)]­benzene (TABPB),\nas building units, referred to as HFPB–TAPA, HFPB–TAPT,\nand HFPB–TABPB, respectively. The micropore dimension down\nto 6.7 Å is achieved in HFPB–TAPA, which is among the\nsmallest pore size of reported 2D COFs. Impressively, both the in-plane\nnetwork and stacking sequence of the 2D COFs can be clearly observed\nby low-dose electron microscopy. Integrating the unique <b>kgd</b> topology with small rhombic micropores, these 2D COFs are endowed\nwith both short molecular diffusion length and favorable host–guest\ninteraction, exhibiting potential for drug delivery with high loading\nand good release control of ibuprofen.