Cairo pentagon tessellated covalent organic frameworks with mcm topology for near-infrared phototherapy.

Abstract

Despite the prevalent of hexagonal, tetragonal, and triangular pore structures in two-dimensional covalent organic frameworks (2D COFs), the pentagonal pores remain conspicuously absent. We herein present the Cairo pentagonal tessellated COFs, achieved through precisely chosen geometry and metrics of the linkers, resulting in unprecedented mcm topology. In each pentagonal structure, porphyrin units create four uniform sides around 15.5 Å with 90° angles, while tetrabiphenyl unit establish a bottom edge about 11.6 Å with 120° angles, aligning precisely with the criteria of Cairo Pentagon. According to the narrow bandgap and strong near-infrared (NIR) absorbance, as-synthesized COFs exhibit the efficient singlet oxygen (¹O₂) generation and photothermal conversion, resulting in NIR photothermal combined photodynamic therapy to guide cancer cell apoptosis. Mechanistic studies reveal that the good ¹O₂ production capability upregulates intracellular lipid peroxidation, leading to glutathione depletion, low expression of glutathione peroxidase 4, and induction of ferroptosis. The implementation of pentagonal Cairo tessellations in this work provides a promising strategy for diversifying COFs with new topologies, along with multimodal NIR phototherapy.