Heterosporous Phenylpyridine-Based Covalent Organic Framework Microflowers for Highly Selective Sensing of Hydrogen Sulfide

Covalent organic frameworks (COFs) demonstrate considerable promise for gas and chemical sensing applications. Although there has been notable advancement in synthesizing such crystalline materials, the utilization of template-free approaches to fabricate COFs with flower-like microstructures remains infrequent. Herein, we report the synthesis of microflower-like and hollow microtubular phenylpyridine-based COFs─TAPP-TFBZ and TAPP-TFBP COFs─through template-free [4 + 4] polycondensation of 5′-(2,6-bis(4-aminophenyl)pyridin-4-yl)-[1,1′:3′,1″-terphenyl]-4,4″-diamine (TAPP-4NH2) with 4′,5′-bis(4-formylphenyl)-[1,1′:2′,1″-terphenyl]-4,4″-dicarbaldehyde (TFBZ-4CHO) and 5′,5″-bis(4-formylphenyl)-[1,1′:3′,1″:3″,1‴-quaterphenyl]-4,4‴-dicarbaldehyde (TFBP-4CHO), respectively. The resultant COFs exhibit exceptional thermal stability beyond 592 °C and possess high Brunauer–Emmett–Teller (BET) surface areas surpassing 943 m2 g–1. The TAPP-TFBZ COF has a dual porosity feature, whereas the TAPP-TFBP COF demonstrates a singular porosity. Interestingly, the TAPP-TFBZ COF microflowers have promising capabilities as a prospective fluorescent chemosensor, enabling the sensitive and selective sensing of H2S. Our developed sensing assay demonstrates a time efficiency of 10 min for completion while achieving a limit of detection of 1.6 nM. This work will advance research into the design concepts of flower-shaped COF materials that hold potential for applications in gas and chemical sensing.