Regulating the Azo‐Functionalization of Covalent Organic Frameworks for Photo‐Modulated Adsorption and Sensing of Aniline

Abstract Photoresponsive materials have garnered considerable attention, particularly azo‐functionalized covalent organic frameworks (COFs), due to their unique ability to undergo cis/trans isomerization under UV/visible light irradiation, making them highly promising in the field of adsorption. In this work, the innovative post‐synthetic modification (PSM) approach is developed to introduce azobenzene groups, resulting in the construction of three COFs with varying degrees of azo‐functionalization (ThTFB‐nN = N, n = 1, 2, 3). It is found that ThTFB‐nN = N exhibits reversible isomerization under alternating irradiation with 365 and 450 nm light, and the degree of azo content within the framework, as well as the trans ‐ cis isomerization, can significantly influence the material's properties. Notably, cis ‐ThTFB‐3N = N demonstrates the highest adsorption capacity for aniline at 303.3 mg·g ⁻¹ , representing a nearly tenfold enhancement compared to trans ‐ThTFB‐3N = N (30.7 mg·g ⁻¹ ). Additionally, ThTFB‐3N = N shows excellent fluorescence detection capability for aniline, achieving the detection limit of 22 ppb. To investigate the underlying mechanisms of adsorption and fluorescence detection, density functional theory (DFT) calculations are conducted. In conclusion, this work introduces a novel PSM strategy for incorporating photoresponsive units, leading to a multifunctional material with substantial potential for aniline adsorption and detection.