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Mounting concerns regarding per‐/poly‐fluoroalkyl substances (PFAS) on human health are focusing attention on trace‐level PFAS detection in aqueous environments. Here, we report a readily prepared small molecule, 2,6‐bis(3,5‐diethyl‐1H‐pyrrol‐2‐yl)pyridine (receptor 1), that displays high binding affinities (logKa< = 4.9–6.2) and produces a strong “turn‐on” emission response when exposed to representative PFAS in hexanes. The hydrophobic nature of 1 , and its strong affinity for various PFAS, allowed hexanes solutions of 1 to be used as “turn‐on” emission sensors for dilute aqueous solutions of long‐chain (≥C8) PFAS under acidic conditions (pH 2) by liquid‐phase extraction (LPE). In the case of perfluorooctanoic acid (PFOA), the response was rapid (under 10 min) and sensitive. Limits of detection (LOD) as low as 250 ppt were readily achievable by direct naked‐eye observation. LOD as low as 40 and 100 ppt, respectively, could be reached for deionized and tap water solutions of PFOA using a smartphone color‐scanning application. Little change in the sensitivity was seen in the presence of a range of inorganic and organic species that could act as potential interferants. Support for the present findings came from UV–vis absorbance, fluorescence, 1 

Abstract Practical applications of lithium metal batteries are often limited by low cycling efficiencies and uncontrolled lithium dendrite growth caused by unstable and heterogeneous lithium‐electrolyte interfaces. To address this issue, a calix[4]pyrrole‐based wavy covalent organic framework (WCOF) is developed that acts as a protective layer to suppress Li dendrite growth and reduce side reactions on the Li anode. The presentWCOFis porous and contains calix[4]pyrrole units acting as “molecular traps” that allow efficient PF₆⁻anion capture while allowing for uniform Li⁺diffusion. This provides structurally stable artificial protective layers that permit high Li⁺transference numbers. The resulting solid electrolyte interphases permit ultralong‐term stable cycling at a current density of 1 mA cm⁻²and reversible lithium plating/stripping (over 2500 h) at an areal capacity of 2 mAh cm⁻². The protected anodes of this study also demonstrated excellent cell stability through 260 cycles when paired with high‐voltage cathodes (NCM811 with high mass loading: 20 mg cm⁻²).