Acidity modulation mechanisms governing selective extraction of nitrogen heterocycles in dual‐acid <scp>DESs</scp>

Abstract Selective capture of structurally diverse molecules remains a major challenge in chemical separations. Here, we introduce dual‐acidic deep eutectic solvents (DESs) in which Lewis acids modulate the Brønsted acidity, creating a synergistic environment for the simultaneous extraction of basic and non‐basic nitrogen‐containing molecules. Brønsted sites, activated by adjacent Lewis centers, preferentially bind basic heterocycles, while the Lewis sites coordinate with non‐basic species, achieving unprecedented extraction efficiencies. Mechanistic studies combining FT‐IR spectroscopy, density functional theory, and molecular electrostatic potential analysis reveal that proton transfer, Lewis acid–base coordination, and π–cation interactions collectively govern selective recognition. This dual‐acidic design strategy is generalizable across different LA‐metal DES compositions and robust against competing chemical species. Our findings demonstrate a rational approach to fine‐tune cooperative acid functionalities, establishing a versatile platform for selective molecular capture and separations beyond conventional single‐acid systems.