Interfacially Assembled Fluorescent Nanofilm for Ultra‐Sensitive Formic Acid Detection via Hydrogen Bonding Affinity and Recognition

Abstract High‐performance film‐based sensors are key innovations driving advancements in sensing technologies. An ultra‐sensitive formic acid sensor based on a polymer fluorescent nanofilm synthesized via interfacial assembly using a tetraphenylethylene derivative functionalized with aldehyde and hydroxyl groups is reported. These groups promote imine bond formation and enhance selectivity. The nanofilm, prepared through dynamic condensation with 4,4′‐diaminodiphenyl ether at the air‐DMSO interface, exhibits excellent luminescence, flexibility, and tunable surface topography. Its bright fluorescence is primarily due to the aggregation‐induced emission (AIE) property and hydrogen bonding interactions within the film structure. Imines serve as recognition sites for formic acid, where weak hydrogen bonding alters the electronic environment of the imine groups, blocking proton donors (─OH) and promoting non‐radiative decay, leading to selective fluorescence quenching. The sensor achieves an ultra‐low detection limit of 550 ppt, a rapid response time of 0.3 s, and excellent reversibility. It also demonstrates high selectivity for formic acid over other VOCs, making it suitable for real‐time monitoring. Additionally, the nanofilm's multimodal sensing capabilities, including responses to HCl and NH 3 , highlight its potential for diverse environmental and industrial applications.