Precise Donor‐π‐Acceptor Strength Modulation in Interfacial Nanofilms Toward Ultrasensitive Fluorescence Detection

Abstract A majority of 2D covalent organic frameworks (COFs) exhibit weak fluorescence in the solid state, and achieving precise donor‐ π ‐acceptor (D‐ π ‐A) strength modulation for high‐performance fluorescence sensing remains a significant challenge. Herein, four fluorescent nanofilms are rationally prepared through an interfacial dynamic condensation strategy. An atomically precise approach is demonstrated to tune D‐ π ‐A strength by incorporating diverse electron‐withdrawing acceptors, which feature different numbers of N ‐heterocyclic atoms and a tailored microenvironment. Beneficial from their high porosity and large surface area, the nanofilms afford channels for rapid mass transfer and abundant responsive nitrogen sites, which in turn realize highly efficient fluorescence detection of a sarin mimic, diethyl chlorophosphate (DCP). Leveraging the key laminated sensor component developed in Fang's group, a detector prototype is integrated and applied to detect DCP selectively and reversibly. It features the merits of rapid turn‐on response (3.0 s), ultrasensitive detection limit (0.066 ppt), and excellent reversibility (55 cycles). Based on the dynamic responses, effective discrimination between DCP and acid interferents can be achieved. This work not only presents a strategy for modulating D‐ π ‐A strength in interfacial nanofilms to achieve turn‐on and ultrasensitive fluorescence detection, but also paves the way for reliable on‐site and real‐time monitoring of nerve agents.