Jianyu Tuo, Yong Chen, Kaixiang Cui, Ruijuan Wen, Taihong Liu,* Liping Ding,* and Yu Fang. https://doi.org/10.1021/acs.analchem.6c03767

Fig. 1. Schematic illustration of the heterostructural cyano‑functionalized nanofilm for hydrazine vapor sensing

Fig. 2. (a) Test environment simulating the real scenario of N₂H₄ volatilization; (b) Fluorescence response of the nanofilms to N₂H₄ vapor in the test environment; (c) Double-blind field tests for evaluating the performance of the nanofilms for N₂H₄ detection; (d) Smartphone-based image capture of the nanofilms under UV light followed by RGB values extraction and Y values calculation; (e) Fluorescence images of the nanofilms after exposure to different concentrations of N₂H₄. (f) Y analysis to quantify N₂H₄ based on the fitted calibration equation.

Interfacially self-assembled nanofilms represent a class of ultrathin functional materials that underpin a wide range of applications, including separation, catalysis, energy storage, environmental remediation, and chemical sensing. Their appeal originates from the intrinsic confinement of interfacial reactions, which enables nanoscale thickness control, structural continuity, and a highly tunable interfacial microenvironment, conferring distinct advantages over conventional bulk membranes or coatings. Nevertheless, the majority of interfacially assembled nanofilms are still constructed from highly symmetric or isotropically distributed building blocks, which favor ordered packing and structural continuity but often generate chemically homogeneous networks. In the majority of cases, such uniform architectures provide limited spatial differentiation in charge distribution, interfacial polarity, and molecular stacking, which to a certain extent restrict the formation of directional transport pathways, heterogeneous adsorption sites, and anisotropic interfacial responses. Encoding molecular asymmetry into the building blocks therefore represents a direct and powerful strategy to overcome the intrinsic limitations of conventional symmetric nanofilms and to expand their structure-function tunability.

This study prepared an asymmetric building block CNHA featuring two different functional groups of acylhydrazide and cyanomethyl. By combining the acylhydrazone condensation and Knoevenagel condensation reactions, the film-forming process is completed with tetraphenylethylene tetraaldehyde under the interfacially confined conditions, and dynamic C=N bonds and conjugated C=C bonds are also synchronously constructed within the covalent network. The as-prepared TFPE-CN nanofilms exhibited excellent physical properties including structural robustness, flexibility, and uniform morphology, while the heterostructural linkage promoted π-electron delocalization and strengthened intramolecular charge transfer, leading to a favorable PLQY of 30.8% and a pronounced Stokes’ shift of 185 nm. The TFPE-CN nanofilms achieved critical detection of N₂H₄ vapor through synergistic interaction of hydrogen bonding and the generated new adduct. Integrated into a home-built portable sensing platform, the TFPE-CN nanofilm enables real-time, in situ detection of N₂H₄ vapor, delivering ultrahigh sensitivity (detection limit ≈ 130 ppt), rapid response, excellent selectivity, and robust stability. In practical detection scenarios, the nanofilm also enables naked‑eye recognition of N₂H₄ vapor through distinct fluorescence color changes. This work offers an asymmetric molecular engineering strategy for fabricating interfacial nanofilms and lays a foundation for developing high-performance and portable sensing platforms for N₂H₄ vapor.

First Author: Tuo Jianyu, master’s student, Shaanxi Normal University

Correspondence Authors: Prof. Ding Liping, Assoc. Prof. Liu Taihong, Shaanxi Normal University

Full Text Link: https://doi.org/10.1021/acs.analchem.6c03767