Through‐Space Charge Transfer: A New Way to Develop a High‐Performance Fluorescence Sensing Film towards Opto‐Electronically Inert Alkanes

New strategies are in high demand for fast, sensitive, selective, on-site and real-time detection of the important but challenging alkane vapors owing to their opto-electronic inertness. Herein, we report, for the first time, a high-performance fluorescent film sensor (FFS) for the alkanes with a rationally designed through-space charge transfer (TSCT) molecule as the sensing fluorophore. Steady-state fluorescence, femto-second transient absorption spectroscopy and theoretical studies revealed continuous TSCT dynamics in the excited U-shaped molecule with increasing medium polarity. Furthermore, the interlocked, face-to-face alignment between the donor and acceptor favors mass transport of the analyte molecules in the film state. As anticipated, the compound-based FFS showed an experimental detection limit of ≈10 ppm for n-pentane, less than 5 s for a full detection, negligible interference and super-stability, revealing the effectiveness of the design strategy. Notably, the sensor is small (≈3.7 cm3 ), power-saving, and workable at room temperature.