Interface‐Directed High Fluorescence Efficiency Two‐Dimensional Molecular Crystals With Surface‐Exposed Active Sites

ABSTRACT Two‐dimensional (2D) molecular crystals offer significant advantages for many applications due to their ultrahigh surface‐to‐volume ratio. Nonetheless, controlling the oriented growth of 2D crystals to expose more active sites remains a challenge. Herein, we develop a strategy that combines molecular design with interfacial assembly to achieve the oriented formation of 2D crystals of Me‐FBSe . Uniquely, this architecture preserves the high photoluminescence quantum yield intrinsic to the crystalline state, while simultaneously ensuring the high‐density surface exposure of active sites. The integration of high luminescence efficiency and accessible active sites enables ultrasensitive detection of dimethyl sulfide (DMS) vapor at 50 ppb. Notably, this sensing material can detect DMS in aqueous environments via headspace vapor analysis, with a minimum detectable concentration of 100 ppb, demonstrating its reliability in practical monitoring applications. This work establishes a new strategy for the directional exposure of functional groups in high‐performance sensors.