Hydrogen-Bond-Regulated Tb³⁺-Centered Emission in a Zn^II–Tb^III Heterometallic Compound for Water Sensing in Ethanol and Gasoline

Luminescent lanthanide compounds stand out for their distinctive characteristics including narrow emission bands, substantial Stokes shifts, high quantum yields, and unique luminescent colors. However, Ln³⁺ is highly susceptible to vibrational quenching from X-H (X = O/N) high-energy oscillators in the embedded organic antenna, resulting in significant nonradiative energy dissipation of the ⁵D excited states of Ln³⁺. Herein, we introduce a strategy based on supramolecular interactions to modulate the nonradiative transitions in a new Zn^II-Tb^III heterometallic compound, [ZnTb(HL)₂(NO₃)Cl₂]·2CH₃CN·H₂O (<b>ZnTb</b>), based on a phenyl-substituted pyrazolinone-modified salicylamide-imide ligand (<b>H</b>_<b>2</b><b>L</b>). The regulation mechanisms are explored in detail both experimentally and theoretically. With the <i>N</i>,<i>N</i>'-dimethylformamide (DMF)-boosted Tb³⁺ luminescence, <b>ZnTb</b>⊃DMF (1 mg of <b>ZnTb</b> + 2 mL of DMF) realizes a rapid (3s) and sensitive detection of water in DMF with a detection limit of 0.021%. Further, <b>ZnTb</b>⊃DMF can detect trace amounts of water in ethanol and ethanol gasoline with a low detection limit of 0.023% and 0.048%. In addition, portable paper strips of <b>ZnTb</b>⊃DMF are prepared to improve its practicability, which can afford real-time and faster (1 s) in situ visual sensing of trace amounts of water in common organic solvents and ethanol gasoline with sensitivity comparable to the titration results. This study provides a new idea for the lanthanide luminescence modulation and application in the field of fluorescence sensing.