A Luminescent Mixed-Lanthanide-Organic Framework Sensor for Decoding Different Volatile Organic Molecules

A flexible tripodal polyaromatic acid (4,4′,4″-(((2,4,6-trimethylbenzene-1,3,5-triyl)-tris­(methylene))-tris­(oxy))­tribenzoic acid, H3TCM) was used to adapt the coordination sites of lanthanide ions for the construction of microporous lanthanide-organic frameworks (LOFs) [LnTCM­(H2O)2]·3DMF·H2O (Ln-TCM; Ln = La, Eu, and/or Tb). In these LOFs, the emission band of TCM matches well with the excitation energy of lanthanide ions (Eu3+ and Tb3+) which results in high-efficient resonance energy transfer from TCM to lanthanide ions. Moreover, the mixed EuxTb1–x–TCM has tunable pores to adapt different induced-fit-type host–guest interactions which can modulate both the energy transfer efficiency from TCM to Ln3+ ions and the energy allocation between Eu3+ and Tb3+ ions in the luminescence spectra. We demonstrate that the EuxTb1–x–TCM sensor has the capability of decoding different volatile organic molecules (VOMs) with a clearly differentiable and unique emission intensity ratio of 5D0 → 7F2 (Eu3+, 614 nm) to 5D4 → 7F5 (Tb3+, 545 nm) transitions for every different VOM. Compared with the traditional absolute emission intensity method, such a self-referencing emission intensity strategy has generated self-calibrating, highly differentiable, and very stable luminescent signals for decoding different VOMs from the unique EuxTb1–x–TCM platform, which has great potential for practical applications.