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 (Eu(3+) and Tb(3+)) 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 Ln(3+) ions and the energy allocation between Eu(3+) and Tb(3+) ions in the luminescence spectra. We demonstrate that the Eu(x)Tb(1-x)-TCM sensor has the capability of decoding different volatile organic molecules (VOMs) with a clearly differentiable and unique emission intensity ratio of (5)D0 → (7)F2 (Eu(3+), 614 nm) to (5)D4 → (7)F5 (Tb(3+), 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 Eu(x)Tb(1-x)-TCM platform, which has great potential for practical applications.