Luminescent lanthanide metal-organic frameworks for chemical sensing and toxic anion detection.

Prototype lanthanide metal-organic frameworks (LnMOFs), Ln(BTC) (Ln = Eu and Tb; BTC = benzene-1,3,5-tricarboxylate), have been considered as luminescent sensors for detecting toxic anions, while their neutral pore structures have limited the entrance and encapsulation of anions to produce highly anion-responsive photoluminescence (PL). To facilitate anions to enter the pore space of Ln(BTC), a one-pot synthesis method was proposed in which BTC was partially replaced with its structural analogue L·BF (HL·BF = 2,4,6-tricarboxy-1-methylpyridinium tetrafluoroborate) which consists of an anion affinity site of cationic methylpyridinium. Compared to the original Ln(BTC), the co-doped cationic framework EuTb-BTCL is highly sensitive for detecting different toxic anions by tuning the energy absorption of organic chromophores, the energy transfer efficiency to Ln ions and the energy allocation between different Ln ions in the PL spectra. We demonstrated that the EuTb-BTCL PL sensor has the capability of decoding various toxic anions with a clearly differentiable and unique emission intensity ratio of D → F (Tb, 545 nm) to D → F (Eu, 618 nm) transitions (I/I). Compared to Ln(BTC), the co-doped EuTb-BTCL presents self-calibrating, high distinguishable and stable PL signals for detecting toxic anions.