Two Dynamic ABW-Type Metal Organic Frameworks Built of Pentacarboxylate and Zn²⁺ as Photoluminescent Probes of Nitroaromatics

Self-assembly reactions of Zn²⁺ and L^5– (H₅L = 2,5-(6-(4-carboxyphenylamino)-1,3,5-triazine-2,4-diyldiimino) diterephthalic acid) lead to the formation of two new ABW-type zeolitic metal–organic frameworks (Z-MOFs): (Me₂NH₂)­[Zn₂L]­·3.5DMF (1) and (Me₂NH₂)­[Zn₂L­(H₂O)]­·2DMF­·8H₂O (2) (DMF = N,N-dimethylformamide). They are the first two Z-MOFs which are built of the same pentacarboxylate ligand and metal ion but have two configurations and channel shapes (distorted honeycomb- and herringbone-shaped channels for 1 and 2 respectively). They can demonstrate interesting structural transformations triggered by vacuum heating or soaking in different solvents. While direct transformations between 1 and 2 were revealed to be not feasible, 2 could be first transformed to a crystalline intermediate 3 and then into 1. Furthermore, while transformations between 2 and 3 are irreversible, those between 1 and 3 are reversible, accompanied by a 26 nm shift of their emission peak positions. In comparison to the ligand, 1, 2, and 3 exhibit blue shifts in their luminescent emission peaks and have intensive blue emission in both solid and solution phases. The efficient and selective quenching of their photoluminescence by a series of nitroaromatics (NACs) solutions phase and by nitrobenzene (NB) vapor makes them promising probes for detecting NACs. 1–3 represent the first series of MOFs as promising photoluminescent probes for detecting dinoseb down to 2.4 ppm. The electron transfer, long-range energy transfer, and/or electrostatic interactions between the frameworks and NACs mainly contribute to the quenching mechanisms.