A supramolecular self-assembly material based on cucurbituril and cationic TPE as ultra-sensitive probe of energetic pentazolate salts

The successful synthesis of the pentazolate anion (cyclo-$N_5^{-}$) has been a great breakthrough in the field of energetic materials. However, the detection methods for these energetic materials based on the pentazolate anion are quite rare. Herein, two fluorescent probes for cyclo-$N_5^{-}$ anion were designed. Sensor 1 (TPE2N) was synthesized with a tetraphenylethylene functionalized by two cationic groups which can generate strong electrostatic interactions with pentazolate anion and result in specific fluorescent changes. Sensor 2 was designed based on sensor 1 and supramolecular cucurbit[7]uril (CB[7]). The unique structural features of CB[7] provide sites for the interaction between the cations and $N_5^{-}$ anion in its cavity, which would generate a platform for the detection and enhance the recognition performance. Isothermal titration calorimetry (ITC) experiment and fluorescence titration experiment indicate the binding molar ratio between sensor 1 with CB[7] is 1:2. Both sensors display typical aggregation-induced emission (AIE) features and good water-solubility. The sensors demonstrate excellent sensitivity to pentazole hydrazine salt with high enhancement constant (sensor 1: 1.34 × 10⁶; sensor 2: 3.78 × 10⁶) and low limit of detection (LOD: sensor 1 = 4.33 μM; sensor 2 = 1.54 μM). The formation of an AIE-based supramolecular sensor effectively improves the sensitivity to $N_5^{-}$ anion. In addition, the probes also have good selectivity of $N_5^{-}$ anion salts. The research would shed some light on the design of novel fluorescent sensors to detect pentazolate-based molecules and provides an example of supramolecular chemistry combined with fluorescent probes.