Selective and discriminative detection of -NO2 containing high energy organic compounds such as picric acid (PA), 2,4,6-trinitrotoluene (TNT) and dinitrotoluene (DNT) has become a challenging task due to concerns over national security, criminal investigations and environment protections. Among various known detection methods, fluorescence techniques have gained special attention in recent time. A wide variety of fluorescent chemosensors have been developed for nitroaromatic explosive detection. In this review article, we provide an overview of the recent developments made in small molecule-based turn-off fluorescent sensors for nitroaromatic explosives with special focus on organic and H-bonded supramolecular sensors. The fluorescent sensors discussed in this review are classified and organized according to their functionality and their recognition of nitroaromatics by fluorescence quenching.

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Self-assembly has proven to be a powerful tool for the construction of complex superstructures. The assembly of monomers into supramolecular architectures via non-covalent interactions is chiefly directed by the molecular structures, their functional groups, and environmental conditions. The principal advantage of non-covalent interactions is reversibility, which allows the assembly of monomers into supramolecular structures in situ depending on the local conditions. In addition, the supramolecular approach provides a degree of control over self-assembly at the molecular level, thereby influencing the macroscopic level and facilitating tuning of the bulk material properties. This review discusses the meritorious examples of supramolecular materials constructed through the molecular assembly process, guided by the classical principles of supramolecular chemistry. Furthermore, this year (2017) marks the 50 th anniversary of supramolecular chemistry in honor of the first example of supramolecular structure reported by Charles J. Pedersen and the achievements in the area of supramolecular chemistry ever since.

A π-electron rich supramolecular polymer as an efficient fluorescent sensor for electron deficient nitroaromatic explosives has been synthesized, and the role of H-bonding in dramatic amplification of sensitivity/fluorescence quenching efficiency in the solid state has been established.

The design and preparation of novel M3L2 trigonal cages via coordination-driven self-assembly of pre-organized metalloligands containing octahedral aluminum(III), gallium(III), or ruthenium(II) centers is described. By employing tritopic or dinuclear linear metalloligands and appropriate complementary subunits, M3L2 trigonal-bipyramidal and trigonal prismatic cages are self-assembled under mild conditions. These 3-D cages were characterized with multinuclear NMR spectroscopy (1H and 31P) and high-resolution electronic spray mass spectrometry (HR-ESI-MS). The structure of one such trigonal prismatic cage, self-assembled from an arene ruthenium metalloligand, was confirmed via single-crystal X-ray crystallography. The fluorescent nature of these prisms, due to the presence of their electron-rich ethynyl functionalities, prompted photophysical studies which revealed that electron-deficient nitroaromatics are effective quenchers of the cages' emission. Excited state charge transfer from the prisms to the nitroaromatic substrates can be used as the basis for developing selective and discriminatory turn-off fluorescent sensors for nitroaromatics.