| A new type of fluorescence sensory material has been developed from an acetyl-substituted carbazole-cornered tetracycle (ACTC) and related arylene-ethynylene macromolecules (AEMs). Thin films of the macromolecules can be fabricated on suitable solid substrates using various techniques such as solvent evaporation, sol-gel processing, and phase transfer between two immiscible solvents. Though the performance of the films depended on the mode of preparation employed, all protocols led to stable films with strong affinities towards nitroaromatic explosives and their associated signature compounds. In particular, thin films of ACTC have shown excellent sensitivity to trace levels of 2, 4, 6-trinitrotoluene (TNT) and 2, 4-dinitroluene with very fast response time. It can also be applied successfully to the efficient sensing of the explosive taggant, 2, 3-dimethyl-2, 3-dinitrobutane (DMNB), and cyclonite (RDX), a high explosive of extremely low vapor pressure. The ultra trace sensitivity of ACTC can be attributed to the planar geometry of its molecular structure which leads to efficient cofacial pi-stacking in the solid to produce a one-dimensional nanostructure. The 1D nanostructure facilitates exciton migration across the backbone of the fibril and thereby leads to amplified fluorescence quenching by the nitroaromatics. Furthermore, the assemblage of the individual ninofibers together with their inherent hollow structures of the macromolecules will lead to a three dimensional solid with high void space that allows fast penetration of the quencher molecules deep into the films. The ACTC-based sensor was also tested against possible intereferents such as solvents, cosmetics, and automobile exhaust gases and has shown excellent selectivity, with TNT as the reference. The sensor can be recycled for repetitive use by placing it in a vial of saturated hydrazine vapor for about one hour. |
