Pyrene-Based AIEE-Active Vertically Grown Luminescent Material for Selective and Sensitive Detection of TNT Vapor

Pyrene-based molecules often suffer from the “aggregation-caused quenching” (ACQ) effect because of their rigid planar structure having several π–π stacking interactions, which limit their applications as solid-state luminescent materials. From this perspective, it has been strategized to develop two compounds: 2-(pyren-1-yl)-4,6-bis(4-vinylphenyl)-1,3,5-triazine (VinTr) and 4-chloro-N,N-diphenyl-6-(pyren-1-yl)-1,3,5-triazin-2-amine (PyTrDA) in such a way that pyrene triazine frameworks are transformed into “aggregation-induced enhanced emission” (AIEE)-active molecules. All of the compounds showed positive responses to the quenching of trinitrotoluene (TNT). Within these compounds, PyTrDA showed excellent results on sensing TNT with a high level of sensitivity (limit of detection = 216 pM in solution and ∼7.0 ppb in the vapor phase) and selectivity, extending the results from the solution to the vapor phase. The quenching process is due to the photoinduced electron transfer (PET) from the probe (PyTrDA) to the analyte (TNT), which was confirmed by transient absorption spectroscopy. In addition to the relatively large quantum yield of PyTrDA, the morphology transformation from a planar sheet-type structure (observed in PyTr) to a vertically grown nanorod (in PyTrDA) offers increased surface area. The vertically grown nanostructural morphology of PyTrDA should properly facilitate the diffusion of TNT molecules and provide a confined environment, where one-to-one host–guest interactions between the probe molecule and analytes are possible. To the best of our knowledge, this is the first study that explores the role of nanostructural morphology with an enhanced surface area for improved TNT sensing using small organic molecules.