Highly fluorescent sensing of nitroaromatic explosives in aqueous media using pyrene-linked PBEMA microspheres.

Crosslinked 2-bromoethyl methacrylate polymer (PBEMA) was prepared in micro-spherical form (2-5µm) by precipitation polymerization methodology. The bromide substituent was substituted with an azide group, which was then coupled with 1-[(2-Propynyloxy)methyl]pyrene] via alkyne-azide click chemistry. The pyrene-linked microspheres showed an intense green-blue excimer emission with a maximum at 480nm, implying π-π stacking between the pyrene moieties on the microsphere surfaces. This fluorescence emission is extremely sensitive to the aromatic nitro compounds. So that the green-blue light fades immediately upon addition of trace amounts of 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT) and 2,4,6-trinitro phenol (TNP) in 100% aqueous media. Stern-Volmer plots were employed for comparison of their fluorescence quenching effects. The plots revealed Stern-Volmer constants of 1.33 × 105, 2.451 × 105 and 1.076 × 105M-1 for TNT, TNP and DNT, respectively. Furthermore, it has been observed that, the microspheres can be reused several times, without losing excimer emission properties.