Organic-inorganic hybrid fluorescent ultrathin films and their sensor application for nitroaromatic explosives

The luminescent film materials sensitive to external stimuli are important to develop new types of optical sensors and switches. Herein we report organic-inorganic hybrid ultrathin films (UTFs) with reversible luminescence response to nitroaromatic explosive compounds by the use of layer-by-layer assembly of optical brightener BBU and Mg-Al-layered double hydroxide (LDH) nanosheets. UV-Visible absorption and fluorescence spectroscopy showed an orderly growth of the BBU/LDH films upon increasing the number of deposition cycle. XRD, AFM and SEM measurements indicated that the films feature periodic layered structure with a period of ca. 2 nm as well as uniform surface morphology. The BBU/LDH UTFs exhibit well-defined one/two-photon polarized photoemission with the anisotropy as high as 0.38. Moreover, the UTFs show a fast, selective and reversible luminescence response to different nitroaromatic explosives with the most significant luminescent red-shift occurring for picric acid; in addition, by combining suitable luminescent building blocks, the films can also be extended to other dual-color luminescence systems, which exhibit changes in both luminescence intensity and ratiometric fluorescence upon interaction with explosives, enlightening that these films can serve as new types of selective solid luminescent sensors towards nitroaromatic compounds.