Fluoroalkylated Polysilane Film as a Chemosensor for Explosive Nitroaromatic Compounds

Abstract

The present paper reports a new type of polymer-based chemosensor made of stiff fluoroalkylated polysilane, poly(3,3,3-trifluoropropylmethylsilane) (1), which showed a remarkable sensitivity for explosive nitroaromatic compounds (NACs), such as 2,4,6-trinitrophenol (picric acid), 1,3,5-trinitrobenzene (TNB), 2,4-dinitrotoluene (DNT), and m-dinitrobenzene (DNB), by a decrease in the photoluminescence (PL) intensity in the near-UV region with parts per million concentration of NACs in tetrahydrofuran (THF) solution and in the solid film in water. The PL intensity was completely reversible repeatedly after the removal of NACs from the thin film by rinsing with methanol (or water). A linear Stern−Volmer relationship was observed in all of the cases with high quenching constants. The PL quenching efficiency of 1 (M n = 3.12 × 104, PDI = 3.6, K = 4.15 × 104 M-1) for picric acid is 198 times better than that of nonfluoroalkylpolysilane, poly(n-propylmethylsilane) (2) (M n = 2.93 × 104, PDI = 2.1, K = 2.09 × 102 M-1). The weak noncovalent interaction between Si atoms of σ-conjugated polysilane and N and/or O atoms of electron-deficient NACs may be responsible for electron transfer from the excited state of the polysilane to the electron-deficient NACs, resulting in the PL quenching of 1 in solution and in the thin film by NACs.

Properties and applications of polysilanes

“…Apart from exhibiting UV and photoluminescence spectra, helical polysilanes are active to circularly polarized light and thus give characteristic peaks in the output generated using circular dichroism (CD) . The optical signals of these helical polysilanes greatly depend on the changes in the torsional angles, segmentations, and defects in the structure . It has been reported that the helicity in the linear oligosilanes can be induced by chiral substituents at the terminus …”

Nonclassical forces: Seemingly insignificant but a powerful tool to control macromolecular structures

“…Relative photoluminescence quenching efficiencies were found to be 4.9, 2.7, 1.2, and 1.0 for PA, TNB, DNB, and DNT, respectively. 94 Such high sensitivity can be explained on the basis of electron withdrawing behavior of CF 3 groups, which stabilize the highest occupied molecular HIGHLIGHT orbital (HOMO) and LUMO of polysilanes (Fig. 7).…”

Investigation of common fluorophores for the detection of nitrated explosives by fluorescence quenching

“…In industrial quality control, manufacturers of explosive materials must assure consumers that their products are safe, effective, and free from contamination by monitoring the composition throughout the manufacturing process. Because the requirements in each of these fields are [8][9][10]24,29], indirect laser-induced fluorescence [4,19,20,30], and fluorescence quenching [16,[31][32][33][34][35][36][37][38][39][40]. Unfortunately, many of these methods are difficult to adapt for field use owing to the size of laboratory-scale instrumentation and the need for other accessories that limit portability.…”

“…As mentioned above, one of the most promising approaches for explosives detection is fluorescence quenching [16,[31][32][33][34][35][36][37][38][39][40]. The term "fluorescence quenching" describes any event in which the observed fluorescence signal is decreased [44].…”