Detection of Nitroaromatic Explosives Based on Photoluminescent Polymers Containing Metalloles

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Abstract
The synthesis, spectroscopic characterization, and fluorescence quenching efficiency of polymers and copolymers containing tetraphenylsilole or tetraphenylgermole with Si−Si, Ge−Ge, and Si−Ge backbones are reported. Poly(tetraphenyl)germole, 2, was synthesized from the reduction of dichloro(tetraphenyl)germole with 2 equivs of Li. Silole−germole alternating copolymer 3 was synthesized by coupling dilithium salts of tetraphenylsilole dianion with dichloro(tetraphenyl)germole. Other tetraphenylmetallole-silane copolymers, 4−12, were synthesized through the Wurtz-type coupling of the dilithium salts of the tetraphenylmetallole dianion and corresponding dichloro(dialkyl)silanes. The molecular weights (Mw) of these metallole-silane copolymers are in the range of 4000∼6000. Detection of nitroaromatic molecules, such as nitrobenzene (NB), 2,4-dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT), and picric acid (PA), has been explored. A linear Stern−Volmer relationship was observed for the first three analytes, but not for picric acid. Fluorescence spectra of polymetalloles or metallole-silane copolymers obtained in either toluene solutions or thin polymer films displayed no shift in the maximum of the emission wavelength. This suggests that the polymetalloles or metallole-silanes exhibit neither π-stacking of polymer chains nor excimer formation. Fluorescence lifetimes of polymetalloles and metallole-silanes were measured both in the presence and absence of TNT, and τo/τ is invariant. This requires that photoluminescence quenching occurs by a static mechanism.

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