Synthesis, luminescence properties and explosives sensing with 1,1-tetraphenylsilole- and 1,1-silafluorene-vinylene polymers

The syntheses, spectroscopic characterizations, and fluorescence quenching efficiencies of polymers and copolymers containing tetraphenylsilole- or silafluorene-vinylene repeat units are reported. These materials were prepared by catalytic hydrosilylation reactions between appropriate monomeric metallole alkynes and hydrides. Trimeric model compounds methyl(tetraphenyl)silole-vinylene trimer (1), methyl(tetraphenyl)silole-silafluorene-vinylene cotrimer,(2), and methylsilafluorene-vinylene trimer (3) were synthesized to provide detailed structural and spectroscopic characteristics of the polymer backbone and to assess the extent of delocalization in the luminescent excited state. Poly(tetraphenylsilole-vinylene) (4), poly (tetraphenyl sil ole- silafl uorene-vinylene) (5), and poly(silafluorene-vinylene) (6) maintain a regio-regular trans-vinylene Si-C backbone with possible ground state sigma*-pi and excited state sigma*-pi* conjugation through the vinylene bridge between metallole units. Fluorescence spectra of the polymers show an similar to 13 nm bathochromic shift in lambda(flu) from their respective model compounds. Molecular weights (M-n) for these polymers and copolymers are in the range of 4000-4500. Detection of nitroaromatic explosives by solution-phase fluorescence quenching of polymers 4-6 was observed with Stern-Volmer constants in the range of 400-20 000 for TNT, DNT, and picric acid (PA). A surface detection method for the analysis of solid particulates of TNT, DNT, PA, RDX, HMX, Tetryl, TNG, and PETN is also described for silafluorene-containing polymers. Polymer 6 exhibited detection for all the preceding types of explosive residues with a 200 pg cm(-2) detection limit for Tetryl. Polymers 4 and 5 exhibited only luminescence quenching with nitroaromatic explosives, revealing that the excited-state energy of the sensor plays a key role in the fluorescence detection of explosives.