Hydrosilylation of silole and silafluorene fluorophores is an effective polymerization tool for the synthesis of [Sigma]*-[Pi]/[Pi]* delocalized structures. Improvements in molecular weights (4000-20 000), reaction conditions (0 -50 ⁰C), and functional group variety were obtained for 1, 1-polysilole and 1,1-polysilafluorene materials. The polymers were screened for their ability to detect organic based explosives by a fluorescence quenching mechanism. The explosives screened include the nitroaromatic-based explosives TNT, DNT, PA, and Tetryl, the nitramine-based explosives RDX and HMX, the nitrate ester-based explosives PETN, TNG, and EGDN, and the organic peroxide-based explosives TATP and HMTD. Explosive particulates were targeted to increase the sensitivity of detection for low volatility explosives. Detection limits as low as 1 pg cm⁻² were obtained by the optimization of the polymers properties. Sensitivity is gained by tuning the frontier molecular orbital band gap to better match the LUMO energies of the explosive analytes. The excited state electron transfer process is also improved by Lewis acid/ base interactions between the nitro groups of the explosives and the silacycle core of the silole and silafluorene fluorophores. Sensors target the specific chemical functionalities of nitramine and nitrate ester based explosives for fluorescence imaging. Nitramine and nitrate ester based explosives can be detected selectively through the release of nitrite by an [Alpha]-hydride abstraction and a subsequent acid-catalyzed triazotization with 2,3-diaminaphthalene. The naphthotriazole product is visibly fluorescent as a thin-film providing a turn-on fluorescence signal. Nitrate ester-based explosives can be specifically targeted using a turn-on fluorescence response from the oxo-anion specific oxidation of unprotected fluorene units in polysilafluorene- divinylenefluorene. Both turn-on fluorescence sensors can be used in tandem with the fluorescence quenching sensors to provide selective explosives detection assays based on a fluorescence signal response. Organic peroxide based explosives are targeted through a selective oxidative depolymerization of a boronate-based polymer. The polymer is synthesized by a double transesterification polymerization driven by formation of a stable six-member bis-boronate polymer with fluoran repeat units in the backbone. After exposure to hydrogen peroxide, which can be formed from the UV decomposition of TATP and HMTD, the polymer undergoes a selective oxidative deprotection of the boronate functionalities forming a highly luminescent fluorescein. Detection limits of 3 ppb over an 8 h period are achieved through observation of the turn-on fluorescence response

The high sensitivity of silole- and silafluorene-containing polymers for detecting organic nitro, nitrate, and nitramine explosives cannot be solely attributed to favorable analyte–polymer hydrophobic interactions and amplified fluorescence quenching due to delocalization along the polymer chain. The Lewis acidity of silicon in conjugated poly(silafluorene-vinylene)s is shown to be important. This was established by examining the 29Si NMR chemical shifts (Δ) for the model trimer fragment of the polymer CH3–silafluorene–(trans-C2H2)–silafluorene–(trans-C2H2)–silafluorene–CH3. The peripheral and central silicon resonances are up-field from a TMS reference at −9.50 and −18.9 ppm, respectively. Both resonances shift down-field in the presence of donor analytes and the observed shifts (0 to 1 ppm) correlate with the basicity of a variety of added Lewis bases, including TNT. The most basic analyte studied was acetonitrile and an association constant (K a) of 0.12 M−1 was calculated its binding to the peripheral silicon centers using the Scatchard method. Spin-lattice relaxation times (T 1) of 5.86(3) and 4.83(4) s were measured for the methyl protons of acetonitrile in benzene-d 6 at 20 °C in the absence and presence of the silafluorene trimer, respectively. The significant change in T 1 values further supports a binding event between acetonitrile and the silafluorene trimer. These studies as well as significant changes and shifts observed in the characteristic UV–Vis absorption of the silafluorene group support an important role for the Lewis acid character of Si in polymer sensors that incorporate strained silacycles. The nitro groups of high explosives may act as weak Lewis-base donors to silacycles. This provides a donor–acceptor interaction that may be crucial for orienting the explosive analyte in the polymer film to provide an efficient pathway for inner-sphere electron transfer during the electron-transfer quenching process. Figure