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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 (M(w)) of these metallole-silane copolymers are in the range of 4000 approximately 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 pi-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 tau(o)/tau is invariant. This requires that photoluminescence quenching occurs by a static mechanism.

There are a wide variety of silica nanoformulations being investigated for biomedical applications. Silica nanoparticles can be produced using a wide variety of synthetic techniques with precise control over their physical and chemical characteristics. Inorganic nanoformulations are often criticized or neglected for their poor tolerance; however, extensive studies into silica nanoparticle biodistributions and toxicology have shown that silica nanoparticles may be well tolerated, and in some case are excreted or are biodegradable. Robust synthetic techniques have allowed silica nanoparticles to be developed for applications such as biomedical imaging contrast agents, ablative therapy sensitizers, and drug delivery vehicles. This review explores the synthetic techniques used to create and modify an assortment of silica nanoformulations, as well as several of the diagnostic and therapeutic applications.

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(tetraphenylsilole-silafluorene-vinylene) (5), and poly(silafluorene-vinylene) (6) maintain a regioregular trans-vinylene Si-C backbone with possible ground state σ*-π and excited state σ*-π* conjugation through the vinylene bridge between metallole units. Fluorescence spectra of the polymers show an ∼13 nm bathochromic shift in λ 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.

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The sensitivities of metallophthalocyanine (MPcs: M = Co, Ni, Cu, Zn, and H(2)) chemiresistors to vapor phase electron donors were examined using 50 nm MPc films deposited on interdigitated electrodes. Sensor responses were measured as changes in current at constant voltage. Analytes were chosen to span a broad range of Lewis base and hydrogen bond base strengths. The MPc sensor responses were correlated exponentially with binding enthalpy. These exponential fits were consistent with the van't Hoff equation and standard free energy relationships. Sensor recovery times were found to depend exponentially on binding enthalpy, in agreement with the Arrhenius equation. Relative sensitivities of all MPcs were compared via two-way ANOVA analysis. Array response patterns were differentiated via linear discriminant analysis, and analyte identification was achieved over a range of concentrations with 95.1% classification accuracy for the strong binding analytes. The ability to distinguish among different analytes, regardless of their concentration, through normalization of the responses to a reference sensor is particularly noteworthy.

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The detection of nitroaromatic molecules in air by the quenching of the photoluminescence of porous silicon (porous Si) films has been explored. Detection is achieved by monitoring the photoluminescence (PL) of a nanocrystalline porous Si film on exposure to the analyte of interest in a flowing air stream. The photoluminescence is quenched on exposure to the nitroaromatic, presumably by an electron-transfer mechanism. Detection limits of 500 parts-per-billion (ppb), 2 ppb, and 1 ppb were observed for nitrobenzene, 2.4-dinitrotoluene (DNT), and 2,4,6-trinitrotoluene (TNT), respectively (exposure times of 5 min for each, in air). Specificity for detection is achieved by catalytic oxidation of the nitroaromatic compound. A platinum oxide (PtO2) or palladium oxide (PdO) catalyst at 250 degrees C. placed in the carrier gas line upstream of the porous Si detector, causes oxidation of all the nitroaromatic compounds studied. The catalyst does not oxidize benzene vapor, and control experiments show no difference in the extent of PL quenching by benzene with or without an upstream catalyst. The PL quenching by NO2, released in the catalytic oxidation of nitroaromatic compounds, is less efficient than the quenching of the intact nitroaromatic compound. This provides a means to discriminate nitro-containing molecules from other organic species.