Characterization of free radicals in clathrate hydrates of pyrrole, thiophene and isoxazole by muon spin spectroscopy

Gas hydrates have long been of interest to the petrochemical industry but there has been growing interest in potential applications for carbon dioxide sequestration and hydrogen storage. This has prompted many fundamental studies of structure and host-guest interactions, but there has been relatively little investigation of chemical reactions of the guest molecules. In previous work we have shown that it is possible to use muon spin spectroscopy to characterize H-atom-like muonium and muoniated free radicals formed in clathrate hydrates. Muonium forms in clathrate hydrates of cyclopentane and tetrahydrofuran, whereas furan and its dihydro- derivatives form radicals. The current work extends studies to clathrates hydrates of other 5-membered heterocycles: thiophene, pyrrole and isoxazole. All form structure II hydrates. In addition to the clathrates, pure liquid samples of the heterocycles were studied to aid in the assignment of radical signals and for comparison with the enclathrated radicals. Similar to furan, two distinct radicals are formed when muonium reacts with thiophene and pyrrole. However, only one muoniated radical was detected from isoxazole. Muon, proton and nitrogen hyperfine constants were determined and compared with values predicted by DFT calculations to aid the structure assignments. The results show that Mu adds preferentially to the carbon adjacent to the heteroatom in thiophene and pyrrole, and to the carbon adjacent to O in isoxazole. The same radicals are formed in clathrates, but the spectra have broader signals, suggesting slower tumbling. Furthermore, additional signals in the avoided level-crossing spectra indicate anisotropy consistent with restricted motion of the radicals in the clathrate cages

Free Radical Reactivity of a Phosphaalkene Explored Through Studies of Radical Isotopologues

Muonium (Mu), an H atom analogue, is employed to probe the addition of free radicals to the P=C bond of a phosphaalkene. Specifically, two unprecedented muoniated free radicals, MesP•-CMu(Me)2 (1a, minor product) and MesPMu-C•Me2 (1b, major product), were detected by muon spin spectroscopy (µSR) when a solution of MesP=CMe2 (1: Mes = 2,4,6-trimethylphenyl) was exposed to a beam of positive muons (µ+). The µ+ serves as a source of Mu (i.e. Mu = µ+ + e–). To confirm the identity of the major product 1b, its spectral features were compared to its isotopologue, MesPH-C•(Me)CH2Mu (2a). Conveniently, 2a is the sole product of the reaction of MesPH(CMe=CH2) (2) with Mu. For all observed radicals, muon, proton and phosphorus hyperfine coupling constants were determined by µSR and compared to DFT-calculated values

Investigation of H atom and free radical behaviour in clathrate hydrates of organic molecules

Clathrate hydrates are icy materials composed of a lattice of water molecules containing well-defined cavities which can accommodate small guest molecules. Their large storage capacity makes clathrates attractive media for a variety of gas storage and separation applications, but there is relatively little information on the chemical stability and diffusion of guest molecules. At the fundamental level inter-cage transition energies have been calculated, but the results need to be tested with experimental data. Ideally this should involve single-atom transport, using an isotopic tracer or spin label. Muonium (Mu = µ+e–) qualifies on both counts. As a single-electron atom with the muon as nucleus it may be considered a light isotope of hydrogen. Furthermore muonium and its reaction products may be monitored by muon spin spectroscopy. In recent years we have used this method to probe H-atom and free radical behaviour in clathrate hydrates. The current work extends studies to benzene and acetone clathrate hydrates. Of note is the simultaneous detection of muonium and muoniated radicals in the same sample. This can happen when Mu is trapped in an empty cavity, remote from its reaction partner. Increase in temperature leads to transport of Mu between cages and results in encounters with reactive guest molecules. By studying the temperature dependence of Mu and radical signals, we have been able to determine the activation energy for transport of Mu between cavities

Free Radical Chemistry of Phosphasilenes

Understanding the characteristics of radicals formed from silicon-containing heavy analogues of alkenes is of great importance for their application in radical polymerization. Bulky and electronic substituent effects in such compounds as phosphasilenes not only stabilize the Si=P double bond, but also influence the structure and species of the formed radicals. Herein we report our first investigations of radicals derived from phosphasilenes with Mes (2,4,6-trimethylphenyl), Tip (2,4,6-triisopropylphenyl), Dur (2,3,5,6-tetramethylphenyl) and NMe2 (dimethylamino) substituents on the P atom, using muon spin spectroscopy and DFT calculations. Adding muonium (a light isotope of hydrogen) to phosphasilenes reveals that: a) the electron-donor NMe2 and the bulkiest Tip-substituted phosphasilenes form several muoniated radicals with different rotamer conformations; b) bulky Dur-substituted phosphasilene forms two radicals (Si- and P-centred); and c) Mes-substituted phosphasilene mainly forms one species of radical, at the P centre. These significant differences result from intramolecular substituent effects

Chemie freier Radikale von Phosphasilenen

Das Verständnis der Eigenschaften von Radikalen, die ausgehend von Si-haltigen, schweren Analoga von Alkenen gebildet werden, ist wichtig für ihre Anwendung in der radikalischen Polymerisation. Sterische und elektronische Substituenteneffekte in Phosphasilenen stabilisieren nicht nur die Si=P-Doppelbindung, sondern beeinflussen auch die Struktur und Natur der gebildeten Radikale. Wir berichten hier über Untersuchungen an Phosphasilen-abgeleiteten Radikalen mit Mes-, Tip-, Dur- und NMe2-Substituenten am P-Atom mithilfe von Myonenspinspektroskopie und DFT-Rechnungen. Die Addition von Myonium (einem leichten Isotop von Wasserstoff) an Phosphasilene zeigt, dass a) das Elektronendonor-NMe2- und das sperrigste Tip-substituierte Phosphasilen mehrere myonierte Radikale mit unterschiedlichen Rotamer-Konformationen bilden; b) das sperrige Dur-substituierte Phosphasilen zwei Radikale (Si- und P-zentriert) bildet; und c) Mes-substituiertes Phosphasilen hauptsächlich eine Radikalspezies am P-Zentrum bildet. Diese signifikanten Unterschiede rühren von einem intramolekularen Substituenteneffekt her

Synthesis and characterization of molecular precursors for the preparation of thin transparent semiconducting oxide films and their application for thin film transistors (TFTs).

Ziel dieser Arbeit war es, neue molekulare Precursoren für dünne ITO-, In2O3- und Ga2O3-Filme herzustellen, zu charakterisieren und auf ihre Verwendbarkeit in den Dünnschicht-transistoren (TFTs) als Channel-Material zu testen. Hierzu wurde das trimetallische heteroleptische In(III)-Sn(II)-Alkoxids Br2In{LiSn2 (OCyHex)6} (20) aus [Li(OCyHex)3Sn]2 (16) und InBr3 hergestellt. Die Reaktion von In(OtBu)3 mit Sn(OtBu)2 bzw. Sn[N(SiMe3)2]2 ergab jeweils das neue homoleptische In(III)-Sn(II)-Alkoxid (tBuO)Sn(µ2-OtBu)2In(OtBu)2 (24) bzw. das neue heteroleptische In(III)-Sn(II)-Alkoxid (tBuO)Sn(µ2-OtBu)2 In[N(SiMe3)2]2 (25). Die Precursoren (20), (24) und (25) wurden für die Herstellung von dünnen (30-55 nm) transparenten (85-95 %) Zinn-reichen ITO-Filmen verwendet. Die TFTs mit den Zinn-reichen ITO-Filmen aus diesen Precursoren zeigten gute Elektronenmobilitäten (0.2-1.89 cm2V-1s-1) bei hohen Ion/Ioff–Verhältnissen (106-109). Im zweiten Teil der Arbeit wurden neue In(III)- bzw. Ga(III)-Siloxy-Komplexe hergestellt. Durch die Umsetzung von InMe3 bzw. GaMe3 mit jeweils einem Moläquivalent Et3SiOH bzw. (tBuO)3SiOH wurden heteroleptische Siloxy-Komplexe [Me2In-OSiEt3]2 (29) und [Me2Ga-OSiEt3]2 (32) bzw. isostrukturelle Verbindungen [Me2In-OSi(OtBu)3]2 (30) und [Me2Ga-OSi(OtBu)3]2 (33) hergestellt. (29) lässt sich bereits bei 360°C zu amorphem In2O3 zersetzen. Die TFTs mit dünnen (44-50 nm) transparenten (95 %) In2O3-Filmen zeigten gute Elektronenmobilitäten (0.3 cm2V-1s-1) bei hohen Ion/Ioff–Verhältnissen (108). (30) lässt sich ebenfalls bereits ab 380°C zu amorphem In2O3 zersetzen. (32) und (33) zersetzen sich in trockener Luft bei 380 bzw. 400°C vollständig zu amorphem -Ga2O3. Leider waren die dünnen In2O3- bzw. Ga2O3-Filme, die unter Verwendung von (30), (32) und (33) hergestellt wurden, für die Anwendung in TFTs nicht geeignet.The aim of this work was synthesis and characterization of new molecular precursors for the deposition of thin ITO-, In2O3 and Ga2O3 films. The deposited films were tested for their applicability in the thin film transistors (TFTs) as the channel material. To this end the trimetallic heteroleptic In(III)-Sn(II) alkoxide Br2In{LiSn2(OCyHex) 6} (20) was prepared by reacting [Li(OCyHex)3Sn]2 (16) with InBr3. The reaction of In(OtBu)3 with Sn(OtBu)2 and Sn[N(SiMe3)2]2 yielded the new homoleptic In(III)-Sn(II)-alkoxide (tBuO)Sn(μ2-OtBu)2 (24) and the new heteroleptic In(III)-Sn(II)-alkoxide (tBuO)Sn(μ2OtBu)2In[N(SiMe3)2]2 (25). The precursors (20), (24) and (25) were used for the production of thin (30-55 nm) transparent (85-95%) of tin-rich ITO films. The TFTs with the rich tin-ITO films from these precursors showed good electron mobilities (0.3-1.89 cm2V-1s-1) with high Ion/ Ioff ratios (106-109). In the second part of the work new In (III) and Ga (III) siloxy complexes were prepared. Through the reaction of InMe3 or GaMe3 with one molar equivalent of Et3SiOH and (tBuO)3SiOH, respectively, heteroleptic siloxy complexes [Me2In-OSiEt3]2 (29) and [Me2Ga-OSiEt3]2 (32) as well as isostructural compounds [Me2In-OSi(OtBu)3]2 (30) and [Me2Ga-OSi (OtBu)3]2 (33) were prepared. (29) can be decomposed to amorphous In2O3 at 360 °C. The TFTs with thin (44-50 nm) transparent (95%) In2O3 films showed good electron mobilities (0.3 cm2 V-1 s-1) with high Ion/Ioff ratios (108). (30) can be decomposed at 380 ° C to amorphous In2O3. (32) and (33) decompose completely in dry air at 380 and 400 °C to amorphous Ga2O3. The thin In2O3 and Ga2O3-films that were deposited using (30), (32) and (33) were not suitable for use in TFTs

Анализ путей оптимизации научно-технического обеспечения оборонно-промышленного комплекса Украины

The analysis of ways to optimize scientific and technical support of the military-industrial complex of Ukraine is considered in the article. Main problems and perspective directions of technological development for military purposes are identified. The experience and capacity of higher education institutions in the implementation of scientific and technical developments in this field are studied.У статті проведено аналіз шляхів оптимізації науково-технічного забезпечення оборонно-промислового комплексу України. Визначено основні проблеми та перспективні напрямки розвитку технологій військового призначення. Проаналізовано досвід та можливості вищих навчальних закладів у виконанні науково-технічних розробок у даній сфері.В статье проведён анализ путей оптимизации научно-технического обеспечения оборонно-промышленного комплекса Украины. Определены основные проблемы и перспективные направления развития технологий военного предназначения. Проанализирован опыт и возможности высших учебных заведений в реализации научно-технических разработок в данной сфере

High solid-state fluorescence in ring-shaped AEE-active tetraphenylsilole derivatives

Three ring-shaped AEE-active silole-containing compounds were synthesized by mild condensation reactions. Cyclotrisiloxane compound 1 displays high solid-state quantum yield (Phi(fl) = 0.86) with the fluorescence maximum at 512 nm. This high fluorescence efficiency results mainly from decreased vibrational pathways to fluorescence decay due to the intramolecular C-H center dot center dot center dot pi interactions

Synthesis and High Solid-State Fluorescence of Cyclic Silole Derivatives

Cyclotetrasiloxanes <b>1</b>–<b>3</b> containing different silole-based fluorogenic units (silafluorene, 1,3-diphenyl-9-silafluorene, tetraphenylsilole) were synthesized by cohydrolysis and condensation reactions. Their optical properties in solution and as crystals were studied. These compounds have low quantum yields in solution (Φ_fl = 0.01–0.18) with fluorescence maxima at 359–375 nm for silafluorene-containing compounds <b>1</b> and <b>3</b> and at 491 nm for AEE-active tetraphenylsilole compound <b>2</b>. However, <b>1</b>–<b>3</b> have high solid-state quantum yields (Φ_fl = 0.65–0.78) with fluorescence maxima at 377–390 nm for compounds <b>1</b> and <b>3</b> and at 517 nm for tetraphenylsilole- and silafluorene-containing compound <b>2</b>. Packing analysis of <b>1</b>–<b>3</b> in the crystal structure and MO and excited-state calculations were performed to explore possible fluorescence mechanisms in these compounds

Synthesis and High Solid-State Fluorescence of Cyclic Silole Derivatives

Cyclotetrasiloxanes <b>1</b>–<b>3</b> containing different silole-based fluorogenic units (silafluorene, 1,3-diphenyl-9-silafluorene, tetraphenylsilole) were synthesized by cohydrolysis and condensation reactions. Their optical properties in solution and as crystals were studied. These compounds have low quantum yields in solution (Φ_fl = 0.01–0.18) with fluorescence maxima at 359–375 nm for silafluorene-containing compounds <b>1</b> and <b>3</b> and at 491 nm for AEE-active tetraphenylsilole compound <b>2</b>. However, <b>1</b>–<b>3</b> have high solid-state quantum yields (Φ_fl = 0.65–0.78) with fluorescence maxima at 377–390 nm for compounds <b>1</b> and <b>3</b> and at 517 nm for tetraphenylsilole- and silafluorene-containing compound <b>2</b>. Packing analysis of <b>1</b>–<b>3</b> in the crystal structure and MO and excited-state calculations were performed to explore possible fluorescence mechanisms in these compounds