Synthesis and characterisation of new silicon-perfluoropropenyl compounds.

Novel, stable silicon-pentafluoropropane compounds have been synthesised from the direct reaction of hydrofluorocarbons Z-CFH[double bond, length as m-dash]CFCF3 (Z-HFC-1225ye) with n BuLi, followed by appropriate silicon-halide. The compounds have been characterized by multinuclear NMR studies (19F, 1H, 29Si and 13C), DFT studies and structural confirmation was obtained by X-ray diffraction. Based on the outcome of treating synthetic silicon-pentafluoropropene compounds with different nucleophilic sources ( n BuLi, t BuLi, MeLi, and PhLi) and computed for this reaction DFT energetics, it is clear that the C-F trans bond is more active than C-F gem (F gem and F trans are labelled with respect to Si). This provides a route for efficient modification of pentafluoropropene group, that can be a crucial step in developing pharmaceuticals that include propenyl or vinyl groups, addressing the demand for medicines based on long carbonic chains.

Supercapacitance in graphene oxide materials modified with tetrapyrrole dyes: a mechanistic study.

The global increase in mobile technology usage has created a need for better energy storage systems. With standard batteries reaching their technological limits, alternate energy storage methods are gaining momentum. In this study, we demonstrate a cheap and efficient way of building from scratch high-performance supercapacitors based on graphene oxide (GO) functionalized with tetrapyrrole derivatives: porphyrins and phthalocyanines. We present supercapacitors with capacitances about 30 times larger than those of the pristine graphene oxide-based counterparts. Experimental characterisation methods including X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-VIS), electron paramagnetic resonance (EPR), and density functional theory (DFT) calculations revealed correlations between the structural, magnetic, electronic and thermodynamic properties of these materials and their performance as supercapacitors. Electrochemical studies indicate the complex and versatile nature of capacitive effects associated with thin layers of supramolecular composites of graphene oxide. The electrical double layer (EDL) capacitance, cation intercalation and faradaic processes are coupled. Moreover, differences in the electronic interactions between GO and tetrapyrrolic modifiers have a profound effect on the observed capacitance. At the same time, these interactions are sufficiently weak to induce only subtle spectral changes, as well as a small increase of the interlayer distance as determined by XRD measurements. The present work offers a viable strategy for manufacturing high-performance supercapacitive materials that are superior to the state of the art nanocarbon-based supercapacitors using benign electrolytes in terms of capacitance per mass unit and have the potential for application in future green energy storage technologies. Our study provides insight into the multifarious origins of supercapacitance beyond the well-known EDL mechanism.

Heavy pnictogen chalcohalides: the synthesis, structure and properties of these rediscovered semiconductors.

This review focuses on the synthesis, properties and selected applications of heavy pnictogen chalcohalides, i.e. compounds of the MQX stoichiometry, where M = As, Sb, and Bi; Q = O, S, Se, and Te; and X = F, Cl, Br and I. The first section focuses on their synthesis and crystal structures, and the second section discusses the electronic structure on the basis of quantum chemical modelling and selected experimental data. Finally, the third section discusses their electrical, photoelectrochemical and photocatalytic properties and applications. In contrast to perovskites, chalcopyrites and kesterites, chalcohalides have attracted relatively less attention, but their structure and properties are well suited for numerous applications.

Molecular engineering of logic gate types by module rearrangement in 'Pourbaix Sensors': the effect of excited-state electric fields.

Two types of fluorescent logic gates are accessed from two different arrangements of the same modular components, one as an AND logic gate (1) and the other as a PASS 0 logic gate (2). The logic gates were designed with an 'electron-donor-spacer1-fluorophore-spacer2-receptor' format and demonstrated in 1 : 1 (v/v) methanol/water. The molecules consist of ferrocene as the electron donor, 4-aminonaphthalimide as the fluorophore and a tertiary alkylamine as the receptor. In the presence of high H+ and Fe3+ levels, regioisomers 1a and 1b switch 'on' as AND logic gates with fluorescence enhancement ratios of 16-fold and 10-fold, respectively, while regioisomers 2a and 2b are functionally dormant, exhibiting no fluorescence switching. The PASS 0 logic of 2a and 2b results from the transfer of an electron from the excited state fluorophore to the ferrocenium unit under oxidising conditions as predicted by DFT calculations. Time-resolved fluorescence spectroscopy provided lifetimes of 8.3 ns and 8.1 ns for 1a and 1b, respectively. The transient signal recovery rate of 1b is ∼10 ps while that of 2b is considerably longer on the nanosecond timescale. The divergent logic attributes of 1 and 2 highlight the importance of field effects and opens up a new approach for regulating logic-based molecules.

Understanding 'clean-up' of III-V native oxides during atomic layer deposition using bulk first principles models.

The use of III-V materials as the channel in future transistor devices is dependent on removing the deleterious native oxides from their surface before deposition of a gate dielectric. Trimethylaluminium has been found to achieve in situ 'clean-up' of the oxides of GaAs and InGaAs before atomic layer deposition (ALD) of alumina. Here we propose six reaction mechanisms for 'clean-up,' featuring exchange of ligands between surface atoms, reduction of arsenic oxide by methyl groups and desorption of various products. We use first principles Density Functional Theory (DFT) to determine which mechanistic path is thermodynamically favoured based on models of the bulk oxides and gas-phase products. We therefore predict that 'clean-up' of arsenic oxides mostly produces As4 gas. Most C is predicted to form C2H6 but with some C2H4, CH4 and H2O. An alternative pathway is non-redox ligand exchange, which allows non-reducible oxides to be cleaned-up.