Redox Levels of a closo-Osmaborane: A Density Functional Theory, Electron Paramagnetic Resonance and Electrochemical Study.

A closo-type 11-vertex osmaborane [1-(η(6)-pcym)-1-OsB10H10] (pcym = para-cymene) has been synthesized and characterized by single-crystal X-ray diffraction and elemental analysis, as well as by (11)B and (1)H NMR, UV-visible, and mass spectrometry. The redox chemistry has been probed by dc and Fourier transformed ac voltammetry and bulk reductive electrolysis in CH3CN (0.10 M (n-Bu)4NPF6) and by voltammetry in the ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (Pyrr1,4-NTf2), which allows the oxidative chemistry of the osmaborane to be studied. A single-crystal X-ray diffraction analysis has shown that [1-(η(6)-pcym)-1-OsB10H10] is isostructural with other metallaborane compounds of this type. In CH3CN (0.10 M (n-Bu)4NPF6), [1-(η(6)-pcym)-1-OsB10H10] undergoes two well-resolved one-electron reduction processes with reversible potentials separated by ca. 0.63-0.64 V. Analysis based on a comparison of experimental and simulated ac voltammetric data shows that the heterogeneous electron transfer rate constant (k(0)) for the first reduction process is larger than that for the second step at GC, Pt, and Au electrodes. k(0) values for both processes are also larger at GC than metal electrodes and depend on the electrode pretreatment, implying that reductions involve specific interaction with the electrode surface. EPR spectra derived from the product formed by one-electron reduction of [1-(η(6)-pcym)-1-OsB10H10] in CH3CN (0.10 M (n-Bu)4NPF6) and electron orbital data derived from the DFT calculations are used to establish that the formal oxidation state of the metal center of the original unreduced compound is Os(II). On this basis it is concluded that the metal atom in [1-(η(6)-pcym)-1-OsB10H10] and related metallaboranes makes a 3-orbital 2-electron contribution to the borane cluster. Oxidation of [1-(η(6)-pcym)-1-OsB10H10] coupled to fast chemical transformation was observed at 1.6 V vs ferrocene(0/+) in Pyrr1,4-NTf2. A reaction scheme for the oxidation involving formation of [1-(η(6)-pcym)-1-OsB10H10](+), which rearranges to an unknown electroactive derivative, is proposed, and simulations of the voltammograms are provided.

Solar Cell Enhancement from Supercritical CO2 Dye Surface Modification of Mesoporous TiO2 Photoanodes.

In recent years, in an effort to reach Net Zero Emissions, there has been growing interest by various academic and industry communities to develop chemicals and industrial processes that are circular, sustainable and green. We report the rapid, simple and effective surface modification of a porous metal oxide with organic dyes using supercritical carbon dioxide (scCO2). Titanium dioxide (TiO2) photoanodes were coated in very short times, under mild conditions and the excess dye recovered afterwards for reuse. The process obviates the need for conventional toxic solvents, the generation of unwanted waste streams, and more importantly, we see an unexpected device performance enhancement of 212 and 163 % for TerCOOTMS, 2 a and TerCN/COOTBDMS, 4 dyes, respectively, when compared to the conventional solvent deposition method.

1-Benzyloxy-5-phenyltetrazole derivatives highly active against androgen receptor-dependent prostate cancer cells.

A series of 1-benzyloxy-5-phenyltetrazole derivatives and similar compounds were synthesized and evaluated for their in vitro inhibitory activity against androgen-receptor-dependent (22Rv1) and androgen-receptor independent (PC3) prostate cancer cells. The most active compounds had in vitro IC50 values against 22Rv1 cells of <50 nM and showed apparent selectivity for this cell type over PC3 cells; however, these active compounds had short half-lives when incubated with mouse liver microsomes and/or when plasma concentration was monitored during in vivo pharmacokinetic studies in mice or rats. Importantly, lead compound 1 exhibited promising inhibitory effects on cell proliferation, expression of AR and its splicing variant AR-v7 as well as AR regulated target genes in 22Rv1 cells, which are so called castration-resistant prostate cancer (CRPC) cells, and a 22Rv1 CRPC xenograft tumour model in mice. Structural changes which omitted the N-O-benzyl moiety led to dramatic or total loss of activity and S-benzylation of a cysteine derivative, as a surrogate for in vivo S-nucleophiles, by representative highly active compounds, suggested a possible chemical reactivity basis for this "activity cliff" and poor pharmacokinetic profile. However, representative highly active compounds did not inhibit a cysteine protease, indicating that the mode of activity is unlikely to be protein modification by S-benzylation. Despite our efforts to elucidate the mode of action, the mechanism remains unclear.

Unconventional, Gram-Scale Synthesis of a Molecular Dimer Organic Luminogen with Aggregation-Induced Emission.

Organic luminogens have been widely used in optoelectronic devices, bioimaging, and sensing. Conventionally, the synthesis of organic luminogens requires sophisticated, multistep design, reaction, and isolation procedures. Herein, the products of the melt-phase condensation of benzoguanamine (BG; 2,4-diamino-6-phenyl-1,3,5-triazine) at 370-410 °C display interesting reaction-condition-dependent luminescence properties, including photoluminescence (PL) at a variety of wavelengths in the visible spectrum and quantum efficiencies (PLQE) of up to 58% in the powder form. With a simple and straightforward solvent washing procedure, the prominent blue luminescent component BG dimer was obtained in gram scale with >93% purity (96.5% purity after fractional sublimation). The BG dimer exhibited distinct aggregation-induced emission (AIE) properties. PL measurements indicate that the electronically excited state of the BG dimer undergoes efficient intramolecular nonradiative deactivation in room-temperature solution, leading to a significantly reduced PLQE (<0.1%) in solution. These nonradiative processes are substantially inhibited when the dimer existed in the form of crystals, solid aggregates in solution or being fixed in a rigid polymer film, resulting in a significant increase in the PLQE and lifetime. This work not only provided a new understanding for PL properties of self-condensation luminescent products but also represented an unconventional strategy for large-scale preparation of organic luminogens with high purity.

The generic enhancement of photochromic dye switching speeds in a rigid polymer matrix.

The switching or isomerization speed of photochromic dyes in a rigid polymeric matrix (such as an ophthalmic lens) is generally significantly slower than that observed in the mobile environment of a solution. Here we describe that the attachment of flexible oligomers having a low glass-transition temperature-such as poly(dimethylsiloxane)-to photochromic dyes greatly increases their switching speeds in a rigid polymer matrix. The greatest impact was observed in the thermal fade parameters T(1/2) and T(3/4)-the times it takes for the optical density to reduce by half and three quarters of the initial optical density of the coloured state-which were reduced by 40-95% and 60-99% respectively for spirooxazines, chromenes and an azo dye in a host polymer with a glass-transition temperature of 120 degrees C. The method does not alter the electronic nature of the dyes but simply protects them from the host matrix and provides greater molecular mobility for the switching process. In addition to ophthalmic lenses, the generic nature of the method may find further utility in data recording or optical switching.