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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 (

The discovery of novel corrosion inhibitors for solution and coating applications is still an empirical process because of the large number of parameters that impact efficacy and the varied environmental conditions in which inhibitors are deployed. Moreover, conventional methods such as electrochemical and analytical techniques, and coating standard specifications can be extremely end-use focused, time and material intensive, and costly, making it prohibitive to screen new materials quickly at early stages of the discovery process. In an effort to address these challenges, we have continued to develop and deploy models and assays that can assist in accelerating the materials discovery process around novel corrosion inhibitors for different metals. In this paper we present how computational modelling, coupled with high-throughput optical and high-throughput electrochemical solution and coating assays, can be powerful tools that allow the rapid identification of prime candidates for further study. These experimental techniques are consistent with conventional % inhibition efficiency and neutral salt spray measurements, and provide additional and insightful information that cannot be easily or quickly obtained by traditional methods. Information extracted from the study of these chromium-based and small organic heterocyclic compounds reveals interesting structure–activity and structure–property relationships that will be applied in the design and discovery of new corrosion inhibitors.

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.

Reversible addition fragmentation chain transfer (RAFT) polymerization of methyl methacrylate (MMA) can be carried out in the presence of cyanoisopropyl methyl trithiocarbonate [CH3SC(S)SC(CH3)2CN] and scandium triflate [Sc(OTf)3] to provide simultaneous RAFT-controlled (reversible addition-fragmentation chain transfer controlled) molecular weight and molecular weight distribution (Mw/Mn 95% conversion), Lewis acid-controlled tacticity (mm:mr:rr = 12:44:44 for a mole ratio Sc(OTf)3/MMA = 1:8.5 at 60 °C) and an enhanced rate of polymerization. The tacticities observed for poly(methyl methacrylate) (PMMA) are similar to those observed with scandium triflate in the absence of the RAFT agent. The stability of dithiobenzoate RAFT agents [ZC(S)SR] in the presence of scandium triflate is strongly dependent on both the Z and R substituent. 2-(ethoxycarbonyl)prop-2-yl dithiobenzoate [PhC(S)SC(CH3)2CO2CH3] and the polymeric RAFT agent [PhC(S)S−(CH3)(CO2CH3)CH2−PMMA] appear relatively stable. However, cu...

SUMMARY: Factors affecting the choice of RAFT agent [RSC(Z) = S] for a given polymerization are discussed. For polymerization of methyl methacrylate (MMA), tertiary cyanoalkyl trithiocarbonates provide very good control over molecular weight and distribution and polymerizations show little retardation. The secondary trithiocarbonate RAFT agents with R = CHPh(CN) also gives good control but an inhibition period attributed to slow reinitiation is manifest. Radical induced reduction with hypophosphite salts provides a clean and convenient process for removal of thiocarbonylthio end groups of RAFT-synthesized polymers. Two methods providing simultaneous control over stereochemistry and molecular weight distribution of chains formed by radical polymerization are reported. Polymerization of MMA in the presence of scandium triflate provides a more isotactic PMMA. A similar RAFT polymerization with trithiocarbonate RAFT agents also provides control and avoids issues of RAFT agent instability seen with dithiobenzoate RAFT agents in the presence of Lewis acids. RAFT polymerization of tetramethylammonium methacrylate at 45 °C provides a more syndiotactic PMMA of controlled molecular weight and distribution (after methylation; mm:mr:rr 2:21:77 compared to 3:35:62 when formed by bulk polymerization of MMA).

Free-radical polymerization in the presence of suitable addition−fragmentation chain transfer agents [SC(Z)S−R] (RAFT agents) possess the characteristics of a living polymerization (i.e., polymer products can be reactivated for chain extension and/or block synthesis, molecular weights are predetermined by RAFT agent concentration and conversion, narrow polydispersities are possible). Styrene polymerizations (110 °C, thermal initiation) were performed for two series of RAFT agents [SC(Z)S−CH2Ph and SC(Z)S−C(Me)2CN]. The chain transfer coefficients decrease in the series where Z is Ph > SCH2Ph ∼ SMe ∼ Me ∼ N-pyrrolo ≫ OC6F5 > N-lactam > OC6H5 > O(alkyl) ≫ N(alkyl)2 (only the first five in this series provide narrow polydispersity polystyrene ( trithiocarbonates ∼ dithioalkanoates > dithiocarbonates (xanthates) > dithiocarbamates. However, electron-withdrawing substituents on Z can enhance the...

Molecular mechanics studies have identified 3α-(dimethylstannyl)-24-nor-5β-cholane (5α), 7α-(dimethylstannyl)-24-nor-5β-cholane (6α) and 12β-(dimethylstannyl)-24-nor-5β-cholane (7β) to be effective stannanes for use as enantioselective free-radical reducing agents. Synthetic studies toward the preparation of these stannanes as well as 3α-(dimethylstannyl)-5α-cholestane (21) are presented together with selected enantioselectivity data.

Ab initio molecular orbital calculations using the 6-311G**, cc-pVDZ and aug-cc-pVDZ basis sets, with (MP2, QCISD, CCSD(T)) and without (HF) the inclusion of electron correlation indicate that decarboxylation reactions of alkoxyacyl (alkoxycarbonyl) radicals are significantly exothermic. Transition states (16) for these decarboxylation reactions are calculated to have CTS–OTS separations in the range: 1.813–1.892 A; these distances appear to be affected somewhat by steric compression. At the CCSD(T)/6-311G**//MP2/6-311G** level of theory, energy barriers of 75.9, 72.8, 67.0 and 60.3 kJ mol–1 are calculated for the decarboxylation reactions involving the methoxyacyl, ethoxyacyl, isopropoxyacyl and tert-butoxyacyl radicals (2) respectively, while the reverse reactions are calculated to require energies in excess of 130.9 kJ mol–1. By comparison, the decarbonylation reaction of the acetyl radical (8) is predicted to be significantly endothermic; methyl radicals are calculated to prefer to add to carbon monoxide with an energy barrier of only 24.0 kJ mol–1 at the CCSD(T)/aug-cc-pVDZ//MP2/aug-cc-pVDZ level of theory, in good agreement with available experimental data.Similar calculations for reactions involving (methoxy)thioacyl, (methylthio)acyl and (methylthio)thioacyl radicals (12–14, R = Me) suggest that only (alkoxy)thioacyl radicals (12) provide synthetically useful β-fragmentation reactions, the remaining systems (13, 14) are unlikely to be useful as alkyl radical precursors in synthesis; the reverse reactions are calculated to be competitive with the β-fragmentation process in these cases.

1H, 13C, 29Si, 77Se, 119Sn and 125Te NMR spectroscopies reveal that methyl, primary and secondary alkyl radicals, generated through the reaction of aryltelluroalkanes (4–9) with tributyltin hydride, tributylgermanium hydride or tris(trimethylsilyl)silane) under standard radical conditions (benzene, AIBN) are capable of displacing tributylstannyl, tributylgermyl and tris(trimethylsilyl)silyl radicals from aryltellurotributylstannanes (1, 2), aryltellurotributylgermanes (10, 11) and aryltellurotris(trimethylsilyl)silanes (13, 14) respectively. These observations are in agreement with high-level ab initio molecular orbital studies. Calculations using a (valence) double-ζ pseudopotential basis set supplemented with polarization functions and with the inclusion of electron correlation (MP2/DZP) predict energy barriers for the displacement of stannyl (SnH3), germyl (GeH3) and trisilylsilyl ((H3Si)3)Si) radicals by methyl, ethyl and iso-propyl radicals to lie between 22 and 39 kJ mol−1, with reverse barriers of between 12 and 40 kJ mol−1. Consequently, the use of aryltellurides as alkyl radical precursors together with (standard) chain-carrying reagents such as tributyltin hydride, tributylgermanium hydride and tris(trimethylsilyl)silane may be complicated with equilibria which may result in diminished reaction yields.

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.

Solution-processable derivatives 4a–d of the novel diindeno[1,2-g:1′,2′-s]rubicene ring system have been prepared in three steps from 1,5-dichloroanthraquinone. Charge extraction by linearly increasing voltage measurements indicates that 4a–d have bulk mobilities

Thermolysis provides a simple and efficient way of eliminating thiocarbonylthio groups from RAFT-synthesized polymers. The course of thermolysis of poly(methyl methacrylate) (PMMA) prepared with dithiobenzoate and trithiocarbonate RAFT agents was followed by thermogravimetric analysis (TGA), 1H NMR spectroscopy, and gel permeation chromatography (GPC). The weight loss profile observed depends strongly on the RAFT agent used during polymer synthesis. PMMA with a methyl trithiocarbonate end group undergoes loss of that end group at ~180°C, at least in part, by a mechanism believed to involve homolysis of the C–CS2SCH3 bond and subsequent depropagation. In contrast, PMMA with a dithiobenzoate end appears more stable. Only the end group is lost at ~180°C and the dominant mechanism is proposed to be a concerted elimination process analogous to that involved in the Chugaev reaction.

Phenyltellurotris(trimethylsilyl)silane 4 and (4-fluorophenyltelluro)tris(trimethylsilyl)silane 5 react with methyl, 2-methylpropyl, cyclohexyl and phenyl substituted chloroformates (7, 11, 15, 19) in benzene and in the presence of tetrakis(triphenylphosphine)palladium(0) (4 mol%) to afford the corresponding aryltelluroformate (8, 9, 12, 13, 16, 17, 20, 21) in 50–79% yield; this procedure is also applicable to the preparation of (phenylseleno)formates and seleno- and telluro-esters.

7α-(Dimethylstannyl)-24-nor-5β-cholane (12) and 3β-(dimethylstannyl)-24-nor-5β-cholane (11) have been prepared from cholic and lithocholic acid, respectively, as free-radical reducing agents. Limited enantioselectivity-testing data indicate that these compounds show promise as enantioselective free-radical reducing agents. For example, reaction of ethyl (rac)-2-bromo-2-cyclopentyl-2-phenylacetate with one equivalent of either (11) or (12) in the presence of one equivalent of (S,S)-(–)-N,N’-bis(3,5-di-tert-butylsalycidene)-1,2-cyclohexanediaminomanganese(III) chloride (7) in toluene at –78˚C provides ethyl (S)-2-cyclopentyl-2-phenylacetate, obtained with 62 and 90% ee, respectively.

119 Sn and 125Te NMR spectroscopies reveal that methyl, primary and secondary alkyl radicals, generated by reaction of phenyltelluroalkanes 4, 6, 7 with tributyltin hydride (benzene, AIBN initiator), are capable of displacing tributylstannyl radicals from (4-fluorophenyltelluro)tributylstannane to afford the 4-fluorophenyltelluroalkanes 3, 8, 9.

Progress on the development of high efficiency blue emitter materials for OLED devices based upon phosphorescent iridium complexes, and triaryl pyridine containing molecules exhibiting TADF (thermally activated delayed fluorescence) will be reported.