Effect of water of crystallization on aggregation-induced emission in structurally similar crystals

The 1:0.5 hydrated crystal (I) of 2,2′-(anthra[2,3-b:7,6-b′]difuran-5,11-diylidene)dimalononitrile (1) showed aggregation-induced emission (AIE). However, the structurally similar non-solvated crystal (II) did not show AIE. We found that this was because the lack of water of crystallization changed the geometry of the intermolecular π contacts from two-dimensional in I to three-dimensional in II.     

Quantum Master Equation Approach to Singlet Fission Dynamics in Pentacene Linear Aggregate Models: Size Dependences of Excitonic Coupling Effects

The singlet fission (SF) dynamics of pentacene linear aggregate models are investigated using the quantum master equation method by focusing on the Frenkel excitonic (FE) coupling effects on the SF rate and double triplet (TT) yield as well as on their aggregate size dependences. It is found that for the dimer model, unrealistically large FE couplings are needed to provide significant effects on the SF dynamics, while for the larger aggregate models a realistic FE coupling causes significant variations in the SF dynamics: as increasing the aggregate size, the SF rate rapidly increases, attains the maximum at 8-mer (~3 times enhancement as compared to the non-FE-coupling case) and then decreases, approaching a stationary value after 12-mer, although the stationary TT yield at 20-mer remains slightly smaller than that in the non-FE-coupling case. These features are explained based on the relative relaxation factors between the adiabatic exciton states. The present results contribute to constructing the design guidelines for highly efficient SF aggregates. © 2018 Wiley Periodicals, Inc.     

Fusion and Growth Behavior of Gold Nanoparticles Stabilized by Allylmercaptane

Fusion and growth behavior of gold nanoparticles in a relatively low temperature range were studied using a transmission electron microscopy (TEM). Using allylmercaptane (AM: 2-propene-1-thiol, HS CH₂ CHCH₂) as a particle stabilizer, a colloidal suspension of AM-terminated gold nanoparticles was prepared with a two-phase system. TEM observation revealed that the adjacent nanoparticles formed a particulate neck to give fused nanoproducts even at lower than 65 °C. Such fusion behavior allowed a non-spherical growth of the adjacent nanoparticles. Interestingly, the nanoparticle fused to form a nanowire-type structure when the thermal radical reaction occurred between the terminal double carbon bond of the stabilizer and the hydrogen terminated surface of silicon wafer.     

Pulsed power for a rep-rate, electron beam pumped KrF laser

A new type of pulsed power system has been designed and built for a rep-rate, electron beam, pumped KrF laser. The system consists of two independent 11.2-kJ generators, which operate continuously at 5 Hz and produce two opposing 500-kV, 110-kA, 100-ns flat-top electron beams. The system combines the spark gap prime switch/step-up transformer design from the AIRIX and DAHRT injectors, and the water pulse-forming lines/output switch/vacuum insulator design from the Nike 60-cm amplifier. The system is fully operational, with both sides operating together. One side has operated continuously at 5 Hz for 90000 shots. The paper describes the system and the results of initial tests, including electrode wear     

Growth mechanism of the Pd(100)-p(2×2)-p4g-Al surface alloy

We have studied the growth mechanism of a Pd(100)-p(2×2)-p4g-Al surface alloy by scanning tunneling microscopy (STM). The surface alloy has a bilayer structure and is formed by annealing at 450–700 K (depending on the initial aluminum coverage) after the deposition of aluminum on Pd(100) at room temperature. The ratio of the surface-alloy coverage to the initial aluminum coverage is found to be constant (0.44) irrespective of the initial aluminum coverage from 0.5 monolayers (ML) up to 2 ML. The growth mechanism of the surface alloy is proposed on the basis of the STM measurements at various annealing temperatures. Upon annealing at 450 K, some of the surface aluminum atoms migrate into the bulk and, instead, palladium atoms come out to the surface. These palladium atoms react with aluminum atoms remaining on the surface to form a surface alloy. When the initial aluminum coverage is less than 1 ML, bilayer-high islands of the surface alloy with an average area of 100 nm² are formed at 450–500 K, which diffuse on the terrace at 500–700 K and coalesce to form larger islands. A possible role of the percolation transition of aluminum islands in the formation of the surface alloy is discussed.     

Unified total synthesis of pteriatoxins and their diastereomers

A unified total synthesis is reported to access all of the possible diastereomers of pteriatoxins A-C, with the use of an intramolecular Diels-Alder reaction as the key step to form the carbo-macrocyclic core structure. The C34/C35-diol protecting groups were found to have significant effects on both the exo/endo-selectivity and the exo-facial selectivity of the intramolecular Diels-Alder process.     

An approach for decontamination of beta-lactam antibiotic residues or contaminants in the pharmaceutical manufacturing environment

An effective procedure for decontamination of beta-lactam antibiotic residues or contaminants in the pharmaceutical manufacturing environment was investigated. Decontamination with solutions of hydrochloric acid, sodium hydroxide, hydrogen peroxide and hydroxylamine as agents for degradation was assessed. According to the results, the beta-lactam antibiotics were significantly degraded with sodium hydroxide and hydroxylamine. From the structural analysis of the degradation products of a cephem antibiotic, cefpodoxime proxetil, it was found that hydroxylamine degraded the beta-lactam structure under mild conditions, while sodium hydroxide did not. Therefore, hydroxylamine was considered an appropriate decontamination agent for beta-lactam antibiotics.     

Luminescent amidate-bridged one-dimensional platinum(II)-thallium(I) coordination polymers assembled via metallophilic attraction

The neutral square-planar complexes [Pt(RNH2)2(NHCO(t)Bu)2] (R = H, 1; Et, 2) and [Pt(DACH)(NHCO(t)Bu)2] (DACH = 1,2-diaminocyclohexane, 3) act as metalloligands and make bonds to closed-shell Tl(I) ions to afford one- and two-dimensional platinum-thallium oligomers or polymers based on heterobimetallic backbones. A series of heteronuclear platinum(II)-thallium(I) complexes have been synthesized and structurally characterized. The structures of the Pt-Tl compounds resulted from [Pt(RNH2)2(NHCO(t)Bu)2] and TlX [X = NO3(-), ClO4(-), PF6(-), and Cp2Fe(CO2)2(2-)] are dependent on both counteranions and the amine substituents. The compounds [Pt(NH3)2(NHCO(t)Bu)2Tl]X (X = NO3(-), 8; ClO4(-), 9) adopt one-dimensional zigzag chain structures consisting of repeatedly stacked [Pt(NH3)2(NHCO(t)Bu)2Tl]+ units, whereas [{Pt(NH3)2(NHCO(t)Bu)2}2Tl2]X2 (X = PF6(-), 10) consists of a helical chain. Compound 3 reacts with Tl+ to give [{Pt(DACH)(NHCO(t)Bu)2}2Tl](NO3) x [Pt(DACH)(NHCO(t)Bu)2] x 3 H2O (14) and one-dimensional polymeric [{Pt(DACH)(NHCO(t)Bu)2}2Tl2]X2 (X = ClO4(-), 15; PF6(-), 16). Reactions of [Pt(DACH)(NHCOCH3)2] with Tl+ ions afford one-dimensional coordination polymers [{Pt(DACH)(NHCOCH3)2}2Tl2]X2 (X = NO3(-), 17; ClO4(-), 18; PF6(-), 19). The polymeric [{Pt(DACH)(NHCOR')2}2Tl2]2+ (R = CH3, (t)Bu) complexes adopt helical structures, which are generated around the crystallographic 2(1) screw axis. The distance between the coils corresponds to the unit cell length, which ranges from 22.58 to 22.68 A. The platinum-thallium bond distances fall in a narrow range around 3.0 A. The complexes derived from [Pt(NH3)2(NHCO(t)Bu)2] are luminescent at 77 K. The trinuclear complexes [{Pt(RNH2)(NHCO(t)Bu)2}2Tl]+ do not emit at room temperature but are emissive at 77 K, whereas the polymeric platinum-thallium complexes containing 1,2-diaminocyclohexane are intensively luminescent at both room temperature and 77 K. The color variations are interesting; 15 exhibits intense yellow-green, 16 exhibits green, and 17-19 exhibit blue luminescence. The presence of bonding between platinum and thallium is supported by the short metal-metal separations and the strong low-energy luminescence of these compounds in their solid states.     

Visible light decomposition of ammonia to dinitrogen by a new visible light photocatalytic system composed of sensitizer (Ru(bpy)(3)2+), electron mediator (methylviologen) and electron acceptor (dioxygen)

Visible light decomposition of aqueous ammonia to dinitrogen was successfully achieved by using a new photocatalytic system based on a molecular photoelectron relay composed of a sensitizer (Ru(bpy)(3)2+), an electron mediator (methylviologen) and an electron acceptor (dioxygen), which can be used as a visible light-driven photocatalyst instead of UV-driven semiconductors.