Ultrafast energy-electron transfer cascade in a multichromophoric light-harvesting molecular square

A molecular square with dimensions of about 4 nm, incorporating sixteen pyrene chromophores attached to four ditopic bay-functionalized perylene bisimide chromophores, has been synthesized by coordination to four Pt(II) phosphine corner units and fully characterized via NMR spectroscopy and ESI-FTICR mass spectrometry. Steady-state and time-resolved emission as well as femtosecond transient absorption studies reveal the presence of a highly efficient (>90%) and fast photoinduced energy transfer (k(en) approximately equal to 5.0 x 10(9) s(-1)) from the pyrene to the perylene bisimide chromophores and a very fast and efficient electron transfer (>94%, k(et) approximately equal to 5 x 10(11) up to 43 x 10(11) s(-1)). Spectrotemporal parametrization indicates upper excited-state electron-transfer processes, various energy and electron-transfer pathways, and chromophoric heterogeneity. Temperature-dependent time-resolved emission spectroscopy has shown that the acceptor emission lifetime increases with decreasing temperature from which an electron-transfer barrier is obtained. The extremely fast electron-transfer processes (substantially faster and more efficient than in the free ligand) that are normally only observed in solid materials, together with the closely packed structure of 20 chromophoric units, indicate that we can consider the molecular square as a monodisperse nanoaggregate: a molecularly defined ensemble of chromophores that partly behaves like a solid material.     

Micropatterning of semicrystalline poly(vinylidene fluoride) (PVDF) solutions

Micropatterning of a semicrystalline poly(vinylidene fluoride) (PVDF) solution was performed by a temperature controlled capillary micromolding where the rate of solvent evaporation was controlled by substrate temperature. In order to choose proper solvents for micropatterning, we have investigated the solubility of PVDF in various organic solvents and crystal structures of the PVDF bulk films cast from the solvents. The films prepared from the polar solvents such as dimethylformamide (DMF), dimethyl sulfoxide (DMSO) dominantly showed γ type crystals regardless of preparation temperature, while the films from tetrahydrofuran (THF) exhibit α type crystals and the ones from acetone and methyl ethyl ketone (MEK) show the characteristics of both α- and γ-PVDF. The quality of micropatterns and shapes of the PVDF crystals in the patterns significantly depend on solvent evaporation rates. Micropatterns of PVDF formed in DMF at 120 °C showed the best uniformity in shape. Crystals of the PVDF nucleated at the center regions of microchannels tended to be elongated with the b-axis of γ-PVDF crystals along the channels as the concentration of the solution decreased. In contrast, crystals nucleated at the corner regions of the channels had their b-axis oriented perpendicular to the channels. In line patterns with the width of 2 μm, the corner nucleated crystals were dominant and a resulting bamboo-like crystalline microstructure was observed in which the b-axis of γ-PVDF crystals, fast growth direction, is oriented normal to the microchannels. The crystal structures of the bulk films and the micropatterns were characterized by X-ray diffractometer, Fourier transform infrared spectroscope in Attenuated Total Reflection mode, Polarized Optical and Scanning Electron Microscope.     

Total synthesis and absolute stereochemistry of (9R,10S)-epoxyheptadecan-4,6-diyn-3-one, a diacylglycerol acyltransferase inhibitor from Panax ginseng

Asymmetric synthesis of four possible stereoisomers of (9,10)-epoxyheptadecan-4,6-diyn-3-one was accomplished, and the absolute configuration of the naturally occurring (9R,10S)-epoxyheptadecan-4,6-diyn-3-one (1) was elucidated.     

Intraframework potential energy function of zeolites

Potential energy functions suitable for the (Cs_1–xNa_xT₂O₄)-A type zeolite family were obtained from the known crystal structure of Cs₇Na₅-A zeolite. Using these potential functions, several other crystal structures in these family were obtained by molecular mechanical calculations. The activation energy - to -cage transmission of the H₂ molecule and the void volume of Cs₃Na₉-A zeolite were calculated.     

Morphology and transport properties of protons and methanol through partially sulfonated block copolymers

The morphological changes with different compositions of casting solvents in the membranes of sulfonated polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) were investigated with small-angle X-ray scattering (SAXS) and transmission electron microscope (TEM). Using the single solvent of tetrahydrofuran (THF) and the solvent mixtures of methanol/THF with different compositions, the casting polymer solutions were prepared for the membrane fabrication. The proton conductivity and the methanol permeability of membranes were measured, and the effect of morphological changes on the casting solvents was discussed through Flory–Huggins theory. It was found that the sulfonated SEBS membranes were transformed from well ordered lamellar to disordered co-continuous structure and the morphological difference caused abrupt enhancement in the proton conductivity and the methanol permeability as the concentration of methanol in the mixed solvents (MeOH/THF) increased.     

Ga8Ir4B – ein Gallium-Iridiumborid mit isolierten,annähernd quadratisch planaren Ir4B-Gruppen in einer vom CaF2-Typ abgeleiteten Struktur

Ga₈Ir₄B – a Gallium Iridium Boride with isolated, nearly square planar Ir₄B Groups in a Structure derived from the CaF₂ Type The new compound Ga₈Ir₄B (tetragonal, I4₁/acd, a = 853.69(2) pm, c = 2 105.69(6) pm, Z = 8, 614 reflections, 31 parameters, R = 0.034) was prepared by reaction of the elements at 1 100°C. The structure is derived from the CaF₂ type. It contains isolated Ir₄B groups with boron in an unusual, nearly square planar coordination.     

Regiospecific synthesis of mono- and bicyclic 6-alkoxy-2-pyrones and their use in the preparation of substituted aromatics,anthraquinones, and tetracyclic intermediates for 11-deoxyanthracycline synthesis

Several mono- and bicyclic 6-methoxy-2-pyrones having substituents at C4 and C5 can be prepared regiospecifically by either of two routes: (1) regiospecific construction of a glutaconic half-ester followed by dehydrative cyclization, and (2)regiospecific Friedel-Crafts acylation of 6-methoxy-2-pyrones at C5. These pyrones undergo clean and regiospecific Diels-Alder cycloadditions with various unsymmetrical dienophiles, e.g., quinones, unsaturated esters, etc, with subsequent loss of carbon dioxide. In this manner several polycyclic aromatic natural products have been prepared such as chrysophanol, helminthosporin, pachybasin, 2-acetylemodin and the purported structure for orientalone. The utility of this approach for the synthesis of the anthracyclines is demonstrated by its use in the preparation of various tetracyclic intermediates for anthracycline synthesis.     

Reactions of N-silylphosphoranimines with alcohols: synthesis and structure of cyclotriphosphazenes with nongeminal methyl and phenyl substituents

The reactions of Me(3)SiN=P(OR")RR'(R" = Ph, CH(2)CF(3); R, R' = Me, Ph) with alcohols were investigated. With nonequivalent amounts of CF(3)CH(2)OH, the reactions produced high yields of the cyclic phosphazene (Me(2)PN)(3) and both the cis and trans isomers of nongeminally substituted [(Ph)(Me)PN](3). The isomers of this new cyclic phosphazene were separated by column chromatography and characterized by NMR and IR spectroscopy, elemental analysis, and X-ray crystallography. Crystals of the cis isomer 6a have a monoclinic crystal system, while the trans isomer 6b has a triclinic crystal system with two different molecules in an asymmetric unit. The bond lengths and bond angles are very similar to those of the simpler cyclic trimers (Me(2)PN)(3) and (Ph(2)PN)(3.) A likely pathway for the formation of these compounds is discussed.     

Synthesis of nanosized TiO2/SiO2 particles using microwave processes and their photocatalytic activity on the decomposition of orange II

The nanosized titania and TiO₂/SiO₂ particles were prepared by the microwave-hydrothermal method. The effect of physical properties TTIP/TEOS ratio and calcination temperature has been investigated. The major phase of the pure TiO₂ particle is of the anatase structure, and a rutile peak was observed above 800°C. In TiO₂/SiO₂ particles, however, no significant rutile phase was observed, although the calcination temperature was 900°C. No peaks for the silica crystal phase were observed at either silica/titania ratio. The crystallite size of TiO₂/SiO₂ particles decreases as compared to pure TiO₂ at high calcination temperatures. The TiO₂/SiO₂ particles show higher activity on the photocatalytic decomposition of orange II as compared to pure TiO₂ particles.     

Unique Fluxional Behavior. Synthesis, Structure, and Properties of Novel (Diamine)platinum(II) Complexes of 9-Fluorenylidene- and Benzhydrylidenemalonate Ligands

New (diamine)platinum(II) complexes A(2)PtX(2) (A(2) = trans-(+/-)-1,2-diaminocyclohexane (DACH), tetrahydro-4H-pyran-4,4-diylbis(methylamine)(THPDMA); X(2) = 9-fluorenylidenemalonate(FM), benzhydrylidenemalonate(BHM)) have been synthesized and characterized by means of multinuclear NMR spectroscopy and X-ray analysis. (DACH)Pt(FM) crystallizes in space group P2(1)/c with eight formula units in a cell of dimensions a = 20.071(7) ?, b = 12.717(3) ?, c = 24.512(6) ?, beta = 103.25(2) degrees, and V = 6090(3) ?.(3) (DACH)Pt(BHM) crystallizes in space group P&onemacr; with four molecular units in a cell of dimensions a = 11.048(3) ?, b = 13.639(3) ?, c = 14.043(6) ?, alpha = 90.17(3) degrees, beta = 91.31(4) degrees, gamma = 89.98(3) degrees, and V = 2116(1) ?(3). The platinum atom in both complexes adopts a typical square planar arrangement with two nitrogen atoms in cis position. The 9-fluorenylidene and benzhydrylidene groups of the amine ligands chelated to platinum are strikingly bent up by 88.8(3) and 80.8(2) degrees, respectively, from the platinum square plane in the solid state. Variable temperature (1)H NMR spectra of the title complexes in dimethyl sulfoxide solution reveals that the amine proton resonances are sensitive to the fluxional motion of the remote arylidene groups, and suggests that interconversion occurs between two "bent-up" and "bent-down" forms. The prominent difference between the FM and BHM complexes is observed in solution, due to the presence or absence of the angle constraint of the anionic coligands.