Photophysical property and photostability of J-aggregate thin films of thiacyanine dyes prepared by the spin-coating method

By use of electrostatic interactions of dye molecules and poly(diallyldimethylammonium chloride) (PDDA), the spin-coating technique has been successfully applied to the preparation of stable J-aggregate thin films of thiacarbocyanine dyes on a polycarbonate or quartz plate. The J-aggregate thin films were prepared by the spin-coating of PDDA aqueous solution on dye thin films prepared on a substrate by the spin-coating of 2,2,3,3-tetrafluoro-1-propanol solution of dyes. Photophysical properties of the dye thin films and J-aggregate thin films were studied by measuring the fluorescence spectra, quantum yields, and lifetimes. Coherent size of the J-aggregates was estimated to be 3-12 by means of the absorption bandwidth (full width at half maximum) or radiative lifetime. Photostability of the J-aggregate thin films was also studied in terms of photodegradation efficiency under argon and oxygen in comparison with the dye thin films, and J-aggregate thin films were found to be more stable than the corresponding dye thin films.     

Thermally stable rigid π-allylnickel compounds, (π-CHRCR′CR2)Ni(PPhMe2)C6Cl5

The reaction of C₆Cl₅Ni(PPhMe₂)₂Cl with CHRCR′CH₂MgX (X = Br or Cl) yields π-allylnickel compounds, (π-CHRCR′CH₂)Ni(PPhMe₂)C₆Cl₅ (Ia, R = R′ = H; Ib, R = H, R′ = CH₃; Ic, R = CH₃, R′ = H), which are stable in the solid state below ca. 150°C and are fairly stable in solution in the absence of oxygen. The π-allyl group was found by PMR spectroscopy to be rigid even in the presence of an excess of PPhMe₂, P(OEt)₃ or P(OMe)₃.     

Thermal stability of phthalate esters: Effect of substituents on the β-carbon atom

In order to clarify the mechanism conferring heat resistance on phthalate esters, those with a substituent on the β-carbon atom, such as bis(2-aminobutyl) phthalate, bis(2-nitrobutyl) phthalate, bis(2,4-diphenylbutyl) phthalate and dineopentyl phthalate, were synthesized and their thermal stabilities were studied by thermogravimetry and differential thermal analysis. The analytical results for these phthalate esters were compared with those for dibutyl phthalate, with a straight alkyl chain. As the temperatures required for a 3% weight loss of phthalate esters with a substituent, an electron-donating group (amino group) or an electron-accepting group (nitro group) on the β-carbon atom move to the higher end of the range, the effect of the adjacent group was recognized. The presence of a phenyl group in phthalate esters considerably improved the heat resistance. It is considered that the high heat resistance of bis(2,4-diphenylbutyl) phthalate is due to the obstruction of the planar configuration for cis elimination by the phenyl group and hindrance by the phenyl group of the formation of the six-membered cyclic transition state owing to the interaction between non-bondable molecules.     

Towards the selective formation of specific isomers of fullerenes: T - and p-dependence in the yield of various isomers of fullerenes C60–C84

Systematic fractional change in the yield of various isomers of fullerenes was revealed to strongly depend on temperature of a buffer gas. A new kinetic consideration is proposed for understanding the observed temperature- and pressure-dependence of yield of fullerenes. The model consists of three competitive reactions in consideration of plausible behaviors of a precursor, (1) decomposition into smaller fragments, (2) isomerization leading to formation of a stable fullerene cage, and (3) growth into a larger carbon cluster. Arrhenius activation energy of formation of stable fullerenes was determined to be 0.8 eV for both C₆₀ and C₇₀, while a higher energy of 2.0?3.3 eV for seven different isomers of higher fullerenes ranging from C₇₆ to C₈₄. Correlation in the activation energy is noted for a series of higher fullerenes with different sizes, suggesting the existence of a specific precursor in their formation processes.     

Langmuir monolayers of a cholesterol-armed cyclen complex that can control enantioselectivity of amino acid recognition by surface pressure

The cholesterol-armed cyclen Na(+) complex formed stable Langmuir monolayers at the air-water interface. The π-A isotherm displayed a reasonable limiting molecular area of ～1.57 nm(2) and the areas expanded when amino acids were dissolved in water, indicating the efficient accommodation in the monolayers. Brewster angle microscopy (BAM) images exhibited almost no defects of the compressed Langmuir monolayers regardless of the presence of amino acids. Based on the idea that the increase in the limiting molecular areas corresponds to the amount of the adsorbed amino acid, the binding constants of three enantiomeric amino acids, namely valine (Val), leucine (Leu), and phenylalanine (Phe), were calculated at different surface pressures. Remarkably, a surface pressure dependent enantioselectivity of amino acid recognition was observed. Upon compression of the monolayers, the binding constants of amino acids increased accompanying an inversion of chiral selectivity from the D- to L-form in the case of Val and, conversely, from L- to D-form in the case of Phe.     

Pyridylazulenes: synthesis, color changes, and structure of the colored product

A facile method for the synthesis of 1- and 2-pyridylazulenes, and of 1,3-dipyridylazulenes, is described. Color and spectral changes of these pyridylazulenes upon the addition of either acid or metal ions were investigated in detail. The color changed from blue to red upon the addition of trifluoroacetic acid or soft metal ions, depending on the substitution patterns of the pyridyl group on the azulene skeleton. The structures of the protonated or coordinated products were examined on the basis of the spectral data. It was found that the protonation or coordination of metal ions occurred on the nitrogen atom of the pyridine ring, but not on the carbon atom of azulene ring. The transition intervals of several pyridylazulenes for use as pH indicators were also determined.     

Quantitative determination of benzalkonium chloride in treated wood by solid-phase extraction followed by liquid chromatography with ultraviolet detection

Ammoniacal copper quat (ACQ) compound wood preservative is comprised of copper and quaternary ammonium compounds with benzalkonium chloride (BAC) as the active ingredient. Solid-phase extraction (SPE) followed by liquid chromatography with ultraviolet detection (LC-UV) was developed for quantitative determination of BAC in treated wood. Five species of wood were used, Japanese cedar (Cryptomeria japonica), Japanese larch (Larix leptolepis), Yezo spruce (Picea jezoensis), Sakhalin fir (Abies sachalinensis), and western hemlock (Tsuga heterophylla). BAC used in the present study was composed of 66% C12, 33% C14 and less than 1% C16. BAC was added to each wood species (500 mg) then extracted with HCl-ethanol (20 ml) and quantitatively determined with LC-UV (262 nm). Wood extractives from the heartwood of each species, except western hemlock, interfered with quantitative determination of BAC, but SPE with an Oasis MCX cartridge was effective in preventing this. Using the present methods, BAC homologue peaks were clearly confirmed without interference. Recoveries from wood ranged from 92 to 101% and the limit of quantitation was approximately 240 microg/g wood for the C12 and C14 homologues.     

One-pot preparation of chiral beta-amino esters by rhodium-catalyzed three-components coupling reaction

Chiral beta-amino esters are synthesized in one-pot from three components, amines, aldehydes, and ethyl bromoacetate, under the rhodium-catalyzed Reformatsky-type reaction condition, where complete diastereoselection is achieved in the nucleophilic addition step of ethyl bromoacetate to the imines prepared in     

Zinc chelation and photofluorochromic behavior of spironaphthoxazine intercalated into hydrophobically modified montmorillonite

Spironaphthoxazine (SNO) and Zn2+ were intercalated into montmorillonite interlayers hydrophobically modified by the alkyltrimethylammonium cation during UV light irradiation. The fluorescence spectra of the montmorillonite composites were observed to vary with an increase in the UV and visible light irradiation times. These composites exhibited two types of fluorescence emissions: F1, which originates from a new species, Xs, which is different from SNO (ring-closed form) and merocyanine (MC; ring-open form), and F2, which originates from the MC-Zn complex. With increasing UV light irradiation time, the F1 intensities decreased, whereas the F2 intensities increased. Xs, which is an intermediate species between SNO and MC, was transformed into MC and then coordinated with Zn2+ (i.e., MC-Zn complex) during the UV light irradiation. The reaction rate of the formation of the MC-Zn complex decreased for the hydrophobically modified montmorillonite due to a longer alkyl chain. The retrieval changes in the F1 and F2 intensities were observed with an increasing visible light irradiation time, implying the dissociation of the MC-Zn complex into Xs and Zn2+. The dissociation especially occurred for the hydrophobically modified montmorillonite with a longer alkyl chain. The formation and disappearance of Xs and the MC-Zn complex obeyed first-order kinetics, and therefore the interconversion between Xs and MC could be regarded as the rate-determining step of the whole reaction during the UV and visible light irradiations. The photoinduced reactions of the SNO species and Zn2+ were profoundly affected by the physicochemical environment provided by the clay interlayers. It is concluded that the present photoreactions can be controlled not only by the amounts of the intercalated SNO species and Zn2+, but also by the hydrophobic environment created by the surfactant molecules.