Polydimethylsiloxane‐coated partitioning sample collection device for the precise quantification of polycyclic aromatic hydrocarbons in air

A novel partitioning collection device comprising a glass cartridge packed with poly(dimethylsiloxane)‐coated macroporous silica particles was developed for the precise quantification of polycyclic aromatic hydrocarbons in air. The analyte collection and elution performances achieved using different amounts of poly(dimethylsiloxane) coating were quantitatively evaluated. The sample retention power increased with increasing the coating, and more than 250 L of air could be collected without analyte breakthrough at a sampling temperature of 35°C. During the air collection, the moisture in the air was not retained on the particles due to the hydrophobic surface of the sorbent. A complete and rapid elution of the collected analytes from the device was accomplished by the passage of only 10 mL of acetone with ultrasonication for 1 min. The proposed method was successfully applied for the determination of airborne polycyclic aromatic hydrocarbons in tunnel air.     

Stepwise and one-pot syntheses of Ir(III) complexes with imidazolium-based carbene ligands

We report the preparation, crystal structure, electrochemistry, and emission properties of Ir(Cinsertion markC:)3, where Cinsertion markC: is an N-heterocyclic carbene ligand. Two synthetic approaches are introduced for generating Ir(III) complexes bearing imidazolium-based carbene ligands whose precursors are [pypiH2][Cl] (1a) (pyridyl[1,2-a]{2-phenylimidazol}-3-ylidene chloride) and [pympiH2][Cl] (1b) (pyridyl[1,2-a-{2-(p-methoxy)phenylimidazol}-3-ylidene chloride). The first method is a stepwise reaction: treatment of [Ir(mu-Cl)(COD)]2, where COD is 1,5-cyclooctadiene, with 4 equiv. of the corresponding carbene (Cinsertion markC:) ligands in the presence of an excess amount of sodium methoxide affords Ir(III) dimers [Ir(mu-Cl)(Cinsertion markC:)2]2 (2a, Cinsertion markC: = pypi(-); 2b, Cinsertion markC: = pympi(-)). These chloro-bridged dimers 2a and 2b react with the corresponding carbene (Cinsertion markC:) ligands to form the desired homoleptic compounds Ir(Cinsertion markC:)3 (3a, Cinsertion markC: = pypi(-); 3b, Cinsertion markC: = pympi(-)). The second method, using a one-pot reaction of [Ir(mu-Cl)(COD)]2 with 6 equiv. of the corresponding carbene (Cinsertion markC:) ligands 1a and 1b in the presence of excess amounts of Ag2O, affords Ir(Cinsertion markC:)3. The two methods are convenient and reproducible procedures for the synthesis of Ir(Cinsertion markC:)3. Complexes 3a and 3b are obtained as mixtures of meridional and facial isomers, which can be separated by recrystallization or flash column chromatography.     

A partially crosslinked bicontinuous cubic phase exhibiting a temperature range of more than 100 °C

A new methodology of partial crosslinking is presented for stabilizing the bicontinuous cubic phase without losing its dynamic nature. It was applied to a mixture of 1,2-bis[4'-(9'-decenyloxy)benzoyl]hydrazine with a bi-functional linker, remarkably stabilizing the phase in comparison with the neat compound having no C=C bond at the end of the alkyl tail.     

Picoliter droplet formation on thin optical fiber tips

In this paper, we present experimental results on how minute droplets are formed on fiber optic end faces. Results show that reproducible picoliter volumes can be generated when fibers are retracted from an aqueous phase contained under an inert fluorinated immiscible liquid, with a coefficient of variation (CV) of 0.7-2.3%. The droplet formation was analyzed as a function of the fiber diameter, retraction speed, and wettability. Experiments reveal a volume-determining critical equilibrium contact angle between 60 degrees and 75 degrees , defining the onset of fiber end-face dewetting. The dynamics of the droplet snap-off progression was characterized using high-speed imaging in order to explain the observed wettability-volume dependency.     

Spectroscopic study of laser-induced phase transition of gold nanoparticles on nanosecond time scales and longer

The pulsed laser induced phase transition of gold nanoparticles in aqueous solution was observed via a transient absorption on nanosecond time scales and longer. Gold nanoparticles were excited with an intense picosecond laser pulse (355 nm, 30 ps), and the subsequent changes were monitored using two continuous wave laser wavelengths (488 and 635 nm). On the nanosecond time scale, below 6.3 mJ cm(-2), no change was observed; however, in the low fluence region between 6.3 and 17 mJ cm(-2), gold nanoparticles produced a bleach signal (488 nm) attributed to the melting of the gold nanoparticles, which decreased linearly with increasing laser fluence. Laser fluences above 17 mJ cm(-2) resulted in a strong absorption at both wavelengths, which is ascribed to vaporization of gold nanoparticles rather than solvated electrons (ejected from gold nanoparticles) or light scattering. The decay of both signals was faster than the 5 ns time resolution used in our experimental system. On the microsecond time scale, increase in absorbance at 635 nm was observed with a time constant of 1.0 micros, while no change was observed at 488 nm. It is considered that this increase is attributed to the formation of smaller gold nanoparticles resulting from pulsed laser induced size reduction of initial gold nanoparticles.     

Exciton recurrence motion in aggregate systems in the presence of quantized optical fields

The exciton dynamics of model aggregate systems, dimer, trimer, and pentamer, composed of two-state monomers is computationally investigated in the presence of three types of quantized optical fields, i.e., coherent, amplitude-squeezed, and phase-squeezed fields, in comparison with the case of classical laser fields. The constituent monomers are assumed to interact with each other by the dipole-dipole interaction, and the two-exciton model, which takes into account both the one- and two-exciton generations, is employed. As shown in previous studies, near-degenerate exciton states in the presence of a (near) resonant classical laser field create quantum superposition states and thus cause the spatial exciton recurrence motion after cutting the applied field. In contrast, continuously applied quantized optical fields turn out to induce similar exciton recurrence motions in the quiescent region between the collapse and revival behaviors of Rabi oscillation. The spatial features of exciton recurrence motions are shown to depend on the architecture of aggregates. It is also found that the coherent and amplitude-squeezed fields tend to induce longer-term exciton recurrence behavior than the phase-squeezed field. These features have a possibility for opening up a novel creation and control scheme of exciton recurrence motions in aggregate systems under the quantized optical fields.     

Naphthalene-1,8-diylbis(diphenylmethylium) as an organic two-electron oxidant: benzidine synthesis via oxidative self-coupling of N,N-dialkylanilines

Naphthalene-1,8-diylbis(diphenylmethylium) exhibits a unique electron-transfer reduction behavior due to the close proximity of the two triarylmethyl cations, which form a C-C bond while accepting two electrons, leading to 1,1,2,2-tetraphenylacenaphthene. The preparation of the dication was readily accomplished under anhydrous conditions starting from a cyclic bis(triarylmethyl) ether, derived from 1,8-dibromonaphthalene. The process proceeded via deoxygenation accompanying the formation of a disiloxane on treatment with a silylating agent (Me3SiClO4 or Me3SiOTf) in 1,1,1,3,3,3-hexafluoropropan-2-ol. The dication was successfully employed for oxidative coupling of N,N-dialkylanilines at the para-position to afford the corresponding benzidines in good to excellent yield.