Furopyridines. XXXI. Birch reduction of furopyridines

Birch reduction of four furopyridines 1a‐d effected the characteristic cleavage of the furan ring, giving ethnylpyridinols 2a‐d , vinylpyridinols 3b,d , and ethylpyridinols 4a‐d , and the reduction of the furan ring, giving dihydrofuropyridine 5c,d.     

Transport properties of a lateral semiconductor quantum dot defined by a single connected metallic front-gate

We present studies on the electric transport in a lateral GaAs/AlGaAs quantum dot defined by a patterned single connected metallic front-gate. This gate design allows to easily couple a large number of quantum dots and therefore holds high potential in the design of new materials with tailor-made band structures based on quantum dot superlattices of controlled shape. Clear Coulomb diamond structures and well pronounced tunneling peaks observed in experiment indicate that single-electron control has been achieved. However, the dependence on electron density in the heterostructure embedding the dot, which is controlled by an additional back-gate, reveals that transport characteristics are strongly influenced supposedly by potential fluctuations in the dot and lead regions.     

A remarkable effect of ionic liquids in transition-metal-free aerobic oxidation of benzylic alcohols

The transition-metal-free aerobic oxidation of benzylic alcohols is uniquely accelerated by a 1-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF₆)/PhCF₃ biphasic system and Cs₂CO₃ to afford the corresponding ketones in good yields. The reaction system is also applicable to an oxidative cross-esterification of primary benzyl alcohols with a higher aliphatic alcohol.     

Quantum yields and quantitative spectra of firefly bioluminescence with various bivalent metal ions

We measured quantitative spectra of firefly (Photinus pyralis) bioluminescence in the presence of Zn²⁺ and other bivalent metal ions to investigate the effects of these metal ions on luciferin‐luciferase reaction. We studied the dependence of the quantum yield and spectrum on quantity and kind of bivalent metal ions. Adding various amounts of Mg²⁺, Mn²⁺ and Ca²⁺ produced virtually no change in the quantum yields or the spectra of bioluminescence. In contrast, increasing amounts of ions such as Zn²⁺ and Cd²⁺ decreased quantum yields and changed the bioluminescence color from yellow‐green to red. Quantitative analysis showed that the sensitivities of the quantum yield and color to various metal ions were in the order of Hg²⁺>Zn²⁺, Cd²⁺>Ni²⁺, Co²⁺, Fe²⁺≫Mg²⁺, Mn²⁺, Ca²⁺. We propose that the changes in quantum yield and spectrum caused by the metal ions are due to their effect on luciferase that surrounds oxyluciferin during its radioactive decay. We also found that having more metal ions accelerated bioluminescence reactions. The sensitivity of the reaction rate had no correlation with those of the quantum yield and spectrum.     

In situ preparation of highly fluorescent dyes upon photoirradiation

Photoswitchable or photoactivatable fluorescent dyes are potentially applicable to ultrahigh density optical memory media as well as super-resolution fluorescence imaging when the dyes are highly fluorescent and have large absorption coefficients. Here, we report on highly fluorescent photochromic dyes, which are initially nonluminous in solution under irradiation with visible light but activated to emit green or red fluorescence upon irradiation with ultraviolet (UV) light. The dyes 5a-9a are sulfone derivatives of 1,2-bis(2-ethyl-6-phenyl(or thienyl)-1-benzothiophen-3-yl)perfluorocyclopentene. It was found that substitution of phenyl or thiophene rings at 6 and 6' positions of the benzothiophene-1,1-dioxide groups is effective to increase the fluorescence quantum yields of the closed-ring isomers over 0.7 and absorption coefficients over 4 × 10(4) M(-1) cm(-1). The phenyl-substituted derivatives 5a-7a undergo photocyclization reactions to produce yellow closed-ring isomers 5b-7b, which emit brilliant green fluorescence at around 550 nm (Φ(F) = 0.87-0.88) under irradiation with 488 nm light. Any absorption intensity change of the closed-ring isomers was not observed even after 100 h storage in the dark at 80 °C. The closed-ring isomers slowly returned to the initial open-ring isomers upon irradiation with visible (λ > 480 nm) light. The ring-opening quantum yields (Φ(C→O)) were measured to be (1.6-4.0) × 10(-4). When the phenyl substituents are replaced with thiophene rings, such as compounds 8a and 9a, the absorption bands of the closed-ring isomers shift to longer than 500 nm. The closed-ring isomers exhibit brilliant red fluorescences at around 620 nm (Φ(F) = 0.61-0.78) under irradiation with 532 nm light. The ring-opening reactions are very slow (Φ(C→O) < 1 × 10(-5)). The fluorescence lifetimes of these sulfone derivatives were measured to be around 2-3 ns, which is much longer than the value of the closed-ring isomer of 1,2-bis(2-methyl-1-benzothiophen-3-yl)perfluorocyclopentene (τ(F) = 4 and 22 ps). The closed-ring isomer 8b in 1,4-dioxane exhibits excellent fatigue resistant property under irradiation with visible light (λ > 440 nm) superior to the stability of Rhodamine 101 in ethanol.     

Communication: exploring the reorientation of benzene in an ionic liquid via molecular dynamics: effect of temperature and solvent effective charge on the slow dynamics

The rotational time correlation function (RTCF) of solute benzene molecules in the ionic liquid (1-butyl-3-methylimidazolium chloride) has been studied using classical molecular dynamics simulation. The effect of solvent charge on the functional form of RTCF was investigated by comparing four force fields for the solvent where the total charge on the anion and the cation was set to ±1e, ±0.7e, ±0.5e, and 0, respectively. For all three charged solvent models, the RTCF exhibits a long-time tail where the relaxation rate exhibits a significant slowdown. This feature is strengthened by higher solvent charges as well as lower temperatures, indicating the influence of the strong Coulombic fields arising from the solvent charges. The long-time tail is caused by the extraordinarily slow solvent structural relaxation of ionic liquids compared to the time scale of their local vibrational and librational dynamics.     

Computational studies of room temperature ionic liquid-water mixtures

Room temperature ionic liquids (IL) have been used in numerous applications in chemistry. Addition of water alters many of their properties making it possible to custom design solvents for specific applications. Along with experiments, computational studies using various approaches have provided key insights into the structure and dynamics of IL systems, as well as aggregate formation and phase behavior of the IL/water mixtures. These systems provide computational challenges since ILs and IL/water mixtures are viscous liquids with intrinsically slow processes and structural organization over surprisingly large length scales, which push the limits of applicability of the available techniques. Recent developments in the studies of IL/water mixtures using computational methodologies are reviewed and the future prospects for the field are briefly discussed.     

Water-dispersible ultrathin Au nanowires prepared using a lamellar template of a long-chain amidoamine derivative

Straight ultrathin Au nanowires (NWs) with diameters less than 2 nm were synthesized using the lamellar structure of C18AA in an organogel and its selective adsorption for specific gold surfaces. In addition, the potential to form a bilayer structure with interdigitated hydrocarbon chains enabled the production of water-dispersible Au NWs without morphological change.     

Ultrafast excited state dynamics of fucoxanthin: excitation energy dependent intramolecular charge transfer dynamics

Carotenoids containing a carbonyl group in conjugation with their polyene backbone are naturally-occurring pigments in marine organisms and are essential to the photosynthetic light-harvesting function in aquatic algae. These carotenoids exhibit spectral characteristics attributed to an intramolecular charge transfer (ICT) state that arise in polar solvents due to the presence of the carbonyl group. Here, we report the spectroscopic properties of the carbonyl carotenoid fucoxanthin in polar (methanol) and nonpolar (cyclohexane) solvents studied by steady-state absorption and femtosecond pump-probe measurements. Transient absorption associated with the optically forbidden S(1) (2(1)A) state and/or the ICT state were observed following one-photon excitation to the optically allowed S(2) (1(1)B) state in methanol. The transient absorption measurements carried out in methanol showed that the ratio of the ICT-to-S(1) state formation increased with decreasing excitation energy. We also showed that the ICT character was clearly visible in the steady-state absorption in methanol based on a Franck-Condon analysis. The results suggest that two spectroscopic forms of fucoxanthin, blue and red, exist in the polar environment.     

Laser-induced periodic surface structures formed on the sidewalls of microholes trepanned by a femtosecond laser

Laser-induced periodic surface structures (LIPSSs) were observed on the sidewalls of 300-μm-diameter holes trepanned on cemented tungsten carbide using femtosecond laser pulses at a wavelength of 800 nm. For a circularly polarized beam, LIPSSs were formed at a period of 300 nm and oriented perpendicularly to the plane of incidence on the sidewalls. For a linearly polarized beam, LIPSS formation was dependent on the relative angle α between the polarization direction and the plane of incidence. For relative angles α from 0° to 70° and from 110° to 180°, LIPSS spacing was 300 nm. However, there were two types of LIPSSs coexisting from 70° to 110°. One had a spacing of 120 nm and the other had a spacing that varied from 500 to 760 nm. It was found that the orientation angle of LIPSSs measured between the LIPSS orientation and the plane of incidence had a nonlinear dependence on α. To understand this dependence, a model was proposed in which LIPSSs are assumed to align perpendicularly to the direction of the absorbed electric field lying in the tangent plane of the sidewall of a drilled hole. The calculated results from this model showed good agreement with the experimental results.