Photochromism of dihydroindolizines. Part XVI: first attempts toward molecular wires comprising photochromic dihydro 5-azaindolizines and π-extended ethynyl and butadiynyl oxadiazole derivatives

Eight new photochromic dihydro 5-azaindolizines (DHAIs) linked with 2,5-diaryl-1,3,4-oxadiazole (OXD) derivatives containing terminal ethynes and butadiyne substituents on the fluorene part of the DHAI skeleton are synthesized via palladium-mediated coupling reaction pathways. Irradiation of the DHAI-OXD derivatives with polychromatic light affords red- and green-colored betaines.     

Photochromism of dihydroindolizines part X. Photo‐responsive self‐assembling organogelators based on photochromic dihydroindolizines and 11‐aminoundecanoic acid (AUDA)

Multi‐addressable photophysical properties of new synthesized photochromic materials based on photochromic dihydroindolizine system (DHI) covalently linked to N‐acyl‐11 aminoundecanoic acid (AUDA) or to its sodium salt or to its ester, through an amidic or urethane linkage have been studied. The DHI skeleton in these compounds is substituted in both the fluorene part (region A) or in the heterocyclic base (region B) with the gelling moieties. These molecules have been designed to respond to their environment. Interestingly, they are shown to act as efficient gelators for polar organic fluids, water and obviously they exhibit a thermosensitive answer as low molecular mass organogelators. In these fluids, the aggregative properties are totally suppressed upon conversion to neutral carboxylic species. The gels of these carboxylate sodium salts are shown to be markedly affected by light irradiation. Supramolecular gelating assemblies can be disrupted by the photoinduced ring opening of the DHI subunit, so that the macroscopic flowing property is recovered. Upon a further thermal treatment, the system is reversibly converted back to the supramolecular network. Controlled gelation could be achieved using temperature, light, or acidity as external stimuli. These new synthesized photochromic gels with their multi‐addressable properties will find their applications as super photoresponsive materials. Developing and tuning of the photophysical properties of the synthesized compounds by the amide and urethane substituents in the 4‐position of the fluorene and pyridazine regions have been achieved. The absorption maxima (λ_max) and the half‐lives (t_1/2) of the colored betaines were detected in all cases using UV/VIS spectrophotometric measurements. Irradiation of DHI 12‐20 in CH₂Cl₂ or in acetonitrile solutions at ambient temperature with polychromatic light leads to the formation of red to red‐violet colored betaines 12 ′ ‐20 ′. The kinetics of the bleaching process of betaines 12 ′ ‐20 ′ to DHIs 12‐20 were found to take place in the second range (96‐218 s) and fit well the first order thermal back reaction. Some of these DHIs showed a photostability higher than that of the standard one. These interesting photophysical properties will help this family of compounds to find useful applications. Copyright © 2008 John Wiley & Sons, Ltd.     

The influence of treatment temperature on the acidity of MWCNT oxidized by HNO3 or a mixture of HNO3/H2SO4

The nature of multi-walled carbon nanotubes (MWCNTs) varies with the change in oxidation conditions. In this work, the effect of treatment temperatures on the acidity of MWCNTs was studied. Oxidation was performed by refluxing the MWCNTs in nitric acid or mixtures of sulfuric acid and nitric acid at different temperatures. After oxidative treatment, a quantitative characterization of o-MWCNTs has been performed using acid-base titrations which show that the number of surface acidic functional groups increased by increasing the treatment temperatures. Energy dispersive X-ray (EDX) measurements show that the oxygen content increased with increasing treatment temperatures. Fourier transform infrared absorption spectroscopy (FTIR) was used for qualitative characterization. It has been demonstrated that the acidity is a function of the type of oxidizing agent used and the treatment temperatures. Due to the importance in attachment strategies and functionalization, this study adds to the global discussion of the possibility of controlling the MWCNTs’ surface chemistry which plays a crucial role in determining its reactivity.     

Low operating temperature of oxygen gas sensor based on undoped and Cr-doped ZnO films

Undoped and doped ZnO with 1 at.% (atomic percentage) chromium (Cr) was synthesized by RF reactive co-sputtering for oxygen gas sensing applications. The prepared films showed a highly c-oriented phase with a dominant (0 0 2) peak at a Bragg angle of around 34.2°. The operating temperature of the prepared ZnO sensor was around 350 °C and shifted to around 250 °C for the doped ZnO sensor which is lower than that of previously reported work. The sensitivity of the sensor toward oxygen gas was enhanced by doping ZnO with 1 at.% Cr. Good stability and repeatability of the sensor were demonstrated when tested under different concentration of oxygen atmosphere.     

A Two-Parameter Deformed N = 2 SUSY Algebra

A two-parameter deformed N = 2 SUSY algebra is constructed by using the q-deformed bosonic and fermionic Newton oscillator algebras. The Fock space representation of the (q ₁,q ₂)-deformed N = 2 SUSY algebra is analyzed. The comparison between the algebra constructed and earlier versions of deformed N = 2 SUSY algebras is also made.     

3-Chloropropyl and 4-chlorobutyl phenyl ethers as sources of 1, 3-dilithiopropane and 1,4-dilithiobutane: sequential reaction with carbonyl compounds

The reaction of 3-chloropropyl and 4-chlorobutyl phenyl ethers (1) with lithium powder and a catalytic amount of DTBB (5% molar) in THF at -78 degrees C followed by successive treatment with a carbonyl compound [R(1)R(2)CO = Bu(t)CHO, Me(2)CO, (CH(2))(5)CO, (-)-menthone] at -78 to 20 degrees C and, after 1.5 h at this temperature, with a second one [R(3)R(4)CO = Bu(t)CHO, PhCHO, Me(2)CO, MeCOPr(n), (CH(2))(5)CO, (-)-menthone] at -78 degrees C leads, after hydrolysis with water, to the corresponding 1,5- and 1, 6-diols (2). Because of the competition of two different reductive cleavages, 1,4- and 1,5-diols 3 were also obtained as side-reaction products.     

Indirect spectrophotometric determination of chromium(VI)

A new simple and sensitive spectrophotometric method for the determination of chromium(VI) is established. It relies upon the oxidation of iron(II) with the titled ion, in acidic medium, to form iron(III) which is complexed with tiron to form a stable blue color with maximum absorption at 650 nm. Adherence to Beer's law is observed in the range 10–100 μg of chromium(VI) per 25 ml, with a molar absorptivity of 5.6 × 10³ liters mol^?1 cm^?1, sensitivity index of 0.0093 μg cm^?1, relative error of ?5.0 to +0.3%, and relative standard deviation of 0.3–4.0%, depending on the concentration level. Furthermore, the reaction needs neither temperature control nor an extraction step.     

An efficient method for the debutylation of o-and p-t-butylphenols and for the hydrolysis of aryl acetates : [Protective group; quinones]

t-Butyl groups can be removed from mono-, di-, or tri-t-butylphenols by refluxing with 70% trifluoroacetic acid. In the same way sterically hindered as well as unhindered aryl acetates can be hydrolysed.