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.     

Sol–gel synthesis and characterization of conducting polythiophene/tin phosphate nano tetrapod composite cation-exchanger and its application as Hg(II) selective membrane electrode

Nano tetrapod based on conducting polythiophene (PTh) and tin-phosphate (SnP) were synthesized by in situ chemical oxidative polymerization. The morphology of the resulting polythiophene tinphosphate composite was characterized by elemental analysis, fourier transform infrared spectroscopy, thermogravimetric analysis, powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The physico-chemical characterization carried out on the composite showed that SnP was modified by conducting PTh with an enhancement of various properties. On the basis of highest distribution coefficient values for Hg(II), the composite was also used for the preparation of Hg(II) selective membrane electrode. The electrode showed working concentration range of 1 × 10^?1 to 1 × 10^?7 with Nernstian slope of 29.29 mV per decade change in concentration and the electrode may be used for wide working pH range of 4–8 having quick response time about 23 s. The life of electrode is 4 months without any notable drift in potential.     

Synthesis and Spectral Properties of 4‐(2,5‐Dimethoxyphenylmethelene)‐2‐phenyl‐5‐oxazolone (DMPO)

An interesting flourophore, 4‐(2,5‐dimethoxyphenylmethelene)‐2‐phenyl‐5‐oxazolone (DMPO) was synthesized by mixing an equivalent molar quantity of hippuric acid and 2,5‐dimethoxybenzaldehyde in acetic anhydride in the presence of anhydrous sodium acetate. The absorption and fluorescence characteristics of 4‐(2,5‐dimethoxy‐phenylmethelene)‐2‐phenyl‐5‐oxazolone (DMPO) were investigated in different solvents. DMPO dye exhibits red shift in both absorption and emission spectra as solvent polarity increases, indicating change in the dipole moment of molecules upon excitation due to an intramolecular charge transfer interaction. The fluorescence quantum yield depends strongly on the properties of the solvents, which was attributed to positive and negative solvatokinetic effects. A crystalline solid of DMPO gave strong excimer like emission at 630 nm due to the excitation of molecular aggregates. This is expected from the idealized crystal structure of the dye that belongs to the B‐type class of Steven's Classification. DMPO displayed fluorescence quenching by triethylamine via nonemissive exciplex formation.     

Functional 2-benzyl-1,2-dihydro[60]fullerenes as acceptors for organic photovoltaics: facile synthesis and high photovoltaic performances

A new series of functional 2-benzyl-1,2-dihydro[60]fullerenes, BnHCs, were synthesized efficiently via co-catalyzed selective monofunctionalization of C₆₀ with functional benzyl bromides. Photophysical and electrochemical properties of the new BnHCs were investigated. PSCs based on 2-MeO–4-CO₂Me–BnHC as new acceptor and P3HT as donor showed a power conversion efficiency of 3.75%, which is comparable to that of PC₆₁BM under the same device conditions.     

Flow‐Induced Polymer Degradation During Ink‐Jet Printing

We report for the first time evidence of flow‐induced polymer degradation during inkjet printing for both poly(methyl methacrylate) (PMMA) and polystyrene (PS) in good solvent. This has significance for the deposition of functional and biological materials. Polymers having either less than 100 kDa or greater than approximately 1 000 kDa show no evidence of molecular weight degradation. The lower boundary condition is a consequence of low Deborah Number De imposed by the printhead geometry and the upper boundary condition due to visco‐elastic damping. For intermediate molecular weights the effect is greatest at high elongational strain rate and low solution concentration with higher polydispersity polymers being most sensitive to molecular weight degradation. For low polydispersity samples, PDi ≤ 1.3, chain breakage is essentially centro‐symmetric induced either by turbulance or overstretching when the strain rate increases well beyond a critical value, that is the stretching rate is high enough to exceed the rate of relaxation. For higher polydispersity samples chain breakage is consistent with almost random scission along the chain, inferring that the forces required to break the chain are additionally transmitted either by valence bonds, i.e. network chains and junctions or discrete entanglements rather than solely by hydrodynamic interaction.

     

Semiconductor nanoparticles for photoinitiation of free radical polymerization in aqueous and organic media

Photoinduced free radical polymerization of vinyl monomers by using semiconductor inorganic nanoparticles (NPs) is investigated. Zinc oxide and iron‐doped zinc oxide were used as photosensitive compounds to initiate the polymerization of acrylamide as a water‐soluble monomer in aqueous environment and methyl methacrylate as an oil‐soluble monomer in organic media under UV‐light irradiation. The method uses photochemically generated electrons and holes from the NPs to form initiating hydroxyl radicals in aqueous media, while tertiary amines and iodonium salt served as coinitiator in organic media. The initiation mechanism in organic media involves hydrogen abstraction or reduction processes via charge carriers, respectively. The kinetic of the polymerization in both environments was studied by means of a photo‐differential scanning calorimetry. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1500–1507