Regiospecific photoisomerization of fluorinated (E,E)-1,4-diphenyl-1,3-butadienes

Photoisomerization of five fluorinated E,E-1-(R-phenyl)-4-phenyl-1,3-butadienes in solution (R = 1: p-monofluoro, 2: m,m′-difluoro, 3: m,m′,p-trifluoro, 4: o,o′,m,m′-tetrafluoro, 5: o,o′,m,m′,p-pentafluoro) was investigated via direct irradiation. Our results indicated that cis-trans photoisomerization of the fluorinated 1,4-diphenyl-1,3-butadienes in the excited singlet state took place exclusively at the CC bonds closer to the fluorine substituents.     

The Effect of cis-trans Isomerism on the Electronic-vibrational Structure of the Ground and Excited States and Reactivity of 2-(2-Furyl)- and 2-(2-Thienyl)oxazole

The fluorescent properties, structure, and electronic structure of the ground and excited singlet and triplet electronic states of the cis and trans forms of 4,5-dihydro-2-(2-furyl)oxazole, 4,4-dihydro-2-(2-thienyl)oxazole, 2-(2-furyl)oxazole (FO), and 2-(2-thienyl)oxazole (TO) have been studied. The orbital nature of the lower excited singlet and triplet states has been studied by the semiempirical INDO/S (valence approximation) and PPP/S ( approximation) methods. It was shown that for FO and TO molecules the lower triplet state is of the * type, for which delocalization of the electronic excitation on atoms is characteristic. In the singlet excitation state inversion was observed of the energy levels of the delocalized * states and n* states localized over several bonds (for the free TO and FO molecules the lower excited singlet states S₁* were assigned to * and n* types respectively). Owing to the low position of the T * and T _n* levels relative to the singlet level of * type, the rate constant for intercombination conversion is greater than the rate constant for radiative decay. Consequently an efficient population of the triplet states of the molecules occurs under conditions of electronic-vibrational excitation. The direction of reactions during synthesis was compared with the localization indices in the ground state for electrophilic, nucleophilic, and radical substitution, and also with the excitation localization numbers L for a wide selection of electronically excited states. It was concluded that the change in the structure of the azole molecule on replacing an O atom by an S atom, or on changing from a partially hydrogenated to a heteroaromatic system, was the main reason for the change of all the spectral parameters characterizing the electronic-vibrational or the spin-orbital interaction of the most reactive groups of atoms in the molecular structure.     

Soluble polymers with pendant thionine groups: Synthesis and evaluation as singlet oxygen photosensitizers

Thionine ( 1 ) has been covalently bound to linear copoly(styrene-p-vinylbenzyl chloride) and to linear copoly(acrylic acid-2-ethylhexyl acrylate). The resulting polymeric dyes, purified by ultrafiltration, present quantum yields of singlet oxygen generation in dimethylformamide solution lower than their corresponding low-molecular-weight models thionine hydrochloride ( 1.HCl ) and N(3)-acetylthionine ( Ac-1 ), the decrease being more pronounced in the case of the polystyrene-dye photosensitizer. High chromophore concentrations within the volume encompassed by each macromolecule in the solution can explain this fall in efficiency. The free dyes thionine hydrochloride and its hydrolysis products thionoline ( 2 ) and thionol ( 3 ) behave as good singlet oxygen generators, with quantum yields of 0.71, 0.62, and 0.63, respectively. © 1993 John Wiley & Sons, Inc.     

脂肪胺结构与密度和折光指数关系的探讨

本文用拓扑方法探讨了脂肪胺的密度和折光指数与其分子结构之间的关系。提出一个既适用于密度又适用于折光指数的定量关系。应用这一定量关系, 不仅能够描述脂肪胺密度和折光指数的变化规律。预测脂肪胺的密度和折光指数,而且能够合理表征物质结构与性能之间的关系。     

Refractive index of water-AOT-n-heptane microemulsions

Refractive index measurements on water/AOT/n-heptane microemulsions as a function of the volume fraction of the dispersed phase (water plus AOT) and of the water/AOT molar ratio R have been performed at 25°C. The refractive index was found to vary monotonically with without any change in rate during the crossover of the percolation threshold. Such a behavior suggested that, well above the percolation threshold, the water-AOT-n-heptane microemulsions are still formed by water-containing AOT reversed micelles dispersed in the oil phase. The analysis of the experimental data allowed an evaluation the fraction of the water molecules bonded to the AOT head group as a function of R.     

Reactions of 1S, 1D,and 3P carbon atoms with water. Oxygen abstraction and intermolecular formaldehyde generation mechanisms; An MCSCF study

Reactions of singlet and triplet carbon atoms with water are explored theoretically using CASSCF–MCQDPT2, CCSD, and DFT methodologies. The ¹S carbons are found to be unreactive. Depending on the carbon atom generation method and the reaction medium, gas‐phase C(³P) attacking water may generate CO and atomic hydrogen as the end products. Reaction paths of the C(¹D) + H₂O system are complicated due to the involvement of two reactive potential energy surfaces with branchings occurring along each. Modifications in product distributions for reactions taking place in condensed phases are elaborated. The decisive reaction conditions, under which the oxygen abstraction and intermolecular formaldehyde generation dominate, are suggested to clarify the discrepancy related with experimental CO observation. The findings are consistent with available experimental data on this system. Oxygen abstraction and intermolecular formaldehyde generation mechanisms suggested here are capable of serving as models for similar reactions of alcohols. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Synthesis of polydithiourethanes and their thermal,optical, and mechanical properties originated from monomers structure

Polyaddition of various diisothiocyanates and dithiols was achieved with triethylamine in dimethylformamide at 25 °C for 12 h under nitrogen, and then the corresponding polydithiourethanes (PDTUs) were obtained with high yield and molecular weight without depending on the monomer structures, although the dithiol monomer of the low nucleophilicity was unsuitable for polyaddition in this system. The chemical and physical properties of the obtained PDTUs such as solvent solubility, glass transition temperature, thermal stability, transparency, refractive index, and tensile strength, were analyzed in detail by gel permeation chromatography, nuclear magnetic resonance, Fourier transform infrared–attenuated total reflection, ultraviolet–visible, differential scanning calorimetry, thermogravimetric analysis, and tensile testing measurements. These results proved that PDTUs and their cast films having the aliphatic diisothiocyanate and dithiol moieties exhibited excellent chemical and physical properties compared to that of the aromatic PDTUs. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2255–2262     

Synthesis and nanoimprinting of high refractive index and highly transparent polythioethers based on thiol-ene click chemistry

This work demonstrates the UV nanoimprinting lithography (UV-NIL) of high refractive index and highly transparent polythioethers based on thiol-ene click chemistry. Herein, 9,9-bis(3-mercaptopropylphenylether)fluorene (BMPF) is designed as a new thiol monomer with a high refractive index, high transparency, and good processability for UV-NIL. Colorless polythioethers are synthesized from BMPF and ene monomers under mild thiol-ene click reaction conditions. Excellent transmittance (96%) of 400 nm light is observed in all the polymer films and high refractive index values of 1.5972–1.6382 are attained. UV-NIL using thiol-ene photopolymerization affords polymer nanoimprinting patterns with various features on the order of 100–500 nm without any fractures. To the best of our knowledge, this is the first report on UV-NIL of high refractive index and highly transparent polymers. Through proper monomer and polymer design, novel polythioethers with suitable glass transition temperature (T _g) values are developed with high refractive index, high transparency, and good UV-NIL processability. Furthermore, UV-NIL based on thiol-ene click chemistry is accomplished at the nanoscale. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2175–2182     

Shear-induced band texture of side group liquid crystalline polymers

The shear-induced band texture of conventional end-on fixed side group liquid crystalline polymers (LCPs) has been investigated by using polarizing optical microscopy (POM), small angle light scattering (SALS) and infra-red dichroism techniques. The band spacing is about 1 μm, which increases very slightly on increasing the temperature of shearing and is independent of shearing rate within the range studied. The band texture is not seen to exhibit an interchange of dark and bright bands on rotation of the sample with respect to the polarizer/analyser, but a typical periodical structure is reflected by the SALS patterns of the band texture. The relaxation behaviour of the bands indicates that the band texture formed here is the result of the orderly aligning of domains exhibiting the focal-conic texture, and this is totally different from the case of main chain LCPs where the band texture is substantially an optical effect of the periodic zigzag or sinusoidal structure of parallel aligned microfibrils. Infra-red dichroism and rotating parallel-plate shearing measurements show that the axes of the backbone of the polymer tend to orient in the shearing direction and the end-on fixed mesogenic side groups tend to align perpendicular to the shearing direction.     

Singlet Oxygen Photo‐Oxygenation in Water/Pluronic F‐127 Hydrogels: Increased Reaction Efficiency Coupled with a Switch in Regioselectivity

Pluronic F‐127 hydrogels are highly efficient microenvironments for photochemical reactions, as demonstrated for singlet oxygen reactions of monoalkenes. Nonpolar substrates are localized in the nanosized polymer compartment, which can be visualized by neutron scattering. The efficiency of ¹O₂ reactions is strongly increased for tiglate derivatives and the regioselectivity of the ene reaction of trisubstituted alkenes is completely switched in comparison with solution phase and inverted in comparison with intrazeolite photo‐oxygenations.