2,3-di-n-decyloxy-6,7-dichloroanthracene (Cl2DDOA), a new low-molecular-mass fluorescent organogelator: physical properties and structures

To extend the family of 2,3-didecyloxyanthracene (DDOA, 1), an organogelator having a rodlike shape, a high polarity, and fluorescing properties, the 6,7-dichloro derivative (Cl2DDOA, 2), was designed and prepared. Compound 2 forms gels in alcohols, nitriles, and alkanes. The electronic absorption spectra of the gel show a finer structure than those of the isotropic solutions, pointing to a specific degree of packing of the molecules; such an aggregation mode is also supported by fluorescence data. The gel-to-sol temperatures (Tm) were determined as a function of gelator concentration and the corresponding enthalpies (DeltaHm) were extracted. Scattering experiments have shown that the molecular packing in aggregates of 2 organogels is less reminiscent of the crystalline state than was the situation with DDOA gels. 2 organogels in butanol are made up of 120 A radius fibers much thinner than those observed in DDOA gels (r ca. 300 A) and with rather monodisperse cross sections. In 1-octanol, dodecane, or cyclohexane, the fibrillar organogel networks involve a broader distribution of the related cross sections through anisometric sections of the fibers and/or formation of bundles.     

Nucleation and growth characteristics of a binary low-mass organogel

The system of bis(2-ethylhexyl) sodium sulfosuccinate and 4-chlorophenol, when dissolved in a nonpolar organic solvent, forms an organogel. The fibers of this organogel are formed through a nucleation-growth phenomenon. By reducing evaporation of the pregel solution, the fibers can be directed to grow with extremely long persistence lengths. Alignment of multiple fibers is achieved by inducting growth at the air-solution interface. The interplay of two zones, one above the critical nucleation concentration and the other below, allows orientation to be accomplished as fiber growth proceeds. The observations have implications for the use of the organogel as a template for materials synthesis.     

Structural variations in a family of orthodialkoxyarenes organogelators

A series of low mass organic gelators (LMOGS) 1 to 6 whose chemical structures have in common an orthodialkoxyarene feature was prepared in order to compare the shape of their fibrillar network as investigated by small-angle neutron scattering (SANS) experiments. All members of the family exhibit a pronounced tendency to bundle formation by merging isolated fibers in extended packets of average diameter >500 A. Variations of the 2D packing symmetry are observed from hexagonal to square orderings with close derivatives of the reference member 2,3-didecyloxyanthracene (DDOA). Networks in which the fraction of isolated fibers is significant enough to allow for their SANS identification are those for 6,7-dichloro-2,3-didecyloxyanthracene (Cl(2)DDOA) and 2,3-dodecyloxy-9,10-anthraquinone (5). For this latter, the monodispersity of the cross-sections (thickness=74 A) is remarkable and the rectangular shape (b/a approximately 0.12) accounts for a merging mechanism into anisotropic bundles (ribbons).     

Magnetic deformation of self-assembled sexithiophene spherical nanocapsules

We report the experimental observation of magnetic field deformation of spherical nanocapsules, self-assembled from sexithiophene molecules, into oblate spheroids, confirming a long-standing theoretical prediction. The magnetically deformed objects can be trapped in a compatible organogel to make them suitable for further investigations and applications. Our results show that strong magnetic forces can be effectively used, in a contact-free manner, as a tool to control the self-organization of a whole class of functional organic molecules.     

Use of a self-assembling organogel as a reverse template in the preparation of imprinted porous polymer films

The concept of reverse templating of an organogel to form imprinted porous divinylbenzene polymer films with submicrometer channels is demonstrated. The organogel comprising a 1:1 molar ratio of two organogelators, that is, bis(2-ethylhexyl) sodium sulfosuccinate and 4-chlorophenol, was formed in divinylbenzene. The gel was cast as a thin film before UV polymerization of the solvent, and the organogelators were later removed by simple washing with water and isooctane. The integrity of the fiber bundles of the organogel was preserved during polymerization, and an exact hollow replica was obtained after the organogelators were leached away. It is easily possible to imprint gel fiber bundle structures into polymeric films through this technique. The gel can also be formed on macroporous substrates to yield supported thin porous polymeric films. With the incorporation of functional nanoparticles in AOT inverse micelles and hence the organogel, nanoparticle-containing porous polymer films exhibiting luminescence or magnetic properties are envisioned.     

Brownian dynamics investigation of magnetization and birefringence relaxations in ferrofluids

Brownian dynamics simulations are used to investigate the dynamics of orientational properties of real charge-stabilized ferrofluids, i.e. stable colloidal dispersions of magnetic nanoparticles. The relaxation times of the magnetization and of the birefringence, data accessible by experimental techniques, have been computed at several volume fractions. Besides, the effect of hydrodynamic interactions has been investigated. Equilibrium simulations without field are found to be inadequate to determine the aforementioned relaxation times for the systems under study, the dipolar interaction being too weak. Thus a nonequilibrium simulation procedure that mimics the experimental operating mode has been developed. After equilibrium simulations under a magnetic field, both birefringence and magnetization decays are recorded once the field is suppressed. Birefringence and magnetization decays are markedly impeded as the volume fraction increases, whereas they are barely enhanced when the intensity of the initial magnetic field is increased at a fixed volume fraction. Eventually, hydrodynamic interactions exhibit a slight but systematic lengthening of the relaxation times.     

Novel carbazole-based organogels modulated by tert-butyl moieties

tert-Butyl groups can modulate the self-assembling properties of carbazole derivatives; organogel fibers with a bright blue emission are generated, directed by the cooperation of hydrogen bonding as well as pi-pi interactions.     

Semiconducting Fabrics by In Situ Topochemical Synthesis of Polydiacetylene: A New Dimension to the Use of Organogels

A diyne functionalized 4,6‐O‐benzylidene β‐d ‐galactopyranoside gelator, which can align its diyne motifs upon self‐assembly (gelation) have been synthesized. The organogel formed by this gelator undergoes topochemical polymerization to polydiacetylene (PDA) under photoirradiation. This strategically designed gelator has been used to make semi‐conducting fabrics. By developing the organogel on the fabrics, the gelator molecules were made not only to self‐assemble on the fibers, but also to adhere to fabrics through hydrogen bonding. UV irradiation of the gel‐coated fabric/fiber resulted in the formation of PDA on fibers. The benzylidene motif could be deprotected to get PDA with pendant free sugars that strongly bind to the cotton fibrils through multiple hydrogen bonds. Conductivity measurements revealed the semiconducting nature of these fabrics.     

Virtual isotropic‐nematic transitions in alkyl cyanobiphenyls

Pretransitional fluctuations in the isotropic phase of liquid crystalline and non‐liquid crystalline alkyl cyanobiphenyls have been investigated using light scattering and magnetic birefringence measurements. We find evidence for a virtual isotropic‐nematic phase transition in short‐chain alkyl cyanobiphenyls with no observable nematic phase. The measured temperature dependence of fluctuations is well‐described by mean‐field theory. Virtual phase transition temperatures extrapolated from separate light scattering and magnetic birefringence experiments are in good agreement. Landau–de Gennes model parameters for the compounds investigated are calculated from the experimental results.     

Room-temperature synthesis of soluble, fluorescent carbon nanoparticles from organogel precursors

Carbon nanoparticles were obtained at room temperature by irradiating an organogel made from a 1,8-diaryloctatetrayne derivative in chloroform. During the topochemical polymerization, the morphology of the gel changes from fibers to soluble, yellow fluorescent nanoparticles in high yield. Analyses suggest that the resulting nanoparticles are made of amorphous graphitic carbon.     

Reactive organogels: self-assembled support for functional materials

[reaction: see text] An organogel bearing reactive groups has been used as a platform for the gel-phase synthesis of more sophisticated materials. The results show that reactions take place on the gel fibers and that supramolecular aggregation modifies the product distribution in cases where several compounds can be obtained.     

A dipole interaction model for magnetochiral birefringence

We have developed a classical model to investigate the magnetochiral birefringence of an isotropic chiral medium submitted to a longitudinal magnetic field. This model, which is an extension of the atom dipole interaction model, yields direct calculations from the polarizabilities and positions of the atoms of the considered molecules. The numerical values obtained for the magnetochiral birefringence, as well as for the optical activity and Faraday rotation, are supported by the previously published experimental results on limonene, proline, and tartaric acid.     

Birefringence of highly oriented fibers

A spectrophotometric method was developed for measuring the birefringence of highly oriented synthetic fibers. This method surmounts the low birefringence limit of the standard quartz compensator method and the difficulties in interpretation of the photographic fringe method. A highly oriented aramid fiber gave birefringence values of 0.60–0.75 by this method, compared with 0.25 for polyester and 0.06 for nylon by other conventional methods. The operating principles and excellent results of this new method provide a basis for the extension of routine birefringence characterization to highly oriented fibers.     

Birefringence changes in vertebrate striated muscle.

The changes in birefringence in the rigor to relax transition of single Triton-extracted rabbit psoas muscle fibers have been investigated. The total birefringence of rigor muscle fibers was dependent on sarcomere length and ranged from (1.46 +/- 0.08) X 10(-3) to (1.60 +/- 0.06) X 10(-3) at sarcomere lengths from 2.70 mum to 3.40 mum. An increase in total birefringence was measured dependent on sarcomere length when 55 single fibers were relaxed from the rigor state with Mg-ATP. Pyrophosphate relaxation produced a smaller increase in retardation when compared to Mg-ATP. The expected change in intrinsic birefringence during the rigor to relax transition was calculated assuming a hinge function of the subfragment 2 moiety of myosin. The changes in birefringence during isometric contraction and relaxation have been discussed in relation to possible structural changes.     

Segmental and chain orientational behavior of spandex fibers

The internal structure and orientation behavior of two series of spandex fibers, which were made with different spinning methods and different soft and hard segment types, were studied by FTIR (Fourier Transform Infrared Spectroscopy), polarizing light microscopy, and Instron. The orientation behavior of hard and soft segments was studied with FTIR and those of polymeric chains with polarizing miscroscopy while the fibers were being stretched by the mechanical stretcher. The orientation behavior of dry-spun fibers was observed to be very different from that of the melt-spun fibers, which may be explained in terms of the internal structural difference such as the degree of phase separation and mechanical stability of the hard domains between the two types of fibers. In general, the dry-spun fibers showed better elastic recovery property than the melt-spun fibers. Since the polymer for the dry-spun fibers was synthesized with ethylene diamine as a chain extender resulting in the urea groups in the hard segments, it forms more stable hard domain due to the high cohesion energy between the urea groups. The change of the birefringence values during the cyclic deformation was studied with the polarizing light microscopy. The birefringence behaviors of the two dry-spun fibers were similar, whereas there was a noticeable difference between the two melt-spun fibers. The difference was explained in terms of the effect of crosslinking agent in one of the melt-spun fibers, which can stabilize the hard domain structure against the external stress. Mechanical hysteresis values measured gave results consistent with those of FTIR and birefringence measurements. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1821–1832, 1997     

基于MBA凝胶纤维的RAFT聚合制备聚合物微米管

以三乙二醇双丙烯酸酯(TEGDA)为共聚单体, 通过可逆加成-断裂链转移(RAFT)聚合反应, 将N,N'-亚甲基双丙烯酰胺(MBA)凝胶纤维直接转化为聚合物微米管. 用扫描电子显微镜(SEM)、 透射电子显微镜(TEM)、 红外光谱(FTIR)和元素分析等表征了聚合物微米管的结构和组成. 研究结果表明, TEGDA的加入可显著提高聚合物微米管的产率, 并使其具有自支撑性. 环境扫描电子显微镜(ESEM)原位表征结果表明, 聚合物微米管具有一定的溶剂溶胀性能. 采用流变仪测定了加入TEGDA前后的聚合物凝胶的机械性能, 相对于MBA凝胶, 聚合物凝胶的机械性能显著提高.     

Evolution from lyotropic liquid crystal to helical fibrous organogel of an achiral fluorescent twin-tapered bi-1,3,4-oxadiazole derivative

We report an unprecedented hierarchical self‐assembly of an achiral twin‐tapered bi‐1,3,4‐oxadiazole derivative (2,2‐bis(3,4,5‐trioctanoxyphenyl)‐bi‐1,3,4‐oxadiazole, BOXD‐T8). This molecule can form a layer‐structured lyotropic liquid crystal and further forms a helical fibrous organogel in DMF at concentrations above 0.6 wt %. The self‐assembly process of BOXD‐T8 in DMF is accompanied by a change in its fluorescence. The pitches of the helical fibers are non‐uniform, and both left‐ and right‐handed helical fibers are observed in equal quantities. Intermolecular π–π interactions between aromatic segments have been demonstrated to be the driving force for aggregate formation. This helical structure of BOXD‐T8 is dependent on the solvent, concentration, and the layer‐structured intermediate liquid‐crystalline state.     

The Cotton-Mouton effect of neon and argon: a benchmark study using highly correlated coupled cluster wave functions

The Cotton-Mouton effect (magnetic field induced linear birefringence) has been studied for neon and argon using state-of-the-art coupled cluster techniques. The coupled cluster singles, doubles and triples (CCSDT) approach has been used to obtain static benchmark results and the CC3 model with an approximate treatment of triple excitations to obtain frequency-dependent results. In the case of neon the effect of excitations beyond triples has also been estimated via coupled cluster calculations including quadruple excitations (CCSDTQ), pentuple excitations (CCSDTQP), etc. up to the full configuration-interaction level. The results obtained for the anisotropy of the hypermagnetizability Deltaeta(omega), the molecular property that determines the magnetic field induced birefringence of spherically symmetric systems, are Deltaeta=2.89 a.u. for neon and Deltaeta=24.7 a.u. for argon, with a negligible effect of frequency dispersion. For neon we could estimate an absolute error on Deltaeta of 0.1 a.u. The accuracy of these results surpasses that of recently reported experimental data.