Purple Phase Research Articles

Fluorescence Filter Nanoarchitectonics with Polydiacetylene‐Based Supramolecular Chiral Gel for Generating Tunable Circularly Polarized Luminescence

AbstractCircularly polarized luminescence (CPL) can be generated from chiral luminescent materials. It can also be achieved from achiral emissive dyes by selectively filtering their fluorescence with chiroptical active materials. In this work, a novel polydiacetylene‐based supramolecular chiral gel is fabricated as a handedness‐selective fluorescence filter for generating CPL. The gelator consists of a diacetylene alkyl chain and a chiral histidine (His) head group (HisDA). It can self‐assemble into nanoribbon and turn into the blue phase, purple phase and red phase polydiacetylene‐His (HisPDA) upon photopolymerization. The resulting L/D‐HisPDA gels show variable circular dichroism (CD) with the change in color. Furthermore, multiple CPL signals are achieved after fluorescence excited with achiral dyes D1–D3 passing through HisPDA gel. The intensity of CPL increases gradually in both D1 and D3 dye systems along with the change of the HisPDA gel from blue phase to red phase, while the CPL signal is inverted for the D2 dye system. The handedness of the CPL signal is opposite to the CD signal of HisPDA gel in all the cases, demonstrating that CPL is originated through a handedness‐selective fluorescence adsorption mechanism. This study offers a new strategy for obtaining tunable CPL via adjustable chiral fluorescence filters.

Huenite, Cu4Mo3O12(OH)2, a New Copper-molybdenum Oxy-hydroxide Mineral from the San Samuel Mine, Carrera Pinto, Cachiyuyo De Llampos District, CopiapÓ Province, Atacama Region, Chile

Abstract Huenite, Cu4Mo3O12(OH)2, is a new copper and molybdenum oxy-hydroxide mineral found in the San Samuel Mine, Carrera Pinto, Cachiyuyo de Llampos district, Copiapó Province, Atacama Region, Chile. This new species forms flattened orthorhombic prisms up to 60–70 μm in size, weakly elongated along [001]. Huenite crystals were found on fractured surfaces of a quartz breccia, forming aggregates 1 mm in diameter in close association with lindgrenite, gypsum, dark grayish-brown tourmaline, and an unknown pale purple phase. The color is very dark reddish-brown, with a strong vitreous to adamantine luster. Its streak is pale reddish-brown to pinkish. The mineral is brittle with an irregular fracture and a Mohs hardness of 3.5–4 with a good cleavage on {010}. Its calculated density is 5.1 g/cm3. The calculated refractive index is 2.18. Huenite is non-fluorescent under 254 nm (short wave) and 366 nm (long wave) ultraviolet light. The empirical formula, calculated on the basis of 3 (Mo+S+Si) atoms per formula unit, is (Cu3.519Fe2+0.403)Σ3.922(Mo2.907S0.090Si0.003)Σ3.000O12·(OH)2.229, with H2O content calculated for a total of 100 wt.%. Huenite is trigonal, with space group P31/c and unit-cell parameters a = 7.653(5) Å, c = 9.411(6) Å, and V = 477.4(5) Å3 for Z = 2. The eight strongest measured powder X-ray diffraction lines are: [d in Å, (I/I0), (hkl)]: 2.974 (100) (112), 1.712 (59.8) (132), 3.810 (50.6) (110), 2.702 (41.2) (022), 2.497 (38.1) (120), 1.450 (37.2) (134), 6.786 (24.9) (010), and 5.374 (24.5) (011). The mineral, which has been approved by the CNMNC under number IMA 2015-122, is named in honor of Edgar Huen.

The red, purple and blue modifications of polymeric unsymmetrical hydroxyalkadiynyl-N-arylcarbamate derivatives in Langmuir-Schaefer films

Solid topochemical photopolymerization (STP) of Langmuir-Schaefer films of a new class of unsymmetrical diynes, containing N-arylcarbamate groups in the hydrophobic part and hydroxymethylene groups in the hydrophilic part of the molecules was examined. In addition, the monomeric Langmuir monolayer formation was studied by Brewster angle microscopy and the surface morphology of monomer and polymer films on solid substrates were studied by scanning electron microscopy and atomic force microscopy. Three phases of polydiacetylene (PDA) (red, purple and blue) were observed after UV-light polymerization of above-mentioned films of alcohol diacetylene (DA) derivatives. The substitution of MeO group in the aryl ring substituent by hydrogen atom and the variation of the methylene group number in the hydrophobic part from 5 to 6 changed significantly the result of STP: instead of blue phase PDA observed for diynes with MeO group, the red phase PDA was observed for DA with H-atom from the very beginning of diyne film UV irradiation. For two other diynilic N-arylcarbamates of identical chemical structures except of the substituents in the aryl ring of hydrophobic parts of the molecules, no changes in the efficiency of polymerization or the position and shape of absorption bands were observed. This indicated the formation of the purple phase PDA. For these molecules, the number of methylene groups in hydrophobic and hydrophilic parts of the molecules was 9 and 2, respectively.

The synthesis and characterisation of coordination and hydrogen-bonded networks based on 4-(3,5-dimethyl-1H-pyrazol-4-yl)benzoic acid.

The synthesis, structural and thermal characterisation of a number of coordination complexes featuring the N,O-heteroditopic ligand 4-(3,5-dimethyl-1H-pyrazol-4-yl)benzoate, HL are reported. The reaction of H2L with cobalt(II) and nickel(II) nitrates at room temperature in basic DMF/H2O solution gave discrete mononuclear coordination complexes with the general formula {[M(HL)2(H2O)4]·2DMF} (M = Co (1), Ni (2)), whereas the reaction with zinc(II) nitrate gave [Zn(HL)2]∞, 3, a coordination polymer with distorted diamondoid topology and fourfold interpenetration. Coordination about the tetrahedral Zn(II) nodes in 3 are furnished by two pyrazolyl nitrogen atoms and two carboxylate oxygen atoms to give a mixed N2O2 donor set. Isotopological coordination polymers of zinc(II), {[Zn(HL)2]·2CH3OH·H2O}∞, 4, and cobalt(II), [Co(HL)2]∞, 5, are formed when the reactions are carried out under solvothermal conditions in methanol (80 °C) and water (180 °C), respectively. The reaction of H2L with cadmium(II) nitrate at room temperature in methanol gives {[Cd(HL)2(MeOH)2]·1.8MeOH}∞6, a 2-D (4,4)-connected coordination polymer, whereas with copper(II) the formation of green crystals that transform into purple crystals is observed. The metastable green phase [Cu3(HL)4(μ2-SO4)(H2O)3]∞, 7, crystallises with conserved binding domains of the heteroditopic ligand and contains two different metal nodes: a dicopper carboxylate paddle wheel motif, and, a dicopper unit bridged by sulfate ions and coordinated by ligand pyrazolyl nitrogen atoms. The resultant purple phase {[Cu(HL)2]·4CH3OH·H2O}∞, 8, however, has single copper ion nodes coordinated by mixed N2O2 donor sets with trans-square planar geometry and is threefold interpenetrated. The desolvation of 8 was followed by powder X-ray diffraction and single crystal X-ray diffraction which show desolvation induces the transition to a more closely packed structure while the coordination geometry about the copper ions and the network topology is retained. Powder X-ray diffraction and microanalysis were used to characterise the bulk purity of the coordination materials 1–6 and 8. The thermal characteristics of 1–2, 4–6 and 8 were studied by TG-DTA. This led to the curious observation of small exothermic events in networks 4, 6, and 8 that appear to be linked to their decomposition. In addition, the solid state structures of H2L and that of its protonated salt, H2L·HNO3, were also determined and revealed that H2L forms a 2-D hydrogen bonded polymer incorporating helical chains formed through N–HO and O–HN interactions, and that [H3L]NO3 forms a 1-D hydrogen-bonded polymer.

Zinc modified polydiacetylene Langmuir films

Polydiacetylene (PDA) Langmuir films (LF) containing Zn2+ cations were prepared in different experimental procedures. The incorporation of zinc cations resulted in new morphological and spectral properties. We found that zinc cations stabilize the blue phase of PDA, and inhibit its transformation into the red phase, withstanding prolonged exposure to UV irradiation. The increased stability was accompanied with the loss of the linear strand morphology and appearance of a new, transient purple phase before the final red phase stage. It was found that the most significant differences in film properties occur when the zinc cations are already present in solution during the polymerization stage at sufficient concentration. In such case zinc ions penetrate into the headgroup interlayer in the trilayer organization, and are implicated in the film's chromatic properties. In cases where polymerization was carried out prior to introduction of the cations, the properties of PDA/Zn2+ films are similar to films produced on a pure water subphase.

Crystal Structure of Methyl Orange Derivatives and Their Electronic Spectra

Azo dyes and pigments are widely used in the imaging industry because of their versatile colors as well as their low price. However, it is often pointed out that the color in the solid state is sometimes drastically different from that in solution. An attempt has been therefore made in the present investigation to elucidate the electronic structure of two classical simple azo dyes on the basis of the crystal structure: methyl orange [Na(I)-(dimethylamino)azobenzene-4-sulfonate (MO)] and its derivative [4-(dimethylamino)azobenzene-sulfonic acid (MOH)]. Accordingly the authors found a new trinuclear Na complex (pale red) of MO, as well as a new polymorph (purple) of MOH in addition to the previously reported phase (vivid red). In MO and also in the purple phase of MOH, excitonic interactions are basically responsible for the color change on going from solution to the solid state. On the other hand, the authors found a zwitterionic structure in the vivid-red phase of MOH as formed by NH···O intermolecular hydrogen bonds. The vivid-red color can be interpreted as arising mainly from the zwitterionic structure.

Polymorph and electronic structure of methyl orange derivative

Azo pigments are typical of the classical pigments used widely in painting and imaging industries. In azo pigments, however, there is still a pending problem associated with the azo or hydrazone structure in the solid state. As a step to clarify this, we initiated our investigation on the crystal structure of methyl orange and its derivaqtives that are typical of simple azo compounds. Then, we found a different phase of 4-(dimethylamino)azobenzene-4'-sulfonic acid (MOH) from that reported by Burke et al. Because of this, electronic structure of both phases has been studied in the present investigation on the basis of the crystal structure as well as DFT calculations. A striking difference is observed between two crystal structures, showing that the previous phase is red as characterized by a zwitterionic structure; whereas purple in the new phase. Interesting to say, DFT calculation revealed that the zwitterionic structure (that exists only in the solid state) gives an absorption band at a far longer wavelength of about 660 nm as compared with that of the ordinary MOH structure (about 420 nm). It is this longer wavelength band that gives a red color in the zwitterionic phase; whereas the absorption band lies in the shorter wavelength of the visible region in the purple phase.

POLLINATION ECOLOGY AND THE SIGNIFICANCE OF FLORAL COLOR CHANGE IN LUPINUS PILOSOS L. (FABACEAE)

Floral color change was studied inLupinus pilosusL. to elucidate its ecological significance for both the plant and the pollinators. It was found that the change in the banner spot from white to purple was enhanced by artificial pollination. White phase flowers offered more pollen as reward to foraging pollinators than did purple phase flowers. The changes in color and reward were recognized by the pollinators and affected their foraging behavior. Pollinators preferred pre-change flowers and avoided post-change ones, thus increasing the chance that white phase flowers would be pollinated. It is suggested that the increase in outcrossing rate caused by pollinator activity could be the advantage and the driving force for the evolution of the color change mechanism inL. pilosus.

X-ray absorption and diffraction investigations of iodine-intercalated conducting Langmuir-Blodgett film

X-Ray absorption and diffraction have been used to study a Langmuir-Blodgett film of an iodine-intercalated charge transfer (CT) salt based on EDT-TTF(SC 18) 2. The polarized X-ray absorption near-edge structure (XANES) of I 3 − exhibits a strong angular dependence of the 2s–5p(σ ∗) resonance intensity. To obtain precise information about the I 3 − orientation, the observed polarization dependence is compared with the theoretical calculation. It is shown that the I 3 − molecular axes are distributed randomly in a plane parallel to the substrate. From the viewpoint of the I 3 − distribution, the effect of annealing is also investigated with polarized XANES spectroscopy and X-ray diffraction. It is confirmed that an annealing process is necessary to achieve a well-stabilized and highly conducting film of the present CT salt. In addition, a possible molecular assembly of this annealed purple phase is proposed via a simulation of the X-ray diffraction profile based on the XANES results.

Intermetallic formation in gold-aluminum systems

Intermetallic formation in gold-aluminum systems has been studied at 200°C–460°C using butt-welded diffusion couples. The predominant intermetallic phase was found to be Au 5Al 2, but all five equilibrium phases of the system were present in the couples after annealing at long times. The kinetics of the process were measured and the activation energy for overall intermetallic formation was found to be 15.9 kcal/mol. The effect of silicon on intermetallic formation was also investigated. It was found that while silicon had little effect on the growth rate of AuAl, Au 2Al, Au 5Al 2, and Au 4Al, it substantially increased the amount of purple phase in the couples. An electron microprobe traverse indicated that this purple phase contained 6 wt.% Si. The relative tensile strengths of the intermetallics were determined indirectly by measuring the tensile properties of the diffused couples. It was found that all the intermetallics were stronger than gold or aluminum. However, appreciable voiding occurred in Au 5Al 2 after long times above 300°C and in AuAl 2 after long times above 400°C weakening these phases catastrophically. The voiding was greatly accelerated by intermittent aging.