Qijin Zhang

β-cyclodextrin-functionalized silver nanoparticles for the naked eye detection of aromatic isomers.

We report herein the development of a highly robust, quantitative, sensitive, and naked eye colorimetric detection method for different isomers of aromatic compounds using β-CD-modified silver nanoparticle (AgNPs) probes. This assay relies on the distance-dependent optical properties of Ag nanoparticles and the different inclusion binding strength of the aromatic guests to β-CD host. In the presence of different isomers of aromatic compounds, AgNPs could be rapidly induced to aggregate, thereby resulting in apricot-to-red color change. The variety and concentration of different isomers of aromatic compounds could be determined by monitoring with the naked eye or a UV-vis spectrometer. The present detection limit for different isomers of aromatic compounds is 5 × 10(-5) M. We believe that the surface architectures of AgNPs after the introduction of the CD-based host-guest recognition would be applicable for a range of chemical and bioanalytical molecular sensing systems in aqueous media.

Optical amplification of Eu(DBM)3Phen-doped polymer optical fiber

A preform technique is used to prepare a step-index (SI) polymer optical fiber (POF) doped with Eu(DBM)3Phen. The gain (5.7 dB) at 613 nm of the doped SI POF with Eu3+ content of 4000 in 10(6) wt., 0.4-mm core diameter, and 30-cm fiber length is observed at ambient temperature by end pumping with a YAG at 355 nm. The input signal light is approximately 0.2 W. The results show the possibility of signal gain in a rare-earth-doped POF amplifier and the potential of a polymer doped with rare-earth ions as an active optical device.

Solvent effects on structure, photoresponse and speed of gelation of a dicholesterol-linked azobenzene organogel

By introducing methanol as a co-solvent into cyclopentanone, solvent effects on structure, photoresponse and speed of gelation of a dicholesterol-linked azobenzene organogel DCAZO2 have been investigated. Optical microscopy (OM) and scanning electron microscopy (SEM) images reveal that the gel fibers form macroscopic aggregates by adding methanol. Minimum gelation concentration (MGC) of the gels decreases with increasing methanol content, while the gel-to-sol transition temperature (Tgel) decreases firstly and increases afterwards. For photoisomerization (corresponding to gel-sol transition), the first stage rate constant kg1 of the gels decreases with increasing methanol content. The photoisomerization process of the gel with 5% methanol is different from the other five samples, whose first stage rate constant kg1 is greater than its second stage rate constant kg2. By increasing methanol content from 0% to 30%, gelation time (corresponding to sol–gel transition) of both heated gel and UV-visible light irradiated gel decreases from 7 h to 5 min and 6 h to 0 min (before visible light irradiation is accomplished), respectively. Solubility parameters and Teas plots of the gelator and mixed solvents are systematically calculated to estimate the gelator-solvent interaction. It is found that gelation requires that the gelator-solvent interaction be neither too strong nor too weak, otherwise solution or precipitate are formed.

Photoinduced reversible gel–sol transitions of dicholesterol-linked azobenzene derivatives through breaking and reforming of van der Waals interactions

A series of new symmetric dicholesterol-linked azobenzene gelators with different spacer lengths have been synthesized. The compounds with spacers of zero, two or six methylene units are denoted as DCAZO0, DCAZO2 and DCAZO6, respectively. A gelation test reveals that a subtle change in the length of the spacer can produce a dramatic change in the gelation behavior of the compounds. DCAZO2 obtains the minimum gelation concentration among the three gelators. For cyclopentanone gel of DCAZO2, the reversible gel–sol transitions by irradiation with UV and visible light are investigated by UV-vis absorption and circular dichroism (CD) spectra, SEM, TEM and XRD analyses. Upon UV irradiation of the gel, trans–cisphotoisomerization of the azobenzene groups occurs, the change in molecular polarity leads to the breaking of van der Waals interactions, resulting in the gel–sol transition. The gel can be recovered by the reverse cis–transphotoisomerization after the exposure to visible light. SEM, TEM and XRD studies reveal that the gelator molecules self-assemble into one-dimensional fibers with diameters 50–100 nm in an anticlockwise direction, which further crossed-linked to form three-dimensional networks.

Benzo-15-crown-5 functionalized polydiacetylene-based colorimetric self-assembled vesicular receptors for lead ion recognition

A novel crown functionalized diacetylene monomer, N-(2,3,5,6,8,9,11,12-octahydrobenzo[b][1,4,7,10,13] pentaoxacyclopentadecin-15-yl) pentacosa-10,12-diynamide (BCDA), was synthesized successfully. The copolymerized composite vesicles of BCDA and 10,12-pentacosadiynoic acid (DA) with embedded receptor sites for metal ions have been prepared and characterized. Their response to the presence of metal cations in aqueous solution has been investigated by monitoring changes of color and UV-vis absorption. Upon addition of a series of alkali, alkaline earth and transition metal cations such as Na+, K+, Mg2+, Ca2+, Fe2+, Co2+, Cu2+, Mn2+, Ba2+, Cd2+, Ag+, Pb2+ and Zn2+, only Pb2+ ion could induce a color change from blue to red observable by the naked eye, which clearly showed that PBCDA–PDA composite vesicles could act as a highly selective and sensitive probe to detect Pb2+ ions in aqueous solution with minor interference from other metal ions. The excellent Pb2+ ion selectivity of PBCDA–PDA composite vesicles was mainly attributed to the stronger complexation behavior of Pb2+ with crown ethers and the carboxylic acid at the lipid–solution interface which could perturb the polydiacetylene backbone.

Morphology, structure and chromatic properties of azobenzene-substituted polydiacetylene supramolelular assemblies

An azobenzene mesogen-substituted polydiacetylene which self-assembles into stacks with bilayered two-dimensional structure is investigated in detail by transmission electron microscopy (TEM) as well as X-ray diffraction (XRD). These stacks with bilayer-structure are found to be organized into highly ordered lamellar crystal structures. The substituted polydiacetylene assemblies form a blue phase at room temperature, however, they undergo a well-known thermochromic transition in response to thermal stimulus. In this work, we establish links between chromatic transitions, molecular organization and the morphology of these assemblies. This thermochromic transition has been subjected to detailed investigation by means of Fourier transform infrared spectroscopy (FTIR), XRD as well as TEM. These results demonstrate that the strong intermolecular interaction (π–π stacking) between azobenzene mesogens is essential for complete recovery of chromatic transitions of PDA1 films following thermal stimulation.

Chiroptical switch based on azobenzene-substituted polydiacetylene LB films under thermal and photic stimuli

The azobenzene-substituted diacetylene (NADA) LB films were fabricated and their chiroptical properties were investigated in detail. It was found that the NADA LB films showed supramolecular chirality, although the NADA molecule itself was achiral. Overcrowded packing of azobenzene chromophores were believed to be responsible for the supramolecular chirality formation of NADA LB films. When irradiated by left- and right-handed circular polarized ultra-violet light (CPUL), obviously opposite CD signals for azobenzene chromophores and polydiacetylene (PDA) chains were observed from the resulting polymerized NADA (PNADA) LB films. Reversible changes of CD signals for PDA chains could be observed in response to thermal stimulus. When irradiated by left- and right-handed circular polarized lasers (CPL, 442 nm), a reversible chiroptical switch between two enantiometric structures of PDA chains could be observed by alternating the stereoregular packing of azobenzene chromophores in the side chains. Strong collective non-covalent interactions (π–π stacking) and rapid conformational rearrangement of azobenzene chromophores under CPUL or CPL treatment were believed to be responsible for the supramolecular chirality formation and reversible chiroptical switches upon thermal and photic stimuli. This research provides a novel model system for understanding the detailed mechanism of the chiroptical introduction and modulation in the PDA backbone.

Supramolecular bisazopolymers exhibiting enhanced photoinduced birefringence and enhanced stability of birefringence for four-dimensional optical recording

Extremely stable, high-density information storage media were prepared by the connection of two azobenzene groups via hydrogen bonding to form supramolecular bisazopolymers. The supramolecular bisazopolymers contain 4-((4-hydroxyphenyl)diazenyl)benzonitrile (AzoCN) as a hydrogen bonding donor and poly(6-(4-(pyridin-4-yldiazenyl)phenoxy)hexyl methacrylate) (pAzopy) as a hydrogen bonding acceptor. High quality films of the supramolecular bisazopolymers pAzopy/(AzoCN)x (x = 0.25, 0.5, 0.75, 1.0) with different molar ratios of donor/acceptor were prepared by spin-casting. The supramolecular bisazopolymers spontaneously form lamellar structures with a periodic thickness of 7.1 nm. These samples exhibit optically induced birefringence. The birefringence and proportion of remnant birefringence increase from 0.0265 to 0.1 and 50.5% to 108%, respectively, as the content of AzoCN in the samples increases, which indicates a larger proportion of AzoCN enhances both the birefringence and its stability. We also use an azopolymer without pyridine groups (pAzoCH3) and AzoCN to do a control experiment, which shows that pAzoCH3/(AzoCN)1.0 do not show significant enhanced birefringence and its stability. The enhancements in pAzopy/(AzoCN)x are because of the unique structure of the supramolecular bisazopolymers. A new laser direct writing system has been developed for optical recording on the azopolymers. The pAzopy/(AzoCN)1.0 film is significantly better at image recording than the pAzopy film, because the optically recorded images on the pAzopy/(AzoCN)1.0 film are very clear after storage for four months whereas the optically recorded images on the pAzopy one disappear after just one day. Four-dimensional optical recording has been achieved by integrating the polarization and the intensity of the laser and the two dimensions of a plane. An information density of about 0.93 Gbit cm−2 could be optically recorded on the pAzopy/(AzoCN)1.0 film, which is about 20 times the information density of a normal DVD.

Fabrication of long-period gratings in poly(methyl methacrylate-co-methyl vinyl ketone-co-benzyl methacrylate)-core polymer optical fiber by use of a mercury lamp.

Polymer optical fiber (POF) with a highly photosensitive poly(methyl methacrylate-co-methyl vinyl ketone-co-benzyl methacrylate) core is fabricated. Gratings can be fabricated in the core of a POF with a low-cost mercury lamp. The part of the emission spectrum of the mercury lamp in which the cladding material exhibits photosensitivity is effectively filtered by a 1.5-mm-thick Pyrex glass to ensure that a long-period grating is formed only in the core of a POF. A long-period grating with a 3-dR resonant peak at 1568 nm is fabricated with 0.3 mW/cm2 of UV irradiation over a period of 200 s.

Enantioselective synthesis of helical polydiacetylene by application of linearly polarized light and magnetic field

Magnetic optical activity, which can occur in all media and is induced by longitudinal magnetic field, causes the difference in absorption coefficients of left and right circularly polarized light and has the potential for magnetically induced enantioselectivity in chemical reactions. Compared with the well-established technique with circularly polarized light, there are few reports on the production of helical conjugated polymers in a photochemical reaction based on above magnetochiral anisotropy mechanism. Herein, we demonstrate experimentally that the enantioselective polymerization of diacetylene derivative can be achieved in the liquid crystal phase by application of linearly polarized light under a parallel or antiparallel magnetic field. The screw direction of predominant helical polydiacetylene chain can be rigorously controlled with the relative orientation of linearly polarized light and the magnetic field. Moreover, the prepared helical polydiacetylene assemblies can serve as a direct visual probe for the enantioselective recognition of D- or L-lysine.