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Photoswitches with different numbers of azo chromophores are designed for molecular solar thermal storage. The relationship between the molecular structures and the energy storage performance is investigated.

Discotic π-conjugated supramolecular assemblies, especially with chiral supramolecular nanostructures, have been attracting growing research interest due to their significant optoelectronic properties and the possibilities of their applications in the new generation of organic semiconductors. However, the impact of supramolecular chirality on their mechanical and electrical performances remains poorly understood. Herein, a series of optically active supramolecular gels were formed from achiral triphenylene derivatives by introducing limonene as the chiral source. Owing to the well-ordered supramolecular packing, the homochiral supramolecular gels exhibited greater mechanical strength and higher conductivity, compared to heterochiral architectures. The impact of supramolecular packing in homochiral or heterochiral assemblies on their resulting mechanical and electrical performances was investigated in detail, which might be of great fundamental value for the rational design of chiral π-conjugated supramolecular nanostructures for applications in chiral optoelectronics.

We demonstrate an easy and low-cost approach for the colorimetric differentiation of organic solvents using co-assemblies of polydiacetylenes (PDAs) and metal ions. The co-assemblies were prepared by the self-assembly of amphiphilic 10,12-tricosa diynoic acid with different metal ions (Zn2+, Cu2+, Ni2+, Ca2+) and subsequent photopolymerization. Different metal ions underwent different interactions with the carboxyl groups on the side chains of poly(10,12-tricosa diynoic acid), which influenced the stimuli-responsiveness of the PDA/metal ion co-assemblies. As a result, the PDA/metal ion co-assemblies with different metal ions showed different solvatochromism. Based on this property, the co-assemblies were used as sensors to differentiate organic solvents.

Herein, we study the enantioselective cytotoxicity of vesicles self-assembled by optically active linear polymers (LNPs) and hyperbranched polymers (HBPs). Compared to HBP vesicles, LNP vesicles exhibit properties such as a higher surface charge density and more violent interaction with simulated biomembranes which results in larger cytotoxicity against HeLa cells. Specifically, racemic-LNP vesicles exhibit the largest cytotoxicity of all. More interestingly, there is no significant enantioselective dependence of HBP vesicles on the abovementioned properties. Overall, we proved that the cytotoxicity of vesicles is deeply related to chirality and topological-structures. This research is of great fundamental value for the design of novel bio-interface materials.

Supramolecular chirality is achieved in amphiphilic block copolymer films made through two-step fabrication: self-assembling first and then solution coating. The amphiphilic block copolymer is composed of poly(N-isopropyl acrylamide) (pNIPAM) as hydrophilic segments and poly(methyl methacrylate) with chiral side groups as hydrophobic segments. The films fabricated by two steps show sensible circular dichroism (CD) signals around a wavelength of 200 nm. However, CD signals cannot be detected from films made by directly coating the solution of copolymers on the quartz surface. The CD signal at about 200 nm is from supramolecular arrangement of benzene units connected to the chiral group in the hydrophobic segment. This result is thought to be originated from the aggregation of the copolymer during the first step of the film forming process, and the corresponding investigation into factors affecting this process has been performed in this work. It is also found that the films fabricated by two steps can adsorb chiral small molecules enantioselectively, while the films obtained by coating the solution of copolymers directly have no such enatioselective adsorption ability.

Enantioselective assembly is observed during preparation of vesicles from a solution mixture of an amphipathic block copolymer bearing pendent chiral L- or D-phenylalanine groups in hydrophobic segments and racemic chiral small molecules. Primary experimental results reveal that racemic chiral small molecules have been enantioselectively encapsulated into the hydrophobic shells of assembled vesicles with homochiral bilayer membrane structure, showing reverse CD signals compared with the original vesicles. A further study shows that the enantiomeric excess obtained through the enantioselective assembly is directly dependent on the molecular weight of the hydrophobic chiral chain segments, implying both the hydrophobic interaction and chirality are key points during the assembly of vesicles. Other factors, such as hydrogen-bonding interactions and π-π stacking interaction, are also found to be responsible for the enantioselective assembly phenomenon during the formation of the vesicles.

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.

A series of one-armed cholesterol-linked azobenzene molecules named CholXAzo with different spacers were synthesized, in which Chol6Azo was found to have induced blue phases (BPs) with a concentration of 4.0 wt%. Under irradiation of 385 nm UV light with a density of 15.0 mW cm(-2), photo-responsive behaviour of the 4.0 wt% Chol6Azo doped sample named B3 shows a sensitive temperature dependence, which means that at 38.0 °C a phase transition from BPs to the isotropic phase is induced; however, at 33.0 °C, this phase transition does not take place. Results from the research show that the optically binary phase transition behaviour of B3 is sensitive to the isomerization degree of Chol6Azo, which is closely related to the stability of the BP structure and there is a critical isomerization degree of 13.7% for the phase transition of the B3 liquid crystals. Further POM observation shows that the liquid crystal samples doped with different concentrations of Chol6Azo have an increasing transition temperature for photo-induced phase transition from the BP to the isotropic phase along with the increasing concentration of Chol6Azo, which are found to have the same changing tendency with phase transition temperature from the isotropic phase to BPs and a phase diagram is made to map the optically binary behaviour of Chol6Azo doped blue phase liquid crystals. At last, a simple pattern with the BP and the isotropic phase arranged at an interval was made in this optically binary liquid crystalline blue phase under a suitable photomask.

In this work, three kinds of vesicles are fabricated by the self-assembly of amphiphilic block copolymers (BCPs), in which the hydrophobic chains are side chain azobenzene polymers with spacers of 0, 2 and 6 methylene units, respectively. It has been found that vesicles formed by BCPs with a spacer of 0 methylene units have no photo-responsive behavior and vesicles with a spacer of 6 have a photo-induced swelling behavior under the irradiation of light at 365 nm. Unexpectedly, the vesicle formed by BCPs with a spacer of 2 shows a photo-induced reversible uniform to Janus shape change under the same irradiation. This reversible process means that a bistable shape change of the vesicle can be controlled by the switching of UV light. A UV-visible absorption spectrum and a laser-trapped Raman spectrum (LTRS) are used to investigate differences in the morphology and photo-induced behavior of these vesicles. Results have confirmed that the photo-induced Janus shape of vesicles formed by BCPs with a spacer of 2 is a metastable shape, different from the stable Janus shape of vesicles formed by BCPs with a spacer of 0. This is also testified by a two-photon confocal laser scanning microscope (CLSM). From the results it is realized that the spacer length in the hydrophobic chains of BCPs can affect the photo-induced behavior of vesicles formed by BCPs, which will be a key point in designing functional vesicles with special morphologies.

A novel cholesterol derivative organogelator (CAZODA) containing both azobenzene and diacetylenic units is synthesized. By using XRD, CD, TEM and SEM characterization, the gelation behavior, microscopic morphology and molecular packing structure in CAZODA assemblies are investigated in detail. It is found that the concentration of the CAZODA at the initial stage plays a crucial role in tuning the microstructure from helical fibers to spherulitic gel networks. Upon UV irradiation at 365 nm, the photo-induced transition of the helical packing structures for CAZODA assemblies has been demonstrated by CD characterization, and an explanation based on the co-assembly of both trans- and cis-form CAZODA has been proposed. In addition, upon irradiation at 254 nm for 3 h, the above organogel can be polymerized with concomitant color change from yellow to red. The polymerized gel exhibits enhanced stability upon thermo or photo-stimuli.

Laser-trapping Raman spectroscopy (LTRS) is adopted to detect the photo-induced isomerization of azobenzene in the cross-linked membrane of a single vesicle, which is self-assembled first by an amphiphilic copolymer, poly(N-isopropylacrylamide)-block-poly{6-[4-(4-pyridyazo)phenoxy]hexylmethacrylate} (PNIPAM-b-PAzPy6), and then cross-linked by reaction between 1,3-dibromopropane and pyridine groups in the copolymer chain. A series of polymer vesicles with different cross-linking degrees were made to meet the need of vesicles with different softness during this research work. Vesicles with 0.0% and 18.7% cross-linking degrees have characteristic photo-induced swelling–shrinking, others with higher cross-linking degrees do not. The isomerization of azobenzene is observed in situ by LTRS along with photo-induced swelling of single vesicles with different cross-linking degrees. Results from analysis of the obtained Raman spectra show that photo-induced isomerization of azobenzene is a trigger of the photo-induced swelling process and the swelling degree is mainly dependent on the degree of cross-linking, namely, the softness of the polymer vesicle. The former result is different from that obtained by analysis of UV-Vis spectroscopy for vesicle solutions and shows that photo-induced swelling–shrinking vesicles can be constructed by amphiphilic copolymers bearing azobenzene units in the minority.

A new concept of the efficient fabrication and design of three layer photoresponsive core–shell–corona (CSC) nanostructures by the co-assembly of diblock copolymers with azobenzene-containing homopolymers is presented. Depending on the azobenzene-containing homopolymer content, the formation of CSC vesicles and CSC micelle-like nanostructures are observed, which are characterized by UV–vis absorption spectroscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM) and dynamic light scattering (DLS). The observed nanostructures confirm the recent computer simulations of Xu et al. (J. Phys. Chem. B, 2010, 114, 1257). All co-assemblies are photoresponsive and show reversible cis–transphotoisomerization. Irradiation of the spherical CSC micelle-like nanostructures by polarized light induces their deformation to ellipsoidal-core-within-ellipsoidal-shell and ellipsoidal-core-within-spherical-shell nanostructures, respectively. The type of photoinduced deformation depends on the initial size of the spherical CSC micelle-like nanostructures. These CSC nanostructures could be used as photo-controlled templates for complex nanostructures.

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.