ABSTRACT
Understanding how particles pack in space and the mechanisms underlying symmetry selection across soft matter is challenging. The Frank-Kasper (F-K) phase of complex spherical packing is amongst the most fascinating phases; however, it has not been observed in discotic liquid crystals until now. Herein, we report the first observation of F-K phases of charge transfer complexes (CTCs) obtained from triphenylene derivatives as donors and 2,4,7-trinitro-9-fluorenone as the acceptor. The CTCs were characterized using experimental and theoretical calculations, indicating that the F-K A15 cubic lattice possesses a unit cell containing 8 sphere-like supramolecules, each of which was self-assembled from 3 CTC complexes. The lattice constant was only 3.2 nm, which is by far the smallest for the A15 phase. Interestingly, the supramolecular assembly can be regarded as the molecular column splitting into isolated spherical fragments, impeding charge transfer and turning it into one insulator. This provides a simple and effective method for preparing asymmetric complex compounds for the design of unconventional self-assembled nanostructures.
ABSTRACT
Light-activated self-oscillators have drawn enormous attention for their potential applications in mobile machines, energy harvesting, signal modulation, etc. Herein, we report one graphene oxide (GO)/liquid crystalline network (LCN) actuator that presents a unique light-activated oscillation with amplitude and frequency superposition. The GO/LCN composite film is prepared by the one-step polymerization of LC monomers, which favors a splay orientation in LC cells made by gluing together two glass sheets, one coated with photothermal agent GO and the other coated with a rubbed polyimide alignment layer. Owing to the asymmetric contraction/expansion, changing the cutting direction gives rise to notably different actuation behaviors for GO/LCN composite films. Moreover, it twists a little during the deflection process as a result of experimental error during the cutting process, which may cause the strip to be cut inaccurately. When the composite film is embedded in a self-shadowing system, it produces an unconventional hybrid oscillation mode upon near-infrared light irradiation, i.e., bending and twisting oscillation coupled. Furthermore, when the aspect ratio of the film decreases, the twisting mode is suppressed and the actuator changes from a coupled mode to a single bending mode. The proposed strategy may extend the application of GO/LCN composite materials and enrich light-activated self-oscillating behaviors.
ABSTRACT
Mechanical swing is common in nature, such as sound waves, wingbeat of birds, and heartbeat, which is important to convert input energy into continuous motion. Here, we report a photodriven swing actuator composed of commercially available polyimide (Kapton) and azobenzene-containing liquid-crystalline polymers. The liquid-crystalline polymers act as the photoactive layer, which were synthesized by copolymerization of one benzenecarboxylic acid-containing monomer (M6BCOOH) and one azobenzene-containing monomer (M6ABOC2) with different molar ratios. The Kapton layer with a high elastic modulus is photoinert and functions as the substrate layer. After thermal annealing, the film displays chaotic swing under continuous irradiation of actinic light. Interestingly, the swing amplitude is greatly enhanced by the existence of supramolecular hydrogen bonding in liquid-crystalline polymer films. It is the introduction of M6BCOOH to the copolymer that accelerates the trans-cis photoisomerization rate of azobenzenes. Also, it forms a hydrogen bond as physical crosslinking sites, enabling the polymer film to work as a whole. Thus, it enhances the driving force for photomechanical deformation. Moreover, it improves the elastic modulus of the photoactive layer and modulates the swing behavior of the bilayer strip. More importantly, the formation of a hydrogen bond in the form of acidic dimers has a spatial confinement effect, extending the timescale of photodriven swing. The photomechanical self-vibration of the bilayer film can be ascribed to the combination of the photoisomerization process of azobenzenes with the local photosoftening effect of liquid-crystalline polymers.
ABSTRACT
A series of discotic liquid crystals based on hexapentyloxytriphenylene (HAT5) have been investigated where one out of the six ether side chains of a triphenylene core was replaced by an ester side chain and named for 5a-5h. During the process of studying these compounds, the characteristic straight line defect of ordered columnar structure was identified by polarizing optical microscopy (POM) and liquid crystal state over a wide temperature range was obtained by differential scanning calorimetry (DSC). Basic phase structure and molecular arrangement were assigned by one-dimensional wide-angle X-ray diffraction (1D WAXD), small-angle X-ray scattering (SAXS), two-dimensional wide-angle X-ray diffraction (2D WAXD), and transmission electron microscope (TEM). Combined with sharp and regular dots in 2D WAXD patterns and characteristic peaks at small angle in SAXS pattern which indicated the existence of superlattice, we proved that 2D superlattice formed from self-assembly of discotic molecules with a polar group via π-π stacking and dipole-dipole interaction. In order to verify the effect of orientation on charge carrier mobility, their electron and hole mobilities were measured by time-of-flight (TOF) device, among which the charge carrier mobility could achieve almost twice as that of HAT5. The formation of superlattice no doubt improved their electronic properties and made them more attractive in organic electronics.
ABSTRACT
A clear structure-property relationship was revealed in a series of triphenylene-based dimers, which contained two triphenylene nuclei each bearing five ß-OC4H9 substituents and are linked through a flexible O(CH2)nO polymethylene chain (n=6-12). Dimers with the linkage close to twice the length of the free side chains (n=8, 9) exhibited a single Colhp phase, while others with the linkage shorter (n=6, 7) or longer (n=10, 11, 12) showed multiphase behaviors with a transition from the Colhp phase to Colh phase; hole mobilities of Colhp phases reached 1.4×10(-2) cm2 V(-1) s(-1) in the dimer for which the linkage is exactly twice the length of the free side chains (n=8), and decreased regularly both with linkage length becoming shorter or longer. This modulation of phase behaviors and charge carrier mobilities was demonstrated to be generated by various steric perturbations introduced by linkages with different lengths, which result in different degrees of lateral fluctuations of discotic moieties in the columns.
