Photoinduced Bending Behavior Research Articles

The Factor beyond Schmidt's Criteria Impacting the Photo-Induced [2+2] Cycloaddition Reactivity and Photoactuation of Molecular Crystals Based on Cyclic Chalcone Analogues.

Generally, the potential reactive "olefin pairs" in the molecular crystals satisfying Schmidt's criteria could undergo topological [2+2] cycloaddition. In this study, another factor that affects the photodimerization reactivity of chalcone analogues was found. The cyclic chalcone analogues of (E)-2-(2,4-dichlorobenzylidene)-2,3-dihydro-1H-inden-1-one (BIO), (E)-2-(naphthalen-2-ylmethylene)-2,3-dihydro-1H-inden-1-one (NIO), (Z)-2-(2,4-dichlorobenzylidene)benzofuran-3(2H)-one (BFO), and (Z)-2-(2,4-dichlorobenzylidene)benzo[b]thiophen-3(2H)-one (BTO) have been synthesized. While the geometrical parameters for the molecular packing of the above four compounds did not exceed Schmidt's criteria, [2+2] cycloaddition did not occur in the crystals of BIO and BTO. The single crystal structures and Hirshfeld surface analyses revealed that interactions of C=O⋅⋅⋅H (CH2 ) existed between adjacent molecules in the crystal of BIO. Therefore, the carbonyl and methylene groups linked with one carbon atom in carbon-carbon double bond were tightly confined in the lattice, acting as a tweezer to inhibit free movement of the double bond and suppressing [2+2] cycloaddition. In the crystal of BTO, similar interactions of Cl⋅⋅⋅S and C=O⋅⋅⋅H (C6 H4 ) prevented free movement of the double bond. In contrast, the intermolecular interaction of C=O⋅⋅⋅H only exists around the carbonyl group in the crystals of BFO and NIO, leaving the C=C double bonds to move freely and allowing the occurrence of [2+2] cycloaddition. Driven by photodimerization, the needle-like crystals of BFO and NIO displayed evident photo-induced bending behavior. This work demonstrates that the intermolecular interactions around carbon-carbon double bond affect the [2+2] cycloaddition reactivity except for Schmidt's criteria. These findings provide valuable insights into the design of photomechanical molecular crystalline materials.

Multiple hydrogen-bonded cross-linked photo-responsive liquid crystal elastomers with photo-responsive fluorescence

Luminescent liquid crystal elastomers (LCEs) have wide application prospect in fluorescent soft actuators and dynamic display devices. α-Cyanostilbene shows a rigid rod structure, aggregation-induced emission enhancement (AIEE) characteristic and photo-induced trans-cis isomerization, which can be used as multifunctional building block to prepare stimulus responsive luminescent LCEs. In this paper, a series of physically cross-linked luminescent LCEs showing photo-induced deformation behavior and photo-responsive fluorescence are obtained (named as LCE-M(x)-L(y), x and y denote the feed mole fraction of M6PVPC10 and ME6UPy respectively, x + y = 1, y = 0.04, 0.06, 0.08, 0.10, 0.12). The photo-induced deformation, luminescent property, and the intrinsic relationship between the luminescent behavior and the photo-induced bending behavior of LCEs were studied in particular. Under the irradiation of 365 nm ultraviolet light, the prepared uniaxially oriented LCEs bent toward the direction of light. The deformation rate, the maximum bending angle of polymers are sensitive to crosslinking agent content, and increase with increasing crosslinking agent content. All the prepared LCEs also behave AIEE characteristic and can emit strong fluorescence in solid state. Meanwhile, LCE-M(x)-L(y) presents stimuli-sensitive fluorescence, and the emission intensity decreases with increasing of 365 nm UV light irradiation time. The emission intensity variation with 365 nm UV irradiation is proved to be related to the photo-induced deformation, which can be used to monitor the deformation of LCEs.

Positive/Negative Phototropism: Controllable Molecular Actuators with Different Bending Behavior

Herein, a series of molecular actuators based on the crystals of (E)-2-(4-fluorostyryl)benzo[d]oxazole (BOAF4), (E)-2-(2,4-difluorostyryl)benzo[d]oxazole (BOAF24), (E)-2-(4-fluorostyryl)benzo[d]thi...

Dependence of Photoinduced Bending Behavior of Diarylethene Crystals on Ultraviolet Irradiation Power

The photoinduced bending behavior of diarylethene crystals upon irradiation with various ultraviolet (UV) light intensities was investigated. The bending velocity of the photoinduced bending crystals was estimated from the curvature of the bending crystal. The initial velocity of curvature change (Vinit) increased in proportion to the power of the incident UV light even when the crystal thickness was different, which suggests that the local strain caused by photoisomerization makes a cumulative contribution to the bending behavior. Moreover, for all UV light intensities, the relationship between Vinit and the crystal thickness was well explained by the easily handled Timoshenko bimetal model. This result provides a validated method for the quantitative evaluation of the photoinduced bending velocity in various molecular crystals.

Photo-Induced Bending Behavior of Post-Crosslinked Liquid Crystalline Polymer/Polyurethane Blend Films.

Photoresponsive blend films with post-crosslinked liquid crystalline polymer (CLCP) as a photosensitive component and flexible polyurethane (PU) as the matrix are successfully fabricated. After being uniaxially stretched, even at low concentration, the azobenzene-containing CLCP effectively transfers its photoresponsiveness to the photoinert PU matrix, resulting in the fast photo-induced bending behavior of whole blend film thanks to the effective dispersion of CLCP. Specifically, the blend film shows photo-induced deformations upon exposure to unpolarized UV light at ambient temperature. The film unbends after thermal treatment, and the randomly orientated mesogens in the film can be realigned by the mechanical stretching, which endows the film with a reversible deformation behavior. The photosensitive blend film possesses favorable mechanical property and good processability at low cost, and it is a promising candidate for a new generation of actuators.

Precise Actuation of Bilayer Photomechanical Films Coated with Molecular Azobenzene Chromophores.

Bilayer photomechanical films are fabricated by depositing one layer of molecular azobenzene chromophores onto flexible low-density polyethylene substrates. The photoinduced bending and unbending behavior of five azobenzene derivatives including azobenzene, 4-hydroxy-azobenzene, 4-((4-hydroxyphenyl)diazenyl)bezoitrile, 4-((4-methoxyph-enyl)diazenyl)phenol, and 4-(phenyldiazenyl)phenol is systematically studied by considering the incident light intensity and the thickness of the coated chromophore layers. Precise control of photoinduced curling of the bilayer film is successfully achieved upon irradiation with two beams of UV light, and the curled films can be recovered by thermal relaxation in the dark. The easily fabricated bilayer films show fast photomechanical response, strong photoinduced stress, and stability similar to crosslinked polymeric films.

Dependence of photoinduced bending behavior of diarylethene crystals on irradiation wavelength of ultraviolet light.

The dependence of the photoinduced bending behavior of diarylethene crystals on the ultraviolet light irradiation wavelength was investigated. When irradiated with 365 nm light, a crystal of 1,2-bis(5-methyl-2-phenyl-4-thiazolyl)perfluorocyclopentene (1a) bends toward the incident light. On the other hand, when irradiated with 380 nm light, the crystal of 1a first bends away from the light source and then bends toward the incident light. To explain this bending behavior, we propose a comprehensive mechanism based on the depth of the photochromic reaction from the crystal surface. This mechanism is successfully supported by the change of cell parameters associated with the photochromic reaction upon irradiation with 380 nm light, which was determined by in situ X-ray crystallographic analysis.

Photoinduced bending behavior of cross-linked azobenzene liquid-crystalline polymer films with a poly(oxyethylene) backbone.

Cross-linked azobenzene liquid-crystalline polymer films with a poly(oxyethylene) backbone are synthesized by photoinitiated cationic copolymerization. Azobenzene moieties in the film surface toward the light source are simultaneously photoaligned during photopolymerization with unpolarized 436 nm light and thus form a splayed alignment in the whole film. The prepared films show reversible photoinduced bending behavior with opposite bending directions when different surfaces of one film face to ultraviolet light irradiation.

Preparation of Crosslinked Liquid-Crystalline Polymers by Electron-Beam Irradiation and Their Photoinduced Bending Behavior

We proposed a new approach to fabricate bilayer films with a crosslinked azobenzene liquid-crystalline (LC) polymer. The polyethylene (PE) substrates were coated with linear azobenzene LC polymers, and then the azobenzene layers were crosslinked by irradiation with electron beams (EBs). In the EB-irradiated films with ordered azobenzene moieties, exposure to UV light caused trans-cis isomerization and the change in alignment of azobenzene moieties. Bending of the bilayer films could be induced toward an actinic light source when they were irradiated from the side of the azobenzene layer, while they bent away from the actinic light source upon UV irradiation from the side of the PE layer. In both cases, the bent films reverted to the initial flat state by turning off the light, which could be repeated at room temperature.

Photoinduced bending behavior of crosslinked liquid-crystalline polymer films with a long spacer

An acrylate monomer and diacrylate crosslinker containing a spacer of undecylene were synthesized and crosslinked liquid-crystalline polymer films with different crosslinking densities were prepared by photopolymerization of mixtures of the monomer and the crosslinker. Due to the relatively long spacer, distinct bending behavior was observed in the film with a low crosslinking density: when the temperature was lower than 90 °C, the film first bent away from the light source and then towards it upon the irradiation of UV light. As the temperature was raised above 90 °C, the film bent directly towards the light source. X-ray diffraction was used to probe the phase structures of the film at different temperatures and a plausible mechanism was presented to explain the distinct phenomenon. In addition, when the crosslinking density was increased, all the films bent directly towards the light source with faster speed, which is related to their modulus and order parameters.

Can sunlight drive the photoinduced bending of polymer films?

Photoinduced bending and unbending behavior of crosslinked liquid-crystalline polymers containing azotolane moieties in side chains occurred upon irradiation with sunlight, according to the trans–cisphotoisomerization of the azotolane moieties.

Preparation and Photoresponsive Behavior of Plastic Films Coated with Azobenzene Liquid-Crystalline Polymer Layers

Plastic films coated with crosslinked liquid-crystalline polymer (CLCP) layers containing azobenzene moieties (plastic/CLCP bilayer films) were prepared by thermal polymerization of mixtures of an azobenzene monomer and a crosslinker placed between a plastic film and a glass substrate. When the glass substrate was untreated, the obtained bilayer film bent slightly away from the UV light source when irradiated on the CLCP layer side. This bending direction was the same as that of a hybridly aligned CLCP film. When the glass substrate was coated with a rubbed polyimide to strengthen the homogeneous alignment of the azobenzene moieties of the CLCP surface layer, the obtained bilayer film bent toward the irradiation direction of the incident UV light. It was the same as a homogeneously aligned CLCP film and the degree of bending was larger than that of the untreated sample. This means that the photoinduced bending behavior of the plastic/CLCP bilayer films strongly depends on the alignment of the azobenzene moieties of the CLCP surface layer facing the incident light.

How Does the Initial Alignment of Mesogens Affect the Photoinduced Bending Behavior of Liquid‐Crystalline Elastomers?

How Does the Initial Alignment of Mesogens Affect the Photoinduced Bending Behavior of Liquid‐Crystalline Elastomers?

How Does the Initial Alignment of Mesogens Affect the Photoinduced Bending Behavior of Liquid‐Crystalline Elastomers?

How Does the Initial Alignment of Mesogens Affect the Photoinduced Bending Behavior of Liquid‐Crystalline Elastomers?

Effect of Cross-linking Density on Photoinduced Bending Behavior of Oriented Liquid-Crystalline Network Films Containing Azobenzene

Oriented liquid-crystalline network films with various cross-linking densities were prepared by polymerization of mixtures of mono- and diacrylates, both of which contain azobenzene chromophores. The optical anisotropy in the films was evaluated by polarizing optical microscopy and polarized IR spectroscopy. The dichroic ratios and the order parameters of the films were estimated from polarized UV absorbance. The free-standing films were found to show photoinduced bending and unbending behavior upon alternate exposure to unpolarized UV light at 366 nm and unpolarized visible light at >540 nm. It was observed that the films with different cross-linking densities exhibited different bending extents and speeds.