As light is a good energy source that can be controlled remotely, instantly, and precisely, light-driven soft actuators could play an important role for novel applications in wideranging industrial and medical fields. Liquid-crystalline elastomers (LCEs) are unique materials having both properties of liquid crystals (LCs) and elastomers, [1][2][3] and a large deformation can be generated in LCEs, such as reversible contraction and expansion, and even bending, by incorporating photochromic molecules, such as an azobenzene, with the aid of photochemical reactions of these chromophores. [4][5][6][7][8][9][10][11][12] Herein we demonstrate new sophisticated motions of LCEs and their composite materials: a plastic motor driven only by light.If materials absorb light and change their shape or volume, they can convert light energy directly into mechanical work (the photomechanical effect) and could be very efficient as a single-step energy conversion. Furthermore, these photomobile materials would be widely applicable because they can be controlled remotely just by manipulating the irradiation conditions. LCEs show an anisotropic order of mesogens with a cooperative effect, which leads them to undergo an anisotropic contraction along the alignment direction of mesogens when heated above their LC-isotropic(I) phase transition temperatures (T LC-I ) and an expansion by lowering the temperature below T LC-I . [1,[13][14][15][16][17][18] The expansion and contraction is due to the microscopic change in alignment of mesogens, followed by the significant macroscopic change in order through the cooperative movement of mesogens and polymer segments.It is well known that when azobenzene derivatives are incorporated into LCs, the LC-I phase transition can be induced isothermally by irradiation with UV light to cause trans-cis photoisomerization, and the I-LC reverse-phase transition by irradiation with visible light to cause cis-trans back-isomerization. [19] This photoinduced phase transition (or photoinduced reduction of LC order) has led successfully to a reversible deformation of LCEs containing azobenzene chromophores just by changing the wavelength of actinic light. [4][5][6][7][8][9][10][11][12] Although the photoinduced deformation of LCEs previously reported is large and interesting, it is limited to contraction/expansion and bending, preventing them from being used for actual applications. Herein we report potentially applicable rotational motions of azobenzene-containing LCEs and their composite materials, including a first lightdriven plastic motor with laminated films composed of an LCE film and a flexible polyethylene (PE) sheet.The LCE films were prepared by photopolymerization of a mixture of an LC monomer containing an azobenzene moiety (molecule 1 shown in Scheme 1) and an LC diacrylate with an azobenzene moiety (2 in Scheme 1) with a ratio of 20/ 80 mol/mol, containing 2 mol % of a photoinitiator in a glass cell coated with rubbed polyimide alignment layers. The photopolymerization was conducted at a temperatur...

No abstract

Light moves: Azobenzene liquid‐crystalline elastomer (LCE) films with completely different types of mesogen alignment have been prepared by in situ photopolymerization. Upon irradiation with UV light, an LCE film with homogeneous (parallel) alignment bends toward the light source, whereas an LCE film with homeotropic (normal) alignment bends away from it.

Can light drive a motor? Azobenzene‐containing liquid‐crystalline elastomers (LCEs) and their composite materials have the potential to show three‐dimensional movement by light irradiation. With the LCE laminated films, a first light‐driven plastic motor has been developed, which can convert light energy directly into a continuous rotation without the aid of batteries, electric wires, or gears.

Crosslinked liquid‐crystalline polymer fibers containing azobenzene moieties show three‐dimensional movements under photoirradiation (see figure). The direction of the photomobility of the fibers could be controlled by manipulating the actinic light source. The generated stress upon photoinduced bending reached 210 kPa, which is similar to the stress in human muscles.