sense from right-handed to left-handed. As a result, these springs displayed
complex motion, including winding, unwinding, and helix inversion which
depended on the handedness of the director twist and on their angular offset φ
(Fig. 7c). The ribbons always deformed to accommodate the preferred distortion
along the main axis of the ribbon, and this preferred distortion was determined by
the orientation of the molecules, which was, in turn, determined by the cutting
direction. The mixed-helicity springs comprising two opposite-handed helices
displayed unwinding and winding motion simultaneously under UV irradiation,
which successfully mimicked the movements of plant tendrils (Fig. 7d).
Photodeformation Driven by Visible and NIR Light
To develop applications of light-driven organic actuators in possible biological
systems, low-energy light instead of UV light would be a more suitable stimulating source because low-energy light penetrates deeper into tissues and causes
less damage to biosamples. Moreover, as the stimulating source, UV light is not
environment-friendly and causes harm to our health, limiting its practical applications. Furthermore, sunlight is the origin of all the energy resources that can be
endlessly supplied, and visible light is harmless and more abundant in sunlight.
Thus, it would be useful to develop the CLCPs with photochromic molecules that
undergo a photoinduced deformation in response to visible light, especially
sunlight.
Yu et al. first reported visible light-induced bending and unbending of azotolanecontaining CLCPs, whose deformation even occurred upon exposure to sunlight
(Yin et al. 2009; Cheng et al. 2010b). Compared with 366 nm absorption of usual
azobenzene moieties, the maximum absorption of the azotolane groups shifts toward
a long wavelength region at 385 nm, resulting in a decrease in the energy level
difference between the π and π
* orbital of the tolane groups. Irradiated with shortwavelength visible light at 436 nm, the film bent toward the irradiation direction of
the actinic light due to the trans-cis photoisomerization of azotolane and reverted to
the initial state after irradiation with visible light at 577 nm. The azotolane CLCP
film also underwent photoinduced bending and unbending behavior by means of
manipulating the wavelength of sunlight through a lens and glass filters as shown in
Fig. 8. This kind of sunlight-responsive film is of great importance in development
ä
Fig. 7 (continued) illustration showing the direction in which the ribbons are cut. (c) Spiral ribbons
irradiated for 2 min with UV light (λ = 365 nm) display isochoric winding, unwinding, and helix
inversion (φ was defined as the angle between the orientation of the molecules at midplane and the
cutting direction; R, right-handed; L, left-handed). (d) A coiled tendril of the wild cucumber plant
(left) and a polymer spring that displays a cucumber tendril-like shape, composed of two oppositely
handed helices (middle and right). On irradiation the right-handed helix unwinds, and the lefthanded helix winds (Iamsaard et al. 2014)
13 Photodeformable Liquid Crystalline Polymers (LCPs)
371
complex motion, including winding, unwinding, and helix inversion which
depended on the handedness of the director twist and on their angular offset φ
(Fig. 7c). The ribbons always deformed to accommodate the preferred distortion
along the main axis of the ribbon, and this preferred distortion was determined by
the orientation of the molecules, which was, in turn, determined by the cutting
direction. The mixed-helicity springs comprising two opposite-handed helices
displayed unwinding and winding motion simultaneously under UV irradiation,
which successfully mimicked the movements of plant tendrils (Fig. 7d).
Photodeformation Driven by Visible and NIR Light
To develop applications of light-driven organic actuators in possible biological
systems, low-energy light instead of UV light would be a more suitable stimulating source because low-energy light penetrates deeper into tissues and causes
less damage to biosamples. Moreover, as the stimulating source, UV light is not
environment-friendly and causes harm to our health, limiting its practical applications. Furthermore, sunlight is the origin of all the energy resources that can be
endlessly supplied, and visible light is harmless and more abundant in sunlight.
Thus, it would be useful to develop the CLCPs with photochromic molecules that
undergo a photoinduced deformation in response to visible light, especially
sunlight.
Yu et al. first reported visible light-induced bending and unbending of azotolanecontaining CLCPs, whose deformation even occurred upon exposure to sunlight
(Yin et al. 2009; Cheng et al. 2010b). Compared with 366 nm absorption of usual
azobenzene moieties, the maximum absorption of the azotolane groups shifts toward
a long wavelength region at 385 nm, resulting in a decrease in the energy level
difference between the π and π
* orbital of the tolane groups. Irradiated with shortwavelength visible light at 436 nm, the film bent toward the irradiation direction of
the actinic light due to the trans-cis photoisomerization of azotolane and reverted to
the initial state after irradiation with visible light at 577 nm. The azotolane CLCP
film also underwent photoinduced bending and unbending behavior by means of
manipulating the wavelength of sunlight through a lens and glass filters as shown in
Fig. 8. This kind of sunlight-responsive film is of great importance in development
ä
Fig. 7 (continued) illustration showing the direction in which the ribbons are cut. (c) Spiral ribbons
irradiated for 2 min with UV light (λ = 365 nm) display isochoric winding, unwinding, and helix
inversion (φ was defined as the angle between the orientation of the molecules at midplane and the
cutting direction; R, right-handed; L, left-handed). (d) A coiled tendril of the wild cucumber plant
(left) and a polymer spring that displays a cucumber tendril-like shape, composed of two oppositely
handed helices (middle and right). On irradiation the right-handed helix unwinds, and the lefthanded helix winds (Iamsaard et al. 2014)
13 Photodeformable Liquid Crystalline Polymers (LCPs)
371