Conversion of light into macroscopic helical motion

Journal name:
Nature Chemistry
Volume:
6,
Pages:
229–235
Year published:
DOI:
doi:10.1038/nchem.1859
Received
Accepted
Published online

Abstract

A key goal of nanotechnology is the development of artificial machines capable of converting molecular movement into macroscopic work. Although conversion of light into shape changes has been reported and compared to artificial muscles, real applications require work against an external load. Here, we describe the design, synthesis and operation of spring-like materials capable of converting light energy into mechanical work at the macroscopic scale. These versatile materials consist of molecular switches embedded in liquid-crystalline polymer springs. In these springs, molecular movement is converted and amplified into controlled and reversible twisting motions. The springs display complex motion, which includes winding, unwinding and helix inversion, as dictated by their initial shape. Importantly, they can produce work by moving a macroscopic object and mimicking mechanical movements, such as those used by plant tendrils to help the plant access sunlight. These functional materials have potential applications in micromechanical systems, soft robotics and artificial muscles.

At a glance

Figures

  1. A photoresponsive liquid crystal in a twist-nematic molecular organization.
    Figure 1: A photoresponsive liquid crystal in a twist-nematic molecular organization.

    a, The molecular photoswitch 1 used in this study is an azobenzene derivative. b, Chiral dopants S-811 and R-811 induce a left-handed and right-handed twist in the liquid crystal, respectively. c, Molecular organization in the twist cell (top view) and the angular offset φ, which characterizes the angle at which the ribbon is cut. The orientation of the molecules at mid-plane is shown with a double-headed arrow. The cutting direction, which is also the long axis of the ribbon, is represented by a dotted line. The elongated rods represent molecules. d, The twist-nematic molecular orientation through the thickness of the film (side view).

  2. The ribbons display a variety of shapes that depend on the direction in which they are cut.
    Figure 2: The ribbons display a variety of shapes that depend on the direction in which they are cut.

    The samples display a rich variety of chiral shapes, from left-handed or right-handed ribbons (ribbons B and D) to ribbons for which chirality is not expressed macroscopically (flat ribbon A or open-ring ribbon C).

  3. Shape and photoactuation modes of the polymer springs as a function of the angular offset.
    Figure 3: Shape and photoactuation modes of the polymer springs as a function of the angular offset.

    The angular offset φ is defined here as the angle between the orientation of the molecules at mid-plane and the cutting direction. The experimental error is estimated to ±2°. a, Ribbons doped with S-811, in which the director twist is left-handed. b, Ribbons doped with R-811, where the director twist is right-handed. The two diagrams are symmetric with respect to the photoresponse.

  4. Photoactuation modes of the polymer springs doped with S-811.
    Figure 4: Photoactuation modes of the polymer springs doped with S-811.

    a, Spiral ribbons irradiated for two minutes with ultraviolet light (λ = 365 nm) display isochoric winding, unwinding and helix inversion as dictated by their initial shape and geometry. b, A large amplitude contraction is obtained on light-driven winding of ribbons with φ ≈ 45°, and a large amplitude elongation is obtained on light-driven unwinding of ribbons with φ ≈ 90°. LH, left-handed; RH, right-handed. c, Under irradiation with ultraviolet light, the ribbons contract along the director and expand in the perpendicular directions, as is consistent with an ultraviolet-induced increase of disorder. d, Scheme to represent the mechanisms through which the shape of the ribbons is modified under irradiation with ultraviolet light, for φ = 45°. The ribbons deform to accommodate the preferred distortion along the main axis of the ribbon, and this preferred distortion is determined by the orientation of the molecules.

  5. Mixed-helicity springs doped with S-811 display a complex range of mechanical photoresponses.
    Figure 5: Mixed-helicity springs doped with S-811 display a complex range of mechanical photoresponses.

    a, A coiled tendril of the wild cucumber plant. (Image courtesy of Green Thumb Photography/Beth Hoar) b, The liquid-crystal polymer film is cut to introduce regions that display different dynamic behaviours. c,d, A polymer spring that displays a cucumber tendril-like shape, composed of two oppositely handed helices connected by a kink. On irradiation the right-handed helix unwinds (c) and the left-handed helix winds (d). e, Bending of the spring is achieved and controlled by selective irradiation, which induces a local elongation of the right-handed ribbon. The coloured circles indicate the irradiation spots where elongation occurs.

  6. Proof-of-principle for a mechanical device powered by light.
    Figure 6: Proof-of-principle for a mechanical device powered by light.

    a, On alternate irradiation with ultraviolet and visible light, the central kink of a mixed-helicity ribbon doped with S-811 performs a continuous piston-like motion (Supplementary Movie 3). b, The device displays no sign of fatigue over ten cycles of alternating irradiation. c, A magnet connected to the kink (m ≈ 2 mg) undergoes a push–pull shuttling motion, a motion further transmitted to another magnet placed 10 mm below (m ≈ 0.5 mg).

Compounds

4 compounds View all compounds
  1. (E)-((Diazene-1,2-diylbis(4,1-phenylene))bis(oxy))bis(hexane-6,1-diyl) diacrylate
    Compound trans-1 (E)-((Diazene-1,2-diylbis(4,1-phenylene))bis(oxy))bis(hexane-6,1-diyl) diacrylate
  2. (Z)-((Diazene-1,2-diylbis(4,1-phenylene))bis(oxy))bis(hexane-6,1-diyl) diacrylate
    Compound cis-1 (Z)-((Diazene-1,2-diylbis(4,1-phenylene))bis(oxy))bis(hexane-6,1-diyl) diacrylate
  3. (S)-Octan-2-yl 4-((4-(hexyloxy)benzoyl)oxy)benzoate
    Compound S-811 (S)-Octan-2-yl 4-((4-(hexyloxy)benzoyl)oxy)benzoate
  4. (R)-Octan-2-yl 4-((4-(hexyloxy)benzoyl)oxy)benzoate
    Compound R-811 (R)-Octan-2-yl 4-((4-(hexyloxy)benzoyl)oxy)benzoate

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Author information

Affiliations

  1. Laboratory for Biomolecular Nanotechnology, MESA+ Institute for Nanotechnology, University of Twente, PO Box 207, 7500 AE Enschede, The Netherlands

    • Supitchaya Iamsaard,
    • Sarah J. Aßhoff,
    • Benjamin Matt,
    • Jeroen J. L. M. Cornelissen &
    • Nathalie Katsonis
  2. Laboratory for Molecular Nanofabrication, MESA+ Institute for Nanotechnology, University of Twente, PO Box 207, 7500 AE Enschede, The Netherlands

    • Tibor Kudernac
  3. Department of Chemistry, Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, UK

    • Stephen P. Fletcher

Contributions

N.K. and S.P.F. conceived the research. N.K., T.K. and J.L.M.C. guided the research. S.I. and B.M. synthesized 1. S.I., S.J.A. and B.M. carried out the experiments. All authors discussed the results and commented on the manuscript at all stages.

Competing financial interests

The authors declare no competing financial interests.

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