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. 2019 Jan 23;141(3):1196-1200.
doi: 10.1021/jacs.8b11558. Epub 2019 Jan 9.

Shape-Persistent Actuators from Hydrazone Photoswitches

Alexander Ryabchun  1 , Quan Li  2 , Federico Lancia  1 , Ivan Aprahamian  2 , Nathalie Katsonis  1
Affiliations

Shape-Persistent Actuators from Hydrazone Photoswitches

Alexander Ryabchun et al. J Am Chem Soc. .

Abstract

Interfacing molecular photoswitches with liquid crystal polymers enables the amplification of their nanoscale motion into macroscopic shape transformations. Typically, the mechanism responsible for actuation involves light-induced molecular disorder. Here, we demonstrate that bistable hydrazones can drive (chiral) shape transformations in liquid crystal polymer networks, with photogenerated polymer shapes displaying a long-term stability that mirrors that of the switches. The mechanism involves a photoinduced buildup of tension in the polymer, with a negligible influence on the liquid crystalline order. Hydrazone-doped liquid crystal systems thus diversify the toolbox available to the field of light-adaptive molecular actuators and hold promise in terms of soft robotics.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
(a) Hydrazones H1 and H2. The stator and rotor are drawn in red and blue, respectively. lZ and lE are the calculated lengths of the switching moiety. (b) Absorbance spectra of H1 in toluene (2.6 × 10–5 M). εmax(Z-H1) = 2.86 × 104 M–1cm–1, εmax(E-H1) = 2.03 × 104 M–1 cm–1. (c) Polarized absorbance spectra of Z-H1 and E-H1 in the unidirectionally aligned nematic host, and d) their angular dependence. Parallel and perpendicular directions are defined with respect to the LC alignment. The dichroism of the guest molecules is calculated as D = (A⊥ – A∥)/(A⊥ + A∥). (e) Calculated structures of Z-H1 and E-H1. The acrylic moieties are omitted for clarity. The purple arrows show the direction of the moment associated with the S0 to S1 electronic transition; their direction indicates how the switch interacts with polarized light.
Figure 2
Figure 2
(a) Molecular components of the LC prepolymer. (b) Photoactuation of the polymer ribbons incorporating H1. Thickness 25 μm. (c) Representation of the photoinduced shape-shifting.
Figure 3
Figure 3
(a) Bending angle of the ribbon as a response to illumination. The molecules are aligned along the long axis of the ribbon. The dark gray areas correspond to stages where photogenerated stress builds up. (b) Stability of the curvature mirrors that of the photogenerated gradient.
Figure 4
Figure 4
Macroscopic chirality resulting from the introduction of gradients of mechanical strain. The white stripes indicate the molecular orientation in the sample. Opposite sides of the ribbon are colored in red and blue as a guide for the eyes. (a, b) Flat ribbon with molecular alignment tilted ∼22° with respect to the long axis. The stepwise illumination this flat ribbon includes exposure to blue light, then to UV light. Side A was irradiated during photopolymerization and is thus characterized by a higher cross-linking density. LH and RH indicate left- and right-handedness, respectively.
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