Photomodulated Tricolor-Changing Artificial Flowers - Chemistry of

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Photomodulated Tri-Color-Changing Artificial Flowers Bo Zuo, Meng Wang, Bao-Ping Lin, and Hong Yang Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.8b04204 • Publication Date (Web): 16 Oct 2018 Downloaded from http://pubs.acs.org on October 17, 2018

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Chemistry of Materials

Photomodulated Tri-Color-Changing Artificial Flowers Bo Zuo, Meng Wang, Bao-Ping Lin and Hong Yang* *School of Chemistry and Chemical Engineering, Jiangsu Province Hi-Tech Key Laboratory for Bio-medical Research, Jiangsu Key Laboratory for Science and Application of Molecular Ferroelectrics, State Key Laboratory of Bioelectronics, Southeast University, Nanjing, 211189, China. ABSTRACT: In nature, many flowers can open their petals into blooming flowers or furl them into buds, and simultaneously alter the petal colors under the precise control of light, temperature, pH, humidity or other environmental stimuli. Inspired by this fascinating natural phenomenon, here we report a two-spiropyran-unit-functionalized, monodomain/polydomain bilayer-structured liquid crystal elastomer strategy to fabricate an ultraviolet, green and near-infrared tri-light-modulated tri-color-changing flower mimic soft actuator. Relying on a combination of photochromic effect, thermochromic effect, pigment blending effect, photothermal conversion effect, and gradient stress effect, this flower mimic material can furl or open it “petals” under the on/off stimulation of near-infrared light, meanwhile possess a tri-stable showy color switch system which is tunable through varying the wavelength band (365 nm, 520 nm, 808 nm) of light stimuli. Such a material has wide application prospects in camouflage materials, control devices and biomimetic devices.

INTRODUCTION In nature, many flowers can open their petals into blooming flowers or furl them into buds, and simultaneously alter the color of their petals under the precise control of environmental stimuli or internal signals, such as light, temperature, pH or humidity.1-5 One typical example of such color-changing flowers is Morning Glory (Figure 1a) which can bloom into flowers in the morning and reversibly furl the petals into the original bud shapes in the afternoon, meanwhile switch the color of their petals between reddish-purple and blue under the stimulation of sunlight and internal pH value.3,6-7 Another famous flower, Hibiscus mutabilis Linn has a more diversified tri-color changing capability, its petals will appear in ivory-white in the morning, light rose at noon and pink-red in the evening (Figure 1b).8 These petal furling/unfurling action mechanisms can be interpreted as large-scale bending/unbending motions, which are caused by the tissue turgor pressure variation derived from non-uniform internal pressures between cells, or the release of stored elastic energies generated from non-equilibrium forces between different oriented layers.9-13 As to the colorchanging phenomenon, plants adjust the chemical contents of intrinsic organic pigments (e.g. anthocyanin and chalcone) to modulate their showy colors,14-15 which are indeed the consequence of the color combinations of these pigments.16 Inspired by this fascinating natural phenomenon, we aim to design and fabricate a multi-color-changing flowermimic polymeric material which can furl/unfurl its petals and simultaneously tune the color appearance under external stimuli, as schematically illustrated in Figure 1c. To accomplish this goal, the designed material must possess

Figure 1. The photo images of natural plants (a) Morning Glory (Ipomoea purpurea) and (b) Hibiscus mutabilis Linn blooming from buds to flowers with versatile color changes. (c) Diagrammatic illustration of the proposed tri-colorchanging flower-mimic material possessing petal furling/unfurling actions accompanied with three color changes.

two fundamental characters: (1) the material have to respond to external stimuli by a huge bending motion output; (2) the material must have a tri-stable showy color switch system which can be modulated by different stimuli. To date, many soft actuator materials including hydrogels,17-21 shape-memory polymers/alloys,22-25 and liquid crystal elastomers (LCEs) can execute bending deformation under external stimuli.26-34 Meanwhile, plenty of electrochromic, thermochromic, photochromic and

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mechanochromic materials have also been investigated to present variable stimuli-responsive color appearances.35-40 However most of these materials are tunable between two stable colors and barely have a tri-stable color-switching system. Among them, mechanochromic polymers which rely on external forces (e.g. stretching, squeezing) to trigger the color change of the polymeric matrices, seem to be good candidates for the color-changing flower-mimic materials, because of their enforceable, partial and manageable manipulation of both the shapes and colors of the macroscopic objects.41-44 However, it is difficult for most of known mechanochromic materials to generate from curvature-bending motions large enough forces to induce the color variation. Furthermore, compared with light and heat, force lacks of remote control and is rarely used as an efficient stimulus in nature. Alternatively, we shifted our focus to LCE materials which as a typical representative of two-way shape memory soft actuators, have many technical advantages such as multi-stimuli responsive shape metamorphosis, large strain and ease of functionalization.45-57 Herein, we propose to apply a photothermal-induced LC-to-isotropic phase transition of LCEs chemically bonded with thermochromic/photochromic chromophores to trigger the shape deformation and color change simultaneously. Herein we report in this manuscript a two-spiropyran-unitfunctionalized, monodomain/polydomain bilayerstructured LCE strategy for fabricating a color-changing flower-mimic soft actuator capable of performing reversible bending/unbending deformations and color changes upon light or thermal stimulations. Ultimately, by combination of photochromic effect, thermochromic effect, additive color blending effect, photothermal conversion effect and gradient stress effect, we successfully made an ultraviolet (UV, ca. 365 nm), green (ca. 520 nm) and nearinfrared (NIR, ca. 808 nm) tri-light modulated tri-colorchanging flower mimic material, as originally proposed in Figure 1c. RESULTS AND DISCUSSION Design and Fabrication of Color-Changing FlowerMimic LCE Actuators. The design of such multi-color changing flower mimics is schematically illustrated in Figure 2. The multi-color changing function is built based on spiropyran (SP),58-60 a classical photochromic/thermochromic compound which can undergo reversible transformation between the colorless SP form and the colored zwitterionic merocyanine (MC) form. Functionalized spiropyran derivatives could be chemically bonded onto macromolecular backbones, thus providing versatile photochromic/thermochromic polymeric materials.58-60 Interestingly, recent examples showed that different functionalization positions of spiropyran would empower their derivatives with different thermochromic properties, although their photochromic performances were consistent (UV favored MC form, green light favored SP form).61-63 For example, spiropyran analogues with two alkoxyl-attachments on the C8 position of the benzopyran ring and the C5’ position of the indole ring,

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would transform from SP form to MC form on heating,61 whereas the solo alkyl-attachment on the N-position of the indole ring showed a thermal-induced color-fading feature instead,62-63 as shown in Figure 2a. Based on this knowledge, we designed and synthesized two spiropyran derivatives, 8,5’-bis(undecylenic alkoxyl)-functionalized SP molecule named as SP1 (its colored form was named as MC1), and N(undecylenic alkoxy ethyl)-functionalized SP molecule named as SP2 (its colored form was named as MC2), as shown in Figure 2b. To induce the bending motion of the flower mimics, we designed a bilayered LCE structure whose mesogens constituting the upper layer and bottom layer were aligned in monodomain and polydomain manners respectively.64-66 Thus, when the LCE material was heated to isotropic phase transition temperature, the upper layer and bottom layer would have asymmetric in-plane shrinkage ratios which would consequently generate gradient stress in the normal direction to force the LCE membrane to bend towards the upper layer, as shown in Figure 2c. In order to trigger the simultaneous bending deformation and color changing of such materials, we chemically incorporated spiropyran derivatives onto LCE matrices, and applied temperature variation to induce the LC-to-isotropic phase transition of mesogens and thermochromic effect of spiropyran derivatives at the same time. Furthermore, by physically blending the LCEs with photothermal conversion reagents, we could rely on the photothermal effect to change the direct heating stimulus to light stimulus, a more efficient remote controlled stimulus, to modulate the showy colors and the macroscopic shape deformations of the flower mimics. The detailed chemical compositions of the upper LCE layer and bottom LCE layer (named as LCE0) are presented in Figure 2b. As to the upper LCE layer, we synthesized three different LCE samples: LCE1, LCE2 and LCE3, all prepared from a polymethylhydrosiloxane (PMHS) backbone, a classical nematic monomer 4-methoxyphenyl4-(1-buteneoxy) benzoate (MBB) and Karstedt catalyst as the major components. The differences between these LCE samples were related to the nature of the incorporated crosslinkers and spiropyran derivatives. In LCE1, we applied two-vinyl functionalized SP1 as one of the crosslinkers; in LCE2, we used 1,4-bis-undec-10-enyloxybenzene (11UB) as the crosslinker and grafted monovinyl functionalized SP2 laterally onto the polysiloxane backbones; while in LCE3, both SP1 and SP2 were chemically bonded onto the LCE matrix, and some 11UB crosslinker was also incorporated to dilute the color of LCE membranes and raise the LC-to-isotropic phase transition temperatures. The chemical composition of the bottom LCE0 layer was similar to the polysiloxane-based upper LCE layer, except that no spiropyran derivatives were incorporated and a NIR absorbing dye YHD796 (0.04 wt%) was embedded as a photothermal conversion reagent, which could trigger the LC-to-isotropic phase transition of LCE samples by using NIR light stimulus as an indirect heating source.67-70 In addition, despite the incorporation of a trace amount of YHD796, the bottom LCE0 layer was nearly colorless.


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Figure 2. (a) Two spiropyran derivatives with different functionalization positions show same photochromic performances but different thermochromic properties. (b) The chemical compositions of the upper and bottom LCE layers (all the mole equivalents of the monomers and crosslinkers were calculated based on the mole number of Si-H groups of PMHS). (c) Schematic illustration of color change and bending deformation of the bilayered LCE material under the illumination of NIR stimulus. (d) Schematic illustration of the preparation protocol of bilayered LCE membranes.

The bilayered LCE membranes were fabricated according to the classical two-step hydrosilylation crosslinking method, as demonstrated in Figure 2d.71 In detail, two mixtures of the above-mentioned reagents dissolved in toluene were transferred into two polytetrafluoroethylene (PTFE) rectangular molds (upperlayer LCE mold, 2.0 cm long × 2.0 cm wide × 1.5 cm deep; bottom-layer LCE mold, 3.0 cm long × 3.0 cm wide × 1.5 cm deep) respectively, and further ultrasonicated at room temperature for 1 min. The two molds were heated in an oven at 60 oC for 2 h, and then slowly cooled down to room temperature. The resulting two pre-crosslinked LCE

samples (upper and bottom layers) were removed from the molds, naturally dried under ambient conditions for 4 h and sliced into strips. The pre-crosslinked upper-layer LCE strips were uniaxially stretched to ca. 150 % of their original lengths, to obtain a monodomain alignment of mesogens as demonstrated in Figure S1a-f, whereas the pre-crosslinked bottom-layer LCE strips were unstretched so that their LC molecules were oriented in polydomain state as demonstrated in Figure S1g,h. Subsequently, three different upper-layer LCE (LCE1, LCE2, LCE3) strips were placed on the top of three bottom-layer LCE strips respectively, the bilayered pre-crosslinked LCE membranes



were heated in an oven at 60 oC for 48 h to complete the second-step hydrosilylation crosslinking procedure, during which the two layers would be spontaneously glued together, with the help of the interfacial hydrosilylation reaction between the unreacted vinyl groups and Si-H groups which survived the first pre-crosslinking stage.66 The corresponding bilayered LCE membranes were named as LCE1B, LCE2B and LCE3B. In figure S2 are presented the merged Fourier transform infrared (FT-IR) spectra of two SP molecules, three LCE samples and the starting polymer PMHS. The disappearances of the vibrational bands at ca. 2170 and 3079 which were ascribed to the Si-H and =C-H groups in the FT-IR spectra of LCE1, LCE2 and LCE3 samples, demonstrated that the hydrosilylation reaction was highly efficient and all the Si-H and vinyl groups which were fed in an 1-to-1 ratio have been completely consumed. The interfacial hydrosilylation reaction between two precrosslinked LCE films was also very effective as proved in Figure S3 which presented the scanning electron

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microscope (SEM) images of the cross-sectional areas of the bilayered LCE1B, LCE2B and LCE3B films. Apparently, the two layers have been successfully glued together to become a single object, and the average thickness of the bilayered LCE films was ca. 300 um. Photo/thermochromic properties and actuation behaviors of the spiropyran-functionalized LCE materials. With the monodomain LCE1, LCE2, LCE3 samples and the bilayered LCE1B, LCE2B, LCE3B films in hand, we started to investigate the photo/thermochromic properties and actuation behaviors of the spiropyran-functionalized LCE materials. As shown in Figure 3a-c, all the LCE samples revealed a fully reversible heat-induced shrinkage performance and photo-modulated color appearance variations. The stepwise color changing processes along with temperature variation were illustrated in Figure S4. Apparently, LCE1, LCE2 and LCE3 samples had three different color switching behaviors, because of the opposite thermochromic properties of SP1 and SP2 grafted on the macromolecular matrices.

Figure 3. Shape and color appearance variations of (a) LCE1, (b) LCE2 and (c) LCE3 samples under the stimulation of UV, green light and heat. UV-vis absorption spectra of (d) LCE1B, (e) LCE2B and (f) LCE3B samples measured after irradiation of UV (365 nm), green (520 nm) and NIR (808 nm) light. (g) Shape deformation L/Liso of LCE1, LCE2 and LCE3 along the stretching direction at any designated temperature during the heating process. (h) The surface temperature versus NIR light illumination time diagrams of LCE1, LCE2, LCE3 and their corresponding bilayered LCE1B, LCE2B, LCE3B films. (i) The induced angle θ versus NIR light illumination time diagrams of three bilayered LCE ribbons.


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Ultraviolet-visible (UV-vis) spectroscopy was applied to further investigate the photochromic properties of three bilayered LCE membranes (LCE1B, LCE2B and LCE3B).32c As shown in Figure 3d-f, after the UV light irradiation, all three samples exhibited a sharp increase in the optical absorption range between 500 nm and 600 nm wavelength (named as state I); when exposed to green light, all three samples presented a dramatic decrease of the 500-600 nm absorption band (named as state II), due to the transformation from the colored MC form of spiropyran to the colorless SP form. However when the three LCE samples were irradiated by NIR light, they showed three totally different optical absorption performances. The UV-vis spectra of LCE1B and LCE2B were close to the original State I and State II respectively, whereas LCE3B reached to a medium level (named as state III). Different from UV/green light induced photochromic effect, NIR-modulated phtotochromic behaviors of LCE samples were intrinsically the thermochromic performances of spiropyran molecules driven by heat which was transformed from NIR photons through the photothermal effect of the incorporated NIR dye YHD796. Since SP1 and SP2 favored the MC form and SP form under heating condition respectively, the corresponding optical absorption properties of LCE1B and LCE2B samples under NIR illumination would thus be similar to UV-induced state I and green light-induced state II respectively, whereas LCE3B grafted with both SP1 and SP2 molecules would show a color combination of MC1 and SP2 units which was indeed a medium state between state I and state II. To study the actuation behaviors of the bilayered LCE membranes, we firstly measured the thermal-shrinkage (L/Liso) values of the three single-layered LCE samples, where L was the longitudinal length of the ribbons measured at any designated temperature, and Liso was the minimum length of the ribbons above the clearing temperature. As shown in Figure 3g, all the three LCE samples showed a thermal shrinkage jump from 135% to 100% at the temperature range of ca. 55-75 oC during heating process. LCE3 sample was the fastest one that reached to the final thermal shrinkage due to the lowest LCto-isotropic phase transition temperature (ca. 57 oC), which matched well with the differential scanning calorimetry (DSC) results, as illustrated in Figure S5. In addition, we found from the DSC data that grafting more spiropyran molecules onto the LCE matrice would dramatically lower the LC-to-isotropic phase transition temperature, increase the glass transition temperature and narrow the mesophase temperature range of the corresponding LCE samples. For example, as shown in Figure S5g, a control LCE sample containing 10 mol% SP1 cosslinker had a relatively low clearing point at ca. 50 oC. Benefiting from the photothermal effect of the embedded NIR absorbing dye YHD796, these bilayered LCE membranes could be efficiently heated up to above their LCto-isotropic phase transition temperatures (60~70 oC) under the stimulation of NIR light (0.83 W·cm−2, Center wavelength: 808 ± 3 nm) within 13 s, whereas the surface temperature of the single-layered LCE samples containing no NIR dyes could be elevated to less than 40 oC in even longer illumination time, as demonstrated in Figure 3h. The

photoresponsive rates of LCE1B, LCE2B and LCE3B films bending towards the NIR light were examined by measuring the real-time-based induced angles θ between line l1 (tangent line to the right endpoint of the arc bending sample) and l2 (horizontal line), as illustrated in Figure 3i. All the three bilayered LCE samples were sensitive to NIR light, and bent continuously with the induced angle θ growing in an exponential responsive manner. The induced angles θ of the three samples could all reach to around 90 degree within several seconds (10-13 s). Among them, LCE3B showed an obvious faster photoresponsive rate because of its relatively lower clearing temperature. Fabrication of versatile tri-color-changing flower mimics. To prepare the designed color-changing “flowers”, we first tried to tailor the bilayered LCE1B and LCE2B membranes into the petaloid shapes (7.0 mm long × 3.0 mm wide), and glued them symmetrically onto a rounded, yellow poly(vinyl chloride) tape to fabricate a flower-mimic actuator which possessed 6 “petals” around the yellow “stamen”, as shown in Figure 4a. Through the modulation of light with different wavelengths, both LCE1B (Figure 4b) and LCE2B (Figure 4c) “flowers” could bloom or unbloom, and meanwhile vary their color appearances, as demonstrated in Supplementary Movies 1-2. Specifically, NIR light would force the blooming “flowers” to furl into buds because of the photothermal conversion effect, removing NIR irradiation would reopen their petals. Since the grafted SP1 and SP2 molecules had the same photochromic property but opposite thermochromic behaviors, the corresponding LCE1B and LCE2B “flowers” both appeared in purple red under UV irradiation and faded to pale yellow under green light, while NIR or heating source would turn the showy color of LCE1B “flower” to purple red and contrarily let LCE2B “flower” to have a lightyellow appearance.

Figure 4. (a) Schematic illustration of the preparation protocol of a flower-mimic soft actuator. Bicolor-changing (b) LCE1B and (c) LCE2B “flowers” with their blossoms blooming and unblooming modulated by light with different wavelengths.

Nonetheless, the above LCE1B and LCE2B “flowers” were limited to a purple red-light yellow bistable colorswitching system. How to introduce more versatile showy colors into the flower-mimic actuators and how to further empower them with an advanced tri-stable color-switching capability, were two key challenges for real applications of these spiropyran-functionalized LCE materials.



To grant the flower-mimic actuators with versatile showy colors, we applied the additive color blending effect to produce diversified colors by incorporating different pigments into the LCE matrices. For example, as illustrated in Figure 5a, doping a dye into LCE2 would give a mixed showy color of SP2 and the dye. At ambient environment, the showy color would be a blend color of the embedded dye’s color and purple red derived from the MC form of SP2; at elevated temperatures (above 60 oC), SP2 molecules should turn to SP form and the showy color would indeed be a homochromatism of the incorporated dye. As shown in Figure 5a and Supplementary Movies 3, the dyeincorporated LCE2 films doped respectively with 0.2 wt% of Green 575, Blue 623, Yellow 110 and Red 306 dyes (from left to right), starting with four blend colors of blue-violet, mazarine, scarlet and crimson at room temperature, shrunk under heating condition and eventually changed their showy colors to green, blue, yellow and red.

Figure 5. (a) Schematic illustration of the additive color blending effect, and the shape and color appearance variations of four different LCE2 samples doped with green 575, blue 623, yellow 110 and Red 306 organic dyestuffs under heat stimulation. (b) The (x,y) chromaticity diagram (standard CIE 1931) showing the color-changing pathways of four different LCE2 samples doped with green 575, blue 623, yellow 110 and Red 306 organic dyestuffs under heat stimulation.

The detailed thermochromic processes changing from the blend colors to the corresponding homochromatisms were recorded in a CIE 1931 chromaticity diagram, as shown in Figure 5b.72 The transformation matrix within the RGB color system and 1931 coordinate (x,y) were figured

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out based on the following equations 1-2,72 where R, G, B (red, green, blue) were the three vital color components captured from the raw image pixels of the LCE films, and X, Y, Z were the tristimulus values mapped from the R, G, B values. An example of the dye-incorporated LCE2B “flower” doped with Green-575 (0.5 wt%), which was capable of switching its petal color between fuchsia and green, meanwhile could tune the opening and closing states of its blossom by light with different wavelengths, was also demonstrated in Supplementary Movie 4 and Figure S6.

[] [

X 2.7689 Y = 1.0 Z 0 x=

1.7517 4.5907 0.0565 X

X+Y+Z

][ ]

1.1302 R 0.0601 G 5.5943 B y=

Y X+Y+Z

(1) (2)

To endow this LCE “flower” material with a versatile tri-stable color-switching capability, we brought the additive color blending effect into LCE3B which exhibited three different optical properties under illumination of UV, green and NIR light, to construct a tri-light modulated tricolor-changing soft actuator. The working principle is illustrated in Figure 6a. In the irradiation by UV light, the first showy color of the LCE3 sample was a blend color of the embedded dye’s color and the additive purple red color derived from the two MC forms of SP1 and SP2 units; when exposed to NIR light, which was actually an indirect heating source, the second showy color turned to a new blend color of the embedded dye’s color and pink color contributed solely by the MC form of SP1 units, since SP2 units transformed into the colorless SP form due to the thermochromic effect; after green light illumination, the third showy color became a homochromatism of the incorporated dye because both SP units would rely on the photochromic effect to be present in colorless SP form. For example, three different regions of one pure LCE3 ribbon exposed to UV, NIR and green light showed purple red, pink and light yellow respectively as shown in Figure 6b, where the corresponding regions of a comparison LCE3 ribbon doped with 0.5 wt% of Green 575 dye would present a different change, between murrey, red-brown and green as shown in Figure 6c. Eventually, we fabricated a tri-stable color-switching “flower” based on a dye-incorporated LCE3B actuator (doped with 0.5 wt% of Green 575). As demonstrated in Figure 6d and Supplementary Movie 5, a blooming LCE3B “flower” could furl into buds with color changing from murrey to red brown under NIR illumination, reopen the petals to produce a red brown blooming “flower” after removal of NIR light, change the petal color to green under the irradiation of green light, and finally recover to murrey when exposed to UV light.


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Figure 6. (a) Schematic illustration of the designed tri-stable color-changing system modulated by UV, green and NIR light. The color appearances of three different regions of two LCE3 films incorporated (b) without or (c) with Green 575 dye (0.5 wt%), exposed to UV, NIR and green light respectively. (d) A tri-color-changing LCE3B “flower” with its blossom blooming and unblooming modulated by light with different wavelengths.

CONCLUSION Stimuli responsive materials with shape-morphing and color-changing capability have attracted extensive scientific interests and are becoming one of the most popular research areas in recent years. Inspired by the famous color-changing flower Hibiscus mutabilis Linn, we developed a two-spiropyran-unit-functionalized, monodomain/polydomain bilayer-structured LCE strategy to fabricate a tri-light-modulated tri-color-changing flower mimic soft actuator, which could open it “petals” into blooming “flowers” or furl them into “buds” under the on/off stimulation of NIR light, meanwhile possessing a tristable showy color switch system which could be modulated by varying the wavelength band of light stimuli (UV, green, NIR light). The working function of such a material is indeed a combination of photochromic effect, photothermal conversion effect, thermochromic effect, additive color blending effect and gradient stress effect. We hope this strategy will provide a new perspective on

developing versatile camouflage materials and biomimetic control devices, etc. EXPERIMENTAL SECTION General Considerations. All the used reagents, starting materials and instrumentation descriptions are described in supporting information. The LC monomer MBB, crosslinker 11UB,73,74 YHD796 and 1’,3’,3’-trimethyl-6nitrospiro[chromene-2,2’-indoline]-5’,8-diol, SP1 and SP2 were synthesized according to the literature procedures.5860,70,75

Preparation of pre-crosslinked LCE1 film. PMHS (50.0 mg, 0.83 mmol Si-H groups), MBB (198.7 mg, 0.67 mmol), 11UB (20.7 mg, 0.05 mmol) and SP1 (22.9 mg, 0.03 mmol) were dissolved in 2 mL toluene, followed by the addition of 5.0 μL Karstedt catalyst solution (Platinum(0)-1,3-divinyl1,1,3,3-tetramethyldisiloxane complex solution in xylene, Pt ~2%). Then, the mixture was ultrasonicated for 1 min in a PTFE foursquare mould (2.5 cm long × 2.5 cm wide × 1.5 cm deep). After heating in an oven at 60 oC for 2 h, the pre-



crosslinked LCE1 film was obtained and cut into a strip (2 cm long × 1 cm wide), which was uniaxially stretched to ca. 150 % of its original length at room temperature . Preparation of pre-crosslinked LCE2 film. PMHS (50.0 mg, 0.83 mmol Si-H groups), MBB (193.7 mg, 0.65 mmol), 11UB (34.5 mg, 0.08 mmol) and SP2 (8.6 mg, 0.02 mmol) were dissolved in 2 mL toluene, followed by the addition of 5 μL karstedt catalyst solution (Platinum(0)-1,3-divinyl1,1,3,3-tetramethyldisiloxane complex solution in xylene, Pt ~2%). The mixture was ultrasonicated for 1 min in a PTFE foursquare mould (2.5 cm long × 2.5 cm wide × 1.5 cm deep). After heated in an oven at 60 oC for 2 h, the precrosslinked LCE2 film was obtained and cut into a strip (2 cm long × 1 cm wide), which was uniaxially stretched to ca. 150 % of its original length at room temperature. Preparation of pre-crosslinked, dye-incorporated LCE2 film. PMHS (50.0 mg, 0.83 mmol Si-H groups), MBB (193.7 mg, 0.65 mmol), 11UB (34.5 mg, 0.08 mmol) and SP2 (8.6 mg, 0.02 mmol) and the commercial organic dyestuff (1.54 mg, 0.5 wt%) were dissolved in 2 mL toluene, followed by the addition of 5.0 μL karstedt catalyst solution (Platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex solution in xylene, Pt ~2%). Then, the mixture was ultrasonicated for 1 min in a PTFE foursquare mould (2.5 cm long × 2.5 cm wide × 1.5 cm deep). After heating in an oven at 60 oC for 2 h, the pre-crosslinked LCE2-dye film was obtained and cut into a strip (2 cm long × 1 cm wide), which was uniaxially stretched to ca. 150 % of its original length at room temperature . Preparation of pre-crosslinked, dye-incorporated LCE3 film. PMHS (50.0 mg, 0.83 mmol Si-H groups), MBB (193.7 mg, 0.65 mmol), 11UB (27.6 mg, 0.07 mmol), SP1 (11.4 mg, 0.02 mmol), SP2 (8.6 mg, 0.02 mmol) and the commercial organic dyestuff (1.54 mg, 0.5 wt%) were dissolved in 2 mL toluene, followed by the addition of 5.0 μL Karstedt catalyst solution (Platinum(0)-1,3-divinyl-1,1,3,3tetramethyldisiloxane complex solution in xylene, Pt ~2%). Then, the mixture was ultrasonicated for 1 min in a PTFE foursquare mould (2.5 cm long × 2.5 cm wide × 1.5 cm deep). After heating in an oven at 60 oC for 2 h, the precrosslinked LCE3-dye film was obtained and cut into a strip (2 cm long × 1 cm wide), which was uniaxially stretched to ca. 150 % of its original length at room temperature . Preparation of pre-crosslinked LCE0 film. PMHS (43.0 mg, 0.72 mmol Si-H groups), MBB (170.8 mg, 0.57 mmol), 11UB (29.7 mg, 0.07 mmol) were dissolved in 2.5 mL toluene. The mixture was cast into a PTFE rectangular mould (4.0 cm long × 2.5 cm wide × 1.5 cm deep). Then 25 μL CH2Cl2 solution containing 0.1 mg YHD796 and 5.0 μL Karstedt catalyst solution (Platinum(0)-1,3-divinyl-1,1,3,3 tetramethyldisiloxane complex solution in xylene, Pt ~2%) were added. After an ultrasonication process for 1 min, the mixture was heated in an oven at 60 oC for 2 h, and the precrosslinked LCEB film was obtained in unstretched state. Preparation of the bilayer-structured LCE “flower”. In general, the pre-crosslinked upper-layer LCE strips (LCE13) were placed on the top of three bottom-layer LCE strips (LCE0) respectively, followed by heating in an oven at 60 oC for 48 h to complete the second-step hydrosilylation crosslinking procedure. The obtained bilayered LCE membranes were tailored into the petaloid shapes (7.0 mm

Page 8 of 13

long × 3.0 mm wide), and glued them symmetrically onto a rounded, yellow poly(vinyl chloride) tape coated with rubber pressure-sensitive adhesives (SHUSHI GROUP CO., LTD.) to fabricate a flower-mimic actuator which possessed 6 “petals” around the yellow “stamen”.

ASSOCIATED CONTENT Supporting Information. This material is available free of charge via the Internet at http://pubs.acs.org. Synthetic route schemes, NMR and mass spectra. Supplementary Movie 1 presents a side and top view of the LCE1B actuator under green and NIR light modulation. Supplementary Movie 2 presents a side and top view of the LCE2B actuator under UV and NIR light modulation. Supplementary Movie 3 presents a top view of the dyeincorporated LCE2 films (from left to right: doped with Green 575, Blue 623, Yellow 110 and Red 306) under heating condition. Supplementary Movie 4 presents a side and top view of a Green 575 dye-incorporated LCE2B “flower” under UV, green and NIR tri-light modulation. Supplementary Movie 5 presents a side and top view of a Green 575 dye-incorporated, tri-color-changing LCE3B “flower” under UV, green and NIR tri-light modulation.

AUTHOR INFORMATION Corresponding Author Correspondence and requests for materials should be addressed to H.Y. (email: [email protected]).

Notes The authors declare no competing ﬁnancial interests.

ACKNOWLEDGMENT This research was supported by National Natural Science Foundation of China (No. 21374016), Jiangsu Provincial Natural Science Foundation of China (BK20170024), the Fundamental Research Funds for the Central Universities (2242017K3DN12), the Priority Academic Program Development of Jiangsu Higher Education Institutions and the Open Research Fund of State Key Laboratory of Bioelectronics, Southeast University.

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