Broad-Wavelength Light-Fuelled Organic Crystal Oscillators Driven by Multimodal Photothermally Resonated Natural Vibration

doi:10.21203/rs.3.rs-4302535/v1

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Broad-Wavelength Light-Fuelled Organic Crystal Oscillators Driven by Multimodal Photothermally Resonated Natural Vibration

https://doi.org/10.21203/rs.3.rs-4302535/v1

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Photomechanical crystals have applications in light-fuelled actuators and soft robots. Herein, we describe light-responsive, versatile, anthraquinone dye crystal oscillators actuated via natural vibrations that are resonated by a photothermal effect. A black needle-shaped crystal cantilever oscillates at 70 Hz in the first mode of natural vibration upon irradiation by broad-wavelength light ranging from the ultraviolet through the visible to the near infrared, and also under continuous-wavelength light (400–2000 nm). The second and third natural vibration modes are induced at higher frequencies (530 and 1350 Hz) and evidence complex flagellum-like motions. The frequency can be readily tuned by moving the support of a crystal piece; this is analogous to playing a guitar. The crystal exhibits high durability (more than 10,000 cycles): the high elasticity prevents deterioration. Oscillatory motions can be designed via simulations using finite element analysis. This work will facilitate the use of photomechanical crystals in light-fuelled soft robots.

Physical sciences/Materials science/Materials for devices/Actuators

Physical sciences/Materials science/Soft materials/Organic molecules in materials science

Physical sciences/Chemistry/Photochemistry/Light harvesting

Physical sciences/Materials science/Structural materials/Mechanical properties

Mechanically responsive materials that exhibit macroscopic deformations in response to external stimuli have attracted wide interdisciplinary interest given their potential applications in sensors, actuators, and soft robots.¹ Of the various possible stimuli, light is attractive in that the properties thereof (wavelength, intensity, and polarisation) can be optimised for specific needs, associated with high spatial and temporal resolutions and remote controllability.² Our focus is on photomechanical organic crystals. These are superior to polymers because they have stronger output force owing to their highly ordered structures,^1,3,4 and exhibit more rapid oscillatory frequencies (Supplementary Fig. 28). Researchers working over the past decades have described photomechanical crystals that bend,^5–7 twist,⁸ and jump⁹ after light irradiation that triggers molecular photoisomerisation. Recently, we reported on crystals that exhibited high-speed bending (up to 500 Hz) attributable to a photothermal effect upon pulsed ultraviolet (UV) irradiation.^10,11 Next, we reported high-speed (up to 700 Hz) significant crystal oscillation upon pulsed UV irradiation attributable to photothermally resonated natural vibration.¹² Given that the photothermal effect can be induced by light of all wavelengths¹³, and that the natural frequency and resonance are ubiquitous for all materials, crystals that exhibit high-speed and significant oscillation under broad-wavelength light could be created by exploiting photothermal-induced, resonated natural vibrations.

To this end, we focused on crystals of 1,4-di-p-toluidinoanthraquinone (Solvent Green 3, 1, Fig. 1a).^14,15 1 is an anthraquinone dye that, in solution, exhibits a broad absorption band from the UV to the visible (Supplementary Fig. 1,3,4), and indeed to the near-infrared region (NIR) in the solid state (Fig. 1c). As expected, crystal 1 oscillated in the first photothermal-induced mode of natural vibration, exhibiting high-speed large-amplitude oscillations.¹² Surprisingly, we discovered for the first time that the crystal could be actuated by the second and third modes of natural vibration at higher frequencies than the first mode, and then exhibited unprecedented, complex flagellum-like oscillations. These oscillatory movements were induced regardless of the light wavelength, thus from the UV to the visible, in the NIR, and even by a halogen lamp delivering light over a wide range of wavelengths. Moreover, the oscillatory frequencies of the crystal could be tuned by moving a support that appressed the crystal, just as the pitch of a guitar or a violin changes depending on where the fingers are placed.

Physical properties of the crystal

Black needle-shaped crystal 1 was obtained via slow evaporation of a toluene solution at room temperature under atmospheric pressure (Fig. 1b). Transient absorption spectroscopy (TAS) revealed that the relaxation process of the photoexcited crystal 1 proceeded within 50 µs in the solid state (Supplementary Fig. 5c). The photoluminescence quantum yields (PLQYs) of crystal 1 were less than 0.5% at all excitation wavelengths from 375 to 638 nm (Supplementary Fig. 6), indicating that absorbed light energy is efficiently converted to heat rather than light within 50 µs, thus one-to-three orders of magnitude faster than the speed of crystal oscillation (10–1000 Hz, vide infra). The powder X-ray diffraction (PXRD) profile was consistent with that derived from the previously reported crystal structure (Supplementary Fig. 10, Supplementary Table 2).¹⁵ PXRD measurements from 25 to 100°C revealed that crystal 1 exhibited a colossal positive coefficient of thermal expansion (CTE) of 2.71× 10^–4 K^–1 along the a-axis (the longitudinal direction of the single crystal)¹⁵ (Supplementary Fig. 11). This is four-fold the average axial CTE of organic crystal¹⁶ and one to two orders of magnitude larger than the CTEs of inorganic material.¹⁷ The large CTE is attributable to the weak π-π interactions of the aromatic rings along the a-axis (Supplementary Fig. 12). The three-point bending test revealed that the Young’s modulus of crystal 1 along the longitudinal direction (the a-axis) was 2.14 ± 0.27 GPa, and that crystal 1 withstood strains of 0.89 ± 0.21% within the region of elasticity, indicating that crystal 1 is elastic (Supplementary Fig. 13), possibly attributable to weak π-π intermolecular interactions that extend in all directions (Supplementary Fig. 12). Thus, crystal 1 would well withstand deformation. The thermal diffusivity of crystal 1 along the direction of thickness (the b-axis) measured via micro-temperature wave analysis (µTWA)¹⁸ was 1.57 ± 0.02 × 10^–7 m²s^–1, which is comparable to that of other organic molecular crystals (Supplementary Fig. 8, Supplementary Table 1) but one to three orders of magnitude smaller than those of inorganic materials.¹⁷ The large thermal expansion along the direction of length and the low thermal conduction along the direction of thickness both contribute to the significant photothermal-bending.¹¹ Crystal 1 was expected to exhibited significant bending attributable to the photothermal effect, and as a result, evidenced notable movements caused by photothermally induced natural vibration upon UV, visible light, and NIR irradiation.

Crystal oscillations in the first mode of natural vibration

A needle-like crystal I (a specimen of crystal 1, length 10,150 µm, width 169 µm, thickness 35.1 µm) was fixed to a glass plate at its left tip. When the crystal was irradiated from the top with a UV laser (375 nm, 961 mW cm⁻²) for 0.1 s (Fig. 2a,b), the crystal oscillated at 70 Hz in the first mode of natural vibration and bent by 1.54° in the direction opposite that of irradiation by the photothermal effect (Fig. 2c,d, Supplementary Video 1). On irradiation with pulsed UV light at 70 Hz (375 nm, 961 mW cm⁻²), the first natural vibration mode was dramatically amplified via resonance (Fig. 2e, Supplementary Video 2). The bending angle (the difference between the maximum and minimum bending angles over a cycle) attained 11.4° in the stationary state, thus 7.4-fold that of UV irradiation for 0.1 s (1.54°, Fig. 2c,e). The bending amplification afforded by resonance was most significant at 70 Hz for UV pulse frequencies from 5–140 Hz, and the bending angle decreased as the pulse frequency moved away from 70 Hz (Fig. 2g, black circles, Extended Data Fig. 1). Notably, resonance was also observed at 23 Hz, thus at one-third of the natural frequency (Fig. 2f,g), which is consistent with our previous finding that resonance occurred not only at the natural frequency but also at it odd fractions.¹² The finite element analysis (FEA)¹² results reproduced the pulse frequency dependence of the bending angle (Fig, 2g, red circles, Supplementary Fig. 27).

We next investigated the oscillatory behaviour of crystal I during laser irradiation at different wavelengths (Fig. 2h,i, Supplementary Fig. 15, Supplementary Video 3). Figure 2h presents the relationship between the light intensity and the bending angle of crystal I in the steady state during 70-Hz pulsed laser irradiation. At all wavelengths, the bending angle increased linearly in proportion to the light intensity; maximum bending was observed under 375-nm UV light, followed by 520-nm green, 450-nm blue, and 638-nm red lights; the minimum bending was observed under 808-nm NIR light, owing to lower absorption around the NIR compared to the UV-visible region (Fig. 1c). The bending angles were smaller under red and blue light than under UV and green light, possibly due to the lower photothermal conversion efficiencies (Supplementary Fig. 9). Figure 2i presents the dependence of the temperature increase (ΔT) on the bending angle. UV and visible lights exhibited the same trend: when ΔT attained 1°C, the bending angle was ~ 5°. In contrast, the bending angle under NIR was smaller because the lower absorption coefficient at 808 nm (Fig. 1c) allowed deep penetration, associated with a smaller temperature difference between the top and back surfaces. Additionally, we successfully generated oscillatory behaviour under a halogen lamp delivering a continuous spectrum of light (400–2000 nm, λ_max: 1000 nm; 3400 mW cm^–2, Supplementary Fig. 16, Supplementary Video 3), indicating that crystal 1 has excellent properties as a candidate for sunlight-driven actuators/oscillators.

Next, we explored the relationship between crystal shape, size, and oscillatory behaviour by focusing on the photomechanical motions of crystal 1 of different sizes and shapes (Fig. 2j–l, Supplementary Table 3 and Supplementary Fig. 17,18). The tip displacements under non-resonated photothermal bending and resonant oscillation increased linearly in proportion to the crystal length (Fig. 2j). In contrast, the natural frequency and speed of tip displacement rose in proportion to [thickness/length²] (Fig. 2k,l). For a rectangular cantilever beam, the natural frequency is given by Eq. (1):¹⁹

$$\begin{array}{c}{f}_{calc}=\frac{h}{4\pi }{\left(\frac{\eta }{l}\right)}^{2}\sqrt{\frac{E}{3\rho }}\#\left(1\right)\end{array}$$

where h is the thickness, l is the length, $\eta =$ 1.875 for the first natural frequency, E is Young’s modulus along the direction of length, and ρ is the density.¹⁹ Indeed, the natural frequency was almost proportional to thickness/length² (Fig. 2k), in line with Eq. (1). These results indicate that longer and thinner crystals exhibit large but slow actuation; shorter and thicker specimens evidence small but high-speed oscillation, in accordance with our previous report.¹² The oscillatory performance of crystal 1 is summarised and compared to those of other light-driven oscillators in Supplementary Table 5 and Supplementary Fig. 28.

Crystal oscillations in the second and third modes of natural vibration

We discovered for the first time that crystal oscillation could be induced not only by the first mode of natural vibration, but also by the second and third modes (Fig. 3, Extended Data Fig. 2,3). In the second and third modes, crystal I exhibited complex flagellum-like motions (Fig. 3b,c, Supplementary Video 4). Figure 3m presents the UV pulse dependence of the crystal I bending angle under pulsed irradiation from 5 to 1600 Hz. Interestingly, bending amplification induced by resonance occurred when the pulse frequencies were 530 and 1350 Hz, in addition to 70 Hz. Figure 3e,f presents the time dependencies of the measured bending angles under 530- and 1350-Hz pulsed UV irradiation, respectively. As was the case under 70-Hz pulsed light irradiation (Fig. 3d), the bending angle gradually increased to attain the steady state, indicating that resonance was in play. Figure 3g–i presents the various contributions to the bending angle: these are the photothermal effect and the first, second, and third modes of natural vibration. Under 530-Hz pulsed UV irradiation, the second mode of natural vibration was selectively amplified but the first mode of natural vibration was attenuated (Fig. 3h). The same trend was observed under 1350-Hz pulsed UV irradiation; the third mode of natural vibration was selectively amplified whereas the first and second modes of natural vibration were not (Fig. 3i). Note that the second and third natural frequencies of a rectangular cantilever beam are also given by Eq. (1) when η = 4.694 and 7.855 respectively. The calculated second and third natural frequencies for crystal I were 447.4 and 1,252.7 Hz respectively, lower than those of the measured values of 530 and 1,350 Hz, probably because crystal I was not perfectly rectangular.

Next, we analysed the time dependencies of displacements at different crystal positions to investigate the detailed oscillatory motions at 530 and 1350 Hz (Supplementary Fig. 20,22). During the second mode of natural vibration at 530 Hz, the left side of the crystal (0 to 7.7 mm distant from the left root) bent away from the light when the light was on, whereas the right side (7.7 to 10.15 mm distant from the root) bent toward the light. As a result, the crystal exhibited complex oscillatory motions with two nodes and two antinodes (Fig. 3b,k), unlike the oscillation during the first mode of natural vibration in which all parts of the crystal bent toward the same direction simultaneously (Fig. 3a,j). Similarly, during the third mode of natural vibration at 1350 Hz, the crystal exhibited three nodes (0, 5.25, 8.5 mm) and three antinodes (3, 7, 10.15 mm) in which the three regions between the nodes oscillated in phases that were opposite to those of their neighbours (Fig. 3c,l). Of note, such complex motions during the second and third modes of natural vibration could also be induced by visible and NIR lasers (Supplementary Fig. 21,23). In summary, complex flagellum-like oscillations with more than one node and antinode were created for the first time by exploiting the higher modes of natural vibration induced by the photothermal effect.

Tuning of crystal oscillation.

Equation (1) indicates that the natural frequencies of crystal cantilever beams can be varied by tuning the length and/or thickness. Indeed, eight specimens of crystal 1 (crystals I–VIII) of different sizes and shapes resonated at different frequencies (Fig. 2j–l, Supplementary Table 3). In this section, we describe how we tuned the frequencies driven by the first mode of photothermally resonated natural vibration of the same crystal sample by changing the length and/or thickness of the oscillatory body (Fig. 4). As depicted in Fig. 2,3, crystal I resonated at 70 Hz during the first mode of natural vibration. When a support was placed at the bottom 2.48 and 4.37 mm distant from the left root, crystal I resonated at higher frequencies: 125 and 218 Hz, respectively (Fig. 4a, Supplementary Video 5), because the length of the oscillatory body had decreased. Notably, the values of f_calc when supports were placed at 2.48 and 4.37 mm were 123.3 and 217.0 Hz, respectively, in good agreement with the experimental values. We thus revealed that the vibrational frequencies could be adjusted by placing a support, just as the pitch of a violin or a guitar changes when fingers press strings.

Next, we explored the oscillation of a crystal with one end fixed and another end simply supported. Crystal II (15,130 × 45.9 × 63.1 µm³) resonated at 60 Hz during the first mode of natural vibration (Fig. 4b, black). When a support was placed on the right tip and crystal II was then irradiated with UV, the centre of the crystal oscillated (Supplementary Video 6). The red dots in Fig. 4b show the UV pulse frequency dependence of the displacement 9 mm distant from the left root; the largest displacement was observed at 250 Hz, in good agreement with the f_calc value (253 Hz, Supplementary Fig. 24). Next, we shifted the natural frequencies by changing the irradiated face. When crystal II was rotated through 180° and the back surface then irradiated, resonance was observed at 60 Hz (Supplementary Fig. 19, Supplementary Video 7) because the thickness of the oscillatory body had not changed. In contrast, when crystal IV (4,151 × 76.1 × 18.2 µm³), which resonated at 200 Hz, was rotated through 90° and a side face then irradiated, the resonant frequency increased from 200 to 990 Hz (Fig. 4c, Supplementary Video 8) because the thickness of the oscillatory body increased from 18.2 to 76.1 µm. The calculated f_calc values on irradiation of the top and side faces were 208 and 925 Hz, respectively, thus comparable to the measured values. These results confirm that the oscillatory behaviour of crystal 1 can be tuned by changing the irradiated face.

We also measured the oscillatory behaviours of two connected crystals. Crystal X (4,348 × 90.7 × 32.3 µm³) was recrystallised with crystal IX (5,955 × 79.4 × 65.6 µm³); it became attached to the top face of crystal IX, forming a branched shape (Fig. 4d). Figure 4e presents the UV pulse frequency dependencies of tip displacement for crystal IX (red circles) and crystal X (black circles) when pulsed UV irradiation was delivered to the top. Unlike the other resonance curves shown in Fig. 4a–c, in which the profiles exhibit unique, symmetric resonance peaks, the resonance curves of crystals IX and X were asymmetric and exhibited two resonance peaks at 400 Hz and 335 Hz, respectively, at which points the crystals exhibited the largest tip displacements (Supplementary Video 9). At all pulse frequencies, the motions of the two crystals were synchronised in-phase (Supplementary Fig. 25), indicating that oscillation of crystal IX affects that of crystal X and vice versa. Vantomme et al. reported that two strip-like liquid crystalline network (LCN) oscillators connected via a joint exhibited synchronised oscillations on UV irradiation by virtue of energy transmission through the joint.²⁰ Our results indicate that collective synchronised oscillations also occur in photomechanical crystals.

Finally, we investigated oscillation of a crystal bearing a weight. We loaded a weight (645 µg) onto the right side of crystal IV (4,151 × 76.1 × 18.2 µm³, total crystal weight: 7.31 µg, Fig. 4f). Even though the weight was 88-fold heavier than the crystal, the crystal did not break given its high elasticity. Upon UV light irradiation of the crystal for 0.1 s, the crystal oscillated markedly at 16 Hz and bent away from the light because of the photothermal effect (Fig. 4h, red). The natural frequency (16 Hz) was much lower than that without the weight (200 Hz, Fig. 4h, black) because the oscillatory body became heavier on addition of the weight. Under pulsed UV irradiation at 16 Hz, the bending increased to 20° because of resonance; high-speed weight-lifting work was thus performed (Fig. 4g,i, Supplementary Video 10). Such reversible oscillation with a weight persisted for more than 10,000 cycles without any notable decrease in the bending angle or breaking of the crystal, indicating the system was extremely durable (Fig. 4j). Oscillations at 16 Hz were also induced by 638-nm red and 808-nm NIR lights (Supplementary Fig. 26). The calculated power densities of crystal 1 were 4×10³–4×10⁴ W m^–3 (3–30 W kg^–1). To the best of our knowledge, these values are higher than those afforded by any other photomechanical crystals, hydrogels, and most light-responsive polymers (Supplementary Fig. 29, Supplementary Tables 6, 7) and are comparable to those of solenoid actuators and biological muscles.^21,22

In conclusion, we developed light-responsive organic crystal oscillators driven by the photothermally resonated first, second, and third modes of natural vibration. The oscillators function under broad-wavelength light including UV, visible light, and NIR, and under continuous wavelengths, rendering the crystals excellent candidates for sunlight-driven actuators and oscillators. The resonance frequencies were readily tuned by changing the length, thickness, and weight of the oscillatory body. Our findings demonstrate that soft robots such as sailboats, object transporters, and insect-like robots will be realized in future, that require no electricity and are powered by sunlight, thus the cheapest and most readily available natural energy source.

Material preparation and characterisation. Commercially available 1,4-di-p-toluidinoanthraquinone (Solvent Green 3; 1) was obtained from TCI and used as received without further purification. A 300-mg sample was dissolved in a toluene solution (4 mL) in a conical flask without stirring at room temperature under atmosphere pressure. After several days of slow toluene evaporation, specimens of needle-like black crystal 1 were obtained.

The UV-vis diffuse reflectance spectra of powdered crystal 1 were measured using a spectrophotometer (Lambda 650; PerkinElmer) equipped with an integrating sphere. Powder was mounted on a glass base and covered with a quartz plate. Measurements were conducted from 200 to 900 nm at 1-nm resolution.

Femtosecond transient absorption spectroscopy (fs-TAS) and nanosecond TAS (ns-TAS) experiments were performed using home-built pump-probes. A Yb:KGW regenerative amplifier (Light Conversion, PHAROS, central wavelength: 1030 nm, pulse duration: 190 fs, pulse energy: 1 mJ per pulse, repetition rate: 1 kHz) served as the light source. The output pulse was split into two optical paths using a beam splitter. During fs-TAS, one of the split outputs was fed into an optical parametric amplifier (OPA, Light Conversion, ORPHEUS) for which the output wavelengths were tuned to 620 nm and 800 nm, and the latter light converted to 400 nm by a β-BaB₂O₄ (BBO) crystal to serve as a pump pulse. The other output was focused on a sapphire crystal (3-mm thickness), thus generating white light from 500 to 950 nm for the probe pulse. During ns-TAS, the output pulse (410 nm, 3 ns) of an optical parametric oscillator (OPO, EKSPLA, NT242) receiving the third harmonic generation (THG) of a Nd:YAG laser (central wavelength: 1064 nm, 6 ns) as the excitation pulse served as the pump pulse. The probe light was the same as that for fs-TAS. The Q-switch of the OPO system and the delayed trigger of the Yb:KGW amplifier were synchronised to the operation of the Yb:KGW amplifier using a picosecond delay generator (Stanford Research Systems, DG535) that afforded precise delay times in the nanosecond range. The pump and probe polarisations differed by the magic angle (~ 54.7°). Each probe pulse that passed through a sample was dispersed via a polychromator (JASCO, CT-10; 300 grooves/500 nm) and then detected by a multichannel system featuring a complementary metal-oxide semiconductor sensor (UNISOKU, USP-PSMM-NP). All samples were prepared from 2 × 10^–5 M acetonitrile solution in a 1-mm cell, and ground powder from a single crystal was sandwiched between two glass plates (Supplementary Fig. 2).

The thermal diffusivity of crystal 1 along the direction of thickness at room temperature was measured via microscale temperature wave analysis (µTWA).¹⁸ A specimen of crystal 1 with flat surfaces and no cracks was sandwiched between an indium-tin oxide glass micro-heater and a nickel-gold micro-thermocouple sensor. Periodic Joule heating was delivered by the heater and detected by the sensor. Thermal diffusivity was estimated from the phase delays of the temperature waves between the heater and the sensor. The details have been described in our previous work;¹⁸ see also Supplementary Fig. 8.

Powder X-ray diffraction (PXRD) measurements were conducted with the aid of a high-resolution X-ray diffractometer (SmartLab, Rigaku) equipped with a monochromatic Cu–Kα radiation source (λ = 1.54187 Å). Powdered samples of crystal 1 were placed on a platinum plate and heated from 25 to 100°C followed by cooling to 25°C. PXRD data were collected at 25, 40, 60, 80, and 100°C.

The Young’s moduli of crystal 1 samples were determined using the three-point bending test and a universal material testing machine (RTG-1210; A&D). A single crystal was mounted on a two-point support (copper wires) on copper blocks, and a force (a load) then applied to the centre using a metal jig. The details are shown in Supplementary Fig. 13.

Measurement of crystal oscillations. Photoactuation of crystal 1 was measured using digital high-speed microscopes (VW-6000; Keyence, or MEMRECAM HX-6; NAC Image Technology). Frames per second (fps) were set to at least 10-fold the pulse frequency. Each crystal was placed with one tip fixed to a glass plate and the largest surface facing up, unless otherwise noted. The top surface of each crystal was irradiated with a UV laser (λ = 375 nm; FOLS-03; SAWAKI Kobo), visible lasers (λ = 450, 520, 638 nm; FOLS-03; SAWAKI Kobo), an NIR laser (λ = 808 nm; FOLS-03; SAWAKI Kobo), or a halogen lamp (400 < λ < 2000 nm; λ_max = 1000 nm, HCV-AC100-200V/–DC12V-300W; Heat-tech). The lasers were equipped with fibre line generators (FLG10FC-633; Thorlabs) and the length and width of each light spot were 16 mm and 2 mm, respectively, thus sufficient to illuminate the entire crystal surface. The irradiated surface temperature was measured using an IR thermographic camera (FSV-2000; Apiste). Pulse irradiation was controlled using a microcontroller (UNO; Arduino) when lasers were employed or an optical chopper (300CD; Scitec Instruments) when the halogen lamp was used (Supplementary Fig. 14). The duty cycles were 50%. The time dependencies of the bending angle and crystal tip displacement were semi-automatically extracted via Tracker, a video analysis and modelling tool.²³

Finite Element Analysis. Finite element analysis (FEA) was performed using commercial software (ANSYS 2023 R1; ANSYS, Inc.),²⁴ and revealed the oscillatory mechanism of crystal 1. First, a three-dimensional (3D) model that mimicked a crystal cantilever beam was created using solid-modelling computer-aided design (CAD) software (Ansys SpaceClaim).²⁴ Next, the physical properties of crystal 1, including heat capacity (Supplementary Fig. 7), thermal conductivity (Supplementary Fig. 8), coefficients of thermal expansion (Supplementary Fig. 11), and Young’s modulus (Supplementary Fig. 13) were incorporated into the 3D model. A heat flux was then delivered to the top surface of the model and the time dependence of the temperature distribution was computed. Based on the thermal strain by the temperature distribution, the time dependence of deformation of the cantilever beam was calculated. The parameters used in the FEA are summarised in Supplementary Table 4.

Acknowledgements

This research was supported by JSPS Grant-in-Aid for Scientific Research B (17H03107) for H.K., JSPS Research Fellowship for Young Scientists (22J22384 and 21J20125) for S.H. and Y.H., respectively, Iketani Science and Technology Foundation (0351227-A) for S.H., the Grant-in-Aid for Young Scientists (Early Bird) at Waseda Research Institute for Science and Engineering for S.H. and Y.H. S.H. and Y.H. thank the Graduate Program for Power Energy Professionals (PEP), Waseda University from MEXT WISE Program. We thank Mr. Masanori Uji and Prof. Dr. Nobuhiro Yanai at Kyushu University for the measurement of PLQY. The DFT calculations were performed using Research Center for Computational Science, Okazaki, Japan (Project: 23-IMS-C279).

Author contributions

H.K. conceived the project. S.H. conducted all the experiments, data analysis, and calculations except for the UV-vis diffuse reflectance spectrum measurement, which was conducted by T.G., TAS measurements and analysis, which was conducted by T.R. (solid sample) and T.E. (solution sample) and supervised by T.O., K.M., and K.O., and the thermal diffusivity measurement, which was conducted by R.M. and supervised by J.M. Y.H. instructed S.H. on data analysis and FEA. T.E., T.R., and T.O. instructed S.H. on the DFT calculations. S.H., Y.H., and H.K. interpreted the results. S.H. and H.K. wrote the manuscript. T.A. assisted with the project.

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Broad-Wavelength Light-Fuelled Organic Crystal Oscillators Driven by Multimodal Photothermally Resonated Natural Vibration

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Version 1

Abstract

Figures

Main

Physical properties of the crystal

Crystal oscillations in the first mode of natural vibration

Crystal oscillations in the second and third modes of natural vibration

Methods

Declarations

References

Additional Declarations

Supplementary Files

Status:

Version 1