Light‐Powered Autonomous Flagella‐Like Motion of Molecular Crystal Microwires

Abstract

The ability to exhibit life‐like oscillatory motion fueled by light represents a new capability for stimuli‐responsive materials. Although this capability has been demonstrated in soft materials like polymers, it has never been observed in molecular crystals, which are not generally regarded as dynamic objects. In this work, it is shown that molecular crystalline microwires composed of (Z)‐2‐(3‐(anthracen‐9‐yl)allylidene)malononitrile ((Z)‐DVAM) can be continuously actuated when exposed to a combination of ultraviolet and visible light. The photo‐induced motion mimics the oscillatory behavior of biological flagella and enables propagation of microwires across a surface and through liquids, with translational speeds up to 7 μm s−1. This is the first example of molecular crystals that show complex oscillatory behavior under continuous irradiation. A model that relates the rotation of the transition dipole moment between reversible E→Z photoisomerization to the microscopic torque can qualitatively reproduce how the rotational frequency depends on light intensity and polarization.

Mechanical Bending and Modulation of Photoactuation Properties in a One-Dimensional Pb(II) Coordination Polymer

“…In recent years, great efforts have been made to mimic nature artificially for fabricating actuators that can work with accuracy in response to external stimuli by transduction of energy. − Mechanically responsive actuators hold tremendous potential for their use in smart medical devices, artificial muscles, flexible electronics, etc. ,− A new class of macroscopic crystals also known as “soft crystals” exhibits mechanical movements induced by pressure, heat, and light, which often results in hopping, splitting, bending, curling, coiling, twisting, and swimming of the crystals. ,− With the upsurge of dynamic crystals, several examples of mechanically flexible crystals have been reported in the literature showing elastic and plastic deformation upon the application of an external force. − Apart from actuation by mechanical force, photomechanical actuation is of great advantage due to its remotely controlled process. ,− Examples of flexible crystals and photomechanical actuators have been reported separately in the literature where most of them are organic crystals. ,,, However, multistimuli-responsive crystals are rarely encountered in the literature. ,,, Flexible organic crystals have been explored for optical waveguiding properties. , In general, fabrication of multifunctional materials demands the combination of several functionalities for imbibing multiple properties. Designing single-component smart materials that can perform multiple functions in response to different stimuli is a challenge in fundamental chemistry as well as materials fabrications.…”

Photochemical Synthesis of (2E,4Z)-5-(anthracen-9-yl)-2-cyanopenta-2,4-dienamide

“…This spectral overlap reduces conversion to 4 to less than 100%. This is typical for such anthracene derivatives as was previously shown for similar derivatives [7,10]. We could not separate 3 and 4 using column chromatography or prep-TLC due to their overlapping Rf values.…”

“…Photo-mechanical molecular crystals are an emerging class of smart materials that can convert UV or visible light to mechanical motion of the crystal [1,2]. Our group has pioneered the use of photomechanical crystals made from anthracene derivatives as the photo-harvesting chromophore [3][4][5][6][7]. To achieve diversity in photomechanical responses like bending [8,9], peeling [10,11], jumping [12,13], etc.…”

Mechanically Responsive Organic Crystals by Light

“…[66] The crystalline microwires of 18 were found to exhibit a continuous actuation in aqueous solution containing a surfactant when exposed to a combination of UV and visible light (Figure 6c). [67] The photo-induced motion mimics the oscillatory behavior of a flagellum and enables the propagation of microwires across a surface and through liquids.…”