Photomechanical Azobenzene Crystals

Taniguchi, Takuya; Asahi, Toru; Koshima, Hideko

doi:10.3390/cryst9090437

Cited by 75 publications

(55 citation statements)

References 59 publications

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“…With the ever‐increasing reports on adaptive crystals, there have been several attempts to compare the performance of individual dynamic molecular crystals to those of other materials . These efforts have been limited with the amount of available data and have been focused on specific examples of dynamic materials.…”

Section: Conclusion and Perspectivementioning

confidence: 99%

Global Performance Indices for Dynamic Crystals as Organic Thermal Actuators

Karothu

Halabi

et al. 2020

Advanced Materials

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same basic thermodynamic principles of energy transduction and are collectively referred to as actuators. [1][2][3][4][5][6][7][8][9][10] While complex natural biomechanical systems have evolved to aid functions such as dispersal and survival, the artificially manufactured actuators are specifically designed for integration in mechatronic or adaptronic systems that range from miniature devices such as navigation and positioning systems in flying machines, to complex systems that can perform tasks in specific environments, such as humanoid robots and spacecraft. The current applications of actuators are many and diverse; they include sensors, [11,12] artificial muscles, [13] soft robotics, [14] and energy-harvesting materials. [15] Simple or complex actuating motions can be induced by heat, light, electricity, pressure, and moisture, among other stimuli, and can be realized with shape-memory polymers, [16] conductive fibers, [17] liquid crystal elastomers, [18] piezoelectric, [19] magnetostrictive, [20] and electromagnetic materials. [21] The energy supplied to the artificial actuators can vary from fluid pressure or flow in the pneumatics, to current, charge or voltage in the electromagnetic, piezoelectric and magnetostrictive actuators, to heat in shape memory and thermal expansion actuators.The active media in actuators include fluids, hard solids such as metals, and even complex soft matter such as tissuesensembles of cells with similar structure that act together to perform a specific function. While molecular crystals do not immediately appeal as working actuating medium, their dynamic properties have recently transpired as an alternative to other materials and they are thought to hold an untapped potential for miniature, soft actuating devices, quickly shaping up into a new research field, crystal adaptronics. [22,23] Smallscale demonstrations of the usefulness of molecular crystals as microscale devices, including cantilevers, [24,25] ratchets, [26] optical waveguides, [27][28][29][30][31][32][33][34][35][36] and other "crystal gears" [37] that can move or reshape are occasionally reported for dynamic crystals. Although being very illustrative, these demonstrations have thus far remained limited to a laboratory scale and have not been implemented in actual, functional devices. Some of the obstacles toward wider applications are difficulties with reproducible growth of crystals of predictable size without the use Crystal adaptronics is an emergent materials science discipline at the intersection of solid-state chemistry and mechanical engineering that explores the dynamic nature of mechanically reconfigurable, motile, and explosive crystals. Adaptive molecular crystals bring to materials science a qualitatively new set of properties that associate long-range structural order with softness and mechanical compliance. However, the full potential of this class of materials remains underexplored and they have not been considered as materials of choice in an engineer's toolbox. A set of general performance metric...

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Section: Conclusion and Perspectivementioning

confidence: 99%

Global Performance Indices for Dynamic Crystals as Organic Thermal Actuators

Karothu

Halabi

et al. 2020

Advanced Materials

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“…Alternatively, crystallization of small molecule azobenzene derivatives can form photomechanical crystals wherein increased elastic moduli and cooperative isomerization offer the potential to dramatically enhance the photomechanical response. [19][20][21][22] However, poor processability of such crystals limits the size and geometry of obtainable materials. Furthermore, these devices are prone to fracture due to the large internal photostresses generated during photoisomerization.…”

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confidence: 99%

Reversible Actuation via Photoisomerization-Induced Melting of a Semicrystalline Poly(Azobenzene)

et al. 2020

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Photoisomerization of azobenzene in polymer matrices is a powerful method to convert photon energy into mechanical work. While most previous studies have focused on incorporating azobenzene within amorphous or liquid crystalline materials, the limited extents of molecular ordering and correspondingly modest enthalpy changes upon switching in such systems has limited the achievable energy densities. In this work, we introduce a semi-crystalline main-chain poly(azobenzene) where photoisomerization is capable of reversibly triggering melting and re-crystallization under essentially isothermal conditions. These materials can be drawn into aligned fibers, yielding optically-driven two-way shape memory actuators capable of reversible bending. Scheme 1. Preparation of semi-crystalline poly(azobenzene)s ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website.

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“…The free‐volume change between the two isomers of a DAE is not very pronounced, which was an initial rationalization for photomotion being possible in these crystals. As a consequence of this assumption, the large free‐volume change required in crystalline AB was thought to preclude motion, however, the first motion of dimethylamino‐AB thin plate‐like crystals was indeed only observed one decade ago . Since then, many examples have been discovered of either E or Z AB crystals or cocrystals exhibiting motion.…”

Section: Crystalline Photoswitchable Materialsmentioning

confidence: 99%

Enlightening Materials with Photoswitches

2020

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reversible conversion between their stable and (meta)stable isomers triggered by light. The return to their native, thermo dynamically most stable isomer is gener ally induced by using another wavelength of light or simply by heat, depending on the thermal stability of the (meta)stable isomer. Retinal-the prototypical photo switch in biology-showcases impressively how structural changes occurring during a lightinduced doublebond isomerization can lead to vision or allow microorganisms to convert photons into metabolic energy. In analogy, over the years, scientists have learned that the lightdriven isomeriza tion of small molecules can be collected, possibly amplified, and transformed into macroscopic property changes, such as mechanical motion, [1] charge carrying ability, [2] assembly and disassembly of macroscopic aggregates, [3] as well as switching of surfaces and their properties. [4] Materials, which for the purpose of this review are consid ered to be solid objects or organized assemblies in solution, provide unique advantages to enhance the function of photo switches and even create new functions when compared to their standalone molecular selves (for the primarily discussed photochromic molecules herein, see Figure 1). One must, how ever, consider the inherent challenges that may present them selves when working with photoswitches in close proximity to one another. Intermolecular interactions, such as aggregation, excitation quenching, low freevolume, as well as the poten tially much higher optical density of materials can drastically lower the overall photoresponse. Yet with proper macromo lecular and supramolecular design, functions can be achieved through the incorporation of photoswitches in a material that simply cannot be obtained by an isolated molecule on its own. Here, we highlight recent examples from the literature that have appeared during the past decade since our previous review in this journal, [5] with particular focus on the order of the photos witches in relation to their environment and its impact on mate rial properties and device performance.Conceptually, one can think about maximizing a photo switching unit's effect by giving it "order" with relation to its surrounding, in particular to other switching units (Figure 2). The lowest possible order is undoubtedly demonstrated by dis persing photochromic molecules in a bulk amorphous material. If aggregation of the photoswitches can be overcome, switching units are placed in random orientation to each other giving rise to a more or less isotropic material. Starting from this scenario of randomly distributed photochromic entities, one can think about providing order in two dimensions by placing Incorporating molecular photoswitches into various materials provides unique opportunities for controlling their properties and functions with high spatiotemporal resolution using remote optical stimuli. The great and largely still untapped potential of these photoresponsive systems has not yet been fully exploited due to the fundamental challenge...

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Photomechanical Azobenzene Crystals

Cited by 75 publications

References 59 publications

Global Performance Indices for Dynamic Crystals as Organic Thermal Actuators

Global Performance Indices for Dynamic Crystals as Organic Thermal Actuators

Reversible Actuation via Photoisomerization-Induced Melting of a Semicrystalline Poly(Azobenzene)

Enlightening Materials with Photoswitches

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