Effect of Crystal Packing on the Thermosalient Effect of the Pincer‐Type Diester Naphthalene‐2,3‐diyl‐bis(4‐fluorobenzoate): A New Class II Thermosalient Solid

Abstract

The pincer-like double ester naphthalene-2,3-diyl-bis(4-fluorobenzoate) (2) is pentamorphic. Upon heating crystals of form I to below their melting point (441-443 K), they undergo a phase transition accompanied by a thermosalient effect, that is, rare and visually striking motility whereby the crystals jump or disintegrate. The phase transition and the thermosalient effect are reversible. Analysis of the crystal structure revealed that form I is a class II thermosalient solid. Crystals of form III also underwent a reversible phase transition in the temperature range of 160 to 170 K; however, they were not thermosalient. Comparison of the structures and the mechanical responses of the two polymorphs revealed that the thermosalient effect of form I was due to reversible closing and opening of the arms of the diester molecules in a tweezer-like action.

Global Performance Indices for Dynamic Crystals as Organic Thermal Actuators

“…As has been demonstrated with a number of examples, an unusually rapid and efficient energy transduction can be accomplished with the thermosalient (TS) crystals—a subclass of dynamic materials that undergo cooperative martensitic transitions with rapid release of elastic energy that is manifested as motion across distances that can vary from several millimeters to meters . The effect was first noted in 1983, and after a long hiatus, it was explored in greater detail in the anticholinergic agent oxitropium bromide in 2010 .…”

Shape-memory effects in molecular crystals

“…They can effectively transduce energy to work by bending 1–10 , jumping 11–19 , twisting 20–23 , or curling 9,24 , and occasionally exhibit properties that are typical for polymers, as it has been recently demonstrated with self-healing organic crystals 4,25–27 . Soft-matter-like properties of molecular crystals can be accomplished by using heat 11,13–15,18,19 , light 28–32 , and/or pressure 33–39 . The most rapid transduction of energy was observed with thermosalient 4,11–15,18,19,40,41 and photosalient 28–32 crystals; the latent elastic energy that accumulates within these materials upon structural transformation is released instantaneously and results in swift movements, self-propulsion, and even ballistic events 11–16,18,40,41 .…”

“…Soft-matter-like properties of molecular crystals can be accomplished by using heat 11,13–15,18,19 , light 28–32 , and/or pressure 33–39 . The most rapid transduction of energy was observed with thermosalient 4,11–15,18,19,40,41 and photosalient 28–32 crystals; the latent elastic energy that accumulates within these materials upon structural transformation is released instantaneously and results in swift movements, self-propulsion, and even ballistic events 11–16,18,40,41 . However, for applications that require continual operation such as microfluidics or actuating switches, crystals that can deform reversibly and retain their integrity during operation are the preferred material of choice, and this has inspired studies into the mechanistic details and energetic profiles of their deformation 1,20,23,27,29–32 .…”

Micromanipulation of Mechanically Compliant Organic Single‐Crystal Optical Microwaveguides

“…In conjunction with their long‐range structural order, which accounts for added anisotropy in mechanical, optical, electronic and other properties, these assets favor these underexplored materials for fabrication of a wide array of electronic components, including single‐crystal actuators, sensors and (opto)electronic elements . It has already been established that mechanical compliance and dynamic response in such organic crystals can be elicited by stimulation using pressure, heat, and light . Conceptually, a single crystal that responds to a stimulus with deformation or motion combines sensing and responsive capabilities within the same, single‐component entity, and thus it can be considered equivalent to a smart, integrated adaptive system .…”

“…[5] Thee xtraordinary mechanical compliance of such organic crystals is rooted in their structures,w hich are governed by non-covalent intermolecular interactions that are comparably weaker relative to the covalent, ionic or metallic bonds,a nd provide softness and flexibility.I nc onjunction with their long-range structural order,w hich accounts for added anisotropy in mechanical, optical, electronic and other properties,t hese assets favor these underexplored materials for fabrication of awide array of electronic components,i ncluding single-crystal actuators, sensors and (opto)electronic elements. [6][7][8][9][10][11] It has already been established that mechanical compliance and dynamic response in such organic crystals can be elicited by stimulation using pressure, [12] heat, [13][14][15][16][17][18][19] and light. [20][21][22][23] Conceptually, as ingle crystal that responds to as timulus with deformation or motion combines sensing and responsive capabilities within the same,s ingle-component entity,a nd thus it can be considered equivalent to as mart, integrated adaptive system.…”