Perpetually Self-Propelling Chiral Single Crystals

Abstract

When heated, single crystals of enantiomerically pure D- and L-pyroglutamic acid (PGA) are capable of recurring self-actuation due to rapid release of latent strain during a structural phase transition, while the racemate is mechanically inactive. Contrary to other thermosalient materials, where the effect is accompanied by crystal explosion due to ejection of debris or splintering, the chiral PGA crystals respond to internal strain with unprecedented robustness and can be actuated repeatedly without deterioration. It is demonstrated that this superelasticity is attained due to the low-dimensional hydrogen-bonding network which effectively accrues internal strain to elicit propulsion solely by elastic deformation without disintegration. One of the two polymorphs (β) associated with the thermosalient phase transition undergoes biaxial negative thermal expansion (αa = -54.8(8) × 10(-6) K(-1), αc = -3.62(8) × 10(-6) K(-1)) and exceptionally large uniaxial thermal expansion (αb = 303(1) × 10(-6) K(-1)). This second example of a thermosalient solid with anomalous expansion indicates that the thermosalient effect can be expected for first-order phase transitions in soft crystals devoid of an extended 3D hydrogen-bonding network that undergo strongly anisotropic thermal expansion around the phase transition.

Dual Stress and Thermally Driven Mechanical Properties of the Same Organic Crystal: 2,6-Dichlorobenzylidene-4-fluoro-3-nitroaniline

“…Thermosalient crystals have attracted attention owing to their potential sensing and actuating behavior. [29][30][31][32][33][34] Thermosalient behavior occurs during a phase transformation and there are small yet distinctly anisotropic changes in the crystallographic unit cell parameters across the phase transition. The overall packing in the two phases is usually the same in terms of symmetry and space group, but the phase transitions are associated with fast, rapid release of accumulated strain energy.…”

“…The overall packing in the two phases is usually the same in terms of symmetry and space group, but the phase transitions are associated with fast, rapid release of accumulated strain energy. [32][33][34][35][36][37] In order that one might obtain a deeper insight into the relevant structure-property relationships, the structural changes need to be investigated. For example, Panda et al studied colossal positive and negative thermal expansion in a pentamorphic organometallic martensite.…”

Visible chiral discrimination via macroscopic selective assembly

“…Although chirality transfer and chiral recognition from the microscopic to the macroscopic scale have promise for many practical applications, e.g., chiral separation [3][4][5] , optical memories and switches [6][7][8][9] , and functional sensors and actuators [10][11][12][13] , they still remain key challenges in artificial systems 1,2,14 . To scale up chirality, a supramolecular strategy is generally employed to obtain various chiral architectures via assemblies of chiral or achiral molecules through non-covalent interactions [15][16][17] .…”

Acoustic Emission from Organic Martensites

“…[1][2][3][4][5][6][7][8][9][10] This phenomenon, termed the thermosalient effect, is astriking demonstration of afundamental process of energy transduction-the conversion of disordered molecular motion (heat) into an ordered motion (movement) by collective and concerted action of molecules in the ordered solid state.T he motion of crystals can also be triggered by light, following ap hotochemical reaction (photosalient effect), [11][12][13][14] or by mechanical stimulation of ap restrained crystal (mechanosalient effect). [1][2][3][4][5][6][7][8][9][10] This phenomenon, termed the thermosalient effect, is astriking demonstration of afundamental process of energy transduction-the conversion of disordered molecular motion (heat) into an ordered motion (movement) by collective and concerted action of molecules in the ordered solid state.T he motion of crystals can also be triggered by light, following ap hotochemical reaction (photosalient effect), [11][12][13][14] or by mechanical stimulation of ap restrained crystal (mechanosalient effect).…”

“…Possible reasons for this observation are fragmentation of the parent crystal and the slightly different temperature of the reverse transition (from b to a) of the individual pieces,which would result in distinct acoustic hits.A lthough l-PGA crystals are unusually robust [2] the probability of fragmentation increases in crystals that have been restrained from motion by which they would otherwise relax;t hat is,b yt ransducing the accumulated strain energy into kinetic energy of motion. Thus, structural relaxation and thermal contraction of the crystal lattice could also contribute to the generation of the acoustic signals during cooling.A ss upportive evidence of this argument, we found that racemic crystals of PGA, which remain immotile, [2] also produce distinct emission hits during both heating and cooling;although the intensity of the signals was much lower than those from the chiral crystals (Supporting Information, Figure S1 and Table S2). Thus, structural relaxation and thermal contraction of the crystal lattice could also contribute to the generation of the acoustic signals during cooling.A ss upportive evidence of this argument, we found that racemic crystals of PGA, which remain immotile, [2] also produce distinct emission hits during both heating and cooling;although the intensity of the signals was much lower than those from the chiral crystals (Supporting Information, Figure S1 and Table S2).…”