Molecular Hopper Crystals and Electron Beam-Triggered Reversible Actuation

Abstract

Molecular crystals with unusual morphologies characteristic of "hopper crystals" have rarely been explored; such structures are potentially useful for eliciting specific responses to external fields or stimuli. Upon simple reprecipitation and controlled growth, select members of a family of strongly zwitterionic molecules, assembling in non-centrosymmetric lattices, are shown to form microcrystals with novel "hopper" morphology. The molecular aggregation is monitored by their characteristic fluorescence enhancement; X-ray diffraction, microscopy, and surface potential mapping provide insight into the development of the unique morphology. Under optimized conditions of electron beam irradiation in a scanning electron microscope, the prototype microcrystal is found to exhibit smooth, prominent, and reversible actuation. Even though electrically triggered macromolecular actuators as well as mechanically responsive and photo/ thermosalient molecular crystals are known, controlled bending/folding induced by electron beams are rare and have been demonstrated only in specialized nanostructures. The current observations with a simple small-molecule-based hopper microcrystal are analyzed by a detailed examination of the crystal lattice structure and asymmetric dipole distribution, together with the simulations of the electron beam interactions. An empirical model developed for the responses in the local electrostatic field provides a mechanistic understanding of the actuation process.

Reversible Thermosalience in a One-Dimensional Coordination Polymer Preceded by Anisotropic Thermal Expansion and the Shape Memory Effect

“…Physical manifestation of stimuli responsiveness has been emerging as an important research topic in the area of crystalline materials. Mechanical motions of molecular crystals induced by light, heat, and pressure have been explored in macroscopic crystals for their potential use as actuators acting as energy transducers in a controllable manner. − Macroscopic dynamism such as bending, jumping, curling, deformation, or rotation has been observed in response to external stimuli due to amplification of microscopic perturbation during molecular reconfiguration. − ,− These properties enable these materials for their potential applications in diverse fields ranging from sensors and smart energy harvesting materials to artificial muscles and soft robotics. − Rapid transduction of energy leads to the release of stress accumulated within the materials due to structural transformation and/or reconfiguration, which results in hopping, explosion, splitting, and ballistic motions. ,− Photosalient (PS) ,− and thermosalient (TS) ,,− ,,− phenomena have been studied in single crystalline materials showing these events in response to light and heat, respectively. Single crystals have advantages over polymers and liquid crystals because of their dense and long-range ordered packing, which can trigger a fast mechanical response with smaller configurational changes at the molecular level. , In terms of actuation, systems that can operate continually have advantages over single time operating materials for obvious reasons.…”

Capillary-force-driven self-assembly of carbon nanotubes: from ab initio calculations to modeling of self-assembly

“…w is x À R ext , for R ext ¼ R CNT + d being the external radius of CNT, where d ¼ 0.335 nm is CNT thickness. The magnitude of F C decreases from 8.36 to 0.124 pN for CNT armchair (4,4), and from 31.8 to 0.6 pN for CNT armchair (15,15), within the probed interval of w. We determine F el from eqn (6) for all the CNTs, where the corresponding Young's moduli are reported in Table 1. We calculate I CNT as the area moment of inertia of a tube, p  (R ext 4 À R int 4 )/ 4, with R int ¼ R CNT .…”

“…The exposure to an electron beam, for instance, during characterization through scanning electron microscope, has been reported to bend semiconductor NWs with subsequent formation of NW bundles. [3][4][5][6] Procedures involving wet etching or cleaning also result in reshaping of the vertical arrangement of NWs [7][8][9] and CNTs. In all these cases, a drying step occurs where capillary menisci between adjacent nano-pillars induce lateral forces that may bring these in contact 10,11 and eventually assemble together.…”

Photophysical, electrochemical properties and flexible organic solar cell application of 7,7-bis(1-cyclopropyl carbonyl piperazino)-8,8 dicyanoquinodimethane

“…[1][2][3] Interestingly the selection of amine plays a significant role in fine tuning the well-defined structures; accompanied it's fascinating and unpredictable properties, manifested by versatile DADQs which holds them into focus. This results in divergent applications such as organic semiconductors, 4 molecular hopper crystals, 5 non-linear optical [6][7] and mechanochromic materials. 8 Di-substituted TCNQ derivatives [9][10][11] usually display enhanced fluorescence in their solids;…”

“…[1][2][3] Interestingly the selection of the amine plays a significant role in fine tuning the well-defined structure of the material, accompanied by the fascinating and unpredictable properties of the different DADQs formed, which makes them a good research focus. This results in the production of materials that have a diverse range of applications, such as organic semiconductors 4 and molecular hopper crystals, 5 as well as non-linear optical 6,7 and mechanochromic materials. 8 Di-substituted TCNQ derivatives [9][10][11] usually display enhanced fluorescence in their solid form owing to the hydrophobic nature, and can be converted into CT complexes/salts for bio-imaging purposes.…”