Twinning-Based Organosuperelasticity and Chirality in a Single Crystal of an Achiral Donor–Acceptor Type Schiff Base Induced by Charge-Transfer Interactions

Abstract

A charge-transfer (CT) interaction stabilizes molecular assemblies and can form a useful supramolecular synthon in crystal engineering. Herein we demonstrate preparation of a chiral single crystal showing twinning-based organosuperelasticity by forming a CT complex of an achiral donor–acceptor type Schiff base: N-(2,3,4,5,6-pentafluorophenyl)-1-phenylmethanimine. Pseudo-180° symmetry of a single-component CT complex originating from an antiparallel molecular assembly is the key to mechanical twinning. The chiral crystallization induced by CT interactions is also noteworthy because of the potential development of materials showing CT-based functions coupled with chirality.

Versatile Organosuperelastic Deformability by Multiple Mechanical Twinning

“…Molecular single crystals also show superelasticity but in a strict manner, i.e. bending in a specific direction by a specific angle by keeping single crystallinity in a deformed region, due to their anisotropic nature. ,,,,− Functionalization of organosuperelastic materials can be produced by the selection of molecular components. For example, superelastically switchable gas permeation, the coexistence of superelasticity and superplasticity, a semiconducting property, or chirality , originating from weak noncovalent interactions, π-conjugated molecules, or confined molecular movement, respectively, guest- or shear-direction-dependent superelasticity–ferroelasticity switching based on the strong anisotropy of molecular and crystal structures, ,,, and superelastochromism, i.e.…”

“…bending in a specific direction by a specific angle by keeping single crystallinity in a deformed region, due to their anisotropic nature. ,,,,− Functionalization of organosuperelastic materials can be produced by the selection of molecular components. For example, superelastically switchable gas permeation, the coexistence of superelasticity and superplasticity, a semiconducting property, or chirality , originating from weak noncovalent interactions, π-conjugated molecules, or confined molecular movement, respectively, guest- or shear-direction-dependent superelasticity–ferroelasticity switching based on the strong anisotropy of molecular and crystal structures, ,,, and superelastochromism, i.e. superelasticity along with color changes, have been achieved in superelastic molecular crystals.…”

Perpendicularly Oriented Dual Organosuperelasticity Correlated with Molecular Symmetry

“…SE has also been found in molecular single crystals (organosuperelasticity). − Superelastic organic crystals can show attractive functions coupling or coexisting with SE, e.g. gas permeability and its directional switching, superplasticity, superelastochromism, polarity switching, semiconducting properties, and supramolecular chirality, ,,, depending on the component molecules and their crystal structures.…”

“…SE has also been found in molecular single crystals (organosuperelasticity). − Superelastic organic crystals can show attractive functions coupling or coexisting with SE, e.g. gas permeability and its directional switching, superplasticity, superelastochromism, polarity switching, semiconducting properties, and supramolecular chirality, ,,, depending on the component molecules and their crystal structures. In contast to the versatile SE in polycrystalline SMAs, superelastic molecular crystals have strict deformability, deformation in a specific bending angle and direction, in maintaining their crystal integrity and are useful in applications demanding precise mechanical responses.…”

“…According to previous experimental and theoretical studies about mechanical twinning, a twin axis, which can almost correspond to a molecular C 2 axis, is normal (out of plane) 8,9,14,15 or parallel (in plane) 10,12 to its twin planes 18,27 in 180°rotational twinning. This suggests an approach from the viewpoints of organic chemistry and crystal engineering: 30−33 i.e., twinning-based superelasticity in two perpendicularly oriented directions can be actualized by exploiting a C 2symmetric molecule (Figure 1b).…”