Abstract
It is generally believed that organic single crystals composed of a densely packed arrangement of anisotropic, organic small molecules are less useful as functional materials due to their mechanically inflexible and brittle nature, compared to polymers bearing flexible chains and thereby exhibiting viscoelasticity. Nevertheless, organic crystals have attracted much attention because of their tunable optoelectronic properties and a variety of elegant crystal habits and unique ordered or disordered molecular packings arising from the anisotropic molecular structures. However, the recent emergence of flexible organic crystal materials showing plasticity and elasticity has considerably changed the concept of organic single crystals. In this review, the author summarizes the state-of-the-art development of flexible organic crystal materials, especially functional elastic organic crystals which are expected to provide a foothold for the next generation of organic crystal materials.
Highlights
Organic molecular crystals have been believed to be inflexible and brittle (Figure 1a,b), because they have a densely packed, three-dimensional (3D), supramolecular structure and do not possess a mechanism for relaxation of the stress loaded
‘optical intermolecular packing so as to relax the stress loaded. Wire bundles, such as the electronic functions’ of organic molecular crystals [16,17,18,19,20,21,22,23,24], which is most likely to open up a new field fibril lamella structure, can exhibit high flexibility, as seen molecules in the macrostructure fibers of organic crystal materials chemistry
Crystals of π-conjugated molecules have attracted much attention owing to their potential applications in organic optoelectronic devices [58,59,60,61]
Summary
Organic molecular crystals have been believed to be inflexible and brittle (Figure 1a,b), because they have a densely packed, three-dimensional (3D), supramolecular structure and do not possess a mechanism for relaxation of the stress loaded. It is known that several organic molecular crystals display plastic-like bending deformability, i.e., plasticity [1,2,3,4,5,6,7]. These crystals are plastically bended by photoirradiation or deformed by external stress (Figure 1a,c). The regularly arranged molecular packing were forced to change to an irregular state and could not return to the packingCrystals according to the second law of thermodynamics
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