Two versatile exfoliation approaches generate both hydrophilic and hydrophobic nanosheets from an organic layered compound.

compound ( Figure 1 ). If the intercalation of guests changes crystal structures of the organic layered compound, the dynamic properties can be tuned by not molecular design but intercalation. In the present work, temperature-and stress-induced color-change properties of a crystalline layered PDA were tuned by intercalation of guest metal ions in the layered structure.PDAs with π -conjugated backbone are synthesized by polymerization of diacetylene (DA) monomers. [21][22][23] For example, 10,12-Pentacosadiynoic acid (PCDA) forms the layered crystal structure with the lamellar bilayer molecular assembly (Figure 1 ). When the distance between the diacetylene moieties is shorter than 0.5 nm in the assembled states, the topochemical polymerization without changes of the molecular arrangement is achieved by irradiation of UV light, X-ray, and γ-ray. [ 24,25 ] PDAs have a wide variety of applications, such as transistors and sensors. [26][27][28][29][30][31][32][33][34][35][36] One of the most characteristic properties of PDAs is stimuli-responsive color changes. [ 24,25 ] However, the stimuli-responsive properties of PDAs, such as color, responsivity, and reversibility, were not tuned by simple approaches except molecular design. In general, the blue color of PDA derivatives irreversibly turns to the red one by application of external stimuli, such as temperature rise. Since the external stimuli cause the torsion of the PDA main chains, shortening of the conjugation length induces the irreversible color changes. [26][27][28][29][30] The reversible color change was observed on the PDAs with the designed molecular structures. [ 37,38 ] The PDAs deposited on the specifi c substrates showed the reversible color changes. [ 39,40 ] The results imply that the structures of PDAs have an infl uence on the color-change properties. In our previous work, [ 41 ] the reversible color changes were observed with temperature increase and decrease on the thinfi lm crystals of the layered PDA with intercalation of zinc ion (Zn 2+ ) in the interlayer space. If the structures of the original PDAs are modifi ed by the intercalation, the color-change properties, such as color, responsivity, and reversibility can be tuned by the simple method. Here we focused on the intercalation of metal ions in the layered PDAs for tuning of the structures and the color-change properties. The metal salts of precursor PCDA crystals and their polymerized structures were prepared in the crystalline states and Langmuir-Blodgett

In nature, biological macromolecules control the growth of inorganic crystals under mild conditions in aqueous media. Inspired by biomineralization, biomimetic approaches have been studied for growth control of inorganic crystals in aqueous media by using organic molecules and polymers. The approaches were not applied to nonaqueous systems for the development of functional organic materials. Here, we have applied biomimetic approaches to growth control of organic crystals in nonaqueous media. Morphology and orientation of 10,12-pentacosadiynoic acid (PCDA) crystals, a diacetylene derivative, were controlled in organic media with the additive organic polymers and surface-modified substrates. The oriented PCDA ribbons were obtained by an advanced biomimetic approach. After topochemical polymerization, the resultant polydiacetylenes (PDA) ribbons were applied to the thermochromic materials with intercalation of metal ions and the semiconductor layer of an organic field-effect transistor. The present work implies that biomimetic approaches can be applied to morphology and orientation control of organic crystals.

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