The surface skin of a banded blue-sprat had the mesocrystal structures of biogenic guanine crystals and cytoplasm. The platy guanine crystals were organized in the parallel direction to the surface skin with incorporation of cytoplasm. The size of the platy guanine crystal as a unit was larger than that of the other fish. Inspired by the biogenic structures, we studied the morphology and orientation control of molecular crystals consisting of organic molecules. When guanine was recrystallized on a glass substrate in the absence of any organic molecules, an aggregate of the platy crystals arranged perpendicular to the substrate was formed. The morphology and orientation of recrystallized guanine were different from those of the biogenic one. We have applied biomimetic approaches to control the morphology and orientation of the molecular crystals. The thin platy guanine crystals were formed parallel to the chitosan substrate through the recrystallization in the presence of additive organic molecules. The additive organic molecules and the modified substrates facilitated the morphology and orientation control. The present results suggest that biomimetic approaches for the morphological control of inorganic and ionic crystals can be applied for controlled deposition of a variety of organic and molecular crystals.

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.