Chirality is expressed not only at a molecular level but also at a molecular assembly level, such as liquid crystals or solid-state crystals. The dissymmetric arrangement of molecules in a non-covalent assembly is called enantiomorphism. Even achiral molecule can be crystallized in enantiomorphic or racemic crystals. So far, controlling crystalline chirality has been attempted. Especially, external stimulations-induced transformations with crystalline chirality changes have been much attracted because of their high potential for developing smart materials. Our group has intensively studied mechanochromism with crystal to crystal phase transition of gold(I) isocyanide complexes. Herein, we report an achiral molecule, biphenyl gold complex 1 which exhibits the first phase transitions upon mechanical stress from the amorphous phase (1a) to the enantiomorph (1ch) or racemic crystals (1rac), and from 1ch to 1rac with optical properties alternation. After purification and evaporation of 1, the orange viscous liquid 1a was obtained. 1a showed yellow emission under UV light. Upon sonication for 20 min, 1a was transformed into the white-gray powder 1rac, which shows weak blue-green photoluminescence. Interestingly, pricking 1a by a needle at the room temperature afforded two different phases: the green crystals 1ch or white gray crystals 1rac. Under UV light, 1ch and 1rac showed green and blue-green emission, respectively. Single crystal XRD revealed that 1ch is enantiomorph, crystallized in chiral space group P212121, and 1rac is racemic crystal with a space group of P-1. Upon grinding by ball milling, 1ch was changed into white-gray powder 1rac, confirmed by powder XRD patterns changes. Thermal analysis data, photophysical properties, and crystal structures of 1a, 1ch and 1rac will be compared.

Mechanoconglomeration and mechanoracemization of gold(I) complex crystals with optical properties alternation

253rd National Meeting (2017)

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