Mechanochromic Luminescence Based on Crystal-to-Crystal Transformation Mediated by a Transient Amorphous State

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• 作者：Shiki Yagai ; Tomohiro Seki ; Hiroaki Aonuma ; Kohsuke Kawaguchi ; Takashi Karatsu ; Takuma Okura ; Aya Sakon ; Hidehiro Uekusa ; Hajime Ito
• 刊名：Chemistry of Materials
• 出版年：2016
• 出版时间：January 12, 2016
• 年：2016
• 卷：28
• 期：1
• 页码：234-241
• 全文大小：542K
• ISSN：1520-5002

文摘

Photoluminescent materials that exhibit tunable emission properties when subjected to mechanical stimuli have numerous potential applications. Although many organic/inorganic and organometallic compounds display this property, called mechanochromic luminescence, most of these materials undergo a crystalline-to-amorphous (C → A) phase transition; examples of crystalline-to-crystalline (C₁ → C₂) transformation are rare. Single-crystal X-ray diffraction may allow direct analysis of the molecular packing of mechanochromic luminescence materials before and after C₁ → C₂ transformation, which may help to understand the underlying mechanism of this transformation. Reported herein is a mechanochromic luminescence material that displays an unprecedented type of C₁ → C₂ transformation mediated by a transient amorphous phase (C₁ → [A] → C₂). This mechanochromic luminescence material was developed by introducing soft triethylene glycol side chains in a crystalline gold(I) complex that exhibits mechanochromic luminescence based on a C → A phase transition. When this new gold(I) complex bearing triethylene glycol chains was subjected to a mechanical or thermal stimulus, dynamic phase changes were observed with irreversible luminescence color changes from blue to yellow to green in both the cases. The crystallinity of the mechanically generated C₂ phase was lower than that of the thermally generated C₂ phase. This is because the mechanically induced C₁ → [A] → C₂ process was finished within seconds, whereas the thermal C₁ → [A] → C₂ process occurred over a few minutes. To control the C₁ → [A] → C₂ transformation, we doped the complex with an inactive soft component. This successfully made the transformation reversible (from green to blue) upon thermal annealing of the mechanically obtained C₂ phase. This approach allowed the development of an imaging process involving invisible information storage even under UV illumination.