Silver to Gold Metallic\nLuster Changes in Stimuli-Responsive\nDiacetylene Derivatives Uniquely Arranged within Crystals

Eye-catching metallic luster materials, especially those\nwhose\ncolors can be controlled by external stimuli, have many potential\napplications. Here, we present a silver luster material that changes\ncolor to gold upon UV irradiation. Diacetylene (DA) derivatives with\nstilbenes introduced via linkers at both ends (<b>DS-DA</b><i><b>n</b></i> (<i>n</i> = 1–6)) exhibited\nsignificantly different metallic luster and color change behaviors\ndepending on the linker carbon number (<i>n</i>). The results\nrevealed that the stacked structure of platelet crystals consisting\nof <b>DS-DA1</b> with the shortest linker carbon chain exhibited\na silver luster and changed its appearance to gold upon UV irradiation;\nthis was an exceptional property of this material. More importantly,\nwe found a unique crystal structure formed by <b>DS-DA1</b>,\nwhere the two assembled states coexisted. Partial topochemical polymerization\nof DA within this unique crystal structure dramatically changed its\ncolor from silver to gold. The findings of this study not only contribute\nto the development of the basic science of DA polymerization but also\nfacilitate the development of new applications of metallic luster\nmaterials due to their attractive features that are adaptable to photomask\npatterning and UV laser lithography.