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We found that methyl salicylate (MS), a colourless liquid, transforms into a vivid yellow liquid with distinct absorption and fluorescence spectral characteristics when an alkoxy chain with a carbon number of four to seven is attached to the 5-position of MS. This phonomenon suggests the presence of microscopic local structures in the liquids, where π-electrons are delocalized across multiple MS molecules. X-ray diffraction (XRD) measurements supported this interpretation by indicating aggregates in the 10–15 Å range, composed of about three to five MS molecules arranged in a face-to-face π-stacking configuration. When the alkylated MS liquids are heated from temperatures below their glass transition temperature, they exhibit the property of crystallizing from a supercooled liquid state, known as cold crystallization. Furthermore, free-volume analysis using positron annihilation lifetime spectroscopy (PALS) suggested that the yellow liquids have fewer free-volume regions compared to the unsubstituted MS colourless liquid. Consistent with these findings, time-resolved fluorescence spectroscopy of the neat yellow liquids revealed a relatively longer lifetime of 20 ns, which is likely attributable to fluorescence from π-aggregates, distinct from the 0.5 ns shorter lifetime component observed for single molecules in diluted solutions. All of these results support the presence of π-aggregates, which contribute to the colour and fluorescence of the liquids. Supramolecular aggregates in liquids have been studied both experimentally and theoretically; however, the alkoxylated MS liquids represent the first example in which they significantly affect the optical properties of the liquids.

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• cc-by-3.0
  

キーワード: Solvent-free liquids, Inhomogeneous π-aggregates, Methyl salicylate, Fluorescence, Supercooled liquid state

刊行年月日: 2025-10-22

出版者: Royal Society of Chemistry (RSC)

掲載誌:

• Chemical Science (ISSN: 20416520) vol. 16 issue. 46 p. 21797-21805

研究助成金:

• Takahashi Industrial and Economic Research Foundation
• Ministry of Education, Culture, Sports, Science and Technology KAKENHI, Grant No. 25K0870, Category C
• National Institute for Materials Science 2024-49 (NIMS連携拠点推進制度)

原稿種別: 著者最終稿 (Accepted manuscript)

MDR DOI: https://doi.org/10.48505/nims.5931

公開URL: https://doi.org/10.1039/d5sc06148b

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更新時刻: 2025-11-28 08:30:07 +0900

MDRでの公開時刻: 2025-11-28 08:22:40 +0900