Download file (1000 KB)
Download as zip (954 KB)

Collection

Citation

Description:

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.

Rights:

• cc-by-3.0
  

Keyword: Solvent-free liquids, Inhomogeneous π-aggregates, Methyl salicylate, Fluorescence, Supercooled liquid state

Date published: 2025-10-22

Publisher: Royal Society of Chemistry (RSC)

Journal:

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

Funding:

• 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)

Manuscript type: Author's version (Accepted manuscript)

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

First published URL: https://doi.org/10.1039/d5sc06148b

Related item:

Other identifier(s):

Contact agent:

Updated at: 2025-11-28 08:30:07 +0900

Published on MDR: 2025-11-28 08:22:40 +0900