Probing local structure of glass with orientation-dependent luminescence

• Published in: Physical chemistry chemical physics : PCCP Vol. 25; no. 41; pp. 28113 - 28118
• Main Authors: Tokoro, Yuichiro, Nakagawa, Tetsuya, Yamamoto, Shin-ichi, Koizumi, Toshio, Oyama, Toshiyuki
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 25.10.2023
• Subjects: Crystal growth; Dichloromethane; Ethanol; Glass; Glass formation; Glass transition; Hexanes; Melting points; Orientation; Photoluminescence; Spectra
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d3cp03565d

The local ordering of particles is considered an important process in glass transition. Ordering is usually observed in simulation and micrometer-sized colloid. However, clear information on local ordering at the molecular level is difficult to obtain experimentally. In this study, we prepared an easily glass-forming fluorophore with a color change owing to the intermolecular arrangement in the liquid, glass, and crystal states. The bathochromic shifts of the photoluminescence spectra indicated a change in the intermolecular orientation upon immediate cooling of the melt. The recovery of the spectra by successive heating indicated that rotation contributed to the change in the intermolecular orientation. The orientation in the glass was distinct from that during crystal growth, which was observed as a slow bathochromic shift by maintaining the temperature between the melting points of the blue- and green-luminescent crystals obtained from dichloromethane/ethanol and dichloromethane/hexane, respectively. Our results demonstrate that the anisotropic interaction between glass-forming luminophores is useful for uncovering molecular-level events in the glassy state. A rigid glass-former revealed local structures of glass and super-cooled liquid by luminescence related to globally and locally stabilized packing.