Gold-colored organic crystals formed from an azobenzene derivative

Akiko Matsumoto, Maho Kawaharazuka, Yutaka Takahashi, Norio Yoshino, Takeshi Kawai, Yukishige Kondo

Research output: Contribution to journalArticlepeer-review

17 Citations (Scopus)


The azobenzene derivative 4,4′-bis{1-[2-(N,N-dimethylamino)]ethoxy}azobenzene has been found to form gold-colored plate-like crystals. The thin film obtained by accumulating the crystals has a maximum specular reflectance of ca. 15% for visible light. To investigate the structure of the gold-colored crystals, UV-vis, X-ray diffraction (XRD), and IR analyses were performed. UV-vis measurements show that the molecules in the crystal produce J-aggregates. Furthermore, XRD measurements estimated the long-range d-spacing for the crystal as 1.51 nm. These results indicate that the azobenzene moieties are oriented diagonally against the crystal surfaces. When the crystals are placed in a desiccator (humidity 40%) for 1 d, their color changes from gold to yellow. IR measurements show that the gold-colored crystals contain crystallized water, while there are no water molecules in the yellow crystals, in which the structure of the J-aggregates is disrupted. These results show that the crystallized water molecules are essential for the formation of the J-aggregates and the resultant gold luster.

Original languageEnglish
Pages (from-to)151-156
Number of pages6
JournalJournal of oleo science
Issue number3
Publication statusPublished - 2010 Feb 3
Externally publishedYes


  • Azobenzene
  • Gold crystal
  • J-aggregate
  • Thin film

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)


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