title: Gold-colored organic crystals formed from an azobenzene derivative.
abstract: 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.
authors.affiliation: Department of Industrial Chemistry, Faculty of Engineering, Tokyo University of Science, Shinjuku, Tokyo, Japan.
authors.forename: Akiko
authors.initials: A
authors.lastname: Matsumoto
authors.forename: Maho
authors.initials: M
authors.lastname: Kawaharazuka
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Takahashi
authors.forename: Norio
authors.initials: N
authors.lastname: Yoshino
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kawai
authors.forename: Yukishige
authors.initials: Y
authors.lastname: Kondo
mesh_terms: D001391:Azo Compounds / Q000737:chemistry*; D003116:Color; D003460:Crystallization; D009930:Organic Chemicals / Q000138:chemical synthesis*; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared; D014961:X-Ray Diffraction
chemical_list: D001391:Azo Compounds; D009930:Organic Chemicals; C009850:azobenzene