title: Photochromism of 2-(phenylazo)imidazoles.
abstract: The isomerization behaviors of 2-(phenylazo)imidazole (Pai-H) and 1-N-methyl-2-(phenylazo)imidazole (Pai-Me) have been investigated. The crystal structure of trans-Pai-Me was determined, revealing that key structures around the azo group are nearly identical among azobenzene, Pai-H, and Pai-Me. Pai-Me undergoes reversible cis/trans photoisomerization, whereas Pai-H responds poorly to irradiation. The quantum yields of trans-to-cis isomerization of Pai-Me on 454 and 355 nm excitation are 0.35 +/- 0.03 and 0.25 +/- 0.03, respectively, in toluene. The wavelength-dependent isomerization quantum yield is well-known for azobenzene, but these values are substantially higher than those of azobenzene. The activation energy of thermal cis-to-trans isomerization of Pai-Me in toluene is 79.0 +/- 3.5 kJ mol(-1), which is lower than that of azobenzene by 15 kJ mol(-1). The thermal cis-to-trans isomerization of Pai-H is even faster. Density functional theory calculations were performed, revealing that the energy gaps between the azo n-orbital and the highest pi-orbital of azoimidazoles are much narrower than that of azobenzene. Finally, a preliminary study suggested that metal ions can modulate the absorption spectrum of Pai-Me without a loss of the gross photochromic behavior.
authors.affiliation: College of Science and Technology, Nihon University, 1-8-14 Kanda Surugadai, Chiyoda-ku, Tokyo 101-8308, Japan. otsuki@ chem.cst.nihon-u.ac.jp
authors.forename: Joe
authors.initials: J
authors.lastname: Otsuki
authors.forename: Kazuya
authors.initials: K
authors.lastname: Suwa
authors.forename: Koichi
authors.initials: K
authors.lastname: Narutaki
authors.forename: Chittaranjan
authors.initials: C
authors.lastname: Sinha
authors.forename: Isao
authors.initials: I
authors.lastname: Yoshikawa
authors.forename: Koji
authors.initials: K
authors.lastname: Araki