title: Photoinduced formation of an azobenzene-based CD-active supramolecular cyclic dimer.
abstract: A series of new photo-responsive amino acid-derived azobenzenedicarboxylic acid derivatives (S)-1 a-e were synthesized. Compound (S)-1 a in the trans form exhibited no circular dichroism (CD) signal in DMF under ambient conditions, whereas intense Cotton effects were observed upon UV irradiation, indicating the formation of a chiral supramolecular structure in the cis form. The CD signals disappeared when trifluoroacetic acid (TFA) was added to the solution. The ester counterpart [(S)-1 a'] showed no CD signal. Hydrogen bonding between the carboxy groups seemed necessary for constructing the supramolecular structure. The kinetic studies of cis to trans isomerization of (S)-1 a demonstrated that the formation of a chiral supramolecule enhances the stability of the cis-azobenzene structure. The ESI mass spectrum of stilbenedicarboxylic acid (S)-4, an analogue of (S)-1 b, confirmed the formation of a dimer. A theoretical CD study revealed that (S)-1 a in the cis form should be present as a cyclic chiral dimer.
authors.affiliation: Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura Campus, Nishikyo-ku, Kyoto 615-8510 (Japan); Present Address: Department of Organic and Polymeric Materials, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo 152-8552 (Japan).
authors.forename: Hiromitsu
authors.initials: H
authors.lastname: Sogawa
authors.forename: Kayo
authors.initials: K
authors.lastname: Terada
authors.forename: Yu
authors.initials: Y
authors.lastname: Miyagi
authors.forename: Masashi
authors.initials: M
authors.lastname: Shiotsuki
authors.forename: Yoshihito
authors.initials: Y
authors.lastname: Inai
authors.forename: Toshio
authors.initials: T
authors.lastname: Masuda
authors.forename: Fumio
authors.initials: F
authors.lastname: Sanda
keywords: UV/Vis spectroscopy; amino acids; hydrogen bonding; photoresponsiveness; supramolecular chemistry