title: Photon-, electron-, and proton-induced isomerization behavior of ferrocenylazobenzenes.
abstract: 3-, 4-, and 2-ferrocenylazobenzenes, 1, 2, and 3, respectively, and several derivatives of 1 were synthesized, and their photoisomerization behaviors were examined. The molecular structures of 1 and its derivatives, 2-chloro-5-ferrocenylazobenzene (5) and 3-ferrocenyl-4'-hydroxylazobenzene (11), were determined by X-ray diffraction analysis. 3-Ferrocenyl compound 1 undergoes reversible trans-to-cis isomerization with a single green light source and the Fe(III)/Fe(II) redox change. 4- and 2-Ferrocenyl compounds, 2 and 3, also respond to green light in addition to UV light, exciting the pi-pi* transition, but the cis molar ratio in the photostationary state (PSS) is lower than that of 1. The response to green light in 2 and 3 is caused by the MLCT (from Fe d orbital to azo pi* orbital) band excitation, while the character of the MLCT band, as estimated by time-dependent density functional theory calculations, differs between 1 and 2. The oxidized form of 2 undergoes facile cis-to-trans thermal isomerization. Both 1 and 2 undergo facile protonation and show proton-catalyzed cis-to-trans isomerization. Among the derivatives of 1, 2-chloro-5-ferrocenylazobenzene (5) exhibits the highest cis molar ratio (47%) in the PSS of green light irradiation.
authors.affiliation: Department of Chemistry, School of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Aiko
authors.initials: A
authors.lastname: Sakamoto
authors.forename: Akira
authors.initials: A
authors.lastname: Hirooka
authors.forename: Kosuke
authors.initials: K
authors.lastname: Namiki
authors.forename: Masato
authors.initials: M
authors.lastname: Kurihara
authors.forename: Masaki
authors.initials: M
authors.lastname: Murata
authors.forename: Manabu
authors.initials: M
authors.lastname: Sugimoto
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nishihara
mesh_terms: D001391:Azo Compounds / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004583:Electrons; D005296:Ferrous Compounds / Q000737:chemistry*; D007536:Isomerism; D008958:Models, Molecular; D015394:Molecular Structure; D010084:Oxidation-Reduction; D017785:Photons; D011522:Protons; D013053:Spectrophotometry
chemical_list: D001391:Azo Compounds; D005296:Ferrous Compounds; D011522:Protons; C009850:azobenzene