title: Photoresponsive change of oxygen-binding affinity of a cobalt schiff-base complex with an axially coordinating stilbazole residue of a copolymer.
abstract: The reversible binding reaction of oxygen to N,N'-ethylene bis(salicylideneiminato) cobalt(II) (CoS), to which a photoisomerizable stilbazole residue of copolymer 1 coordinated, was investigated. The E form of the stilbazole residues coordinating to CoS, (E)-1-CoS, showed photoisomerization into the Z form, (Z)-1-CoS, on direct ultraviolet irradiation and negligible reverse isomerization. The oxygen-binding equilibrium constant (K) values for (E)-1-CoS and (Z)-1-CoS in toluene were 3.3 x 10(-2) mmHg-1 and 4.8 x 10(-3) mmHg(-1), respectively, at 10 degrees C. Although the pK(a) values of the E and Z forms of the stilbazole residue were similar, the oxygen-binding affinity of (Z)-1-CoS was small in terms of the linear correlation of the logarithm of K (ln K) versus the pK(a). Steric hindrance of the polymer chain of 1 on the coordination of the stilbazole residue of (Z)-1 to CoS was thought to cause the small K. A photoresponsive change of apparent oxygen-binding affinity of 1-CoS along with the E/Z isomerization of the stilbazole residues was observed. The ratio of (Z)-1-CoS converted from (E)-1-CoS by the ultraviolet irradiation could be estimated from analysis of absorption spectra for the oxygen binding of a resulting mixture of (E)-1-CoS and (Z)-1-CoS.
authors.affiliation: Tokyo Denki University, Department of Green and Sustainable Chemistry, 2-2 Nishiki-cho Kanda, Chiyoda-ku, Tokyo 101-8457, Japan. suzutaka@cck.dendai.ac.jp
authors.forename: Takayuki
authors.initials: T
authors.lastname: Suzuki
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Suzuki
authors.forename: Norihisa
authors.initials: N
authors.lastname: Oda
authors.forename: Jun
authors.initials: J
authors.lastname: Ohkubo
authors.forename: Hiraku
authors.initials: H
authors.lastname: Shinozaki