Complexation of 4-dimethylaminoazobenzene with various kinds of cyclodextrins: Effects of cyclodextrins on the thermal cis-to-trans isomerization

On the basis of the change in electronic and induced circular dichroism spectra for complex formation the complexation of 4-dimethylaminoazobenzene (DAAB) with four kinds of cyclodextrins (α- and β-cyclodextrin (CD), heptakis(2,6-di-O-methyl)-β-cyclodextrin, and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin) was studied in methanol-water and dimethyl sulfoxide-water mixtures. It was found that the trans and cis isomers of DAAB form two different types of complex (inclusion and lid type) with CDs. depending on the kinds of CDs and solvents. Further, we have examined the effect of CDs on the thermal cis-to-trans isomerization of DAAB. The accelerated or decelerated effect on the thermal isomerization was observed upon adding CDs. The effects of CDs on the thermal isomerization are discussed in connection with the complexation of the cis-isomer of DAAB with CDs.