Effect of metal cation on photoisomerization of azobenzenes in zeolite nanocavities

In the photostationary state, the cis/trans isomer ratio of azobenzene and 3,3′-dimethylazobenzene adsorbed in zeolite NaY increases significantly to ca. 90:10, in contrast to the reaction in cyclohexane. However, for azobenzene-4,4′-dicarboxylic acid diethyl ester the formation of the cis isomer is remarkably suppressed to ca. 30%. On the basis of ab initio MO calculations, it is suggested that electrostatic interaction between these azobenzenes and the metal ions in zeolite nanocavities regulates the cis-trans photoisomerization process. In addition, it is found that the photoisomerization behavior of azobenzenes adsorbed on silica gel is similar to that in NaY.