Trans–cis isomerization of arylether dendrimers with azobenzene core and terminal hydroxy groups

Abstract

Azobenzene-cored arylether dendrimers 2a–2c with polar hydroxy groups at the periphery have been prepared from hydroboration–oxidation reaction of azobenzene-cored arylether dendrimers 1a–1c with nonpolar vinyl groups at the periphery. Trans → cis photoisomerization of central azo group has been investigated by UV–vis spectral changes after photolysis. The results show that dendrimers 1a–1c and 2a–2c in methanol/dichloromethane (1/1, v/v) have carried out trans–cis isomerization. Reaction rate for trans → cis photoisomerization of 2a–2c with polar hydroxy groups increases with increasing generation upon irradiation of 350 nm. On the other hand, the reaction rate of cis → trans thermal back isomerization for 2a–2c decreases with increasing the generation. This result is somewhat different from that for 1a–1c with nonpolar vinyl groups. Both the reaction rates of trans → cis photoisomerization and cis → trans thermal back isomerization for 1a–1c decrease in higher generation.