Synthesis and photoisomerization of optically active 1,4-polyketones substituted by azobenzene side chains

Photoresponsive gamma-polyketones substituted by azobenzene side chains were synthesized via asymmetric alternating copolymerization of the corresponding alpha-olefins in the presence of the Pd-(R,S)-BINAPHOS complex. C-13 NMR of the polyketone having a tetramethylene spacer between the backbone and the azobenzene moiety disclosed that both ketone and spiroketal units existed in chloroform and that the spiroketal unit was transformed back to a ketone unit upon dissolution in 1,1,1,3,3,3-hexafluoro-2-propanol. Conformation of the polymer containing only ketone units was not affected by trans-cis photoisomerization of the side-chain azo chromophore, whereas the corresponding ketone/spiroketal polymer drastically changed its main-chain conformation upon trans-to-cis photoisomerization, as evidenced by increase of CD intensity by 70% at a carbonyl region.