Synthesis and Light-Mediated Structural Disruption of an Azobenzene-Containing Helical Poly(isocyanide)

Helical poly(isocyanide)s are an important class of synthetic polymers possessing a static helical structure. Since their initial discovery, numerous examples of these helices have been fabricated. In this contribution, the synthesis of a chiral, azobenzene (azo)-containing isocyanide monomer is reported. Upon polymerization with nickel(II) catalysts, a well-defined circular dichroism (CD) trace is obtained, corresponding to the formation of a right-handed polymeric helix. The helical polymer, dissolved in chloroform and irradiated with UV light (365 nm), undergoes a cis to trans isomerization of the azobenzene side-chains. After the isomerization, a change in conformation of the helix occurs, as evidenced by CD spectroscopy. When the solution is irradiated with LED light, the polymer returns to a right-handed helical conformation. To open up the possibility for chain-end post-polymerization modification of this light-responsive system, an alkyne-functionalized nickel(II) catalyst is also used in the polymerization of the azobenzene monomer, resulting in a stimuli-responsive, terminal-alkyne-containing helical poly(isocyanide).