Establishment of a molecular design to obtain visible-light-activated azoxy polymer actuators

The development of visible-light-activated photoswitches has significantly progressed in the past few decades. Herein, two kinds of photoresponsive azoxy polymers were prepared directly from bis-/trinitro-functionalized monomers via an efficient small molecular synthetic method with ultraviolet/visible light irradiation under metal-free and mild conditions. This strategy avoids the use of metal complexes and toxic compounds, while proceeding with high yields (up to 97%) and excellent selectivity without generating azo, amine, or inorganic compounds. Moreover, polymerization showed an efficient process with very high monomer conversion and perfect selectivity. The obtained main-chain linear and hyperbranched azoxy polymers were characterized by 1H NMR, GPC, UV-vis and FT-IR spectra. The π–π* absorptions of the obtained polymers in the UV-vis spectra showed a significant red-shift to the visible light region. Therefore, the photoisomerization of the prepared polymers can be driven by visible light, representing the first visible-light-driven aromatic azoxy polymer actuators.