A photoresponsive azobenzene-bridged cubic silsesquioxane network

An azobenzene (AZO)-bridged cubic silsesquioxane network exhibiting reversible photoisomerization behavior in nonpolar solvents has been prepared via hydrosilylation reaction between 4,4′-diallyloxy-azobenzene and octahydridosilsesquioxane (H₈Si₈O₁₂; H-POSS). Approximately 70 % of the corner Si–H groups of H-POSS are reacted to form a three-dimensional gel network while maintaining the cubic siloxane structure. The dried gel has a high thermal stability, which is attributed to the highly cross-linked cubic silsesquioxane network where AZOs are covalently incorporated in the main chain. The gel exhibits reversible swelling behavior in nonpolar solvents during wetting–drying cycles. In toluene, a large extent of reversible trans–cis isomerization of the AZO moiety is observed. These results are promising for the design of a new class of photoresponsive materials applicable in host–guest chemistry.