Self-directed assembly of photoactive hybrid silicates derived from an azobenzene-bridged silsesquioxane.

Hybrid silicate materials derived from organo-bridged silsesquioxane precursors, RO3-Si-R'-Si-OR3, where R and R' are organic ligands, represent a remarkably diverse class of nanocomposites capable of forming both Si-O-Si and Si-C-Si bonds with molecular scale homogeneity. Recently, in an effort to better control their structure and function, surfactant-directed self-assembly or self-directed assembly has been used to synthesize hierarchical organo-bridged polysilsesquioxanes that exhibit order over multiple length scales. Here we report the synthesis and self-directed assembly of an optically active azobenzene-bridged silsesquioxane, 4,4'-bis(3-triethoxysilylpropylureido)azobenzene 1. Hydrogen-bonding interactions between the three active centers of the bis-ureide groups (-NH-CO-NH) combined with pi-pi interactions between the azobenzene groups serve to self-assemble 1 into a highly ordered lamellar mesostructure in which the d-spacing is optically controlled through photoisomerization of the azobenzene moiety before or after assembly.