Three-arm star compounds composed of 1,3,5-tri(azobenzeneethynyl)benzene cores and flexible PEO arms: synthesis, optical functions, hybrid Ormosil gel glasses

A three-arm star rod-coil block conjugated compound composed of 1,3,5-tri(azobenzeneethynyl)benzene core and flexible poly(ethylene oxide) arms was synthesized. For comparison, two others with the same core but different end groups were also prepared. The compounds show thermotropic discotic liquid crystalline phase behavior and properties of optical limiting and photo-induced trans–cis isomerization. The star-shaped compound with poly(ethylene oxide) arms can be homogeneously dispersed into Ormosil gel glass monoliths up to 12 wt% without any compatibilizer. The glasses are mechanically stable and highly transparent in the visible and near IR region. The nonlinear optical and optical limiting properties of the gel glasses are comparable or superior to those of the corresponding solutions. The photochromic property of the azobenzene units can be maintained in the gel glass state.