Photoresponsive Hybrid Materials:
Synthesis and Characterization
of Coumarin-Dimer-Bridged Polysilsesquioxanes
Chem. Mater. 2008, 20, 1870—1876
The syn-ht photodimer of 7-allyloxycoumarin was elaborated to the bis(triethoxysilyl) derivative. Sol–gel polymerization produced a robust hybrid glass (see equation below) that was cast as transparent colorless thin films. Photopatterning with UV light (254 nm) produces fluorescent and refractive index patterns which are revealed by fluorescence microscopy (λex ) 330 nm, (λem ) 392 nm and imaging ellipsometry. At short irradiation times the photoinduced cleavage produces a slight collapse of the silsesquioxane network (∼3%) that is attributed to rupture of the coumarin photodimer cross-links. This material provides a new robust matrix for producing “hidden” fluorescent images, refractive index gratings, and topographical features in dense, hybrid glassy materials. Prolonged irradiation at short wavelengths results in a hard to soft transformation that deforms and “melts” the hard brittle thermoset.
Changes in absorption (a and b) and appearance of fluorescence emission (c and d, λex = 351 nm) in 100 nm thin films before (a, c) and after (b, d) irradiation with <300 nm light for 3 min at room temperature.
A fluorescent anteater photo patterned by irradiation of photoresponsive hybrid films.
Refractive index pattern generated by lithographic patterning of hybrid film and imaged by ellipsometry