Photobleaching of γ-Glycidoxypropyltrimethoxysilane-Chelated metal alkoxide gel film

Abstract

γ-glycidoxypropyltrimethoxysilane (GPTS) is a useful precursor for sol-gel preparation of inorganic-organic hybrid materials. The silica network is formed by hydrolysis and condensation of a methoxy radical in the presence of water and poly(ethylene oxide) polymeric network is made by polymerization of epoxy ring with an addition of polymerization initiator. Crack free thick films of the silica PEO hybrid materials can be made due to flexibility of polymer in silica network. On the other hand, metal alkoxides are very reactive to hydrolysis and condensation. Thus, the chemical modification of metal alkoxides with organic additives such as β-diketones and β-ketoesters is known to be very effective method to control the reactivity of metal alkoxides and final properties of gels. These chemically modified metal alkoxides present optical absorption band in the UV-region due to the photoexcited π-$π_*$ transition state of 6-membered chelate ring. A number of photochemical studies involving β-diketonated metal complexes have shown that a photon dissociates the chelate bond by excitation of π-$π_*$ transition and reduces their solubility in organic solvents or acid aqueous solutions due to the structural changes associated with the photodecomposition of chelate rings. Thus, the direct photoinscription of inorganic sol-gel materials is possible via the photochemical feature of β-diketone in sol-gel matrix. This method has been used to fabricate micropatterning, gratings, and planar waveguides. The chelated metal complex can be incorporated with inorganic-organic hybrid materials to fabricate micropatterning of thick hybrid gel films. In this study, we investigate the photochemical properties of gel films fabricated using GPTS as a precursor for hybrid materials and chelated metal alkoxides, $Ti(OEt)_4$, $Al(OBu^sec)_3$, $Zr(OPr^n)_4$, as a refractive index modifier as well as photobleaching agent. GPTS with various metal - Ti, Zr, Al, chelated with β-diketone (BzAc) or...