Synthesis of mono-dispersed spherical silica particles containing covalently bonded chromophores

Organic-inorganic ultraviolet (UV) active hybrid materials have been prepared by a sol-gel process from benzophenone derivatives and tetraethylorthosilicate. The silica particles are spherical in shape and have a narrow size distribution which remains unchanged up to organic chromophore concentrations of 0.2 mmol g(-1). At higher concentrations the spheres become less regular and fuse. A dependence of the material absorption properties on the particle size (at the same organic chromophore concentration) and on the concentration of surface grafted chromophores was noted. The most effective UV filter materials were found in a combination of silica incorporated chromophores and surface grafted chromophores at an overall low chromophore concentration. A comparison of the photostability of chromophores at standardized UV irradiation revealed an increase in stability for silica incorporated and surface immobilized benzophenone compared to benzophenone in a homogeneous solution.