Polymer modified sol-gel materials for photochromic applications

The chromophoric materials were prepared by copolymerization of various methacrylic monomers. The incorporation of the chromophore groups was done by coupling reaction of diazonium salts of the sulfonamide such as: sulfomethazine or sulfisomidine). The copolymers having free OH groups were able to react with 3-triethoxypropyl isocyanate forming intermediates used to prepare hybrid transparent films by sol-gel technique. The films of both copolymers as well as of hybrid sol-gel structures showed photochromic properties via trans-cis isomerization of the diazo groups. The absorption maximum of the trans form was ca. 435-445 nm depending on chemical composition of the material. Illumination of the films with coherent laser beams (two-beam coupling) resulted in formation of diffraction grating. The diffraction efficiency reached 4-5 % and refractive index modulation was in the range up to 0.0032.