Refractive index modulation in polymeric photochromic films

Photochromic properties of methylacrylate monomers and polymers containing azobenzene groups with heterocyclic sulfonamide functionalities viz sulfisomidyne (4-amino-N-[2,6-dimethylpyrimidyn-4-yl]benzenesulfonamide) and sulfamethoxazole (4-amino-N-[5-methylisoxazol-3-yl]benzenesulfonamide) substituents were investigated. On illumination with light the azobenzene group underwent trans-cis isomerisation, which was manifested by a drop in the absorbance of the maximum absorption peak at ca. 450 nm and by decrease in refractive index. Quantum chemical calculations showed significant differences in UV-VIS spectra, dipole moments, polarizability and refractive index between both cis and trans form of the chromophoric monomers. The illumination of spin-coated polymer films during ellipsometry measurements resulted in a change in refractive index within the range of 0.014 to 0.025. The dynamics of growth and decay of refractive index changes, was described by biexponential functions approach.