Photochemical transformations of chromophoric methacrylates under the influence of light and laser radiation

Methacrylate type polymers of 2-methyl-2-[4-({4-[(5-methylisoxazol-3-yl-amino)sulfonyl]phenyl}diazenyl)phenylamino]ethyl methacrylate (PMMI), 2-n-butyl-2-[4-({4-[(5-methylisoxazol-3-ylamino)sulfonyl]phenyl}diazenyl)phenylamino]ethyl methacrylate (PMBI) and 2-n-butyl-2-[4-({4-[(1,3-thiazol-2-ylamino)sulfonyl]phenyl}diazenyl)phenylamino]ethyl methacrylate (PMBT) were obtained. The polymers were deposited as thin films onto glass plates either by the Langmuir–Blodgett technique or by spin coating. On illumination with both unpolarized and linearly polarized light trans–cis isomerisation of the azobenzene group took place as evidenced by a drop of the absorbance of the maximum absorption peak at ca. 450 nm. The samples illuminated with p-polarized light showed essentially no drop of absorbance when observed in an s-polarized UV-VIS spectrophotometer beam. Degenerate four wave mixing experiments carried out with two 512 nm writing beams and a 632 nm probe beam showed formation of a diffracted beam with 4 and 7% efficiency for PMBI and PMMI, respectively; both were methylisoxazole derivatives with methyl and butyl groups, respectively, at the tertiary nitrogen atom. Refractive index modulation of the PMMI film was equal to 0.004. The illumination of the samples in ellipsometric measurements resulted in a change in the refractive index of the films in the range of 0.012 due to trans–cis isomerisation.