REFRACTIVE-INDEX CHANGES IN PHOTOCHROMIC DIARYLETHENE DERIVATIVES IN POLYMETHYLMETHACRYLATE FILMS

We investigated photochromism and the refractive index change Delta n in polymethylmethacrylate (PMMA) films made using 16 compounds of 1,2- diarylethene derivatives. The derivatives were classified as maleic an hydride or hexafluorocyclopentene diarylethene in type according to th eir structure. In PMMA films, the photochromic reactivity of maleic an hydride diarylethene derivatives strongly depends on their substituent structure. On the contrary, the photochromism of hexafluorocyclopente ne diarylethene derivatives is observed in PMMA films regardless of th eir substituent. We found that hn increased in proportion to the absor bance charge increase. Moreover, both Delta n and Delta A were also pr oportional to the concentrations of the photochromic compounds. We bel ieve that both Delta n and Delta A are related to changes in the molec ular structure of 1,2-diarylethene derivatives. We fabricated one tran sparent PMMA film of each type. Each film contained a high concentrati on of dispersed diarylethene derivatives. The changes in refractive in dex and absorbance of the maleic anhydride diarylethene type saturated at more than 15 wt.%. However, the changes in the hexafluorocyclopent ene diarylethene type with a long alkyl chain were in proportion to th e concentrations of the compound, and we obtained the largest refracti ve index change (0.0018) yet reported for 1,2-diarylethene derivatives in transparent PMMA films.