Refractive index changes in photochromic diarylethene derivatives in polymethylmethacrylate films

Abstract

We investigated photochromism and the refractive index change Δn in polymethylmethacrylate (PMMA) films made using 16 compounds of 1,2-diarylethene derivatives. The derivatives were classified as maleic anhydride or hexafluorocyclopentene diarylethene in type according to their structure. In PMMA films, the photochromic reactivity of maleic anhydride diarylethene derivatives strongly depends on their substituent structure. On the contrary, the photochromism of hexafluorocyclopentene diarylethene derivatives is observed in PMMA films regardless of their substituent. We found that Δn increased in proportion to the absorbance charge increase. Moreover, both Δn and ΔA were also proportional to the concentrations of the photochromic compounds. We believe that both Δn and ΔA are related to changes in the molecular structure of 1,2-diarylethene derivatives. We fabricated one transparent PMMA film of each type. Each film contained a high concentration of dispersed diarylethene derivatives. The changes in refractive index and absorbance of the maleic anhydride diarylethene type saturated at more than 15 wt.%. However, the changes in the hexafluorocyclopentene diarylethene type with a long alkyl chain were in proportion to the concentrations of the compound, and we obtained the largest refractive index change (0.0018) yet reported for 1,2-diarylethene derivatives in transparent PMMA films.