Isomerization behavior of diarylethene-type photochromic compounds under X-ray irradiation: application to dosimetry

We fabricated poly(methyl methacrylate)-based films containing 1,2-bis[2-methylbenzo[b]thiophen-3-yl]-3,3,4,4,5,5-hexafluoro-1-cyclopentene (BMTH) and investigated its isomerization behavior under X-ray irradiation. The visible-light absorbance at 529 nm increased with UV irradiation; that around 400-550 nm, with X-ray irradiation. This indicates that BMTH undergoes a photochromic reaction. In addition, the irreversible increase of absorbance in 400-500 nm was observed only for X-ray irradiation. This result indicates that BMTH undergoes another reaction in addition to isomerization. The change in absorbance at 529 nm increased with the concentration of 2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole (b-PBD), and the absorption peak at 529 nm became more prominent. These results suggest that b-PBD enhanced the sensitivity to X-rays via the isomerization reaction caused by excitation energy transfer from b-PBD. The linearity of the change in the optical absorbance suggests that this material has applicability to radiation dosimeters in the range 0-30 kGy.