Photochromism of 1,2-Bis(2-methyl-6-nitro-1-benzothiophen-3-yl)perfluorocyclopentene in a Single-Crystalline Phase: Dichroism of the Closed-Ring Form Isomer

1,2-Bis(2-methyl-6-nitro-1-benzothiophen-3-yl)perfluorocyclopentene was found to undergo a
reversible photochromic reaction in the single-crystalline phase. Upon irradiation with 366-nm light, the single
crystal turned green with keeping the crystal shape. The colored crystal showed dichroism. When the crystal
was rotated under polarized light, the color changed from yellow to blue. The yellow and blue colors were
attributed to two perpendicular electronic transitions at 465 and 600 nm of the closed-ring form. The two
transition moments coincide with the directions of short and long axes of the closed-ring form isomers, which
were regularly packed in the crystal lattice.