Crystallographic, spectroscopic, and computational characterization of a diiodonaphthoquinone diarylethene photochrome: halogen bonding and photocrystallography

We report the synthesis and characterization of 2,3-bis(5-iodo-2-methylthiophen-3-yl)naphthalene-1,4-dione and its ring-closed isomer. The ring-closed isomer crystallizes in the space group P2₁ with unit cell parameters of a = 11.93119(10), b = 7.4644(6), c = 12.4586(10), β = 117.024(2)°. Photoisomerization in solution is reversible and similar to that of other quinone based diarylethenes. The crystal structure of the ring-closed isomer consists of halogen bonded 2-D sheets. Upon irradiation, single crystals of the ring-closed isomer fracture along well-defined cleavage planes parallel to the sheet layers. Subsequent X-ray diffraction measurements revealed that the light-induced fracturing is due to the formation of the ring-open isomer.