Single-Crystalline Photochromism of a Diarylethene Dimer

Abstract A fluorene derivative having two diarylethene units at the 9,9′-positions was synthesized, and the photochromic behavior was examined in a single-crystalline phase as well as in solution. Upon irradiation with ultraviolet light (λ = 313 nm), a hexane solution of the diarylethene dimer (1a) turned blue. The blue solution was found to contain the one closed-ring form dimer (1b) and the two closed-ring form dimer (1c). Both 1b and 1c returned to 1a upon irradiation with visible light (λ > 500 nm). The photocyclization quantum yields of 1a to 1b and 1b to 1c were determined to be 0.46 and 0.29, respectively. The photocycloreversion quantum yields of 1c to 1b and 1b to 1a were 5.8 × 10−3. The single crystal of the dimer exhibited photochromism. The diarylethene chromophores were aligned almost perpendicular to each other in the crystal, and one of the units in the dimer could be selectively isomerized by irradiation with linearly polarized light.