　　Three dithienylethene derivatives having anthracene substituents 1a, 2a and 3a were prepared, and their photochromic reactivity was examined in solution as well as in the single-crystalline phase. Although 1, 2 and 3 undergo similar photochromism in cyclohexane solution, photochromic reactivity of 1a, 2a and 3a are different in the single-crystalline phase. Single crystals of 1a and 2a did not show any color change upon UV irradiation, while 3a single crystal turned blue. Only 3a single crystal exhibits the photochromic reactivity. X-Ray crystallographic analysis and DFT calculation revealed that conformation of the anthracene substituents plays an important role in the crystalline photochromism.