A series of diaryl acenaphthylenes has been synthesized, and their photochromic properties are studied both in solution and in the crystalline state. 2,4-Dimethyl-5-phenylthiophene derivative 1a showed no photochromic reaction, while 2-methyl-5-phenylthiophene derivative 2a and 5-methyl-2-phenylthiazol derivative 3a showed reversible photochromism in solution. Fluorescence spectrum of compound 3a changed