Photochromic cyclization reaction efficiency and fluorescence of colloidal solutions, amorphous films, and polymer cast films of two dithienylethenes were studied. Photochromic cyclization reaction efficiency of colloidal solution of cis-1,2-dicyano-1,2-dithienylethene (1) was as high as that of hexane solution of 1. Amorphous films of 1 also showed high efficiency. On the other hand, neither colloidal solution nor polycrystal of 2,3-bis(2,4,5-trimethyl-3-thienyl)maleic anhydride (2) was photochromic; only amorphous films of 2 were colored very slightly by UV irradiation. While photochromic cyclization reaction efficiency of 1 depends little on the kind of polymer matrix, that of 2 depends significantly on the Tg (glass transition temperature) and polarity of polymer matrix, Long-wavelength fluorescence which can be assigned to the colored closed-ring form was observed for 1 in the solid states, though deeply colored hexane solution did nor give any long-wavelength fluorescence.