On irradiation with UV light, the photochromic dimer of 1,4-bis(imidazolyl)tetrafluorobenzene produced the colored transient species in solution and solid. Though the dimerization reaction to form the photochromic dimer prevents the isolation and characterization of the colored species at room temperature, the single crystals of the colored species could be successfully obtained from the light-irradiated toluene solution of the dimer at 200K, and the molecular structure of the colored species is unambiguously determined by the X-ray diffraction analysis.