A class of diarylethenes with a imidazole bridge unit has been synthesized and shows photochromic properties with UV/vis light irradiation. It is found that electronic properties of substituent in the imidazole bridge unit have a great effect on both photochromism and fluorescence of diarylethenes because of intramolecular charge transfer. Both "turn-on" and "turn-off" fluorescent diarylethenes systems can be achieved by simple modification of molecular structure and electronic properties of substituent, which provides a strategy for the design of new fluorescent diarylethene systems to be used as switches.