Photochromism of a diarylethene dimer

A fluorene derivative having two diarylethene units at the 9,9'-positions was synthesized, and the photochromic behavior was examined in solution. Upon irradiation with UV (240nm), the solution of the diarylethene dimer turned yellow. It can returned to ring-open form upon irradiation with visible light (405nm). Two diarylethene chromophores are connected to the fluorene without π-conjugation between them in the dimer. Its synthesis can be performed on a large scale from cheap commercial products and no expensive drugs were concerned in the synthetic route.