A diarylethene-pyrene diad and a diarylethene-pyrene-diarylethene triad were synthesized to investigate the photoinduced two-dimensional ordering change at a solution-HOPG interface. The molecular arrangements were detected by STM. The different photochromic isomers showed different orderings reflecting the differences in their molecular structures. For the diarylethene-pyrene-diarylethene triad, a new ordering appeared upon irradiation with UV light and returned to the original ordering upon subsequent irradiation with visible light. The new arrangement was assigned to the ordering of the closed-closed isomers based on the images of the isolated open- and closed-isomers. The relationship between the nature of the two-dimensional ordering and the molecular structure is discussed.
