The relationship between molecular conductance and molecular structure is an important issue in molecular electronics. Photochromic molecules can interconvert their molecular structures by light, so that the molecular conductance should be photocontrolled. According to this strategy the networks composed of photochromic diarylethene dithiols and gold nanoparticles were prepared, and the photochemical reactivity and photoswitching of the conductance were studied. The networks showed a completely reversible photoswitching of the conductance according to the photochromic reactions of the diarylethene units. The switching behavior is attributed to the change of the π-conjugation length of the molecule. Because of the high switching ratio and good reversibility this switching system opens up the possibility of sophisticated molecular electric circuits.

A unique photoinduced change in the molecular ordering of a photochromic diarylethene derivative having amide groups was investigated at the liquid/highly oriented pyrolytic graphite (HOPG) interface by scanning tunneling microscopy (STM). Ordering of the diarylethene was stabilized by the hydrogen-bonded network of amide groups. The open- and the closed isomers formed characteristic stripe-patterned orderings; a different hydrogen-bonding network was formed in each case. In situ UV irradiation resulted in the exclusive formation of a third molecular ordering γ that is composed of the photoirreversible annulated isomer. No photoisomerized molecule was detected in the 2-D orderings, i.e., the open-ring isomer in the ordering of the closed-ring isomer and vice versa, despite the similarity in their molecular structures.