Gold(I)-Coordination Triggered Multistep and Multiple Photochromic Reactions in Multi-Dithienylethene (DTE) Systems

The preparation, characterization, and photochromic properties of a mononuclear gold­(I) complex (<b>1oo</b>) with two identical DTE-acetylides and a dinuclear gold­(I) complex (<b>2ooo</b>) with both DTE-acetylide and DTE-diphosphine are described. Both gold­(I) complexes exhibit multistep and multiple photocyclization/cycloreversion reactions. Particularly, four-state and four-color photochromic switch is successfully achieved for the dinuclear gold­(I) complex upon irradiation with appropriate wavelengths of light. In contrast, fully ring-closed form is unattained through multiple photocyclization for the two corresponding model organic compounds coupling with the same DTE units as gold­(I) complexes but without gold­(I)-participation. It is demonstrated that coordination of gold­(I) ion to DTE-acetylides exerts indeed a crucial role in achieving stepwise and selective photocyclization and cycloreversion reactions for both gold­(I) complexes, in which the coordinated gold­(I) atom acts as an effective “barrier” to prohibit intramolecular energy transfer between multi-DTE moieties