Photochromic Rh(II) complexes based on 1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene

Reaction of [Rh2(O2CC(CH3)3)4] with cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene (cis-dbe) or closed-dbe in benzene and dichloromethane yielded three novel Rh(II) complexes. Their structures were characterized and photochromic properties were studied. X-ray crystallographic analyses revealed that the coordination environments of the three metal complexes are quite different. Complex 2 exhibits a 1-D infinite chain structure with two cyano groups of the ligand bridging two metal ions while in complexes 1 and 3 the metal ions have a direct interaction with at least one of the sulfur atoms of the two bisthienylethene molecules. Closed-dbe of complex 3 was transferred to the ring-open form in the crystalline phase upon photoexcitation with 529 nm light. It underwent a photocycloreversion reaction although the metal atom is coordinated to the thienyl group. The irreversible cyclization reaction was presumably attributed to the fixed rotation of thienyl rings, short RhS distance and steric hindrance of anions.

Graphical abstractThree novel dirhodium pivalate complexes with cis-dbe, trans-dbe and closed-dbe were synthesized and characterized. Complex 3, of which closed-dbe bridges two different dirhodium pivalate moieties through one cyano and one thienyl group, was transferred to the ring-open isomer when excited with 529 nm light in the crystalline phase.Figure optionsDownload full-size imageDownload as PowerPoint slide