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

Reaction of [Rh-2(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 Rh-S distance and steric hindrance of anions. (C) 2006 Elsevier Ltd. All rights reserved.