Imidazo[4,5-f]-1,10-phenanthrolines: Versatile Ligands for the Design of Metallomesogens

• Published in: Chemistry of materials 2008-02, Vol.20 (4), p.1278-1291
• Main Authors: Cardinaels, Thomas, Ramaekers, Jan, Nockemann, Peter, Driesen, Kris, Van Hecke, Kristof, Van Meervelt, Luc, Lei, Shengbin, De Feyter, Steven, Guillon, Daniel, Donnio, Bertrand, Binnemans, Koen
• Format: Article
• Language: English
• Subjects: Liquid Crystals; Self-Assembly and Self-Assembled Materials
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/cm070637i

2-Aryl-substituted imidazo[4,5-f]-1,10-phenanthrolines were used as building blocks for metal-containing liquid crystals (metallomesogens). Imidazo[4,5-f]-1,10-phenanthrolines are versatile ligands because they can form stable complexes with various d-block transition metals, including platinum(II) and rhenium(I), as well as with lanthanide(III) and uranyl ions and they can easily be structurally modified by a judicious choice of benzaldehyde precursor. None of the ligands designed for this study were liquid-crystalline. However, mesomorphism could be induced by their coordination to various metallic fragments. The thermal behavior of the metal complexes depended on the metal-to-ligand ratio and the substitution pattern of the coordinating ligands. Complexes with a metal-to-ligand ratio of 1:1 [ML, with M = Pt(II), Re(I)] were not liquid-crystalline. The lanthanide(III) complexes with a metal-to-ligand ratio of 1:2 [ML2, with M = Ln(III)] formed an enantiotropic cubic mesophase or were not liquid-crystalline, depending on the nature of the lanthanide(III) ion and the substitution pattern of the ligands. A 1:3 uranyl complex of the type [ML3]2+ exhibited a hexagonal columnar mesophase over a broad temperature range. Self-assembled monolayers of a europium(III) complex were investigated by scanning tunneling microscopy, which revealed that the complex formed well-ordered structures over long distances at the 1-octanoic acid−graphite interface. The rhenium(I) complexes and the europium(III) complexes with 2-thenoyltrifluoroacetonate or dibenzoylmethanate and imidazo[4,5-f]-1,10-phenanthroline showed good luminescence properties.