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Aromatic Bent-Core Liquid Crystals: an Opportunity for Introducing Terdentate Binding Units into Mesophases
Auteur(s)
Nozary, Homayoun
Piguet, Claude
Rivera, Jean-Pierre
Tissot, Paul
Morgantini, Pierre-Yves
Weber, Jacques
Bernardinelli, Gérald
Bünzli, Jean-Claude G.
Donnio, Bertrand
Guillon, Daniel
Date de parution
2012
In
Chemistry of Materials, American Chemical Society (ACS), 2012/14/3/1075–1090
Résumé
Lipophilic linear semirigid side arms containing two or three successive phenyl rings separated by carboxylate spacers have been connected to the 5 or 6 positions of bent aromatic terdentate 2,6-bis(benzimidazol-2-yl)pyridine binding units to give extended V-shaped (<b>L11</b>) and I-shaped receptors (<b>L12</b>, <b>L12b</b>, and <b>L13</b>). The carboxylate spacers limit the flexibility of the side arms and provide crossed arrangements of the successive aromatic rings in the crystal structure of <b>L12b</b> (C<sub>63</sub>H<sub>61</sub>N<sub>5</sub>O<sub>10</sub>; triclinic, <i>P</i>1̄, <i>Z</i> = 2) in agreement with semiempirical calculations performed on optimized gas-phase geometries. Moreover, the carboxylate spacers in <b>L11−L13</b> prevent efficient electronic delocalization between the connected aromatic rings and act as weak <i>π</i> acceptors producing a slight increase of the energy of the <sup>1</sup><i>ππ</i>* and <sup>3</sup><i>ππ</i>* levels centered on the terdentate binding unit. Intermolecular <i>π</i>-stacking interactions observed in the crystal of <b>L12b</b> are invoked to rationalize (i) the peculiar excimer emission of <b>L11</b> in the solid state and (ii) the rich and varied calamitic (I-shaped <b>L12</b>, <b>L12b</b>, and <b>L13</b>) and columnar (V-shaped <b>L11</b>) mesomorphism observed at high temperature. The ColR mesophase detected for <b>L11</b> demonstrates that V-shaped bent terdentate binding units are compatible with liquid-crystalline behavior. Complexation of <b>L11</b> with lanthanide(III) produces I-shaped complexes [Ln(<b>L11</b>)(NO<sub>3</sub>)<sub>3</sub>] (Ln = La, Eu, Gd, Tb, and Lu) possessing a large axial anisometry as found in the crystal structure of [Lu(<b>L11</b>)(CF<sub>3</sub>CO<sub>2</sub>)<sub>3</sub>(H<sub>2</sub>O)] (LuC<sub>81</sub>H<sub>87</sub>N<sub>5</sub>O<sub>17</sub>F<sub>9</sub>; triclinic, <i>P</i>1̄, <i>Z</i> = 2), which exists in the solid state as H-bonded dimers. No mesomorphism is detected for the complexes as a result of the large perpendicular expansion brought by the metallic coordination site, but the high energy of the ligand-centered <sup>3</sup><i>ππ</i>* prevents Eu(<sup>5</sup>D<sub>0</sub>) → <b>L11</b> back transfer in the Eu(III) complex, which thus exhibits sizable red luminescence at room temperature, a crucial point for the design of luminescent materials.
Identifiants
Type de publication
journal article
