Faculté des sciences

Bent Tridentate Receptors in Calamitic Mesophases with Predetermined Photophysical Properties: New Luminescent Lanthanide-Containing Materials

Nozary, Homayoun ; Piguet, Claude ; Tissot, Paul ; Bernardinelli, Gérald ; Bünzli, Jean-Claude G. ; Deschenaux, Robert ; Guillon, Daniel

In: Journal of the American Chemical Society (JACS), 1998, vol. 120, no. 47, p. 12274–12288

A new synthetic strategy has been developed to introduce bent and rigid tridentate 2,6-bis(benzimidazol-2‘-yl)pyridine cores into rodlike ligands L11-17. The crystal structure of the nonmesogenic ligand L13 (C39H37N5O4, triclinic, P1̄, Z = 2) shows the expected trans−trans conformation of the tridentate... More

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    Summary
    A new synthetic strategy has been developed to introduce bent and rigid tridentate 2,6-bis(benzimidazol-2‘-yl)pyridine cores into rodlike ligands L11-17. The crystal structure of the nonmesogenic ligand L13 (C39H37N5O4, triclinic, P1̄, Z = 2) shows the expected trans−trans conformation of the tridentate binding unit, which provides a linear arrangement of the semirigid aromatic sidearms. The crystal structure of the related mesogenic ligand L16 (C61H81N5O4, triclinic, P1̄, Z = 2) demonstrates the fully extended conformation adopted by the lipophilic side chains, leading to a slightly helically twisted I-shaped molecule. A rich and varied mesomorphism results which can be combined with the simultaneous tuning of electronic and photophysical properties via a judicious choice of the spacers between the rigid central core and the semirigid lipophilic sidearms. Ligands L13,14 react with Ln(NO3)3·xH2O to give quantitatively and selectively the neutral 1:1 complexes [Ln(Li)(NO3)3] (Ln = La to Lu), which are stable in the solid state at room temperature but partially dissociate in acetonitrile to give the cationic species [Ln(Li)(NO3)2]+. The crystal structure of [Lu(L13)(NO3)3]·3CH3CN (30, LuC45H46N11O13, monoclinic, C2/c, Z = 8) reveals a U-shaped arrangement of the ligand strand arising from the cis−cis conformation of the coordinated tridentate binding unit. This drastic geometric change strongly affects the thermal behavior and the photophysical and electronic properties of the lipophilic complexes [Ln(L14)(NO3)3]. Particular attention has been focused on structure−properties relationships, which can be modulated by the size of the lanthanide metal ions.