Journal of the American Chemical Society, Vol.120, No.47, 12274-12288, 1998
Bent tridentate receptors in calamitic mesophases with predetermined photophysical properties : New luminescent lanthanide-containing materials
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 L-13 (C39H37N5O4, triclinic, P (1) over bar, 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 L-16 (C61H81N5O4, triclinic, P (1) over bar, 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 L-13,L-14 react with Ln(NO3)(3). xH(2)O to give quantitatively and selectively the neutral 1:1 complexes [Ln(L-i)(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(L-i)(NO3)(2)](+). The crystal structure of [Lu(L-13)(NO3)(3)]. 3CH(3)CN (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(L-14)(NO3)(3)]. Particular attention has been focused on structure-properties relationships, which can be modulated by the size of the lanthanide metal ions.
Keywords:MESOMORPHIC 2;2'-BIPYRIDINE DIESTERS, COLUMNAR LIQUID-CRYSTALS;D-F COMPLEXES, BUILDING-BLOCKS, METAL-COMPLEXES, NITROGENLIGANDS, HYDROGEN-BOND, RARE-EARTH, METALLOMESOGENS, DESIGN