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 tri dentate 2,6-bis-(benzimidazol-2'-yl)pyridine cores into rodlike ligands L11 -17. The crystal structure of the nonmesogenic ligand L-13 (C39H37N5O4, tri clinic, 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 th e fully extended conformation adopted by the lipophilic side chains, leadin g to a slightly helically twisted I-shaped molecule. A rich and varied meso morphism results which can be combined with the simultaneous tuning of elec tronic and photophysical properties via a judicious choice of the spacers b etween the rigid central core and the semirigid lipophilic sidearms. Ligand s L-13,L-14 react with Ln(NO3)(3). xH(2)O to give quantitatively and select ively the neutral 1:1 complexes [Ln(L-i)(NO3)(3)] (Ln = La to Lu), which ar e stable in the solid state at room temperature but partially dissociate in acetonitrile to give the cationic species [Ln(L-i)(NO3)(2)](+). The crysta l 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.:T his drastic geometric change strongly affects the thermal behavior and the photophysical and electronic properties of the lipophilic complexes [Ln(L-1 4)(NO3)(3)]. Particular attention has been focused on structure-properties relationships, which can be modulated by the size of the lanthanide metal i ons.