| Abstract
| - Lipophilic linear semirigid side arms containing two or three successive phenyl ringsseparated by carboxylate spacers have been connected to the 5 or 6 positions of bent aromaticterdentate 2,6-bis(benzimidazol-2-yl)pyridine binding units to give extended V-shaped (L11)and I-shaped receptors (L12, L12b, and L13). The carboxylate spacers limit the flexibilityof the side arms and provide crossed arrangements of the successive aromatic rings in thecrystal structure of L12b (C63H61N5O10; triclinic, P1̄, Z = 2) in agreement with semiempiricalcalculations performed on optimized gas-phase geometries. Moreover, the carboxylate spacersin L11−L13 prevent efficient electronic delocalization between the connected aromatic ringsand act as weak π acceptors producing a slight increase of the energy of the 1ππ* and 3ππ*levels centered on the terdentate binding unit. Intermolecular π-stacking interactionsobserved in the crystal of L12b are invoked to rationalize (i) the peculiar excimer emissionof L11 in the solid state and (ii) the rich and varied calamitic (I-shaped L12, L12b, andL13) and columnar (V-shaped L11) mesomorphism observed at high temperature. The ColRmesophase detected for L11 demonstrates that V-shaped bent terdentate binding units arecompatible with liquid-crystalline behavior. Complexation of L11 with lanthanide(III)produces I-shaped complexes [Ln(L11)(NO3)3] (Ln = La, Eu, Gd, Tb, and Lu) possessing alarge axial anisometry as found in the crystal structure of [Lu(L11)(CF3CO2)3(H2O)](LuC81H87N5O17F9; triclinic, P1̄, Z = 2), which exists in the solid state as H-bonded dimers.No mesomorphism is detected for the complexes as a result of the large perpendicularexpansion brought by the metallic coordination site, but the high energy of the ligand-centered 3ππ* prevents Eu(5D0) → L11 back transfer in the Eu(III) complex, which thusexhibits sizable red luminescence at room temperature, a crucial point for the design ofluminescent materials.
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