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Tuning the Thermotropic and Lyotropic Properties of Liquid‐Crystalline Terpyridine Ligands
Author(s) -
Camerel Franck,
Donnio Bertrand,
Bourgogne Cyril,
Schmutz Marc,
Guillon Daniel,
Davidson Patrick,
Ziessel Raymond
Publication year - 2006
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200501431
Subject(s) - mesophase , crystallography , materials science , lyotropic , stacking , terpyridine , columnar phase , lamellar structure , hydrogen bond , amide , liquid crystal , molecule , chemistry , polymer chemistry , organic chemistry , liquid crystalline , optoelectronics , metal , metallurgy
A rational synthetic strategy is developed to provide compact and simple terpyridine (terpy) mesogens that show liquid‐crystallinity both as pure compounds and in organic solution (amphotropic compound). The use of a central 4‐methyl‐3,5‐diacylaminophenyl platform equipped with two lateral aromatic rings, each bearing three appended aliphatic chains, allows connection of a 2,2′:6′,2′′‐terpyridine fragment through a polar group such as an ester, amide, or flat conjugated alkyne linker. For the T 12 ester and T 12 amide scaffolds, the mesophase is best described as a lamellar phase, in which the molecules self‐assemble into columnar stacks held together in layers. In the T 12 amide case, the additional amide link results in significant stabilization of the lamellar phase. The driving forces for the appearance of columnar ordering are the hydrogen‐bonding interactions of the amide groups, which induce head‐to‐tail π‐stacking of the terpy subunits. Replacing the polar linker by a nonpolarized but linear alkyne spacer, as in the T 12 ethynyl compound, provides a columnar mesophase organized in a rectangular lattice of p2gg symmetry. In this arrangement, two nondiscotic molecules arranged into dimers by hydrogen bonding and π–π stacking pile up in a head‐to‐tail manner to form columns. In addition, the T 12 amide compound proves to be an excellent gelator of cyclohexane, linear alkanes, and DMSO. The resulting robust and transparent gels are birefringent and formed by large aggregates that are readily aligned by shear‐flow. TEM and freeze‐fracture microscopy reveal that the gels have an original layered morphology made of fibers.