Tuning Organogels and Mesophases with Phenanthroline Ligands and Their Copper Complexes by Inter- to Intramolecular Hydrogen Bonds

A novel family of highly functionalized molecules consisting of a central 4-methyl-3,5-diacylaminobenzene platform linked in close proximity to the methyl group by two lateral aromatic rings
each equipped with two long alkoxy chains has been rationally designed. The presence of amide tethers
and a chelating phenanthroline fragment connected via an ester dipole formed a new class of gelating
reagents and mesomorphic materials. A few of these compounds have the tendency to form macromolecule-like aggregates through noncovalent interactions in hydrocarbon solvents and were found to exhibit
thermotropic cubic mesophases. In light of the X-ray molecular structure of the methoxy ligand, an infinite
network maintained by intermolecular hydrogen bonds as well as by π−π stacking of the phenyl subunits
was evidenced. FT-IR studies confirm that the common driving force for aggregation in the organogels
and microsegregation in the mesophase is the occurrence of a tight intermolecular H-bonded network that
does not persist in diluted solution. This situation is switched when the ligands are interlocked by a copper(I) cation. A strong intramolecular H-bond confirmed by X-ray diffraction of a single crystal for the methoxy
case provides very stable complexes but inhibits the gelation of the solvents. Heating the complexes bearing
long paraffin chains (n = 12 and 16) in the dried state leads to a self-organization into a columnar liquid-crystalline phase in which the columns are arranged along a 2D oblique symmetry as deduced from powder
XRD experiments. In this case, the complexes with the appended counteranions self-assemble in a specific
way to form columns. A striking observation is that the intramolecular hydrogen bond persists in the
mesophase as it does in solution without any evidence of an extended network. As far as we are aware,
these ligands and complexes are rare examples in which organogelation and thermotropic mesomorphic
behavior could be observed in parallel with molecules bearing a chelating platform. Due to the synthetic
availability of the 4-methyl-3,5-diacylaminobenzene core and the simplicity by which the chelating platforms
can be graphed, this methodology represents a practical alternative to the production of functionalized
organogelators and mesomorphic materials.