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

Abstract

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 pi-pi 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.

Towards a universal organogelator: A general mixing approach to fabricate various organic compounds into organogels

“…In recent years, the organogels with metal complexes have attracted a great deal of interests [41,42]. Since the metal complexes play important roles in the fields of materials chemistry, synthesis and catalysis, the development of metal-containing gels are expected to create the novel soft matters with both the properties of organogels and metal complexes.…”

Tuning the Thermotropic and Lyotropic Properties of Liquid‐Crystalline Terpyridine Ligands

“…Recently, this approach was successfully applied to produce liquid-crystalline phenanthroline ligands and complexes. [42] From a general point of view acylamino platforms have previously been identified as key elements for the production of liquid-crystalline materials and of efficient gelators of various organic solvents. [43,44] Some of these gels seem to have great potential as functional soft materials.…”

Evolution from Lyotropic Liquid Crystal to Helical Fibrous Organogel of an Achiral Fluorescent Twin‐Tapered Bi‐1,3,4‐oxadiazole Derivative

“…[12] PL spectra were collected using a Hitachi F-4500 spectrometer. FE-SEM observations were made with a Hitachi S-4800 apparatus.…”

“…[12] In our previous work, we reported a series of fluorescent liquid-crystalline bi-1,3,4-oxadiazole derivatives. [13] Among these bi-1,3,4-oxadiazole derivatives, an achiral fluorescent twin-tapered bi-1,3,4-oxadiazole derivative (BOXD-T8) was found to exhibit a thermotropic LC phase and various self-assembled structures in solution, such as nanoparticles, helical nanobelts, and flat nanobelts.…”