Ke-Qing Zhao

Star-shaped triphenylene discotic liquid crystalline oligomers and their hydrogen-bonded supramolecular complexes with simple acids

The synthesis and self-assembly properties of four novel star-shaped oligomers containing triphenylene discotic mesogens are reported. These materials have been synthesized in good yields by the Cu-catalyzed coupling cycloaddition reaction (CuAAC) between 1,3,5,-tris(2-trimethylsilylethynyl)benzene and three equivalents of the appropriate discogen bearing a pending terminated-azide alkyl substituent. The molecular structures of the discotic oligomers, thereof consisting of three lateral triphenylenes linked together by various soft methylene spacers to a central 1,3,5-tris(triazolyl)benzene, have been fully characterized by 1H and 13C NMR, and their purity confirmed by elemental analysis. Their thermal and liquid crystalline supramolecular organization behaviours have been studied by combining polarized optical microscopy, differential scanning calorimetry and small-angle X-ray scattering. These investigations showed that only the two oligomers with short spacers display a hexagonal columnar mesophase, while those with long spacer are not mesomorphic. Scanning tunneling microscopy revealed that one of the mesomorphic oligomer self-assembles on a solid/liquid interface into a well ordered two-dimensional architecture that closely resembles to the proposed bulk mesomorphic supramolecular organization deduced from X-ray measurements. Furthermore, columnar mesophases have been induced in the corresponding hydrogen-bonded supramolecular complexes obtained by reaction of one of the non-mesogenic oligomeric derivative with various simple acids, e.g. hexanoic, benzoic, and 4-hexyloxybenzoic acids, respectively, in molar ratios of 1:2 and 1:3. The optical properties of these D–A dyads have been studied by UV-Vis absorption and fluorescent emission.

Molecular arrays formed in anisotropically rearranged supramolecular network with molecular substitutional asymmetry

We have designed two molecular building blocks, 2,6,11-tricarboxydecyloxy-3,7,10-triundecyloxy triphenylene (asym-TTT) and 2,6,10-tricarboxydecyloxy-3,7,11-triundecyloxy triphenylene (sym-TTT) with asymmetric and symmetric carboxyl groups, to construct distinct supramolecular networks. The supramolecular network of asym-TTT facilitates the formation of the directional-oriented molecular arrays of zinc phthalocyanines (ZnPc). The high-resolution scanning tunneling microscopic (STM) images as well as the density-functional theory (DFT) calculations reveal the preferential adsorption of ZnPc dimers in the anisotropic rearrangement of an asym-TTT supramolecular network. The self-repairing process of the molecular arrays after sweeping ZnPc dimers further confirms the anisotropic reconstruction of the asym-TTT network. The controlled experiments on the symmetrically substituted compound indicate the impact of the asymmetrically substituted carboxyl groups on the supramolecular networks.

Molecular miscibility characteristics of self-assembled 2D molecular architectures

Various molecular networks, stabilized by hydrogen bonds or van der Waals interactions, are demonstrated in which the distribution of heterogeneous molecular species could be controlled at the level of single molecules or molecular clusters. The observed miscibility characteristics of the two-dimensional (2D) assembly structures could enable studies on the heterogeneous molecular interfaces of guest–host architectures. In addition, it could be envisioned that large cavity networks should be beneficial for studying the clustering behavior of molecular aggregates of similar or dissimilar species, chemical interactions in nanometre scale constrained areas, as well as the design of complex molecular architectures.

4-Ferrocenylbenzoic Acid

Ferrocene-containing liquid crystals, non-linear optical materials and magnetic materials are of considerable interests for their high thermal stability, tunable redox characteristics and structural variability [1].[...]

(4-hydroxybenzylidene)-4-ferrocenylaniline

(4-Hydroxybenzylidene)-4-ferrocenylaniline has a free hydroxyl group and it can react with carboxylic acids to form esters and it is thus a key intermediate for the synthesis of mono-substituted ferrocenecontaining liquid crystal [1] with Schiffs base and ester group.[...]

Facile transformation of 1-aryltriphenylenes into dibenzo[fg,op]tetracenes by intramolecular Scholl cyclodehydrogenation: synthesis, self-assembly, and charge carrier mobility of large π-extended discogens

The search for new organic semiconductors with enhanced charge transport properties and self-organizing abilities plays a pivotal role in the development of new applications in the emerging field of organic electronics. We have synthesized two series of discotic mesogenic materials derived from hexasubstituted triphenylene, including (i) 1-aryl-2,3,6,7,10,11-hexakis(pentyloxy)triphenylenes (14 new compounds) by a Suzuki cross-coupling reaction between the appropriate 1-bromotriphenylene precursor and various arylboronic acids and (ii) unsymmetrical facial dibenzo[fg,op]tetracene discotic molecules (11 new compounds) by an FeCl3-oxidized cyclodehydrogenation reaction of the former. The mesomorphism has been investigated by polarizing optical microscopy, differential scanning microscopy, and small-angle X-ray scattering. Most aryl-substituted triphenylene derivatives exhibit a single hexagonal columnar mesophase, enantiotropic over small temperature ranges or monotropic, with this low stability being likely attributed to the free-rotating bulky side-on arene group that disrupts a perfect stacking. The corresponding more rigid and flat dibenzo[fg,op]tetracene derivatives also self-organize into a hexagonal columnar mesophase, but with a larger mesophase stability than their parents, and occurring slightly above room temperature. The UV/vis absorption and fluorescence emission spectra have been measured. Tetracenes show stronger photoluminescence than aryltriphenylene in solution, while the reversed is observed in thin films, where a strong excimer emission for one of the polar 1-aryltriphenylenes is observed. The charge carrier mobility of two representative discogens has been measured by the time-of-flight photocurrent technique. The results show that the discogen with a lateral nucleus dipole displays a hole mobility of 10−4 cm2 V−1 s−1 in the mesophase, while the non-polar compound exhibits a hole mobility of 10−2 cm2 V−1 s−1 in its metastable-induced ordered phase. The charge carrier mobility is discussed as a function of the supramolecular organization.

Two-dimensional rigid molecular network with elastic boundaries for constructing hybrid molecular assemblies

The star-shaped molecule, 2,6,10-trihexyloxy-3,7,11-tris[3,4,5-tris(dodecyloxy)benzoyloxy]triphenylene (sym) was used as the building unit for constructing porous molecular networks with large cavities. It has been identified that a variety of guest molecules (such as C60, phthalocyanine and substituted phthalocyanine) can be dispersed in this template to form supramolecular architectures, which were also studied by scanning tunneling microscopy (STM). It is interesting to observe that this template has elastic boundaries and rigid structures, which can accommodate different amounts of guest species by interacting with them, while keeping the size of cavities invariable.

4-Formylphenyl 4-Ferrocenylbenzoate

Ferrocene unit is comparatively large volume and it needs a longer molecular shape in geometry in to support the liquid crystal property [1].[...]

4-Hydroxyphenyl 4-Ferrocenylbenzoate

The reaction of 4-ferrocenylbenzoyl chloride with 1,4-dihydroxybenzene gives 4-hydroxyphenyl 4-ferrocenylbenzoate, which contains a free hydroxyl group and it can be used for the synthesis of ester mono-substituted liquid crystal and hydrogen-bonded supra-molecular liquid crystals [1].[...]

(4-Formylbenzylidene)-4-ferrocenylaniline

The reaction of 4-ferrocenylaniline with 1,4-benzenedicarboxaldehyde in an equimolar ratio in dilute solution, or with a large excess of the aniline, often gives the diimine product.[...]