Tuning the columnar organization of discotic polycyclic aromatic hydrocarbons

Facile bottom-up synthesis of coronene-based 3-fold symmetrical and highly substituted nanographenes from simple aromatics

A facile and efficient self-sorting assemble (CSA) strategy has been paved for bottom-up construction of the 3-fold symmetrical and highly substituted hexa-cata-hexabenzocoronenes (c-HBCs), the trithieno analogues, and larger disc-shaped PAHs from simple chemicals using benzylic carbons as tenon joints and a novel FeCl3-mediated AAA process as a key step. The structures of the as-prepared c-HBCs and related NGs were clearly identified by spectral analyses and X-ray crystallographic studies. Moreover, these can be envisaged to serve as new launching platforms for the construction of larger and more complex π-conjugated molecules and supramolecular architectures because of the modifiable and symmetrical decorations.

Supramolecular transformation from ordered columnar to disordered columnar to tetragonal micellar structures in clicked dodeca-alkylated discotic triphenylene liquid crystals

We prepared three discotic liquid crystals (DLCs) based on a triphenylene (TP) disc functionalized with twelve alkyl peripheries. The synthesis of the discogens was performed by a click reaction using Cu(OAc)2 as the catalyst, with six triazolyl groups connecting the TP core with twelve alkyl chains. According to thermal data from differential scanning calorimetry (DSC), discogen , which has the shortest hexyl peripheries, exhibited two LC phases, and and , with decyl and tetradecyl peripheries, respectively, displayed three LC phases as a function of the temperature. Structural analyses using small- and wide-angle X-ray scattering (SAXS and WAXS) techniques revealed ordered and disordered hexagonal columnar LC phases in all the discogens. On the other hand, an unconventional micellar phase with P42/mnm symmetry consisting of thirty micelles was found only in and , when the temperature increased. The thermally induced transformation from the columnar to the micellar phase can be explained by increased chain entropy at higher temperatures. The complex micellar packing in the noncubic phase is attributed to the softness of the DLC micelles because the micellar corona consists of flexible alkyl chains. The discogen design concept in this study (i.e., the introduction of multibranched alkyl peripheries to the discotic mesogens via click chemistry) resulted in unconventional columnar-to-micellar transformation in conventional TP DLCs.

Electron transport characteristics in nanosegregated columnar phases of perylene tetracarboxylic bisimide derivatives bearing oligosiloxane chains

An electron transport process in columnar phases of perylene tetracarboxylic bisimide derivatives is analyzed based on the one-dimensional Gaussian disorder model.

Host-guest supramolecular nanosystems for cancer diagnostics and therapeutics

Extensive efforts have been devoted to the construction of functional supramolecular nanosystems for applications in catalysis, energy conversion, sensing and biomedicine. The applications of supramolecular nanosystems such as liposomes, micelles, inorganic nanoparticles, carbon materials for cancer diagnostics and therapeutics have been reviewed by other groups. Here, we will focus on the recent momentous advances in the implementation of typical supramolecular hosts (i.e., cyclodextrins, calixarenes, cucurbiturils and metallo-hosts) and their nanosystems in cancer diagnostics and therapeutics. We discuss the evolutive process of supramolecular nanosystems from the structural control and characterization to their diagnostic and therapeutic function exploitation and even the future potentials for clinical translation.

Coexistence of helical morphologies in columnar stacks of star-shaped discotic hydrazones

Discotic hydrazone molecules are of particular interest as they form discotic phases where the discs are rigidified by intramolecular hydrogen bonds. Here, we investigate the thermotropic behavior and solid-state organizations of three discotic hydrazone derivatives with dendritic groups attached to their outer peripheries, containing six, eight, and ten carbons of linear alkoxy chains. On the basis of two-dimensional wide angle X-ray scattering (2DWAXS), the elevated temperature liquid crystalline (LC) phases were assigned to a hexagonal columnar (Colh) organization with nontilted hydrazone discs for all three compounds. With WAXS, advanced solid-state nuclear magnetic resonance (SSNMR) techniques, and ab initio computations, the compounds with six and ten carbons of achiral alkoxy side chains were further subjected to studies at 25 °C, revealing complex crystalline phases with rigid columns and flexible side chains. This combined approach led to models of coexisting helical columnar stacking morphologies for both systems with two different tilt/pitch angles between successive hydrazone molecules. The differences in tilt/pitch angles between the two compounds illustrate that the columns with short alkoxy chains (six carbons) are more influenced by the presence of other stacks in their vicinity, while those with long side chains are less tilted due to a larger alkoxy (ten carbons) buffer zone. The formation of different packing morphologies in the crystalline phase of a columnar LC has rarely been reported so far, which suggests the possibility of complex stacking structures of similar organic LC systems, utilizing small molecules as potential materials for applications in organic electronics.

Columnar self-assembly in electron-deficient heterotriangulenes

A series of soluble carbonyl-bridged heterotriangulenes, in which flexible n-dodecyl chains are attached through different spacers to the planar nitrogen-centered polycyclic core, have been synthesized. The introduction of triisopropylsilylethynyl moieties enabled, for the first time, the characterization of single-crystal columnar packing of a substituted heterotriangulene by X-ray crystallography. Electrochemical studies disclosed the carbonyl-bridged heterotriangulene core as a reasonably strong acceptor for a reversible two-electron transfer. The tendency of substituted heterotriangulenes to self-assemble in solution, on surfaces, and in the bulk appeared to sensitively depend on the nature of the lateral substituents, their steric demand, and the applied solution processing conditions. It can be concluded that 1) additional phenylene moieties between the heterotriangulene core and the n-dodecyl chains facilitate self-assembly by extending the π-conjugated polycyclic disc, 2) the rod-like ethynylene spacers introduce some additional flexibility and hence lower the overall aggregation tendency, and 3) the combination of both features in the phenylene-ethynylene moieties induces thermotropic liquid crystallinity.

Chemical approaches toward graphene-based nanomaterials and their applications in energy-related areas

A 'gold rush' has been triggered all over the world for exploiting the possible applications of graphene-based nanomaterials. For this purpose, two important problems have to be solved; one is the preparation of graphene-based nanomaterials with well-defined structures, and the other is the controllable fabrication of these materials into functional devices. This review gives a brief overview of the recent research concerning chemical and thermal approaches toward the production of well-defined graphene-based nanomaterials and their applications in energy-related areas, including solar cells, lithium ion secondary batteries, supercapacitors, and catalysis.

Substrate-induced crystal plastic phase of a discotic liquid crystal

A new phase of a known discotic liquid crystal is observed at the interface with a rigid substrate. The structure of the substrate-induced phase has been characterized by atomic force microscopy, specular X-ray diffraction, and small-angle and wide-angle grazing incidence X-ray diffraction. The substrate-induced phase, which has a thickness of ∼30 nm and a tetragonal symmetry, differs notably from the bulk phase. The occurrence of such phase casts a new light on alignment of discotic liquid crystals.

Anomalous Optoelectronic Properties of Chiral Carbon Nanorings…and One Ring to Rule Them All23

Carbon nanorings are hoop-shaped, π-conjugated macrocycles that form the fundamental annular segments of single-walled carbon nanotubes (SWNTs). In a very recent report, the structures of chiral carbon nanorings (which may serve as chemical templates for synthesizing chiral nanotubes) were experimentally synthesized and characterized for the first time. Here in our Letter we show that the excited-state properties of these unique chiral nanorings exhibit anomalous and extremely interesting optoelectronic properties with excitation energies growing larger as a function of size (in contradiction with typical quantum confinement effects). Although the first electronic excitation in armchair nanorings is forbidden with a weak oscillator strength, we find that the same excitation in chiral nanorings is allowed because of a strong geometric symmetry breaking. Most importantly, among all the possible nanorings synthesized in this fashion, we show that only one ring, corresponding to a SWNT with chiral indices (n+3,n+1), is extremely special with large photoinduced transitions that are most readily observable in spectroscopic experiments.

Electro-functional octupolar π-conjugated columnar liquid crystals

A series of propeller-shaped π-conjugated molecules based on 2,4,6-tris(thiophene-2-yl)-1,3,5-triazines has been designed and synthesized to obtain ambipolar charge-transporting liquid-crystalline materials. The 3-fold electron-donating aromatic units are attached to the electron-accepting triazine core, which forms electro-functional octupolar π-conjugated structures. These octupolar molecules self-organize into one-dimensional columnar nanostructures and exhibit ambipolar carrier transport behavior, which has been revealed by time-of-flight measurements. In this approach, electron-donor and acceptor electro-active segments are assembled individually in each column to give one-dimensional nanostructured materials with precisely tuned electronic properties. Their desirable electronic structures responsible for both hole and electron conductions have also been examined by cyclic voltammetry and theoretical calculations. The present results provide a new guideline and versatile approach to the design of ambipolar conductive nanostructured liquid-crystalline materials.

Nanostructuring discotic molecules on ITO support

Patterning of organic compounds on a nanometer length scale is of great interest for solar applications: defined control over the donor-acceptor interface will allow design of an optimized nano-morphology promoting exciton separation and reducing charge recombination. Herein we present an imprinting technique using anodized alumina oxide (AAO) hard templates as stamps. We show an exact pattern transfer of the AAO structures into a solution processable hexa-peri-hexabenzocoronene (HBC), a discotic small molecule with acrylate moieties which is polymerized in situ. Film fabrication is realized for a variety of nanowire dimensions on square centimeter areas. The fabrication directly on conductive glass support and control over the formation of a dense barrier layer render this approach appealing for the fabrication of fully organic nanostructured photovoltaic devices.