Combination of an aromatic core and aromatic side chains which constitutes discotic liquid crystal and organogel supramolecular assemblies

Synthesis and organogelating behaviour of amino acid-functionalised triphenylenes

Four novel amino acid-functionalised triphenylenes have been prepared with glycine, l-alanine, l-phenylalanine and l-tryptophan ethyl ester side-chains. The glycine derivative is a good gelator of chloroform, the alanine derivative gels ethanol and toluene, and the phenylalanine derivative gels benzene and toluene. The tryptophan derivative does not gel any of the solvents tested, most probably due to its more bulky structure, but forms microspheres by evaporation-induced self-assembly. The self-assembly properties of the π-gelators have been investigated using infrared, UV-absorption and fluorescence spectroscopy, concentration- and temperature-dependent NMR, and X-ray scattering experiments on dried xerogel as well as the wet organogel. The latter experiments suggest the glycine gel in chloroform includes columnar aggregates, with an overall disordered columnar oblique mesophase. These compounds are of interest because of the well-known hole-transporting properties of triphenylene liquid crystals: 1-D columnar assemblies of these compounds may find applications in organic electronic devices.

Synthesis, Photophysical and Electrochemical Properties, and Self-assembly Behavior of Two Hexaazatriphenylene Derivatives: A Single Bond Makes a Big Difference

A hexaazatriphenylene (HAT) derivative (compound 1) that bears four n-octyl chains and two thienyl groups was designed and synthesized. Further light-induced oxidation coupling reaction led to thienyl-fused compound 2. Their photophysical and electrochemical properties and self-assembly behavior have been investigated by UV/Vis, fluorescence, and (1)H NMR spectroscopies, cyclic voltammetry (CV), scanning electron microscopy (SEM), and powder X-ray diffraction (PXRD). Although the difference in compounds 1 and 2 only lie in one single bond that connects the two thienyl segments, they displayed remarkably different properties, revealing an interesting structure-property relationship.

Turn-on-type emission enhancement and ratiometric emission color change based on the combination effect of aggregation and TICT found in the hexaazatriphenylene-triphenylamine dye in an aqueous environment

Turn-on-type emission enhancement and a ratiometric emission color change were achieved simultaneously due to the aggregation and TICT of a donor–acceptor-type dye.

Methyl Cinnamate-Derived Fluorescent Rigid Organogels Based on Cooperative π-π Stacking and C═O···π Interactions Instead of H-Bonding and Alkyl Chains

A new class of rigid low-molecular-mass organic gelators (LMOGs) was synthesized by McMurry and Heck reactions, and their gels and photophysical properties were investigated. The LMOGs lacked alkyl chain and H-bonding units and produced good gelation ability in selected mixed organic solvents facilitated by cooperative π-π stacking and C═O···π interactions. Sensitive gel-sol transformation by molecular aggregation and disaggregation was easily achieved upon heating and cooling. H-H 2D NOESY and X-ray diffraction (XRD) patterns showed the π-π stacking and C═O···π interactions between tiny methyl acrylate groups as "tails". Importantly, this soft interaction model offers a useful tool for the future design and construction of supramolecular structures. At present, the LMOGs reported herein offer a sensitive gel-formation ability and aggregation-induced emission (AIE) property and thus have promising application potentials as functional soft matter in amorphous materials, photoelectric materials, and so on.

Optimized synthesis of a tert-butyl-phenyl-substituted tetrapyridophenazine ligand and its Ru(ii) complexes and determination of dimerization behaviour of the complexes through supramolecular “Fingerhakel”

A high dimerization constant of a ruthenium complex is observed with the aid of ¹H-NMR spectroscopy. The solid state molecular structure indicates that multiple π-interactions are the reason for strong dimerization.

Hexaazatriphenylene (HAT) derivatives: from synthesis to molecular design, self-organization and device applications

The creativity and inventiveness of chemists working with the 1,4,5,8,9,12-hexaazatriphenylene (HAT) building block is highlighted in this review.

Organogels formed by substituent-free pyrene-appended oligo(m-phenylene ethynylene)s

Substituent-free pyrene-appended m-phenylene ethynylene oligomers have been revealed to gelate organic solvents of low and modest polarity.

Truxene: a promising scaffold for future materials

Truxene (10,15-dihydro-5H-diindeno[1,2-a;1′,2′-c]fluorene), which is a heptacyclic polyarene structure, has attracted a great deal of interest due to its exceptional solubility, high thermal stability and ease with which it may be modified.

Comparison of dipolar, H-bonding, and dispersive interactions on gelation efficiency of positional isomers of keto and hydroxy substituted octadecanoic acids

A systematic study of the importance of functional group position and type on the gelator efficiencies of structurally simple, low molecular-mass gelators is reported. Thus, the gelation abilities of a series of positional isomers of ketooctadecanoic acid (n-KSA) are compared in a wide range of liquids. The gelation abilities of the n-KSA as a function of n, the keto group position along the chain, are characterized by several structural, thermal, and rheological techniques and are compared with those of the corresponding hydroxyoctadecanoic acid isomers (n-HSA) and the parent molecule, octadecanoic acid (SA). Analyses of the gels according to the strengths of functional group interactions along the alkyl chain in terms of group position and type are made. The conclusions derived from the study indicate that gel stability is enhanced when the functional group is located relatively far from the carboxylic headgroup and when group-group interactions are stronger (i.e., hydrogen-bonding interactions are stronger in the n-HSA than dipole interactions in the n-KSA, which are stronger than the London dispersion interactions in SA). Co-crystals of the keto- and hydroxy-substituted octadecanoic acids are found to be less efficient gelators than even the ketooctadecanoic acids, due to molecular packing and limited group interactions within the gelator networks.

A new synthesis of tetra(quinoxalino)tetraazaporphyrin by the retro Diels-Alder reaction of a soluble precursor

Soluble tetra(pyrazino)tetraazaporphyrin was synthesized by the reaction of bicyclo[2.2.2]octadiene-fused dicyanopyrazine. The retro Diels-Alder reaction of the soluble tetra(pyrazino)tetraazaporphyrin gave a tetra(quinoxalino)tetraazaporphyrin in quantitative yield.

Water-induced physical gelation of organic solvents by N-(n-alkylcarbamoyl)-L-alanine amphiphiles

A series of amino acid-based gelators N-(n-alkylcarbamoyl)-L-alanine were synthesized, and their gelation abilities in a series of organic solvents were tested. No gelation was observed in pure solvents employed. All the amphiphilic molecules were found to form stable organogels in the solvents in the presence of a small amount of water, methanol, or urea. The volume of solvent gelled by a given amount of the gelator was observed to depend upon the volume of added water. The gelation behavior of the amphiphiles in a given solvent containing a known volume of water was compared. The effects of chirality and substitution on the acid group on the gelation ability were examined. Although the corresponding N-(n-tetradecylcarbamoyl)-DL-alanine was found to form only weak organogel in pure solvents, the achiral amphiphilic compound N-(n-tetradecylcarbamoyl)-β-alanine, however, did not form gel in the absence of water. The methyl ester of N-(n-tetradecylcarbamoyl)-L-alanine was also observed to form gels in the same solvents, but only in the presence of water. The organogels were characterized by several techniques, including (1)H NMR, Fourier transform IR, X-ray diffraction, and field emission scanning electron microscopy. The thermal and rheological properties of the organogels were studied. The mechanical strength of the organogel formed by N-(n-tetradecylcarbamoyl)-DL-alanine was observed to increase upon the addition of water. It was concluded that water-mediated intermolecular hydrogen-bonding interaction between amphiphiles caused formation of supramolecular self-assemblies.

Star-Shaped Conjugated Systems

The present review deals with the preparation and the properties of star-shaped conjugated compounds. Three, four or six conjugated arms are attached to cross-conjugated cores, which consist of single atoms (B, C⁺, N), benzene or azine rings or polycyclic ring systems, as for example triphenylene or tristriazolotriazine. Many of these shape-persistent [n]star compounds tend to π-stacking and self-organization, and exhibit interesting properties in materials science: Linear and non-linear optics, electrical conductivity, electroluminescence, formation of liquid crystalline phases, etc.

Rational design, synthesis, and optical properties of film-forming, near-infrared absorbing, and fluorescent chromophores with multidonors and large heterocyclic acceptors

A new series of film-forming, low-bandgap chromophores (1 a,b and 2 a,b) were rationally designed with aid of a computational study, and then synthesized and characterized. To realize absorption and emission above the 1000 nm wavelength, the molecular design focuses on lowering the LUMO level by fusing common heterocyclic units into a large conjugated core that acts an electron acceptor and increasing the charge transfer by attaching the multiple electron-donating groups at the appropriate positions of the acceptor core. The chromophores have bandgap levels of 1.27-0.71 eV, and accordingly absorb at 746-1003 nm and emit at 1035-1290 nm in solution. By design, the relatively high molecular weight (up to 2400 g mol(-1)) and non-coplanar structure allow these near-infrared (NIR) chromophores to be readily spin-coated as uniform thin films and doped with other organic semiconductors for potential device applications. Doping with [6,6]-phenyl-C(61) butyric acid methyl ester leads to a red shift in the absorption only for 1 a and 2 a. An interesting NIR electrochromism was found for 2 a, with absorption being turned on at 1034 nm when electrochemically switched (at 1000 mV) from its neutral state to a radical cation state. Furthermore, a large Stokes shift (256-318 nm) is also unique for this multidonor-acceptor type of chromophore, indicating a significant structural difference between the ground state and the excited state. Photoluminescence of the film of 2 a was further probed at variable temperatures and the results strongly suggest that the restriction of bond rotations certainly helps to diminish non-radiative decay and thus enhance the luminescence of these large chromophores.

Control of dynamic helicity at the macro- and supramolecular level

In this review, various systems developed in recent years which aim to control dynamic helicity at the macro- and supramolecular level are discussed. The strong interactions between the individual molecular components in these controlled helical assemblies, ranging from columnar aggregates to helical polymers and cholesteric liquid crystals, result in stereoinduction from the molecular level to the level of these macro- and supramolecular helical architectures. Therefore these systems are potentially useful for various applications, including responsive materials and chirality sensors and amplifiers.

Pyrazine-containing acene-type molecular ribbons with up to 16 rectilinearly arranged fused aromatic rings

A series of acene-type conjugated molecules (1-5) containing 2-6 pyrazine units and up to 16 rectilinearly arranged fused aromatic rings were synthesized by condensation coupling of 1,2-diamines and 1,2-diketones. The energy gap of the molecules estimated from absorption edge decreases with an increase in molecular length, indicating the well-delocalized nature of the molecules. The cyclic voltammetry measurements suggest that the n-type properties of these ribbonlike pyrazine derivatives are dependent on the molecular length and the number of the pyrazine units. As the number of pyrazine units and the molecular length increase, the first reduction wave onset is shifted from -1.16 to -0.62 V (vs Ag/AgCl), corresponding to the LUMO energy levels of -3.24 and -3.78 eV, respectively. These molecules tend to aggregate in solution more readily with an increase in molecular length, as evident by (1)H NMR and UV-vis absorption spectra. Introduction of t-butyl groups in pyrene units can noticeably suppress the aggregation of these molecules in solution. High electron affinity, high environmental stability, and ease of structural modification make these compounds excellent candidates as a new class of n-type semiconductors.

Amplification of chirality in dynamic supramolecular aggregates

The quest to understand the origin of chirality in biological systems has evoked an intense search for nonlinear effects in catalysis and pathways to amplify slight enantiomeric excesses in racemates to give optically pure molecules. The amplification of chirality in polymeric systems as a result of cooperative processes has been intensely investigated. Ten years ago, this effect was shown for the first time in noncovalent dynamic supramolecular systems. Since then, it has become clear that a subtle interplay of noncovalent interactions such as hydrogen-bonding, pi-pi stacking, and hydrophobic interactions is also sufficient to observe amplification of chirality in small molecules. Here we summarize the results obtained over the past decade and the general guidelines we can deduce from them. Predicting amplification of chirality is still impossible, but it appears to be a balance between different types of interactions, the formation of an intrinsically chiral object, and cooperative aggregation processes.