Self-Assembly of a Chiral Lipid Gelator Controlled by Solvent and Speed of Gelation

Solvent-Modulated Chiral Self-Assembly: Selective Formation of Helical Nanotubes, Nanotwists, and Energy Transfer

As the medium for self-assembly processes, solvents strongly influence the supramolecular assemblies via specific solute-solvent interactions, which may result in effective modulation of properties, self-assembled nanostructures, and functions through varying the solvent. Here, two kinds of pyridine-cyanostilbene functionalized chiral amphiphiles (l/d-PyPhG and l-PyG) were designed, and their self-assembly behaviors in different solvents were investigated. It was found that both amphiphiles formed gels in dimethyl sulfoxide (DMSO) and self-assembled into right-handed nanotwists, while they formed suspensions in ethanol consisting of left-handed nanotubes. Although the molecular chirality in the compounds remained unchanged in the two solvents, the nanoassemblies showed opposite handedness at the nanoscale together with opposite circular dichroism (CD) and circularly polarized luminescence (CPL) signals. Furthermore, when the amphiphiles were co-assembled with an achiral dye, it was found that efficient energy transfer took place in the systems composed of nanotubes rather than those composed of nanotwists. Therefore, by assembling molecules with the same molecular chirality in different solvents, a selective formation of helical nanotubes or nanotwists and the regulation of handedness as well as energy transfer efficiency were achieved.

Self-Assembled α-Cyanostilbenes for Advanced Functional Materials

In the specific context of condensed media, the significant and increasing recent interest in the α-cyanostilbene (CS) motif [ArCHC(CN)Ar] is relevant. These compounds have shown remarkable optical features in addition to interesting electrical properties, and hence they are recognized as very suitable and versatile options for the development of functional materials. This progress report is focused on current and future use of CS structures and molecular assemblies with the aim of exploring and developing for the next generations of functional materials. A critical selection of illustrative materials that contain the CS motif, including relevant subfamilies such as the dicyanodistyrylbenzene and 2,3,3-triphenylacrylonitrile shows how, driven by the self-assembly of CS blocks, a variety of properties, effects, and possibilities for practical applications can be offered to the scientific community, through different rational routes for the elaboration of advanced materials. A survey is provided on the research efforts directed toward promoting the self-assembly of the solid state (polycrystalline solids, thin films, and single crystals), liquid crystals, nanostructures, and gels with multistimuli responsiveness, and applications for sensors, organic light-emitting diodes, organic field effect transistors, organic lasers, solar cells, or bioimaging purposes.

Tunable multicolor emissions in a monocomponent gel system by varying the solvent, temperature and fluoride anion

The facile tuning of the fluorescent properties of organogels is highly desirable for optical switches, light-emitting diodes, chemosensors and bioprobes. The design of organic molecules with multiple emission colors but only one molecular platform remains challenging. Herein, a new cholesterol-based organogelator N1 containing D-A pairs (salicylaldehyde and naphthalimide units) was designed. We successfully obtained multiple solvent-tuned emission colors in both the solution and gel states using a unimolecular platform. Moreover, the effects of the solvent on the gel morphology, rheology and anion-responsive properties were studied. Finally, we showed that the gel in benzene displayed reversible thermochromic properties with changes in emission color from yellow-green to red. Several experiments suggested that a short-distance and ordered array of the D-A pairs facilitated the efficient intermolecular electron transfer of the fluorophores.

Self-assembly of the polyoxometalate–cholesterol conjugate into microrods or nanoribbons regulated by thermodynamics

The self-assembly of the polyoxometalate–cholesterol conjugate can be well controlled and regulated by means of a temperature-mediated approach.

Memorized chiral arrangement of gemini surfactant assemblies in nanometric hybrid organic–silica helices

The chiral arrangement of non-chiral gemini surfactant molecules induced by enantiomeric tartrate counterions was maintained by hybridization with silica matrices even after the removal of the counterions as chiral sources.

Solvent-mediated gel formation, hierarchical structures, and rheological properties of organogels

We report the formation of solvent-mediated gels as well as their hierarchical structures and rheological properties. The gelator used is a hybrid with a molecular structure of cholesterol-polyoxometalate-cholesterol, in which the cholesterol dissolves well in toluene and N,N-dimethylformamide (DMF), whereas the polyoxometalate cluster dissolves only in DMF. These solubility differences enable the gelator to form thermally reversible supramolecular organogels by mixing solvents of toluene and DMF when the volume fraction, ftol, of toluene is larger than 85.7 v/v%. We found a V-shaped correlation between the gelation times, tgel and ftol: tgel decreases from 1300 min to 2 min when ftol increases from 85.7 v/v% to 90.0 v/v%. It then increases from 2 min to 5800 min when ftol further increases from 90.0 v/v% to 100.0 v/v%. We observed ribbon-like self-assembled structures in the gels as well as a structural evolution from rigid and straight ribbons to twistable ones from ftol=85.7 v/v% to ftol=100.0 v/v%. These ribbons constitute two three-dimensional (3D) gel networks: one is constructed via physical connection of the rigid and straight ribbon, and the other is built up from ribbons splitting and intertwining. The latter has a better 3D gel network that offers improved rheological properties. Fundamentally, this solvent-mediated approach regulates the balance between solubility and insolubility of this gelator in the mixing solvents. It also provides a new method for the preparation of organogels.

Speed versus stability – structure–activity effects on the assembly of two-component gels

Modifying the peripheral peptides dramatically changes the time required for gelation under ambient conditions, whilst an enthalpy–entropy balance means that as the temperature increases, the thermal stability of the gels is very similar.

Emission enhanced two-component gels for the detection of organic amine vapors

A two-component gelator with enhanced emission could be used to quantitatively detect and discriminate between aliphatic and aromatic organic amine vapors.

Nanofibers of hydrogen-bonded two-component gel with closely connected p- and n-channels and photoinduced electron transfer

An D-A-D gelator (DTCQ) was designed and synthesized using 2,3-dimethyl-5,8-di(thiophen-2-yl)quinoxaline and N-alkyl 3-aminocarbazole units as acceptor and donor, respectively, which were linked by a single bond. The compound could gelate several solvents, such as benzyl alcohol, aniline, acetophenone, and o-dichlorobenzene, as well as self-assemble into one-dimensional (1D) nanofibers in gel phase. The absorption and infrared spectra of the gels indicated that π-π interactions between aromatic moieties, intermolecular hydrogen bonds between amide units, and van der Waals forces were the driving forces for the formation of 1D self-assemblies and gel. DTCQ gel was red and emits red fluorescence because it has a strong absorption band at 487 nm and an emissive band at 620 nm. Moreover, DTCQ and a fullerene carboxylic acid formed two-component gel, in which the two compounds developed a hydrogen bond complex and self-assembled into 1D nanofibers with closely connected p- and n-channels. The nanofibrous xerogel film can rapidly generate a photocurrent under visible-light radiation through electron transfer from the gelator to fullerene, and then, the excellent exciton separation and charge transfer to two electrodes.

Tuning the gelation ability of racemic mixture by melamine: enhanced mechanical rigidity and tunable nanoscale chirality

Understanding the relationship between molecular chirality of the gelators and the properties of the assembled supramolecular gels could be very important for developing novel functional soft matters. Although mixing the enantiomers with different molar ratios has been proved to be useful for modulating supramolecular assemblies, usually the racemates of different chiral molecules are not good gelators. In this study, the coassembly of the glutamic acid-based bolaamphiphile racemate and melamine was found to form hydrogels, while the assembly of the racemate only produced precipitates. Remarkably, the racemic hydrogels show lower CGC value, enhanced mechanical rigidity, and dual pH-responsive ability compared to the pure enantiomer hydrogels. The gelation properties, nanoscale chirality, and nanostructures of the racemic hydrogels can be regulated flexibly by changing molar ratios of different molecular building blocks.

Gelation induced supramolecular chirality: chirality transfer, amplification and application

Supramolecular chirality defines chirality at the supramolecular level, and is generated from the spatial arrangement of component molecules assembling through non-covalent interactions such as hydrogen bonding, van der Waals interactions, π-π stacking, hydrophobic interactions and so on. During the formation of low molecular weight gels (LMWGs), one kind of fascinating soft material, one frequently encounters the phenomenon of chirality as well as chiral nanostructures, either from chiral gelators or even achiral gelators. A view of gelation-induced supramolecular chirality will be very helpful to understand the self-assembly process of the gelator molecules as well as the chiral structures, the regulation of the chirality in the gels and the development of the "smart" chiral materials such as chiroptical devices, catalysts and chiral sensors. It necessitates fundamental understanding of chirality transfer and amplification in these supramolecular systems. In this review, recent progress in gelation-induced supramolecular chirality is discussed.

Self-assembly of azobenzene-based two-component gels

Two-component gels were formed and their photophysical properties were dependent on the ratio of the two compounds.

A new ex-TTF-based organogelator: formation of organogels and tuning with fullerene

A new ex-TTF-based organogelator with L-glutamide-derived lipid unit (compound 1) was synthesized and characterized. The resulting transparent organogels can be obtained with several organic solvents such as toluene, DMSO, and ethanol. It is interesting that its gelation ability can be further enhanced by addition of C(60). The (1)H NMR and absorption spectral studies indicate that the intermolecular interaction between the ex-TTF unit in 1 and C(60) may be responsible for this phenomenon. Further studies imply that the assembly structures in the gel phases in the absence and presence of C(60) may be different. Additionally, organogels can also be prepared with compound 1 and PCBM, and the corresponding xerogel was used to modify ITO electrode. A stable and rapid photocurrent was generated after exposure of the modified ITO electrode to light. This may provide an alternative way for photocurrent generation with high energy conversion efficiency.

Hybrid self-assembly of a pi gelator and fullerene derivative with photoinduced electron transfer for photocurrent generation

A pi-conjugated organogelator (1) was synthesized, and its gelation ability was checked. It was found that it is an excellent gelator for some organic solvents, such as dichloromethane, benzene, o-dichlorobenzene, and DMSO/water. It can self-assemble into 1-D nanofibers induced by hydrogen bonding and pi-pi interactions. Moreover, 1 could form a hybrid gel with C(60)COOH by hydrogen bonds in which 1 and C(60)COOH can act as an electron donor and acceptor, respectively. It was found that the active film from the hybrid 1-D self-assemblies of 1 and C(60)COOH showed remarkably higher photocurrent generation compared with that containing 1 and C(60) because of the construction of interdigitated and ordered assemblies of donors and acceptors.