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A C3-symmetric molecule was found to form organic nanotubes through supramolecular gel formation in organic solvents. These nanotubes can be dispersed in toluene without destroying the tubular nanostructures. Using the dispersions of these organic nanotubes as "spreading solutions", Langmuir-spreading films of these nanotubes were formed. Through repeated compression and expansion cycles, the nanotubes can be aligned to a certain extent. The formed Langmuir films could be subsequently transferred to a solid substrate, and the well-aligned nanotube films were constructed by Langmuir-Blodgett film deposition technique. Interestingly, many guests including polymers, water-soluble or oil-soluble organic molecules can be encapsulated into the nanotubes and further spread on a water subphase. Through elaborate control, large-scale parallel alignment of self-assembled organic nanotubes encapsulated by guests was also realized. This study implies that 2D hierarchical alignment of one-dimensional organic nanostructures can be realized using a simple method. [ABSTRACT FROM AUTHOR]

Supramolecular gelation provides an efficient way of fabricating functional soft materials with various nanostructures. Amphiphiles containing naphthyl group and dialkyl l-glutamide with a methylene spacer, 1NALG and 2NALG, have been designed and their self-assembly in various organic solvents were investigated. Both of these compounds formed organogels in organic solvents. In the case of the alcohol solvents, the initially formed organogel underwent gel-precipitate transformation, which process was monitored by the UV-vis, CD spectra, and SEM observation. It was revealed that both the compounds formed the nanofiber structures in gel phases. Interestingly, in alcohol solvents, during the phase transition from the gel to precipitates, the nanofibers gradually transformed into a series of long coaxial solid nanotoruloid, a unique nanostructure that has never been observed in other self-assembly systems. In addition, during the gel formation, the nanofibers with supramolecular chirality or M-chirality were obtained. However, the coaxial nanotoruloid showed an inversed P-chirality. Comprehensive analysis based on various data and the gelator structure, substituent position, type of organic solvents, it was suggested that the synergistic interactions between the amide H-bond and π-π stacking of the naphthyl groups played important roles in the formation of the gels as well as the nanofiber, while the H-bonding ability of alcohol to the amide group can subtly regulate the gelator-gelator interactions and lead to the dynamic and hierarchical evolution of the unique nanostructures. [ABSTRACT FROM AUTHOR]

The supramolecular self-assembly of copper(II) octaethylporphyrin (CuOEP) and octaethylporphyrin (H2OEP) on graphitic surfaces immersed in organic solvents (dichlorobenzene, dodecane) is studied using scanning tunneling microscopy (STM) and Raman spectroscopy. STM reveals that the self-assembled structure of CuOEP in 1,2-dichlorobenzene is significantly altered by dissolved oxygen within the solvent. Raman spectroscopy reveals that the presence of the oxygen alters the molecule-substrate interaction, which is attributed to the adsorption of oxygen on the Cu center of the CuOEP, which is facilitated by electron transfer from the graphitic surface. Such oxygen-induced changes are not observed for H2OEP, indicating that the metal center of CuOEP plays a critical role. When the solvent is dodecane, we find that solvation effects dominate. CuOEP adsorbed on graphitic surfaces provides a model system relevant to the study of the transport and activation of oxygen by enzymes and other complexes. [ABSTRACT FROM AUTHOR]

We present a general route for the transfer of Au and Ag nanoparticles of different shapes and sizes, from water into various organic solvents. The experimental conditions for each type of nanoparticles were optimized by using a combination of thiolated poly(ethylene glycol) and a hydrophobic capping agent, such as dodecanethiol. The functionalized nanoparticles were readily transferred into organic dispersions with long-term stability (months). Such organic dispersions efficiently spread out on water, leading to self-assembly at the air/liquid interface into extended nanoparticle arrays which could in turn be transferred onto solid substrates. The dense close packing in the obtained nanoparticle monolayers results in extensive plasmon coupling, rendering them efficient substrates for surface-enhanced Raman scattering spectroscopy. [ABSTRACT FROM AUTHOR]

We present a fast and efficient strategyfor the preparation ofphotonic hydrogels for compression and organic solvent sensing bythe self-assembly of monodisperse carbon-encapsulated Fe3O4nanoparticles (NPs). The hydrogel film was composedof acrylamide (AM) and cross-linker N,N′-methylenebis(acrylamide) (BIS), and the formed 1D NPs chainstructure can be fixed within the hydrogels under a magnetic fieldby in situ photopolymerization. The resulting photonic hydrogels displayvivid structural color which can be tuned by pressing and organicsolvent treatment. The 0.2 kPa compression applied to the photonichydrogels can be detected by the 37 nm blue shift of a reflectionpeak. Importantly, the photonic hydrogels can recover to their originalstate (<1 s) after being compressed on a pattern. Moreover, thesensitivity of mechanochromic photonic hydrogels can be adjusted bymanipulating the concentration of monomers, and a large reflectionpeak shift (4.3 kPa, 200 nm) was observed. The detection range ofthe compression sensor can thus increase from 0–4.3 to 0–130.6kPa. The photonic hydrogels are nearly monochromatic, with high sensitivityand stability and fast reversibility, and are potentially useful indisplays, diagnostics, compression and solvent sensing. [ABSTRACT FROM AUTHOR]

Understanding the factors that affectmolecular self-assembly iscrucial to building designed nanoscale structures. We have depositednanoscale films of polyhedral oligomeric silsesquioxane (POSS) ontopolished silicon substrates from a range of organic solvents. We studiedthese films using synchrotron X-ray reflectivity and found that dip-coatingfrom benzene, toluene, or chloroform results in near-substrate orderingonly, but when acetone, hexane, or THF is used, self-assembled layersare formed throughout the entire deposited film. We conclude thatsolvent polarizability is the factor that determines the alignmentof the POSS molecules. We have successfully tested this predictionusing additional solvents selected on the basis of their calculatedpolarizabilities. [ABSTRACT FROM AUTHOR]

Novel,stimulus-responsive supramolecular structures in the formof fibers, gels, and spheres, derived from an azobenzene-containingbenzenetricarboxamide derivative, are described. Self-assembly oftris(4-((E)-phenyldiazenyl)phenyl)benzene-1,3,5-tricarboxamide(Azo-1) in aqueous organic solvent systems results insolvent dependent generation of microfibers (aq DMSO), gels (aq DMF),and hollow spheres (aq THF). The results of a single crystal X-raydiffraction analysis of Azo-1(crystallized from a mixtureof DMSO and H2O) reveal that it possesses supramolecularcolumnar packing along the baxis. Data obtainedfrom FTIR analysis and density functional theory (DFT) calculationsuggest that multiple hydrogen bonding modes exist in the Azo-1fibers. UV irradiation of the microfibers, formed in aq DMSO, causescomplete melting while regeneration of new fibers occurs upon visiblelight irradiation. In addition to this photoinduced and reversiblephase transition, the Azo-1supramolecules display areversible, fiber-to-sphere morphological transition upon exposureto pure DMSO or aq THF. The role played by amide hydrogen bonds inthe morphological changes occurring in Azo-1is demonstratedby the behavior of the analogous, ester-containing tris(4-((E)-phenyldiazenyl)phenyl)benzene-1,3,5-tricarboxylate (Azo-2) and by the hydrogen abstraction in the presence offluoride anions. [ABSTRACT FROM AUTHOR]

The engineering of single moleculesinto higher-order hierarchical assemblies is a current research focusin molecular materials chemistry. Molecules containing π-conjugatedunits are an important class of building blocks because their self-assemblyis not only of fundamental interest, but also the key to fabricatingfunctional systems for organic electronic and photovoltaic applications.Functionalizing the π-cores with “alkyl chains”is a common strategy in the molecular design that can give the systemdesirable properties, such as good solubility in organic solventsfor solution processing. Moreover, the alkylated-π system canregulate the self-assembly behavior by fine-tuning the intermolecularforces. The optimally assembled structures can then exhibit advancedfunctions. However, while some general rules have been revealed, acomprehensive understanding of the function played by the attachedalkyl chains is still lacking, and current methodology is system-specificin many cases. Better clarification of this issue requires contributionsfrom carefully designed libraries of alkylated-π molecular systemsin both self-assembly and nonassembly materialization strategies.Here, based on recent efforts toward this goal, we show the powerof the alkyl chains in controlling the self-assembly of soft molecularmaterials and their resulting optoelectronic properties. The designof alkylated-C60is selected from our recent research achievements,as the most attractive example of such alkylated-π systems.Some other closely related systems composed of alkyl chains and π-unitsare also reviewed to indicate the universality of the methodology.Finally, as a contrast to the self-assembled molecular materials,nonassembled, solvent-free, novel functional liquid materials arediscussed. In doing so, a new journey toward the ultimate organic“soft” materials is introduced, based on alkylated-πmolecular design. [ABSTRACT FROM AUTHOR]

Polymers formed by the self-assembly of a bis(urea)-basedpolymer,2,4-bis(2-ethylhexylureido)toluene (EHUT), in organic solvents suchas octane are promising systems with remarkable rheological properties.This is the first self-assembled polymer recently reported as a hydrodynamicdrag reducer for hydrocarbons. The rheology of diluted and semidilutedEHUT solutions can be tuned by specific interactions between the chains,modulated by the nature of the solvent and the presence of additives.In this article, rheological, thermal and SANS measurements were performedin order to investigate the competition between EHUT self-assemblyand its interaction with specific molecules (benzene, benzyl alcohol,and ethanol) that can interact with EHUT unimers via hydrogen bondsand π–π interactions. No substantial rheological,thermal, or structural effect is observed when benzene is added tothe systems. However, ethanol and benzyl alcohol interact with EHUTunimers through hydrogen bonds, drastically decreasing the viscoelasticityof the solutions. In addition, benzyl alcohol can interact with EHUTpolymers by π-stacking interactions, playing an important rolein tuning the rheological properties of the systems. [ABSTRACT FROM AUTHOR]

Mixed aquo-organic solvents are used in chemical, industrial,andpharmaceutical processes along with amphiphilic materials. Their fundamentalstudies with reference to bulk and interfacial phenomena are thusconsidered to be important, but such detailed studies are limited.In this work, the interfacial adsorption of sodium dodecylsulfate(SDS, C12H25SO4–Na) in dioxane–water(Dn–W) and methanol–water (Ml–W) media in extensivemixing ratios along with its bulk behavior have been investigated.The solvent-composition-dependent properties have been identified,and their quantifications have been attempted. The SDS micellizationhas been assessed in terms of different solvent parameters, and thepossible formation of an ion pair and triple ion of the colloidalelectrolyte, C12H25SO4–Na theDn–W medium has been correlated and quantified. In the Ml–Wmedium at a high volume percent of Ml, the SDS amphiphile formed specialassociated species instead of ion association. The formation of self-assemblyand the energetics of SDS in the mixed solvent media have been determinedand assessed using conductometry, calorimetry, tensiometry, viscometry,NMR, and DLS methods. The detailed study undertaken herein with respectto the behavior of SDS in the mixed aquo-organic solvent media (Dn–Wand Ml–W) is a new kind of endeavor. [ABSTRACT FROM AUTHOR]

In this paper, we report self-assembly of tetrachloroacenes containing pyrazine moieties. The title compounds, phenazine and bisphenazine substituted with four chlorine atoms for increased electron deficiency and alkyloxy side groups for solubility, demonstrated excellent gelation ability in select organic solvents. The assembled structure of these two series of compounds exhibited a morphological difference. Tetrachlorophenazine containing hexadecyloxy side groups induced rigid microbelts, while more extensive entanglement of thinner, more flexible fibers was observed from tetrachlorobisphenazine compounds, characterized by scanning electron microscopy. Tetrachlorophenazine and tetrachlorobisphenazine gels showed quite different emission behavior compared to their solution state. A strong, red-shifted emission compared to that of its diluted solution state was observed from the gel of tetrachlorophenazine. We have ascertained this is a result of J-aggregate formation. From the crystal structure of a model compound, it was found that tetrachlorophenazine cores adopt π–π stacking with a short stacking distance of 3.38 Å, enabling significant intermolecular π-orbital overlap. In addition, the π-cores were displaced longitudinally, indicative of J-aggregate formation. Surprisingly, the gel of tetrachlorobisphenazine showed fluorescence comparable to that of its dilute solution, suggesting that such a close packing of the π-cores may not be possible due to the bulky tert-butyl substituents. [ABSTRACT FROM AUTHOR]

New amphiphilic random copolymers containing hydrophobic dodecyl (C12) chain and hydrophilic l-glutamic acid were synthesized, and their self-assembly in solution as well as on the solid surfaces was investigated. The self-assembly behavior of these polymers are largely dependent on their hydrophilic and hydrophobic balances. The copolymer with a more hydrophobic alkyl chain (∼90%) self-assembled into giant vesicles with a diameter of several micrometers in a mixed solvent of ethanol and water. When the hydrophobic ratio decreased to ca. 76%, the polymer self-assembled into conventional vesicles with several hundred nanometers. The giant vesicles could be fused in certain conditions, while the conventional vesicles were stable. When the content of the hydrophilic part was further increased, no organized structures were formed. On the other hand, when the copolymer solutions were directly cast on solid substrates such as silicon plates, films with organized nanostructures could also be obtained, the morphology of which depended on solvent selection. When ethanol or methanol was used, spheres were obtained. When dichloromethane was used as the solvent, honeycomb-like morphologies were obtained. These results showed that through appropriate molecular design, random copolymer could self-assemble into various organized structures, which could be regulated through the hydrophobic/hydrophilic balance and the solvents. [ABSTRACT FROM AUTHOR]

Microencapsulates with defined core–shell structures are of interest for applications, such as controlled release and encapsulation, because of the feasibility of fine-tuning individual functionalities of different parts. Here, we report a new approach for efficient and scalable production of such particles. Eudragit RS (a co-polymer of ethyl acrylate, methyl methacrylate, and a low content of methacrylic acid ester with quaternary ammonium groups) was used as the main shell component, with silica as the core component, formed upon a single-step spray-drying assembly. The method is capable of forming uniform core–shell particles from homogeneous precursors without the use of any organic solvents. Evaporation-induced self-assembly attained the phase separation among different components during drying, resulting in the core–shell spatial configuration, while precise control over particle uniformity was accomplished via a microfluidic jet spray dryer. Direct control over shell thickness can be achieved from the ratio of the core and shell ingredients in the precursors. A fluorescent compound, rhodamine B, is used as a highly water-soluble model component to investigate the controlled release properties of these microencapsulates, with the release behaviors shown to be significantly dependent upon their architectures. [ABSTRACT FROM AUTHOR]

The self-assembly of diblock copolymers under soft confinement is studied systematically using a simulated annealing method applied to a lattice model of polymers. The soft confinement is realized by the formation of polymer droplets in a poor solvent environment. Multiple sequences of soft confinement-induced copolymer aggregates with different shapes and self-assembled internal morphologies are predicted as functions of solvent–polymer interaction and the monomer concentration. It is discovered that the self-assembled internal morphology of the aggregates is largely controlled by a competition between the bulk morphology of the copolymer and the solvent–polymer interaction, and the shape of the aggregates can be non-spherical when the internal morphology is anisotropic and the solvent–polymer interaction is weak. These results demonstrate that droplets of diblock copolymers formed in poor solvents can be used as a model system to study the self-assembly of copolymers under soft confinement. [ABSTRACT FROM AUTHOR]

Host–guest interactions between cyclohexasilane (Si6H12) and amphiphilic invertible macromolecules based on PEG and sebacic acid in acetonitrile (neither a solvent for cyclohexasilane nor a support for the micellization of amphiphilic invertible macromolecules) have been investigated. Despite the extended conformation of the macromolecules and the absence of self-assembled polymeric domains, a macromolecular amphiphilicity itself contributes to localizing Si6H12by AIP and thus enables Lewis acid–base interactions between Si6H12and the AIP carbonyl groups. The obtained results demonstrate an interesting phenomenon in that insoluble Si6H12can be localized by AIP macromolecules in a medium that does not support the formation of polymeric domains. [ABSTRACT FROM AUTHOR]

Gold nanoparticles functionalized with thiol-modified DNA have been widely used in making various nanostructures, colorimetric biosensors, and drug delivery vehicles. Over the past 15 years, significant progress has been made to improve the stability of such functionalized nanoparticles. The stability of the gold–thiol bond in this system, however, has not been studied in a systematic manner. Most information on the gold–thiol bond was obtained from the study of self-assembled monolayers (SAMs). In this study, we employed two fluorophore-labeled and thiol-modified DNAs. The long-term stability of the thiol–gold bond as a function of time, salt, temperature, pH, and organic solvent has been studied. We found that the bond spontaneously dissociated under all tested conditions. The dissociation was favored at high salt, high pH, and high temperature, and little DNA degradation was observed in our system. Most organic solvents showed a moderate protection effect on the gold–thiol bond. The stability of the gold–thiol bond in the DNA system was also compared with that in SAMs. While there are many similarities, we also observed opposite trends for the salt and ethanol effect. This study suggests that the purified DNA-functionalized gold nanoparticles should be freshly prepared and used in a day or two. Long-term storage should be carried out at relatively low temperature in low salt and slightly acidic buffers. [ABSTRACT FROM AUTHOR]

The self-assembled fibrillar network (SAFIN) organogels of a simple surfactant molecule, sodium laurate (C11H23COONa, SL), in organic solvents were investigated. The sol−gel transformation temperature depended on the SL concentration, the solvent, and the concentration of Na솫 evaluated. An important finding is that Na誉 play an important role in forming organogels, which was regarded as the induction factor of gelation, but other cations, for instance, Li, K, Ca2, and Mg2, do not have this capability. The observations by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) proved that the organogels were network structures with fibers and ribbons by trapping a certain amount of organic solvent. High-resolution TEM (HR-TEM) images indicated that each of the fibers or ribbons was composed of cylindrical micelles. The X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectra demonstrated that SL molecules in gels behave similarly to those in SL crystals. The mechanism of organogel formation was elaborated to provide a better understanding of fibrous surfactant gels in organic solvents. [ABSTRACT FROM AUTHOR]

This paper reports the self-assemblies of vesicles from two tetrathiafulvalene (TTF) derivatives (T1and T2), that bear four or two amphiphilic side chains, in both polar and nonpolar solvents. The formation of vesicles is evidenced by scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), and dynamic light scattering (DLS) experiments, while the microstructural aspects of the vesicles are investigated by UV−vis, 1H NMR, and high resolution TEM, which support a monolayer model for the vesicles. It is revealed that the formation of vesicles is driven by the combination of multiple noncovalent interactions, including π−π stacking, hydrogen-bonding, van der Waals force, and S···S interactions. It is also found that, in the presence of electron-deficient cyclobis(paraquat-p-phenylene) tetracation cyclophane, vesicles of T2can transform into microtubes as a result of the formation of the pseudo[2]rotaxane between the TTF unit of T2and the cyclophane. This process can be reversed by introducing pristine TTF into the solution of microtubes, due to release of T2from the pseudo[2]rotaxane through the formation of a more stable complex between pristine TTF and tetracation cyclophane. [ABSTRACT FROM AUTHOR]

A new type of hybrid supramolecular gel derived from a synergetic self-assembling of organic and inorganic components has been prepared through encapsulating a series of polyoxometalate (POM) clusters with ammonium surfactants bearing two alkyl chains. Among the general organic solvents we employed, some of surfactant-encapsulated POM (SEP) complexes readily gel with nonpolar solvents. Proper alkyl chain density, alkyl chain length, and shape of POM are proven to be favorable for fabricating stable SEP gels based on the results of critical gelation concentration and transition temperature from gel to solution. In addition, the shape of POM influences the aggregation morphologies of SEPs, stripes and spheres in gel phases, as confirmed by polarizing optical microscopic and scanning electron microscopic images. X-ray diffractions reveal that all the SEPs in gel states possess similar lamellar aggregation structures with POM layer inside and alkyl chain bilayers shielding from the nonpolar solvent on both sides. The combination of solvent effect, electrostatic, and dipole interaction is thought to be responsible for the formation of SEP gels. [ABSTRACT FROM AUTHOR]

This paper reports on experiments intended for investigating the feasibility of preparing hybrid thermoreversible gels from covalent polymers and noncovalent self-assembling π-conjugated molecules. The formation and the degree of dispersion of these hybrid gels have been studied with polystyrenes of various tacticities and oligo(p-phenylenevinylene) molecules (OPV) in different nonpolar organic solvents. Detailed investigations of the systems have been carried out by DSC, SAXS, and AFM. It is shown that no liquid−liquid phase separation is involved, indicating that the systems are highly compatible, and that the growth of one type of gel does not interfere with the other. These studies reveal that the resultant hybrid gels are composed of the intermingled fibrillar architectures of both gels. [ABSTRACT FROM AUTHOR]

A series of l-glutamate-based dendrons containing aromatic cores ranging from phenyl to naphthyl to anthryl were synthesized, and their self-assembly in organic solvents as well as in water was investigated. It was found that all of these dendrons formed organogels with hexane and simultaneously formed the hydrogels with water, thus exhibiting ambidextrous properties. Nanofiber structures are essentially formed in organogels and hydrogels, and some nanostrips are formed in some of the hydrogels. During gel formation, both hydrogen bonds between the amide groups and the π−π stacking between the aromatic rings played a predominant role in forming the 1D nanostructures. Both the hydrogels and the organogels containing naphthyl and anthryl groups showed fluorescence emission. In comparison with the corresponding compounds in solution, the naphthyl-containing dendrons showed a strong enhancement of fluorescence in the gel. In the case of anthryl-containing dendrons, fluorescence enhancement was observed for the derivative with anthryl substituted at the 9 position, whereas a decrease was observed for the gels of the 2-substituted derivative. Although the chirality of l-glutamate could not be transferred to the aromatic chromophores in solution, it was transferred to the chromophores in gels as a result of the self-assembly and strong π−π interaction of the gelators. On the basis of the properties of the organogels and hydrogels, a thermally driven chiroptical switch was proposed. That is, the chirality disappeared when the gel was heated to solution, whereas it returned when cooled to a gel. The process can be repeated many times. [ABSTRACT FROM AUTHOR]

Nine esters of a naturally occurring triterpenoid, arjunolic acid (from Terminalia arjuna), with alkyl chains have been synthesized, and their self-assembly has been studied in organic liquids. All of the esters examined were found to be excellent gelators. No birefringence was detected in optical micrographs of the transparent toluene gels with 5% (w/w) ethyl arjunolate or 5% (w/w) p-nitrobenzyl arjunolate as the gelator, but a spherulitic-type pattern was seen for a gel of 1.2% (w/w) p-nitrobenzyl arjunolate in 1/1 (w/w) chloroform/cyclohexane. Electron microscope images revealed self-assembled fibrillar network (SAFIN) structures with right-handed helical ribbons in some gels. With increasing concentration of the gelators, the gel-to-sol transition temperature (Tgel) increased and then approached plateau values. Differential scanning thermograms demonstrated that the heats for transition from transparent gels to sols of ethyl arjunolate or p-nitrobenzyl arjunolate in toluene are very small. Powder X-ray diffractograms revealed that the molecular packing in the SAFINof the 5% (w/w) ethyl arjunoate in the toluene gel was amorphous and similar to the diffractogram recorded for the neat gelator. Although the diffractogram of neat p-nitrobenzyl arjunolate consisted of broad peaks, suggesting disordered packing, the low-angle peaks of the corresponding toluene gel were much sharper; these results indicate more crystalline packing in the SAFINthan in the neat gelator. The kinetics and growth of the transformation of sols of p-nitrobenzyl arjunolate in 1/1 (w/w) chloroform/cyclohexane to their gels have been investigated at different incubation temperatures by circular dichroism spectroscopy. The data have been analyzed to probe the mechanism of SAFINformation and the relationship between the molecular structures of the esters of arjunolic acid and their abilities to function as gelators of a wide variety of organic liquids. [ABSTRACT FROM AUTHOR]

The domain of soluble metallopolymers (i.e., polymers spontaneously obtained from the self-assembly of metal ions and polytopic bridging ligands) is promising for the construction of novel materials with perspectives in magnetic, redox, optical, electrochromic, or mechanical properties. We report the preparation and characterization of metallo-supramolecular gels based on a multitopic cyclam bis-terpyridine platform (CHTT) that are representative of a second generation of molecular gels exhibiting “intelligent” properties. The systems were characterized by UV−visible spectroscopy, cyclic voltammetry, viscosimetry, rheology, and small-angle neutron scattering (SANS). A basic analysis of the viscosity taking into account the interplay of hydrodynamic versus Brownian motions of 1D species is proposed. SANS data demonstrate the formation of rod-like species whose radius Rand aspect ratio f= L/Rwere extracted. Rheological features are typical of weak gels having storage moduli of more than 1 order of magnitude weaker than for ordinary molecular organogels. These new molecular materials exhibit interesting properties: (i) chemosensitivity, with the gelation being dependent on the type of metal, stoichiometry M/CHTT, solvent, and counterion; (ii) electrosensitivity: the Co(II)/CHTTsystem can be electrochemically and reversibly commuted between the gel (red) and liquid (green) states; and (iii) mechanical sensitivity, with the system being able to cycle from weakly to highly viscous states upon fast application/suppression of a shearing stress. [ABSTRACT FROM AUTHOR]

New supramolecular organogels based on all-trans-tri(p-phenylenevinylene) (TPV) systems possessing different terminal groups, e.g., oxime, hydrazone, phenylhydrazone, and semicarbazone have been synthesized. The self-assembly properties of the compounds that gelate in specific organic solvents and the aggregation motifs of these molecules in the organogels were investigated using UV−vis, fluorescence, FT-IR, and 1H NMR spectroscopy, electron microscopy, differential scanning calorimetry (DSC), and rheology. The temperature variable UV−vis and fluorescence spectroscopy in different solvents clearly show the aggregation pattern of the self-assemblies promoted by hydrogen bonding, aromatic π-stacking, and van der Waals interactions among the individual TPV units. Gelation could be controlled by variation in the number of hydrogen-bonding donors and acceptors in the terminal functional groups of this class of gelators. Also wherever gelation is observed, the individual fibers in gels change to other types of networks in their aggregates depending on the number of hydrogen-bonding sites in the terminal functions. Comparison of the thermal stability of the gels obtained from DSC data of different gelators demonstrates higher phase transition temperature and enthalpy for the hydrazone-based gelator. Rheological studies indicate that the presence of more hydrogen-bonding donors in the periphery of the gelator molecules makes the gel more viscoelastic solidlike. However, in the presence of more numbers of hydrogen-bonding donor/acceptors at the periphery of TPVs such as with semicarbazone a precipitation as opposed to gelation was observed. Clearly, the choice of the end functional groups and the number of hydrogen-bonding groups in the TPV backbone holds the key and modulates the effective length of the chromophore, resulting in interesting optical properties. [ABSTRACT FROM AUTHOR]

A novel class of dumbbell-shaped dendritic molecules with a p-terphenylene core was synthesized, and their self-assembling properties were investigated. The incorporation of bulky dendritic wedges to the central stiff aromatic scaffolds could finely tune their solubility in many organic solvents. Unlike the self-assembly behavior of p-terphenylen-1,4′′-ylenebis(dodecanamide), the p-terphenylene cored different generation dendritic molecules could form gels in several kinds of organic solvents through a cooperative effect of the π−π stacking, hydrogen-bonding, and van der Waals forces. Interestingly, significant fluorescence enhancement was observed after gelation. Extensive investigations with atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), rheological measurements, UV−vis absorption spectroscopy, FT-IR spectroscopy, 1H NMR, and X-ray powder diffraction (XRD) revealed that these dendritic molecules self-assembled into elastically interpenetrating one-dimensional nanostructures in organogels. [ABSTRACT FROM AUTHOR]

A new salicylideneaniline-based organogelator has been synthesized, and it can gelatinize organic solvents, including cyclohexane, toluene, benzene, and some mixed solvents. SEM images show that it has self-assembled into 1-D nanofibers, which further cross-link to form 3-D network. On the basis of the results of small-angle XRD and the optimized molecular length by semiempirical quantum calculations, the gelators are supposed to pack into a unimolecular lamellar structure with a period of 3.01 nm. Significantly, reversible chromism is realized with respect of the tautomerism between the NH and OH forms during the sol−gel freezing repetition. Furthermore, the gel can emit intense green light, and the fluorescent quantum yield of the gel is approximately 600 times higher than that of the solution. The aggregation-induced emission enhancement is ascribed to the formation of Jaggregation and the inhibition of intramolecular rotation in the gel state. [ABSTRACT FROM AUTHOR]

The self-assembly of a modified fragment of the amyloid β peptide, based on sequence Aβ(16−20), KLVFF, extended to give AAKLVFF is studied in methanol. Self-assembly into peptide nanotubes is observed, as confirmed by electron microscopy and small-angle X-ray scattering. The secondary structure of the peptide is probed by FTIR and circular dichroism, and UV/visible spectroscopy provides evidence for the important role of aromatic interactions between phenylalanine residues in driving β-sheet self-assembly. The β-sheets wrap helically to form the nanotubes, the nanotube wall comprising four wrapped β-sheets. At higher concentration, the peptide nanotubes form a nematic phase that exhibits spontaneous flow alignment as observed by small-angle neutron scattering. [ABSTRACT FROM AUTHOR]

An atomic force microscope (AFM) was used to measure the forces between gold surfaces with and without hydrophobizing them by the self-assembly of 1-hexadecanethiol. The forces measured between bare gold surfaces were fitted to the Derjaguin−Landau−Verwey−Overbeek (DLVO) theory with a Hamaker constant of 1.2 × 10 −20J, which was close to the value determined using the methylene iodide contact angle method but was lower than that calculated using the Lifshitz theory. When the surfaces were hydrophobized in a 0.01 mM thiol-in-ethanol solution for 10 min, the measured forces exhibited a long-range force with a decay length of 35 nm. Despite its high water contact angle (105°), the force curve was smooth and exhibited no steps. When the surfaces were hydrophobized in a 1 mM thiol solution for longer than 6 h, however, the force curves exhibited steps, indicating that the long-range attractions were caused by bridging bubbles. When the measurements were conducted after washing the substrates with organic solvents, the steps disappeared and long-range attractive forces appeared. In the presence of ethanol, the water contact angle decreased to below 90°, the attraction became weaker, and the force curves became smooth. On the basis of the results obtained in the present work, possible mechanisms for the long-range attractions are discussed. [ABSTRACT FROM AUTHOR]

The mechanism of formation and the stability of spontaneously formed vesicles upon self-assembly of a partially ground-state charge-separated, nonpolar−polar−nonpolar fullerene(C60)-didodecyloxybenzene (DDB) dyad in binary solvent mixtures requiring a critical dielectric constant of ∼30 are reported. Molecular interactions giving rise to defined vesicles with in-plane bilayer packing are detailed from the predominant van der Waals and electrostatic interactions existing on the dyad's framework. The vesicles are formed with a large bending rigidity of 18kBT, which on further extraction into a polar water medium resulted in uniform spheres that corroborated well with the theoretical predictions. Furthermore, the water-extracted spherical dyad aggregates at an increased dyad concentration, leading to the formation of giant micrometer-sized fractals following diffusion-limited cluster aggregation. These dyad aggregates act as efficient quenchers of fluorescent dyes with a quenching rate of 4.6 × 1013M-1s-1. [ABSTRACT FROM AUTHOR]