Interfacial Assembly of a Series of Cinnamoyl-Containing Bolaamphiphiles: Spacer-Controlled Packing, Photochemistry, and Odd–Even Effect

A series of bolaamphiphiles with 4-hydroxycinnamoyl head groups and different length of the alkyl spacers (<i>n</i> = 6–12) were designed to investigate their photochemistry in the organized films obtained from the air/water interface. It has been found that both the length and odd–even number of the spacers can finely tune the molecular packing as well as the photochemistry. When the spacer length was changed from 6 to 12 methylene units, the assemblies changed from J aggregate to H aggregate. The molecules with even-numbered polymethylene spacer tend to form three-dimensional nanorod structure at the air/water interface. For the assembly of derivatives with odd-numbered spacers, diverse morphologies such as nanospirals and nanofibers were observed depending on the chain length and the surface pressures. The different packing of bolaamphiphiles could subsequently affect the photochemistry of the cinnamoyl groups in the organized films. The spacer effect in the assembly can be understood from the cooperation between H-bond of the phenolic hydroxyl and the amide groups, π–π stacking as well as the hydrophobic interactions of the alkyl spacer. A packing model was proposed to explain the phenomenon

Ag/AgBr/Graphene Oxide Nanocomposite Synthesized via Oil/Water and Water/Oil Microemulsions: A Comparison of Sunlight Energized Plasmonic Photocatalytic Activity

In this article, we report that Ag/AgBr nanostructures and the corresponding graphene oxide (GO) hybridized nanocomposite, Ag/AgBr/GO, could be facilely synthesized by means of a surfactant-assisted assembly protocol, where an oil/water microemulsion is used as the synthesis medium. We show that thus-produced nanomaterials could be used as highly efficient and stable plasmonic photocatalysts for the photodegradation of methyl orange (MO) pollutant under sunlight irradiation. Compared with the bare Ag/AgBr nanospecies, Ag/AgBr/GO displays distinctly enhanced photocatalytic activity. More importantly, the as-prepared nanostructures exhibit higher photocatalytic activity than that of the corresponding Ag/AgBr-based nanomaterials synthesized via<i> </i>a water/oil microemulsion and than that of the corresponding Ag/AgCl-based nanospecies synthesized by an oil/water microemulsion. An explanation has been proposed for these interesting findings. Our results suggest that thus-manufactured Ag/AgBr/GO plasmonic photocatalysts are promising alternatives to the traditional UV light or visible-light driven photocatalysts

Reversible Plasmonic Circular Dichroism <i>via</i> Hybrid Supramolecular Gelation of Achiral Gold Nanorods

The fabrication of chiroptical plasmonic nanomaterials such as chiral plasmonic gold nanorods (GNRs) has been attracting great interest. Generally, in order to realize the plasmonic circular dichroism (PCD) from achiral GNRs, it is necessary to partially replace the surface-coated cetyltrimethylammonium bromide with chiral molecules. Here, we present a supramolecular approach to generate and modulate the PCD of GNRs through the hybrid gelation of GNRs with an amphiphilic chiral dendron gelator. Upon gelation, the PCD could be produced and further regulated depending on the ratio of the dendrons to GNRs. It was revealed that the wrapping of the self-assembled nanofibers around the GNRs is crucial for generating the PCD. Furthermore, the hybrid gel underwent a thermotriggered gel–sol and sol–gel transformation, during which the PCD can disappear (solution) and reappear (gel), respectively, and such process can be repeated many times. In addition, the hybrid gel could also undergo shrinkage upon addition of a slight amount of Mg²⁺ ions, during which the PCD disappeared also. Thus, through the gel formation and subsequent metal ion- or temperature-triggered phase transition, PCD can be reversibly modulated. The results not only clarified the generation mechanism of PCD from the achiral GNRs without the chiral modification on the surface but also offered a simple and efficient way to modulate the PCD

Binary Supramolecular Gel of Achiral Azobenzene with a Chaperone Gelator: Chirality Transfer, Tuned Morphology, and Chiroptical Property

Binary supramolecular gels based on achiral azobenzene derivatives and a chiral chaperone gelator, long-alkyl-chain-substituted L-Histidine (abbreviated as LHC18) that could assist many nongelling acids in forming gels, were investigated in order to fabricate the chiroptical gel materials in a simple way. It was found that although the carboxylic acid-terminated achiral azobenzene derivatives could not form gels in any solvents, when mixed with LHC18 they formed the co-gels and self-assembled into various morphologies ranging from nanotubes and loose nanotubes to nanosheets, depending on the substituent groups on the azobenzene moiety. The ether linkage and the number of carboxylic acid groups attached to the azobenzene moiety played important roles. Upon gel formation, the localized molecular chirality in LHC18 could be transferred to the azobenzene moiety. Combined with the trans–cis isomerization of the azobenzene, optically and chiroptically reversible gels were generated. It was found that the gel based on azobenzene with two carboxylic acid groups and ether linkages showed clear optical reversibility but less chiroptical reversibility, whereas the gel based on azobenzene with one carboxylic acid and an ether linkage showed both optical and chiroptical reversibility. Thus, new insights into the relationship among the molecular structures of the azobenzene, self-assembled nanostructures in the gel and the optical and chiroptical reversibility were disclosed

Roles of Long-Range Hopping, Quantum Nuclear Effect, and Exciton Delocalization in Exciton Transport in Organic Semiconductors: A Multiscale Study

Excitation energy transport in organic materials is of significance for determining the efficiency of light-harvesting systems. With the improved material preparation and device fabrication, the experimentally measured exciton diffusion length has increased rapidly in recent years and far exceeds the typical values found in synthetic organic systems on the order of 10 nm, calling for better understanding and evaluation of the intrinsic exciton diffusion property. We investigate the energy transport at three different levels, ranging from the semiclassical Marcus theory, to the quantum nuclear tunneling-mediated hopping, and eventually to the time-dependent exciton diffusion in organic semiconductors. All the calculations are based on first-principles evaluated molecular parameters. We find that the nuclear quantum effect can strongly enhance the exciton diffusion length by orders of magnitude. Both long-range energy transfer and exciton delocalization effects can also be identified

Porphyrin Assemblies via a Surfactant-Assisted Method: From Nanospheres to Nanofibers with Tunable Length

In this paper, we report that a porphyrin, zinc 5,10,15,20-tetra­(4-pyridyl)-21H,23H-porphine (ZnTPyP), could be organized to form one-dimensional (1D) nanofibers via a surfactant-assisted self-assembly (SAS) method. We disclose that when a chloroform solution of ZnTPyP is dropwise added into an aqueous solution of cetyltrimethylammonium bromide (CTAB), spherical nanostructures are formed at the initial stage. The nanospheres are naturally transformed into 1D nanostructures simply by aging under ambient conditions. Interestingly, by adjusting the volume of the employed ZnTPyP chloroform solution, the length of thus-produced 1D nanoarchitectures could be efficiently controlled. It is disclosed that longer nanofibers could be manufactured when a small volume of chloroform solution of ZnTPyP is involved, while shorter 1D nanospecies could be produced when a large volume of chloroform solution of ZnTPyP is employed. The 1D nanostructures are characterized by UV–visible spectra, scanning electron microscopy, low-resolution transmission electron microscopy, high-resolution transmission electron microscopy, and fast Fourier transformation. A solubility experiment has been carried out to disclose the dispersibility of our ZnTPyP in plain water and in CTAB aqueous solution. On the basis of the experimental facts, an explanation is proposed for these interesting new findings. The investigation provides new opportunities for the controllable assembly of porphyrin-based 1D nanomaterials with tunable length, and it sheds new scientific insights on the molecular assembly process occurring in the SAS system, wherein an oil/water system is used as the assembly medium

Self-Assembly of Triangular Amphiphiles into Diverse Nano/Microstructures and Release Behavior of the Hollow Sphere

Amphiphilic triangular derivatives containing imine bond have been designed and used as building blocks for the construction of soft colloidal materials. The acylhydrazone derivative was found to form various nano/microstructures in different solvents. The microspheres, flower-like, and hollow spheres were formed in the polar solvents, while organogels with microporous structures were formed in nonpolar solvents. However, the simple Schiff base amphiphile without amide group did not form any ordered structures in the tested solvents. Therefore, besides the π–π stacking between the aromatic core and the van der Waals interactions between the alkyl chains, the hydrogen bonding between the acylhydrazone moieties played an important role in promoting the formation of various organized structures. More interestingly, the hollow sphere structure which was formed in THF could be used to encapsulate and release the rhodamine B. It was found that rhodamine B was encapsulated within their interiors under neutral conditions and released in an acidic condition due to the breakage of the imine bond

One-Dimensional Porphyrin Nanoassemblies Assisted via Graphene Oxide: Sheetlike Functional Surfactant and Enhanced Photocatalytic Behaviors

Surfactant-assisted self-assembly (SAS) has received much attention for supramolecular nanoassemblies, due to its simplicity and easiness in realizing a controllable assembly. However, in most of the existing SAS protocols, the employed surfactants work only as a regulator for a controllable assembly but not as active species for function improvement. In this paper, we report that a porphyrin, zinc 5,10,15,20-tetra­(4-pyridyl)-21H,23H-porphine (ZnTPyP), could be assembled to form one-dimensional (1D) supramolecular nanostructures via a SAS method, wherein graphene oxide (GO) plays a fascinating role of sheetlike surfactant. We show that, when a chloroform or tetrahydrofuran solution of ZnTPyP is injected into an aqueous dispersion of GO, 1D supramolecular nanoassemblies of ZnTPyP with well-defined internal structures could be easily formulated in a controllable manner. Our experimental facts disclose that the complexation of ZnTPyP with the two-dimensional GO nanosheets plays an important role in this new type of SAS. More interestingly, compared with the 1D ZnTPyP nanoassemblies formulated via a conventional SAS, wherein cetyltrimethylammonium bromide is used as surfactant, those constructed via our GO-assisted SAS display distinctly enhanced photocatalytic activity for the photodegradation of rhodamine B under visible-light irradiation. Our new findings suggest that GO could work not only as an emergent sheetlike surfactant for SAS in terms of supramolecular nanoassembly but also as functional components during the performance of the assembled nanostructures

Dynamic Evolution of Coaxial Nanotoruloid in the Self-Assembled Naphthyl-Containing l‑Glutamide

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

Self-Assembly of Amphiphilic Dipeptide with Homo- and Heterochiral Centers and Their Application in Asymmetric Aldol Reaction

Chiral self-assembly has drawn increasing interest in supramolecular chemistry. Here, we have designed amphiphilic l-Pro–l-Glu and l-Pro–d-Glu dipeptides and investigated their chiral self-assembly as well as asymmetric catalytic performance to disclose the synergistic effect of two stereogenic centers in the self-assembly and catalysis. It was found that both of the diastereomeric dipeptides can easily self-assemble into organogels with nanofibers. When these nanofibers were used as a catalyst for the asymmetric aldol reactions, enhanced enantioselectivity was obtained compared with their molecular state. Moreover, the L–L isomer assemblies showed higher enantioselectivity than the L–D isomer. It was revealed that both the supramolecular chirality of the nanofiber and the chiral catalytic site of l-proline played important roles in the asymmetric catalysis. In addition, the synergistic effect of two homochiral centers led to more efficient supramolecular catalysis that the L–L assemblies showed high yields (up to 97%), anti-diastereoselectivity (up to 99%), and excellent enantioselectivity (up to >99%)