Giant surfactants provide a versatile platform for sub-10-nm nanostructure engineering.

The engineering of structures across different length scales is central to the design of novel materials with controlled macroscopic properties. Herein, we introduce a unique class of self-assembling materials, which are built upon shape- and volume-persistent molecular nanoparticles and other structural motifs, such as polymers, and can be viewed as a size-amplified version of the corresponding small-molecule counterparts. Among them, "giant surfactants" with precise molecular structures have been synthesized by "clicking" compact and polar molecular nanoparticles to flexible polymer tails of various composition and architecture at specific sites. Capturing the structural features of small-molecule surfactants but possessing much larger sizes, giant surfactants bridge the gap between small-molecule surfactants and block copolymers and demonstrate a duality of both materials in terms of their self-assembly behaviors. The controlled structural variations of these giant surfactants through precision synthesis further reveal that their self-assemblies are remarkably sensitive to primary chemical structures, leading to highly diverse, thermodynamically stable nanostructures with feature sizes around 10 nm or smaller in the bulk, thin-film, and solution states, as dictated by the collective physical interactions and geometric constraints. The results suggest that this class of materials provides a versatile platform for engineering nanostructures with sub-10-nm feature sizes. These findings are not only scientifically intriguing in understanding the chemical and physical principles of the self-assembly, but also technologically relevant, such as in nanopatterning technology and microelectronics.

Two-dimensional nanocrystals of molecular Janus particles.

This paper describes a rational strategy to obtain self-assembled two-dimensional (2D) nanocrystals with definite and uniform thickness from a series of molecular Janus particles based on molecular nanoparticles (MNPs). MNPs are 3D framework with rigid shapes. Three different types of MNPs based on derivatives of polyhedral oligomeric silsesquioxane (POSS), [60]fullerene (C60), and Lindqvist-type polyoxometalate (POM) are used as building blocks to construct these amphiphilic molecular Janus particles by covalently connecting hydrophobic crystalline BPOSS with a charged hydrophilic MNP. The formation of 2D nanocrystals with an exact thickness of double layers of molecules is driven by directional crystallization of the BPOSS MNP and controlled by various factors such as solvent polarity, number of counterions, and sizes of the MNPs. Strong solvating interactions of the ionic MNPs in polar solvents (e.g., acetonitrile and dimethylformamide) are crucial to provide repulsive interactions between the charged outlying ionic MNPs and suppress further aggregation along the layer normal direction. The number of counterions per molecule plays a major role in determining the self-assembled morphologies. Size matching of the hydrophobic and ionic MNPs is another critical factor in the formation of 2D nanocrystals. Self-assembly of rationally designed molecular Janus particles provides a unique "bottom-up" strategy to engineer 2D nanostructures.

Self-assembly of fullerene-based janus particles in solution: effects of molecular architecture and solvent.

Two molecular Janus particles based on amphiphilic [60]fullerene (C60 ) derivatives were designed and synthesized by using the regioselective Bingel-Hirsh reaction and the click reaction. These particles contain carboxylic acid functional groups, a hydrophilic fullerene (AC60 ), and a hydrophobic C60 in different ratios and have distinct molecular architectures: 1:1 (AC60 -C60 ) and 1:2 (AC60 -2C60 ). These molecular Janus particles can self-assemble in solution to form aggregates with various types of micellar morphology. Whereas vesicular morphology was observed for both AC60 -C60 and AC60 -2C60 in tetrahydrofuran, in a mixture of N,N-dimethylformamide (DMF)/water, spherical micelles and cylindrical micelles were observed for AC60 -C60 and AC60 -2C60 , respectively. A mechanism of formation was tentatively proposed based on the effects of molecular architecture and solvent polarity on self-assembly.

Giant molecular shape amphiphiles based on polystyrene-hydrophilic [60]fullerene conjugates: click synthesis, solution self-assembly, and phase behavior.

This paper reports a comprehensive study on the synthesis and self-assembly of two model series of molecular shape amphiphiles, namely, hydrophilic [60]fullerene (AC(60)) tethered with one or two polystyrene (PS) chain(s) at one junction point (PS(n)-AC(60) and 2PS(n)-AC(60)). The synthesis highlighted the regiospecific multiaddition reaction for C(60) surface functionalization and the Huisgen 1,3-dipolar cycloaddition between alkyne functionalized C(60) and azide functionalized polymer to give rise to shape amphiphiles with precisely defined surface chemistry and molecular topology. When 1,4-dioxane/DMF mixture was used as the common solvent and water as the selective solvent, these shape amphiphiles exhibited versatile self-assembled micellar morphologies which can be tuned by changing various parameters, such as molecular topology, polymer tail length, and initial molecular concentration, as revealed by transmission electron microscopy and light scattering experiments. In the low molecular concentration range of equal or less than 0.25 (wt) %, micellar morphology of the series of PS(n)-AC(60) studied was always spheres, while the series of 2PS(n)-AC(60) formed vesicles. Particularly, PS(44)-AC(60) and 2PS(23)-AC(60) are synthesized as a topological isomer pair of these shape amphiphiles. PS(44)-AC(60) formed spherical micelles while 2PS(23)-AC(60) generated bilayer vesicles under identical conditions. The difference in the self-assembly of PS(n)-AC(60) and 2PS(n)-AC(60) was understood by the molecular shape aspect ratio. The stretching ratio of PS tails decreased with increasing PS tail length in the spherical micelles of PS(n)-AC(60), indicating a micellar behavior that changes from small molecular surfactant-like to amphiphilic block copolymer-like. For the series of PS(n)-AC(60) in the high molecular concentration range [>0.25 (wt) %], their micellar morphological formation of spheres, cylinders, and vesicles was critically dependent upon both the initial molecular concentration and the PS tail length. On the other hand, the series of 2PS(n)-AC(60) remained in the state of bilayer vesicles in the same concentration range. Combining both of the experimental results obtained in the low and high molecular concentrations, a systematic morphological phase diagram was constructed for the series of PS(n)-AC(60) with different PS tail lengths. The versatile and concentration-sensitive phase behaviors of these molecular shape amphiphiles are unique and have not been systematically explored in the traditional surfactants and block copolymers systems.

A giant surfactant of polystyrene-(carboxylic Acid-functionalized polyhedral oligomeric silsesquioxane) amphiphile with highly stretched polystyrene tails in micellar assemblies.

A novel giant surfactant possessing a well-defined hydrophilic head and a hydrophobic polymeric tail, polystyrene-(carboxylic acid-functionalized polyhedral oligomeric silsesquioxane) conjugate (PS-APOSS), has been designed and synthesized via living anionic polymerization, hydrosilylation, and thiol-ene "click" chemistry. PS-APOSS forms micelles in selective solvents, and the micellar morphology can be tuned from vesicles to wormlike cylinders and further to spheres by increasing the degree of ionization of the carboxylic acid. The effect of APOSS-APOSS interactions was proven to be essential in the morphological transformation of the micelles. The PS tails in these micellar cores were found to be highly stretched in comparison with those in traditional amphiphilic block copolymers, and this can be explained in terms of minimization of free energy. This novel class of giant surfactants expands the scope of macromolecular amphiphiles and provides a platform for the study of the basic physical principles of their self-assembly behavior.

High performance planar heterojunction perovskite solar cells with fullerene derivatives as the electron transport layer.

In this study, we report the utilization of solution-processed high electrical conductive [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) combined with solution-processed TiO2 as the electron transport layer (ETL) to overcome extremely low electrical conductivity of solution-processed TiO2 ETL in planar heterojunction (PHJ) perovskite hybrid solar cells (pero-HSCs). Due to the much more preferable electron extraction and transportation of PC61BM at the cathode side, a tremendously boosted short-circuit current density (JSC), fill factor (FF) and enhanced power conversion efficiency (PCE) are observed. To further address the wettability issues of perovskite materials on the top of PC61BM, water-soluble fullerene derivative is applied to modulate the surface of PC61BM. Consequently, further advanced FF with slightly enlarged JSC and open-circuit voltage (VOC) are observed. The resulted PCE is comparable with the meso-superstructured solar cells in which high PCEs can be produced. Our studies certainly provide a simple approach to boost the efficiency of PHJ pero-HSCs.

Facile synthesis and photophysical properties of sphere-square shape amphiphiles based on porphyrin-[60]fullerene conjugates.

Molecules constructed from a combination of zero-dimensional ([60]fullerene (C60)) and two-dimensional (porphyrin (Por)) nanobuilding blocks represent an intriguing category of sphere-square "shape amphiphiles". These sphere-square shape amphiphiles possess interesting optoelectronic properties. To efficiently synthesize a large variety of C60-Por shape amphiphiles, a facile route based on Steglich esterification was developed. The synthetic strategy enables the preparation of hydroxy-functionalized Por precursors (9-12) with high purity in a one-pot procedure. All of the C60-Por shape amphiphiles (1-5) can be readily synthesized in good yields through subsequent Steglich esterification with a highly soluble carboxylic acid derivative of methanofullerene (13). Photophysical studies indicated weak electronic coupling between the C60 and Por moieties and suggest an edge-to-face alignment for the moieties. The fluorescence of electronically excited Por portions of each amphiphile was efficiently quenched, which was indicative of electron transfer from (1)Por to the C60 group(s). Increasing the number of C60 groups on the shape amphiphiles led to more pronounced quenching of the Por fluorescence, which indicated the potential for more effective generation of charge-separated species, C60(-.)Por(+.), from the photoexcited C60-Por shape amphiphiles.

Poly(beta-alanoid-block-beta-alanine)s: synthesis via cobalt-catalyzed carbonylative polymerization and self-assembly.

The titled diblock copolymers are synthesized via cobalt-catalyzed living carbonylative polymerization of N-alkylaziridines under moderate pressures followed by a deprotection step. The poly(beta-alanine) block is solubilized by the poly(beta-alanoid) block in chloroform and remains fully hydrogen-bonded in the form of a sheet-like assembly.

Self-assembly of a novel alternant amphiphilic poly(OPE-alt-TEO) copolymer: from nanowires to twist fibrillar architectures with molecular dimensions.

A novel alternant amphiphilic polymer poly[1,4-bis(phenylethynyl)-2,5-bis(hexyloxy)benzene-alt-tetra(ethylene oxide)] was prepared. Atom force microscope (AFM) images showed that the molecular self-assembly morphologies changed from molecular nanowires to twist fibrillar architectures with the increase of the solution concentrations. Short and thin wires formed in dilute solution, while large bundles developed in relatively concentrated ones, shown by fluorescence microscope images. The photoluminescence (PL) spectra of the corresponding films indicate a self-assembly process of the polymers under slow solvents evaporation. Coplanar aggregation was confirmed through PL and photoluminescence excitation (PLE) spectra. Furthermore, the self-assembly process in polymer bulk was studied by wide-angle X-ray diffraction. To the best of our knowledge, it is the first time to reveal the change of the molecular morphologies with the altering concentration for the alternant amphiphilic conjugated polymers.