Self-Sorting Supramolecular Polymerization: Helical and Lamellar Aggregates of Tetra-Bay-Acyloxy Perylene Bisimide

A new perylene bisimide (PBI), with a fluorescence quantum yield up to unity, self-assembles into two polymorphic supramolecular polymers. This PBI bears four solubilizing acyloxy substituents at the bay positions and is unsubstituted at the imide position, thereby allowing hydrogen-bond-directed self-assembly in nonpolar solvents. The formation of the polymorphs is controlled by the cooling rate of hot monomer solutions. They show distinctive absorption profiles and morphologies and can be isolated in different polymorphic liquid-crystalline states. The interchromophoric arrangement causing the spectral features was elucidated, revealing the formation of columnar and lamellar phases, which are formed by either homo- or heterochiral self-assembly, respectively, of the atropoenantiomeric PBIs. Kinetic studies reveal a narcissistic self-sorting process upon fast cooling, and that the transformation into the heterochiral (racemic) sheetlike self-assemblies proceeds by dissociation via the monomeric state.     

Nickel catalyzed cross-coupling of aryl C-O based electrophiles with aryl neopentylglycolboronates

The efficiency of mesylates, sulfamates, esters, carbonates, carbamates, and methyl ethers as C-O-based electrophiles attached to the 1- or 2-position of naphthalene and to activated and nonactivated phenyl substrates was compared for the first time in Ni-catalyzed cross-coupling with phenyl neopentylglycolboronates containing electron-rich and electron-deficient substituents in their para-position. These experiments were performed in the presence of four different Ni(II)- and Ni(0)-based catalysts. Ni(II)-based catalysts mediate the cross-coupling of most 2-naphthyl C-O electrophiles with both arylboronic acids and with neopentylglycolboronates when K(3)PO(4) is used as base. The same catalysts are not efficient when CsF is used as base. However, Ni(0)-based catalysts exhibit selective efficiency, and when reactive, their efficiency is higher than that of Ni(II)-based catalysts in the presence of both K(3)PO(4) and CsF. These results provide both reaction conditions for the cross-coupling, and for the elaboration of orthogonal cross-coupling methodologies of various C-O based electrophiles with aryl neopentylglycolboronates. With the exception of mesylates and sulfamates the efficiency of all other 2-naphthyl C-O electrophiles was lower in cross-coupling with aryl neopentylglycolboronates than with arylboronic acids.     

Predicting the size and properties of dendrimersomes from the lamellar structure of their amphiphilic Janus dendrimers

Dendrimersomes are stable, monodisperse unilamellar vesicles self-assembled in water from amphiphilic Janus dendrimers. Their size, stability, and membrane structure are determined by the chemical structure of Janus dendrimer and the method of self-assembly. Comparative analysis of the periodic arrays in bulk and dendrimersomes assembled by ethanol injection in water of 11 libraries containing 108 Janus dendrimers is reported. Analysis in bulk and in water was performed by differential scanning calorimetry, X-ray diffraction, dynamic light scattering, and cryo-TEM. An inverse proportionality between size, stability, mechanical properties of dendrimersomes, and thickness of their membrane was discovered. This dependence was explained by the tendency of alkyl chains forming the hydrophobic part of the dendrimersome to produce the same local packing density regardless of the branching pattern from the hydrophobic part of the dendrimer. For the same hydrophobic alkyl chain length, the largest, toughest, and most stable dendrimersomes are those with the thinnest membrane that results from the interdigitation of the alkyl groups of the Janus dendrimer. A simplified spherical-shell model of the dendrimersome was used to demonstrate the direct correlation between the concentration of Janus dendrimer in water, c, and the size of self-assembled dendrimersome. This concentration-size dependence demonstrates that the mass of the vesicle membrane is proportional with c. A methodology to predict the size of the dendrimersome based on this correlation was developed. This methodology explains the inverse proportionality between the size of dendrimersome and its membrane thickness, and provides a good agreement between the experimental and predicted size of dendrimersome.     

Ni(COD)2/PCy3 catalyzed cross-coupling of aryl and heteroaryl neopentylglycolboronates with aryl and heteroaryl mesylates and sulfamates in THF at room temperature

Reaction conditions for the Ni(COD)(2)/PCy(3) catalyzed cross-coupling of aryl neopentylglycolboronates with aryl mesylates were developed. By using optimized reaction conditions, Ni(COD)(2)/PCy(3) was shown to be a versatile catalyst for the cross-coupling of a diversity of aryl neopentylglycolboronates with aryl and heteroaryl mesylates and sulfamates containing both electron-donating and electron-withdrawing substituents in their para, ortho, and meta positions in THF at room temperature. This Ni-catalyzed cross-coupling of aryl neopentylglycolboronates is also effective for the synthesis of heterobiaryls and biaryls containing electrophilic functionalities sensitive to organolithium and organomagnesium derivatives. In combination with the recently developed Ni-catalyzed neopentylglycolborylation, all Ni-catalyzed routes to functional biaryls and heterobiaryls are now easily accessible.     

Molecular structure of helical supramolecular dendrimers

The molecular structure of helical supramolecular dendrimers generated from self-assembling dendrons and dendrimers and from self-organizable dendronized polymers was elucidated for the first time by the simulation of the X-ray diffraction patterns of their oriented fibers. These simulations were based on helical diffraction theory applied to simplified atomic helical models, followed by Cerius2 calculations based on their complete molecular helical structures. Hundreds of samples were screened until a library containing 14 supramolecular dendrimers and dendronized polymers provided a sufficient number of helical features in the X-ray diffraction pattern of their oriented fibers. This combination of techniques provided examples of single-9(2) and -11(3) helices, triple-6(1), -8(1), -9(1), and -12(1) helices, and an octa-32(1) helix that were assembled from crownlike dendrimers, hollow and nonhollow supramolecular crownlike dendrimers, hollow and nonhollow supramolecular disklike dendrimers, and hollow and nonhollow supramolecular and macromolecular helicene-like architectures. The method elaborated here for the determination of the molecular helix structure was transplanted from the field of structural biology and will be applicable to other classes of synthetic helical assemblies. The determination of the molecular structure of helical supramolecular assemblies is expected to provide an additional level of precision in the design of helical functional assemblies resembling those from biological systems.     

trans-Chloro(1-naphthyl)bis(triphenylphosphine)nickel(II)/PCy3 catalyzed cross-coupling of aryl and heteroaryl neopentylglycolboronates with aryl and heteroaryl mesylates and sulfamates at room temperature

trans-Chloro(1-naphthyl)bis(triphenylphosphine)nickel(II) complex/PCy(3) system has been successfully applied as catalyst for the Suzuki-Miyaura cross-coupling of aryl and heteroaryl neopentylglycolboronates with aryl and heteroaryl mesylates and sulfamates in THF at room temperature. This cross-coupling reaction tolerates various functional groups, including keto, imino, ester, ether, and cyano. Together with the nickel-catalyzed, one-pot, two-step neopentylglycolborylation, this bench stable and inexpensive Ni(II)-based catalyst can be utilized as an alternative to Ni(COD)(2)/PCy(3) to provide an inexpensive, robust, and convenient synthesis of biaryl and heterobiaryl compounds.     

Self-repairing complex helical columns generated via kinetically controlled self-assembly of dendronized perylene bisimides

The dendronized perylene 3,4:9,10-tetracarboxylic acid bisimide (PBI), (3,4,5)12G1-3-PBI, was recently reported to self-assemble in complex helical columns containing tetramers of PBI as basic repeat unit. These tetramers contain a pair of two molecules arranged side-by-side and another pair in the next stratum of the column turned upside-down and rotated around the column axis. Intra- and intertetramer rotation angles and stacking distances are different. At high temperature, (3,4,5)12G1-3-PBI self-assembles via a thermodynamically controlled process in a 2D hexagonal columnar phase while at low temperature in a 3D orthorhombic columnar array via a kinetically controlled process. Here, we report the synthesis and structural analysis, by a combination of differential scanning calorimetry, X-ray and electron diffraction, and solid-state NMR performed at different temperatures, on the supramolecular structures generated by a library of (3,4,5)nG1-3-PBI with n = 14-4. For n = 11-8, the kinetically controlled self-assembly from low temperature changes in a thermodynamically controlled process, while the orthorhombic columnar array for n = 9 and 8 transforms from the thermodynamic product into the kinetic product. The new thermodynamic product at low temperature for n = 9, 8 is a self-repaired helical column with an intra- and intertetramer distance of 3.5 ? forming a 3D monoclinic periodic array via a kinetically controlled self-assembly process. The complex dynamic process leading to this reorganization was elucidated by solid-state NMR and X-ray diffraction. This discovery is important for the field of self-assembly and for the molecular design of supramolecular electronics and solar cell.     

Self-assembly of dendronized perylene bisimides into complex helical columns

The synthesis of perylene 3,4:9,10-tetracarboxylic acid bisimides (PBIs) dendronized with first-generation dendrons containing 0 to 4 methylenic units (m) between the imide group and the dendron, (3,4,5)12G1-m-PBI, is reported. Structural analysis of their self-organized arrays by DSC, X-ray diffraction, molecular modeling, and solid-state (1)H NMR was carried out on oriented samples with heating and cooling rates of 20 to 0.2 °C/min. At high temperature, (3,4,5)12G1-m-PBI self-assemble into 2D-hexagonal columnar phases with intracolumnar order. At low temperature, they form orthorhombic (m = 0, 2, 3, 4) and monoclinic (m = 1) columnar arrays with 3D periodicity. The orthorhombic phase has symmetry close to hexagonal. For m = 0, 2, 3, 4 ,they consist of tetramers as basic units. The tetramers contain a pair of two molecules arranged side by side and another pair in the next stratum of the column, turned upside-down and rotated around the column axis at different angles for different m. In contrast, for m = 1, there is only one molecule in each stratum, with a four-strata 2(1) helical repeat. All molecules face up in one column, and down in the second column, of the monoclinic cell. This allows close and extended π-stacking, unlike in the disruptive up-down alteration from the case of m = 0, 2, 3, 4. Most of the 3D structures were observed only by cooling at rates of 1 °C/min or less. This complex helical self-assembly is representative for other classes of dendronized PBIs investigated for organic electronics and solar cells.     

Self‐Sorting Supramolecular Polymerization: Helical and Lamellar Aggregates of Tetra‐Bay‐Acyloxy Perylene Bisimide

A new perylene bisimide (PBI), with a fluorescence quantum yield up to unity, self‐assembles into two polymorphic supramolecular polymers. This PBI bears four solubilizing acyloxy substituents at the bay positions and is unsubstituted at the imide position, thereby allowing hydrogen‐bond‐directed self‐assembly in nonpolar solvents. The formation of the polymorphs is controlled by the cooling rate of hot monomer solutions. They show distinctive absorption profiles and morphologies and can be isolated in different polymorphic liquid‐crystalline states. The interchromophoric arrangement causing the spectral features was elucidated, revealing the formation of columnar and lamellar phases, which are formed by either homo‐ or heterochiral self‐assembly, respectively, of the atropoenantiomeric PBIs. Kinetic studies reveal a narcissistic self‐sorting process upon fast cooling, and that the transformation into the heterochiral (racemic) sheetlike self‐assemblies proceeds by dissociation via the monomeric state.     

Programming the supramolecular helical polymerization of dendritic dipeptides via the stereochemical information of the dipeptide

Many natural biomacromolecules are homochiral and are built from constituents possessing identical handedness. The construction of synthetic molecules, macromolecules, and supramolecular structures with tailored stereochemical sequences can detail the relationship between chirality and function and provide insight into the process that leads to the selection of handedness and amplification of chirality. Dendritic dipeptides, previously reported from our laboratory, self-assemble into helical porous columns and serve as fundamental mimics of natural porous helix-forming proteins and supramolecular polymers. Herein, the synthesis of all stereochemical permutations of a self-assembling dendritic dipeptide including homochiral, heterochiral, and differentially racemized variants is reported. A combination of CD/UV-vis spectroscopy in solution and in film, X-ray diffraction, and differential scanning calorimetry studies in solid state established the role of the stereochemistry of the dipeptide on the thermodynamics and mechanism of self-assembly. It was found that the highest degree of stereochemical purity, enantiopure homochiral dendritic dipeptides, exhibits the most thermodynamically favorable self-assembly process in solution corresponding to the greatest degree of helical order and intracolumnar crystallization in solid state. Reducing the stereochemical purity of the dendritic dipeptide through heterochirality or by partially or fully racemizing the dendritic dipeptide destructively interferes with the self-assembly process. All dendritic dipeptides were shown to coassemble into single columns regardless of their stereochemistry. Because these columns exhibit no deracemization, the thermodynamic advantage of enantiopurity and homochirality suggests a mechanism for stereochemical selection and chiral amplification.