Molecular design principles of helical pyramidal chirality self-organized from achiral hexakis(alkyloxy)triphenylene

2,3,6,7,10,11-Hexakis(alkyloxy)triphenylene (HATn) containing n = 4 to 12 carbons in its alkyl groups, are a classic group of discotic molecules self-organizing columnar liquid crystals. The structure of the crystalline assemblies of these discotic molecules were neglected since they were invented 45 years ago. Recently, we discovered that the crystal state of HAT4 consists of a highly ordered 8/1 helical chiral pyramidal 3D self-organization. In this publication we report the structural analysis of all 3D self-organizations of HATn containing n = 4 to 12 carbons in their achiral alkyls. Unexpectedly, the highly ordered 8/1 helical chiral pyramidal crystalline columns assembled from the crown-conformation of HAT4 is encountered also in the crystalline periodic array of HAT5. HAT6 self-organizes a 5/1 helical chiral pyramidal 3D column. HAT7 to HAT10 maintain their crown conformation in their 3D supramolecular pyramidal columns. However, their 3D pyramidal assemblies exhibit a nonhelical criss-cross arrangement. HAT11 and HAT12 self-organize 3D nonhelical columns from criss-cross arrangements of disc-like conformers. The structures of all these 3D helical and nonhelical pyramidal as well as of nonhelical discotic columns were resolved for the first time at the molecular level by reconstruction of their oriented fiber X-ray diffractograms with the help of molecular models. These results demonstrate that a single self-assembling building block can self-organize either helical chiral pyramidal or nonhelical pyramidal or even nonhelical discotic assemblies via two of its constitutional isomers. This outcome prompts essential questions related to the current standing of helical self-organizations. The most important question is, why over the past many years the scientific community explored helical self-organizations derived from long alkyl groups when the ideal alkyls for this process seem to be short? A hypothetic explanation of the findings reported here and of their impact on the field of helical self-organizations is presented

Losing supramolecular orientational memory via self-organization of a misfolded secondary structure

Supramolecular orientational memory (SOM) provides a route to otherwise inaccessible nanoscale architectures for certain molecules. In these privileged cases, columnar domains organized from self-assembling dendrons undergo reorientation during heating to, and subsequent cooling from, a 3D phase composed of “spheres”, such as a body-centered cubic phase or a Pm[3 with combining macron]n cubic phase, known also as Frank-Kasper A15. The directions of the reoriented columns preserve key interactions from the preceding cubic phase. However, SOM was observed so far in a very limited number of assemblies. The molecular determinants enabling SOM, and its generality, remain poorly understood. Here we report the synthesis and structural and retrostructural analysis of a perylene bisimide (PBI) with two self-assembling benzyl ether dendrons, 3,5-G2-PBI, and compare its assemblies with those of a previously reported PBI, 3,4,5-G2-PBI, which exhibits SOM and has an additional minidendritic building block in its dendrons. The removal of this minidendron in 3,5-G2-PBI eliminates its ability to self-assemble into supramolecular spheres and organize into a cubic phase, thereby precluding 3,5-G2-PBI from exhibiting SOM. This finding demonstrates hierarchical transfer of structural information from primary structure to material function, analogous to the misfolding of proteins into toxic structures such as those implicated in Alzheimer's and Prion diseases. The concepts exemplified here provide new insights into the hierarchical basis for SOM and will aid in the translation of the SOM concept to a broader diversity of soft matter such as block copolymers and surfactants

Light-Induced Reactions within Poly(4-vinyl pyridine)/Pyridine Gels: The 1,6-Polyazaacetylene Oligomers Formation

International audienceCyclic 6-membered aromatic compounds such as benzene and azabenzenes (pyridine, pyridazine, and pyrazine) are known to be light-sensitive, affording, in particular, the Dewar benzene type of intermediates. Pyridine is known to provide the only Dewar pyridine intermediate that undergoes reversible ring-opening. We found that irradiation of photosensitive gels prepared from poly(4-vinyl pyridine) and pyridine at 254 or 312 nm leads to pyridine ring-opening and subsequent formation of 5-amino-2,4-pentadienals. We show that this light-induced process is only partially reversible, and that the photogenerated aminoaldehyde and aminoaldehyde-pending groups undergo self-condensation to produce cross-linked, conjugated oligomers that absorb light in the visible spectrum up to the near-infrared range. Such a sequence of chemical reactions results in the formation of gel with two distinct morphologies: spheres and fiber-like matrices. To gain deeper insight into this process, we prepared poly(4-vinyl pyridine) with low molecular weight (about 2000 g/mol) and monitored the respective changes in absorption, fluorescence, 1H-NMR spectra, and electrical conductivity. The conductivity of the polymer gel upon irradiation changes from ionic to electronic, indicative of a conjugated molecular wire behavior. Quantum mechanical calculations confirmed the feasibility of the proposed polycondensation process. This new polyacetylene analog has potential in thermal energy-harvesting and sensor applications

Tetrahedral arrangements of perylene bisimide columns via supramolecular orientational memory

Chiral, shape, and liquid crystalline memory effects are well-known to produce commercial macroscopic materials with important applications as springs, sensors, displays, and memory devices. A supramolecular orientational memory effect that provides complex nanoscale arrangements was only recently reported. This supramolecular orientational memory was demonstrated to preserve the molecular orientation and packing within supramolecular units of a self-assembling cyclotriveratrylene crown at the nanoscale upon transition between its columnar hexagonal and Pm3̅n cubic periodic arrays. Here we report the discovery of supramolecular orientational memory in a dendronized perylene bisimide (G2-PBI) that self-assembles into tetrameric crowns and subsequently self-organizes into supramolecular columns and spheres. This supramolecular orientation memory upon transition between columnar hexagonal and body-centered cubic (BCC) mesophases preserves the 3-fold cubic [111] orientations rather than the 4-fold [100] axes, generating an unusual tetrahedral arrangement of supramolecular columns. These results indicate that the supramolecular orientational memory concept may be general for periodic arrays of self-assembling dendrons and dendrimers as well as for other periodic and quasiperiodic nanoscale organizations comprising supramolecular spheres, generated from other organized complex soft matter including block copolymers and surfactants

Hierarchical Self-Organization of Perylene Bisimides into Supramolecular Spheres and Periodic Arrays Thereof

Perylene bisimide derivatives (PBIs) are known to form only columnar or lamellar assemblies. There is no known example of a PBI self-assembling into a supramolecular sphere. Therefore, periodic and quasiperiodic arrays generated from spherical assemblies produced from PBIs are also not known. Here, a PBI functionalized at its imide groups with a second generation self-assembling dendron is reported to self-assemble into supramolecular spheres. These spheres self-organize in a body-centered cubic (BCC) periodic array, rarely encountered for self-assembling dendrons but often encountered in block copolymers. These supramolecular spheres also assemble into a columnar hexagonal array in which the supramolecular columns are unexpectedly and unprecedentedly made from spheres. At lower temperature, two additional columnar hexagonal phases consisting of symmetric and asymmetric tetrameric crowns of PBI are observed. Structural and retrostructural analysis via X-ray diffraction (XRD), molecular modeling, molecular simulation, and solid state NMR suggests that inversion of the symmetric tetrameric crowns at high temperature mediates their transformation into supramolecular spheres. The tetrameric crowns of PBIs are able to form an isotropic sphere in the cubic phase due to rapid molecular motion at high temperature, unobservable by XRD but demonstrated by solid state NMR studies. This mechanism of hierarchical self-organization of PBI into supramolecular spheres is most probably general and can be applied to other related planar molecules to generate new functions