Columnar Polymers Research Articles

The key role of chirality and peripheral substitution in the columnar organization of bowl-shaped subphthalocyanines.

The columnar arrangement of bowl-shaped aromatics is a promising strategy for producing high-performing semiconductors. However, the structural factors that dictate the self-assembly of these molecules remain poorly understood. Herein, we show how chirality and peripheral substitution affect the columnar assembly of subphthalocyanines (SubPcs) in solution. Both aspects are found to influence the structure, stability, and formation mechanism of the supramolecular polymer obtained. Whereas enantiopure tri-substituted SubPcs cooperatively polymerize into homochiral head-to-tail arrays, racemic mixtures socially self-sort, leading to heterochiral columnar polymers. In sharp contrast, hexa-substituted SubPcs polymerize following an isodesmic mechanism, producing highly robust columnar systems. As elucidated by molecular dynamics calculations, the conformational flexibility of these SubPcs, as well as the number of peripheral groups able to intermolecularly interact, underlie these significant differences. The results presented herein pave the way for the realistic application of bowl-shaped π-compounds.

Synthesis and characterization of dendronized side chain liquid crystalline Poly(2-oxazoline)s towards biomimetic ion channels

The polymerization of dendronized monomers is an attractive option to synthesize liquid crystalline columnar polymers with side chain dendrons. Following this approach, we report for the first time in the present study the synthesis of a family of side chain liquid crystalline (SCLC) poly(2-oxazoline)s, poly(2-(3,4,5-tris(4-dodecyloxybenzyloxy)phenyl)-2-oxazoline) (PTOx) from its oxazoline monomer precursor, 2-(3,4,5-tris(4-dodecyloxybenzyloxy)phenyl)-4,5-dihydro-1,3-oxazole) (TAPOx), by cationic ring-opening polymerization (CROP). The optimisation of the reaction parameters (temperature, type of initiator, terminating agent, solvent and monomer concentration), combined with the nature of the CROP allowed us to obtain high molecular weight SCLC poly(2-oxazoline)s. NMR investigations were consistent with the targeted molecular weights of the synthesized PTOx and the living nature of TAPOx polymerization. Regarding the mesomorphic characterization, all synthesized acyl-substituted poly(ethyleneimine)s exhibited liquid crystalline mesophases in a broad temperature range. XRD studies demonstrated that these dendronized poly(2-oxazoline)s self-assemble into columnar structures. Mesomorphic and thermal properties suggest that these family of poly(2-oxazoline)s could be excellent candidates to build up membranes for proton transport applications.

Dual-Mode Chiral Self-Assembly of Cone-Shaped Subphthalocyanine Aromatics.

Columnar polymers and liquid crystals obtained from π-conjugated cone-shaped molecules are receiving increasing interest due to the possibility of obtaining unconventional polar organizations that show anisotropic charge transport and unique chiroptical properties. However, and in contrast to the more common planar discotics, the self-assembly of conic or pyramidic molecules in solution remains largely unexplored. Here, we show how a molecular geometry change, from flat to conic, can generate supramolecular landscapes where different self-assembled species, each of them being under thermodynamic equilibrium with the monomer, exist exclusively within distinct regimes. In particular, depending on the solvent nature-aromatic or aliphatic-cone-shaped C3-symmetric subphthalocyanine 1 can undergo self-assembly either as a tail-to-tail dimer, showing monomer-dimer sigmoidal transitions, or as a head-to-tail noncentrosymmetric columnar polymer, exhibiting a nucleation-elongation polymerization mechanism. Moreover, the experimental and theoretical comparison between racemic and enantiopure samples revealed that the two enantiomers (1M and 1P) tend to narcissistically self-sort in the dimer regime, each enantiomer showing a strong preference to associate with itself, but socially self-sort in the polymer regime, favoring an alternate stacking order along the columns.

(Invited) Self-Assembled Molecular Materials Based on Subphthalocyanines

Columnar nanostructures and liquid crystals are an important class of self-assembled organic materials that are making great impact on several optoelectronic technologies like transistors, solar cells, ferroelectric switches or light-emitting diodes. These materials are typically produced by the ordered stacking of functional molecules with a discotic shape. We have here studied related assemblies from a unique class of molecules, Subphthalocyanines, having instead a rigid conical shape and strong axial dipole moment. In solution, these molecules organize into non-centrosymmetric supramolecular columnar polymers that show intriguing dual-mode self-assembly and chiral self-sorting processes, as a result of the intrinsic monomer chirality. In condensed phases, the generation of liquid crystalline materials that can be efficiently aligned in the presence of electric fields and that exhibit permanent or switchable net polarization is observed. This is a novel and appealing attribute that may have important implications in, for instance, technologies that require an efficient directional transport of charges or memory devices combining ferroelectric and semiconducting properties.

Self‐Assembling Multivalency – Supramolecular Polymers Assembled from Monovalent Mannose‐Labelled Discotic Molecules

AbstractSupramolecular synthesis, the “bottom‐up” construction of higher‐order structures from monomeric building blocks, represents a flexible approach for the generation of multivalent materials. Here, monovalent building blocks decorated with a single bioactive ligand were synthesized. In water, these supramolecular elements self‐assemble into columnar polymers that display multiple ligands. The supramolecular effect on the binding affinity was evaluated by using an enzyme‐linked lectin assay, and the self‐assembled architecture exhibited a stronger inhibitory power than that of the monovalent bioactive ligand. This so‐called self‐assembling multivalency enables the rapid and flexible generation of multivalent polymers from monovalent building blocks.

Dynamic and bio-orthogonal protein assembly along a supramolecular polymer

Dynamic protein assembly along supramolecular columnar polymers has been achieved through the site-specific covalent attachment of different SNAP-tag fusion proteins to self-assembled benzylguanine-decorated discotics. The self-assembly of monovalent discotics into supramolecular polymers creates a multivalent, bio-orthogonal and self-regulating framework for protein assembly. The intrinsic reversibility of supramolecular interactions results in reorganization and exchange of building blocks allowing for dynamic intermixing of protein-functionalized discotics between different self-assembled polymers, leading to self-optimization of protein arrangement and distance as evidenced by efficient energy transfer between fluorescent proteins.

Estimation of the molecular weights of noncovalent columnar polymers based on β-cyclodextrin by the measurement of the aggregation rate of their polymer inclusion complexes with polypropylene glycol

Noncovalent columnar polymers (NCPs) based on cyclodextrins (CD) are polymeric assemblies of molecules that have continuous hollow channels, the width of which is determined by the diameter of the cavity of the initial CDs. The repeating fragment in an NCP is the CD molecule. For NCPs that were obtained by the exclusion of polymer backbone macromolecule from the corresponding inclusion complexes (ICs) based on β-cyclodextrin (NCPexcl), the polymer length, expressed as the number of macrocycles in a single chain (n) is determined by the size of the included ligand, polypropylene glycol (PPG), and is the PPG polymerization degree divided by two. The determination of the molecular weight of an NCP obtained by the precipitation method (NCPprec) is rather difficult, since they are present in the aggregated state rather than in the form of individual molecules in solution. To estimate the molecular weight of NCPprec, an indirect method is used, which is based on the determination of the aggregation rate of the ICs formed as a result of the interaction between an NCP and polypropylene glycol with a fixed molecular weight (MW), in this case PPG 1000. The comparison of the aggregation rates of the inclusion between NCPexcb (which were synthesized using PPGs with different molecular weights) and PPG 1000 with the aggregation rate of the inclusion complex on the basis of NCPprec provided the estimation for the MWs of single polymer chains. The fact that the samples of NCPprec contain ∼30% of the monomeric β-CD was taken into account when constructing the calibration curve. It was demonstrated that the MW of the polypropylene glycol corresponding to NCPprec is 1320 Da. Consequently, ∼11–12 molecules of β-CD are included in the single chains of NCPprec.

Noncovalent columnar structures based on β-cyclodextrin

A new method for the synthesis of associates of cyclodextrins (CDs) of the columnar type consisting of the precipitation of CDs from aqueous solutions into acetone at lowered temperatures is developed. It is shown that columnar structures exist in both a crystalline state and in aqueous solutions. Hydrodynamic radii and molecular masses of noncovalent columnar structures (NCSs) in aqueous solutions are determined by the dynamic and static light scattering methods. The degree of association of noncovalent columnar polymers is ∼40. It is revealed the NCS associates based on β-CD are stable and their hydrodynamic radius Rh is equal to 100 ± 10 nm. The kinetics of interactions of initial β-CD and NCS with poly(propylene oxide) (PPO) is studied. The pattern of kinetic curves of Rh growth upon interaction between NCS and PPO indicates that the aggregation of the particles of polymer inclusion complex proceeds in the regime of reaction-limited cluster-cluster aggregation. Kinetic curves describing the interaction processes between β-cyclodextrin and PPO are characterized by the presence of induction period t0. At t > t0, Rh ∞ t0.56 which is typical for the diffusion-limited cluster-cluster aggregation. Schemes of the formation of polymer inclusion complexes between initial β-CD or NCS and poly(propylene oxide) are proposed. Comparison of kinetic data on the complexation of β-CD in solution in the form of associates of two types with PPO demonstrates that columnar forms of associates are reactive species acting as macroreceptors.

Origin of Color of π-Conjugated Columnar Polymers. 1. Poly(p-3-methylbutoxy)phenylacetylene Prepared Using a [Rh(norbornadiene)Cl]2 Catalyst

Stereoregular polymerization of (p-3-methylbutoxy)phenylacetylene (p3MBPA) was successfully performed with a [Rh(NBD)Cl] 2 catalyst to afford poly(p-3-methylbutoxy)phenylacetylene (Pp3MBPA) having a cis-transoid form in high yields when ethanol or 1-butanol in the presence of triethylamine was used as the polymerization solvent. The resulting cis polymer was composed of a pseudohexagonal structure called columnar as π-conjugated self-assembly or π-conjugated self-organization in the solid state. The columnar polymer underwent isomerization from the predominant cis to trans form when compressed at 100 kg/cm 2 at room temperature. The pristine polymer and the compressed polymer were characterized in detail using 1 H NMR, wide-angle X-ray diffraction, laser Raman, electron spin resonance, and diffuse reflective UV-vis methods. Consequently, the data showed that the absorption maximum of the π-conjugated columnar polymer appears in an extremely longer wavelength region, ie., at 490 nm, despite the cis form compared with 450 nm of the amorphous cis form. In the solid state, a large blue shift of the absorption maximum was found to be induced when the columnar structure was destroyed by compression to produce a trans-transoid form which has planar zigzag π-conjugation sequences. The pristine columnar polymer showed the λ max as an entire absorption at notably longer wavelength so that the chromophore of the π-conjugated columnar polymer is not to be simply attributed to the primary structure, e.g., a repeated double-single bond structure, but rather should be ascribed to that of aggregated molecules called the π-conjugated columnar as self-assembly or self-organization. This explanation is a new concept with respect to the color of π-conjugated columnar polymers and is very important for the molecular design of electroluminescense (EL) and nonlinear optical (NLO) materials which are used at present in the solid state.

Formation of Columnar from Poly(p-Methylethynylbenzene) Polymerized Using [Rh(norbornadiene)Cl]2 as a Catalyst. An X-Ray and ESR Study

Columnar polymers of p-methylethynylbenzene (MEB) were synthesized using [Rh(norbornadiene)Cl]2 as a catalyst in alcohol. Polymers having a cis-transoid structure were selectively formed at high yields. The structure and properties of the polymers were analyzed by means of X-ray diffraction and ESR methods. The data showed that the pristine amorphous polymer was converted to a pseudohexagonal columnar one when it was treated with toluene at room temperature. Formation of columnar polymers was also demonstrated by the increase in the linewidth in the ESR spectra of the polymer obtained by the toluene treatment of the pristine amorphous polymer, indicating that a magnetically inhomogeneous line broadening mechanism operates among the radical spins which are heterogeneously distributed in the columnar phase.