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

Abstract

Columnar polymers and liquid crystals obtained from π-conjugated cone-shaped molecules are rising 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 C3symmetric subphthalocyanine 1 can undergo self-assembly either as a tail-to-tail dimer, showing monomer-dimer sigmoidal transitions, or as a head-to-tail non-centrosymmetric 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.

Controlling the length of porphyrin supramolecular polymers via coupled equilibria and dilution-induced supramolecular polymerization

“…Nakashima et al reported a method to tune aggregate length and morphology by balancing the enantiomeric excess (ee) of the components, leading to heterochiral dimers in racemic mixtures or homochiral polymers at high ee’s 39 . Another remarkable example reported the use of topological chirality to achieve narcissistic self-sorting into homochiral dimers, but social self-sorting into a heterochiral polymer with alternating microstructure 40 . Seminal work by George et al demonstrated chirality driven self-sorting and stereoselective seeded supramolecular polymerizations with a series of naphthalene diimide (NDI) functionalized monomers 30 , 31 , 41 , 42 .…”

Alternating Heterochiral Supramolecular Copolymerization

“…More recently, in the supramolecular polymerization of a chiral subphthalo­cyanine derivative, Ortí, Torres, González-Rodríguez, and co-workers computationally suggested that chain growth proceeds in an alternating heterochiral manner. This possibility is interesting, but the authors did not exclude the possibility of concomitant homochiral chain growth because even the enantiomerically pure monomer alone can polymerize under the same conditions …”

Self-sorting assembly of artificial building blocks

“…5a) in both polar and nonpolar aliphatic solvents. 72 In polar aliphatic solvents, 1P and 1M formed self-sorting homochiral dimers in a tail-to-tail manner, in which the molecules had the closest distance and lowest energy according to calculations (Fig. 5b).…”