Extraordinary Tolerance of the Cogwheel Mechanism of Helical Self-Organization to Structural Defects

Our laboratory has reported an unprecedented cogwheel mechanism of helical self-organization, which generates microdomains of single-handed supramolecular columns while disregarding the chirality of its building blocks. Discovered with a dendronized perylene bisimide (PBI), this mechanism arranges the alkyl groups of the self-assembling dendrons parallel to the helical column, providing the most compact helical construct known. Four precise molecular elements were originally considered to be required by the design of this helical structure. The first three elements─alkyl group length, the presence of a chiral methyl group on the alkyl chain, and the parallel arrangement of the helical coat to the column long axis─were demanded by a dimer of the dendronized PBI with 45° internal rotation of PBI units within dimer and a 90° rotation of dimers along the column long axis. Previous experiments demonstrated that a self-repairing process relaxes the number of carbons and eliminates the need for a chiral methyl group within the alkyl chains of the dendronized building block, essential to predict the helical half-pitch and helical coat arrangement. In this work, we demonstrate that the PBI dimer can be replaced by a repeat unit formed from one PBI and three nondendronized aromatic groups. Combined with the previously reported results, this extraordinary tolerance of the cogwheel mechanism to structural defects places it high on the list of models to study the origins of biological homochirality and for numerous practical applications.