Self-Assembled Helical and Twisted Nanostructures of a Preferred Handedness from Achiral π-Conjugated Oligo( p-phenylenevinylene) Derivatives.

Abstract

The formation of chiral nanostructures from the self-assembly of achiral building blocks without external symmetry breaking inducing factors is believed to associate with the origin of chirality. Herein, we reported the synthesis and self-assembly of oligo( p-phenylenevinylene)- b-poly(ethylene glycol) (OPV3- b-PEG17, the subscripts represent the number of repeat unit of each block) in solution. We systematically examined the influence of solvent, heating temperature, and concentration of OPV3- b-PEG17 on the self-assembly of OPV3- b-PEG17 by UV/vis absorption and fluorescence spectrometry, circular dichroism technique, and transmission electron and atomic force microscopy. Interestingly, helical and twisted nanoribbons and nanotubes of a preferred handedness can be formed from achiral OPV3- b-PEG17 in the mixture of water/ethanol (v/v = 1/1) and the solution showed an obvious exciton-coupled bisignated signal, which indicated that symmetry breaking occurred during the formation of these nanostructures without external inducing factors. Our results showed that the occurrence of symmetry breaking is subtle to the experimental factors including solvent, heating temperature, and concentration of OPV3- b-PEG17. The directional π-π stacking along with steric repulsion between PEG domains should be the driving force for the formation of these chiral nanostructures. The occurrence of statistical fluctuations in the initial stage of self-assembly led to an accidental excess of helical or/and twisted structures, that is, symmetry breaking. Subsequently, the autocatalysis effect resulted in the formation of helical or/and twisted nanoribbons with a preferred handedness.