Symmetry Breaking and Amplification in a Self-Assembled Helix from Achiral trans-3-Nitrocinnamic Acid

Understanding the process of chiral symmetry breaking, amplification, and transfer to the macroscopic chirality in the self-assembled system has been a subject of essential challenge and immense interest. Here, we show that a simple trans-3-nitrocinnamic acid (3-NCA) self-assembles into helix in solution with symmetry breaking. Upon casting on a solid substrate, the tiny chiral bias in solution was amplified into macroscopic chirality, which could be detected via circular dichroism measurements. Furthermore, the scanning electron microscopy observation revealed the unequal numbers of left- and right-handed helixes, which account for the net supramolecular chirality. In comparison with the other isomers or related molecules, it was found that only 3-NCA showed symmetry breaking. It was revealed that the hydrogen bond and dipole-dipole interaction are responsible for the spontaneous symmetry breaking. The work provides a further insight into the emergence and amplification of supramolecular chirality in self-assembly systems from achiral molecules.