Achiral molecules with conjugated structures can form chiral supramolecules through interfacial self-assembly. These spontaneous symmetry breaking processes may help elucidate the origin of life and are thus of great importance. So far, the mechanism of interfaciam self-assembly has been discussed in detail. However, dynamics of the chiral assemblies was rarely investigated. In order to clarify whether the chiral structures are stable or dynamic, we employed second harmonic generation linear dichroism (SHG-LD) to investigate the supramolecular chirality of PARC18 at air/aqueous interface. It was shown that PARC18 formed chiral structures with stable chiral state at air/water interface. While at air/NaOH solution interface, the chiral state changed with time. In addition, on NaOH solution subphase, contributions of magnetic dipole to second harmonic signals were dominant. We suggest that this is due to isomerization of PARC18 molecules on NaOH solution subphase. As a result, the two chromophores coupled with each other and the magnetic dipole contribution was enhanced.