Coexistence Of Chiral And Achiral Adsorptions Of Metal-Free Phthalocyanine Molecules On Cd(0001)

We report the single molecule chirality and chiral self-assembly of the achiral phthalocyanine (H2Pc) molecules on Cd(0001) surface. Uniaxial ordering has been found in the submonolayer regime with individual H2Pc molecules aligned or not aligned to the lattice directions of Cd(0001). High-resolution STM images show that the not-aligned molecules exhibit a chiral motif at low bias and a symmetric motif at high bias, whereas the aligned molecules always show a symmetric contrast regardless of the voltage amplitudes. First-principles calculations demonstrate that the observed chiral motifs arise from the symmetry break of molecular frontier orbitals driven by the charge transfer from substrate to molecule, while the molecular frames of not-aligned H2Pc remain symmetric without structural distortion. In addition, the chiral self-assembly of H2Pc with pinwheel-like patterns has been realized in the long-range order domain. These results are significant for understanding the interplay between chiral structures and molecule-substrate interaction.