Visually Constructing the Chemical Structure of a Single Molecule by Scanning Raman Microscopy

The strong spatial confinement of a plasmonic field has made it possible to visualize the inner structure of a single molecule and even distinguish the vibrational modes in real space. With such ever-improved spatial resolution, it is anticipated that full vibrational imaging of a molecule could be achieved to reveal molecular structural details. Here, we present a new technique, named as scanning Raman microscopy, to utilize for visually constructing the chemical structure of a single molecule. It is achieved by taking advantage of three key elements. First, the full mapping of individual vibrational modes with Angstrom-level resolution allows to visually determine the placements of atoms or chemical bonds. Second, the position-dependent interference effect for symmetric and anti-symmetric vibrations enables to identify the connectivity of the chemical groups involved. The third element is the combination of spectromicroscopic images and Raman fingerprints for different chemical groups that conclusively ensures the definite arrangement of constituent components of a single molecule. We demonstrate that the construction of a single Mg-porphine molecule requires only a few vibrational images through a simple Lego-like building process. Our proposed scanning Raman microscopy represents the first technique that allows visually assembling the chemical structure of a single molecule in real space. The protocol established in this proof-of-principle demonstration is expected to stimulate active research in the field as it develops into a mature and universal technology.