Structural Reconstruction of Optically Invisible State in a Single Molecule via Scanning Tunneling Microscope

Molecular dark states, participating in various energy- and electron-transfer processes, are typically beyond direct optical-spectroscopic measurements because of the forbidden transition dictated by the selection rule. In this work, we demonstrate a direct profile of the dark-state transition density of a single molecule on the subnanometer scale by using a scanning tunneling microscope. Our method allows one to resolve the four-lobe configuration in a 1 nm region for the example molecule. The current proposal will bring about a new methodology to study the single-molecule properties in electro-optical devices and light-assisted biological processes.