Fluorescence of CoTPP Mediated by the Plasmon–Exciton Coupling Effect in the Tunneling Junction

Abstract

CoTPP, as a common hypsoporphyrin, is usually not a luminescent molecule because of the open-shell Co ion. In this paper, well-defined multilayer CoTPP molecules self-assembled on Au(111) surface are characterized layer by layer with scanning tunneling microscope (STM) induced luminescence. By using the highly localized STM tunneling current, we not only investigate the influence of bias polarity on the amplitude of distinct plasmonic emission resulted from the interaction between the metal substrate and the metal ions but also first obtain the light emission from the hypsoporphyrins in the tunneling junction. The density-matrix method and the combined approach of classical electrodynamics and first-principles calculation are used to explain the mechanism of the light emission. These findings may expand the underlying physics of plasmon–exciton coupling in STM nanocavity and reveal a new possible path to overcome the fluorescent potential of hypsoporphyrins by the intense localized electric fields.

Electric Field Controlled Single-Molecule Optical Switch by Through-Space Charge Transfer State

“…One of the most important goals in nano-optics is to build nanoscale molecular switches with controlled photon emissions. , Such functional optical devices possess great application potentials in areas ranging from optical data storage/memories to nanoscale light sources. − The developments of experimental techniques have made it possible to build actual nanodevices with single molecules as functional units. , Especially, it has been shown that the tunneling electrons in biased metallic junctions such as in a scanning tunneling microscope (STM) could be applied to induce electroluminescence (EL) from single molecules. ,− These advanced techniques thus opened the door for the design and validation of single-molecule based optical switches at the nanometer scale.…”