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

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.

Automated summary

In this study, the luminescent properties of multilayer CoTPP molecules self-assembled on an Au(111) surface were investigated using STM-induced luminescence. The influence of bias polarity on plasmonic emission and the first light emission from hypsoporphyrins in the tunneling junction were explored, with the mechanism of light emission further elucidated using density-matrix method and classical electrodynamics. These findings expand our understanding of plasmon-exciton coupling in STM nanocavity and suggest a new approach to enhance the fluorescent potential of hypsoporphyrins.