Scanning the sharp metal tip of a scanning tunneling microscope (STM) over a molecule allows tuning the coupling between the tip plasmon and a molecular fluorescence emitter. This allows access to local variations of fluorescence field enhancement and wavelength shifts, which are central parameters for characterizing the plasmon-exciton coupling. Performing the same for phosphorescence with molecular scale resolution remains a significant challenge. In this study, we present the investigation of phosphorescence from isolated Pt-Phthalocyanine molecules by analyzing tip-enhanced emission spectra in both current-induced and laser-induced phosphorescence. The latter directly monitors singlet-to-triplet state intersystem crossing of a molecule below the tip. The study contributes to a detailed understanding of triplet excitation pathways and their potential control at sub-molecular length scales. Additionally, the coupling of organic phosphors to plasmonic structures is a promising route for improving light-emitting diodes.
@article{arxiv.2502.10150,
title = {Single-molecule phosphorescence and intersystem crossing in a coupled exciton-plasmon system},
author = {Abhishek Grewal and Hiroshi Imada and Kuniyuki Miwa and Miyabi Imai-Imada and Kensuke Kimura and Rafael Jaculbia and Klaus Kuhnke and Klaus Kern and Yousoo Kim},
journal= {arXiv preprint arXiv:2502.10150},
year = {2025}
}