Electronic excitation of molecules triggers a variety of physicochemical phenomena, such as chemical dynamics, luminescence, and photovoltaic effects. Understanding and controlling such dynamic phenomena is expected to lead to the creation of various novel functions based on molecules. We have been studying the details of the electronic, excitonic, and optical processes that occur in single molecules by the combination of scanning tunneling microscopy (STM) and optical techniques. This presentation will mainly discuss the following two topics: (1) How excitons are formed by tunneling electrons of STM [1,2] and return to the ground state after energy relaxation process including energy transfer [3]. (2) Interaction between molecules and plasmons localized between the STM tip and metal substrate [4] and resonance Raman scattering process based on the plasmon-molecule interaction [5].

[1] K. Miwa, H. Imada, M. Imai-Imada, K. Kimura, M. Galperin, and Y. Kim, Nano Letters 19, 2803 (2019).
[2] K. Kimura, K. Miwa, H. Imada, M. Imai-Imada, S. Kawahara, J. Takeya, M. Kawai, M. Galperin, and Y. Kim, Nature 570, 210 (2019).
[3] H. Imada, K. Miwa, M. Imai-Imada, S. Kawahara, K. Kimura, and Y. Kim, Nature 538, 364 (2016).
[4] H. Imada, K. Miwa, M. Imai-Imada, S. Kawahara, K. Kimura, and Y. Kim, Physical Review Letters 119, 013901 (2017).
[5] R. B. Jaculbia, H. Imada, K. Miwa, T. Iwasa, M. Takenaka, B. Yang, E. Kazuma, N. Hayazawa, T. Taketsugu, Y. Kim, Nature Nanotechnology _in press_.