Mechano-Optical Switching of a Single Molecule with Doublet Emission

8 pags., 4 figs.The ability to control the emission from single-molecule quantum emitters is an important step toward their implementation in optoelectronic technology. Phthalocyanine and derived metal complexes on thin insulating layers studied by scanning tunneling microscope-induced luminescence (STML) offer an excellent playground for tuning their excitonic and electronic states by Coulomb interaction and to showcase their high environmental sensitivity. Copper phthalocyanine (CuPc) has an open-shell electronic structure, and its lowest-energy exciton is a doublet, which brings interesting prospects in its application for optospintronic devices. Here, we demonstrate that the excitonic state of a single CuPc molecule can be reproducibly switched by atomic-scale manipulations permitting precise positioning of the molecule on the NaCl ionic crystal lattice. Using a combination of STML, AFM, and ab initio calculations, we show the modulation of electronic and optical bandgaps and the exciton binding energy in CuPc by tens of meV. We explain this effect by spatially dependent Coulomb interaction occurring at the molecule-insulator interface, which tunes the local dielectric environment of the emitter.M.Š. and J.D. acknowledge the Czech Science Foundation no. 20-18741S and the Charles University Grant Agency project no. 910120. P.Me. thanks the ERC Synergy Program (grant no. ERC-2013-SYG-610256, Nanocosmos) and Spanish MINECO (MAT2017-85089-C2-1-R) for financial support and the “Comunidad de Madrid” for its support to the FotoArt-CM Project S2018/NMT-4367 through the Program of R&D activities between research groups in Technologies 2013, cofinanced by European Structural Funds. D.N. and P.J. acknowledge the support from grant 18-09914S of the Czech Science Foundation. P.J. acknowledges support of the Czech Academy of Sciences through Praemium Academiae. We acknowledge CzechNanoLab Research Infrastructure supported by MEYS CR (LM2018110). This work was part of the project RVO 61388963 of the IOCB of the CAS