Interplay between motion of nuclei and excitations has an important role in molecular photophysics of natural and artificial structures. Here we provide a detailed analysis of coupling between quantized librational modes (librons) and charged excited states (trions) on single phthalocyanine dyes adsorbed on a surface. By means of tip-induced electroluminescence performed with a scanning probe microscope, we identify libronic signatures in spectra of chirally adsorbed phthalocyanines and find that these signatures are absent from spectra of symmetrically adsorbed species. We create a model of the libronic coupling based on the Franck-Condon principle to simulate the spectral features. Experimentally measured librational spectra match very well the theoretically calculated librational eigenenergies and peak intensities (Franck-Condon factors). Moreover, the comparison reveals an unexpected depopulation channel for the zero libron of the excited state that can be effectively controlled by tuning the size of the nanocavity. Our results showcase the possibility of characterizing the dynamics of molecules by their low-energy molecular modes using µeV-resolved tip-enhanced spectroscopy.

Catalan Institute of Nanoscience and Nanotechnology CSIC and BIST Campus UAB Bellaterra E08193 Barcelona Spain

Faculty of Mathematics and Physics Charles University CZ12116 Praha 2 Czech Republic

Institute of Organic Chemistry and Biochemistry Czech Academy of Sciences CZ16000 Praha 6 Czech Republic

Institute of Physics Czech Academy of Sciences CZ16200 Praha 6 Czech Republic

Instituto de Ciencia de Materiales de Madrid; CSIC E28049 Madrid Spain

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