"Direct" measurement of delocalized molecular excitonic wave functions through excitonic and vibronic photon imaging.

Abstract

Delocalized excitons govern the optoelectronic properties of molecular materials, yet the real-space reconstruction of their wave functions-the spatial distribution of amplitude and phase-has remained a long-standing scientific goal. Here, we demonstrate that scanning tunneling microscopy-induced luminescence enables real-space reconstruction of amplitude and phase of delocalized excitonic states in molecular chains. Through subnanometer-resolved photon imaging of linear molecular chains, coherent purely excitonic (0-0) emission patterns reveal the wave function's relative phases, while incoherent vibronic (0-1) emission maps the squared wave function amplitudes. This near-field technique enables the reconstruction of wave functions for both bright superradiant states and optically dark subradiant states inaccessible by conventional far-field optics. Furthermore, the submolecular resolution of the vibronic maps allows for the contributions of different vibrational symmetries, namely, Franck-Condon and Herzberg-Teller modes, to be distinguished. Our findings establish a unique approach for the excitonic wave function reconstruction and open a route for exploring exciton dynamics and interactions in molecular systems.