Tunable Luminescence From a Single Free-Base Porphyrin Molecule By Controlled Access to Optically Active States

TL;DR

This study demonstrates how substrate work function control and tip-induced gating can tune the luminescence of a single free-base tetrabenzoporphyrin molecule by modulating access to optically active states, revealing new ways to control molecular emission.

Contribution

It introduces a method to control molecular luminescence through substrate and tip manipulation, enabling access to optically excited states in single molecules.

Findings

Controlled access to optically active states achieved.

Luminescence can be switched on or off by energy shifts.

Theoretical models validate experimental results.

Abstract

Scanning tunneling microscopy-induced luminescence (STML) provides access to optical properties of individual molecules through a cascade of relaxation processes between many-body states. Insufficient charge attachment energies quench the relaxation cascade via optically excited states, causing even intrinsically bright molecules to remain dark in STML. Here, we leverage substrate work function control and tip-induced gating of the double barrier tunnel junction to induce an energy shift of the ionic transition state of a single free-base tetrabenzoporphyrin (H2TBP) to control access to optically excited states and bright exciton emission. The experimental observations are validated by a rate equation and polaron model considering the relaxation energy of the NaCl decoupling layer upon charging of the molecule.