Exciton-Trion Conversion Dynamics in a Single Molecule

Area of Science:

• Molecular physics
• Optoelectronics
• Surface science

Background:

• Charged optical excitations, or trions, are vital for optoelectronics, enabling electric field control.
• Tip-enhanced spectromicroscopy can generate excitons and trions in single molecules, but their dynamics remain poorly understood.
• Simultaneous subnanometer spatial and subnanosecond temporal resolution is needed to study exciton-trion dynamics at the single-molecule level.

Purpose of the Study:

• To investigate the dynamics of excitons and trions in single molecules with high spatiotemporal resolution.
• To elucidate the mechanism of trion formation from neutral excitons.
• To understand the influence of bias voltage on exciton-trion lifetimes.

Main Methods:

• Utilizing phase fluorometry, combining radio frequency modulated scanning tunnelling luminescence with time-resolved single photon detection.
• Generating excitons and trions in single Zinc Phthalocyanine (ZnPc) molecules on a NaCl/Ag(111) surface.
• Analyzing system evolution in the picosecond timescale.

Main Results:

• Observed and traced exciton-trion dynamics in single ZnPc molecules over picoseconds.
• Determined the dependence of effective lifetimes on applied bias voltage.
• Identified charge capture as the primary mechanism for neutral exciton to trion conversion.
• Validated findings using a causally deterministic four-state model.

Conclusions:

• Charge capture is the dominant pathway for trion formation in single ZnPc molecules.
• The study provides a detailed picosecond-level understanding of exciton-trion dynamics.
• This research offers insights into controlling charged optical excitations for optoelectronic applications.