Photoinduced Charge Transfer in Single-Molecule p-n Junctions

Area of Science:

• Molecular physics
• Materials science
• Nanotechnology

Background:

• Understanding photoinduced charge separation is crucial for developing efficient molecular electronic devices.
• Current methods often average results, masking molecule-specific behaviors.

Purpose of the Study:

• To investigate photoinduced charge separation in individual C60-tethered 2,5-dithienylpyrrole triad (C60 triad) molecules.
• To spatially resolve charge dynamics with submolecular precision.
• To explore the influence of molecular conformation on charge separation.

Main Methods:

• Utilized a custom-built laser-assisted scanning tunneling microscope.
• Employed evanescent laser illumination via total internal reflection into the tunneling junction.
• Measured changes in tunneling current and electronic spectra upon photoexcitation.

Main Results:

• Photoinduced charge separation was observed in some, but not all, individual C60 triad molecules.
• Variations suggest molecular conformation impacts excitation, lifetime, and charge distribution.
• No photoinduced signal was detected in control molecules lacking C60 moieties.

Conclusions:

• The developed spectroscopic imaging technique provides submolecular insights into photoinduced carrier dynamics.
• This method surpasses the limitations of ensemble-scale measurements.
• Findings can guide the design of molecular p-n junctions for enhanced energy harvesting.