Controlling plasmonic charge carrier flow at a nanoparticle-molecule interface using ligand chemistry.

Area of Science:

• Materials Science
• Surface Chemistry
• Photocatalysis

Background:

• Efficient charge-carrier flow at metal-molecule interfaces is essential for plasmonic catalyst performance.
• Understanding the electronic interactions between ligands and metal substrates is critical for controlling catalytic activity.

Purpose of the Study:

• To investigate how the overlap between ligand frontier molecular orbitals (HOMO/LUMO) and gold electronic states influences charge-carrier dynamics.
• To demonstrate wavelength-dependent optimization of plasmonic catalysts by tuning ligand functionalization.

Main Methods:

• Fabrication of gold nanoprism substrates functionalized with different ligands: (p)NO2-Ph-SH (NO2-TP) and (p)Br-Ph-SH (Br-TP).
• Evaluation of hydrogen production rates under interband (440 nm) and surface plasmon resonance (SPR) (740 nm) excitation.
• Theoretical calculations to analyze the electronic structure and orbital overlap at the metal-molecule interface.

Main Results:

• The NO2-TP substrate showed a 4-fold higher hydrogen production rate under interband excitation compared to the Br-TP substrate.
• The Br-TP substrate exhibited a 10-fold higher hydrogen production rate under SPR excitation compared to the NO2-TP substrate.
• Theoretical analysis revealed that the HOMO of NO2-Ph-SH facilitates hole transport, while the LUMO of Br-Ph-SH promotes hot electron transport.

Conclusions:

• Ligand HOMO/LUMO overlap with specific gold electronic states (d-band or sp band) governs charge-carrier flow (holes vs. electrons).
• Tailoring ligand functionalization allows for wavelength-specific optimization of plasmonic catalysts.
• These findings offer guidelines for designing high-performance plasmonic catalysts for diverse applications.