Near-field circular dichroism of single molecules

Area of Science:

• Molecular spectroscopy
• Nanoscale imaging
• Quantum chemistry

Background:

• Near-field imaging reveals molecular excited orbitals crucial for nanoscale photonic and chemical functions.
• Directly imaging complex single molecules at the nanoscale remains a significant challenge, requiring higher resolution than molecular dimensions.

Purpose of the Study:

• To propose and demonstrate a novel approach for near-field imaging of electronic transition spatial patterns in single molecules.
• To achieve sub-nanometer resolution for visualizing molecular optical properties.

Main Methods:

• Utilized a theoretical method with demonstrated sub-nanoscale resolution based on photoinduced force microscopy (PiFM).
• Employed an extended discrete dipole approximation (DDIM) incorporating microscopic nonlocal optical response.
• Simulated visualization of circular dichroism (CD) signal patterns.

Main Results:

• Successfully demonstrated the capability of PiFM to visualize CD signal patterns at sub-nanometer scale.
• Visualized patterns for both optically allowed and forbidden electronic transitions in single molecules.
• Achieved visualization of complex spatial patterns of electronic transitions.

Conclusions:

• The proposed approach enables direct observation of intricate spatial patterns of electronic transitions in single molecules.
• Provides crucial insights into the optical functions of individual molecules.
• Paves the way for the development of novel functional nanoscale materials and devices.